Heart Failure

Chapter 81


Heart Failure



Heart failure (HF) is a debilitating cardiac syndrome characterized by dyspnea, poor exercise tolerance, and chronic fatigue along with high morbidity and mortality. Heart failure may be defined as the pathophysiologic state in which the heart is incapable of pumping a sufficient supply of blood to meet the metabolic requirements of the body or requires elevated ventricular filling pressures to accomplish this goal. The caveat about high filling pressures acknowledges that a failing heart may continue to maintain systemic perfusion via the compensatory Frank-Starling mechanism, resulting in the maintenance of normal stroke volume (SV) despite reduced ejection fraction (EF). Conversely, low filling pressure with hypoperfusion indicates a pump-priming problem distinct from cardiac disease. The American Heart Association (AHA) and American College of Cardiology (ACC) guidelines define HF related to systolic dysfunction as a left ventricular (LV) ejection fraction (LVEF) less than 40%. Diastolic dysfunction, a pathologic condition involving failure of ventricular relaxation with consequent high filling pressures, may exist in up to half of older individuals with HF.


HF is a progressive and multifaceted disease that begins long before symptoms and signs are evident. A complex neurohormonal regulatory relationship exists between the heart and multiple organ systems. Feedback loops mediated through a variety of vasoactive substances secreted by the heart, autonomic nervous system, kidneys, adrenals, lungs, and vascular endothelium are most important. Perturbations of function in any of these organs affect the others (Fig. 81-1). Accordingly, the cardiovascular system should be viewed as a dynamic one, continually adapting to optimize organ perfusion. Dysfunction of the heart or any component of the cardiopulmonary system initiates adaptive neurohormonal activation of the sympathetic nervous system, renin-angiotensin-aldosterone system (RAAS), natriuretic peptides, endothelin (ET), vasopressin, and other regulatory mechanisms. Neurohormonal activation initially compensates for circulatory system dysfunction. These mechanisms eventually lead to increased mechanical stress on the failing heart, however, causing maladaptive electrical and structural events, progressive cardiac fibrosis and apoptosis, and further impairment of systolic and diastolic function.1 This creates a vicious cycle of increasing myocardial dysfunction causing further neurohormonal modulation, leading to a progressive downward spiral. The degree of myocardial dysfunction depends on both the amount of primary myocardial disease and other pathologic conditions, particularly in the pulmonary, renal, and peripheral vascular systems. Understanding these underlying compensatory mechanisms is leading to progressive improvement in the management of HF, with a shift from a hemodynamic to a neurohormonal model.




Epidemiology


HF represents the only significant cardiovascular disease that is increasing in prevalence in our society. It is a common cause of poor quality of life and premature death. About 5,800,000 individuals (approximately 2% of the population) in the United States in 2009 had HF, and almost 550,000 new cases are diagnosed annually.2 The incidence approaches 10 per 1000 in people older than 65 years.3 Decompensated HF is the most common reason for hospital admission in this age group and also for readmission within 60 days of discharge.4 The ED is the main portal of entry for acute HF patients, with admission rate approximately 80%. HF results in an annual estimated health care cost of about $40 billion.5 It is also responsible for high rates of outpatient visits, hospitalizations, and readmissions. The aging population, coupled with improvements in the medical therapy of HF, will result in increased prevalence of this disease.


HF carries approximately a 50% mortality at 5 years after symptom onset, and one third of patients with the most severe disease die within the first year after diagnosis.5,6 Females have a survival advantage over males.7,8 Progressive hemodynamic deterioration accounts for approximately 50% of deaths, but sudden death resulting from malignant ventricular dysrhythmias occurs in up to half.9 Multiple medical therapies decrease the death rate by improving functional status and slowing progression of pump dysfunction.10


The prognosis in HF is related to a number of factors, including age, LVEF,11,12 exercise tolerance, plasma norepinephrine and B-type natriuretic peptide (BNP) levels, cardiothoracic ratio on chest radiograph,13 resting heart rate (HR),1416 electrocardiogram (ECG) evidence of left ventricular hypertrophy,17 atrial fibrillation (AF),18 or presence of ventricular dysrhythmias, hemoglobin A1c level,19,20 and renal function. One third to one half of patients with HF have some degree of renal insufficiency,21 which is one of the strongest predictors of mortality in patients with HF.2224 HF disproportionately affects black compared with white Americans, and they have a higher mortality.25,26



Cellular Mechanisms


The heart is composed of a mass of individual striated muscle cells (myocytes) that form a branching syncytium. Each myocyte contains an intracellular tubular system termed the sarcoplasmic reticulum, and numerous cross-banded strands termed myofibrils that traverse the length of the myocyte. Myofibrils, in turn, contain multiple subunits called sarcomeres, which form the basic functional unit of myocardial contraction. Sarcomeres occupy approximately 50% of myocardial cell mass and are composed of contractile proteins actin and myosin along with regulatory proteins troponin and tropomyosin. These proteins are surrounded by invaginations of the myocardial cell membrane (sarcolemma) and sarcoplasmic reticulum.


The sarcomere ranges in length from 1.6 to 2.2 µm, depending in part on the tension exerted on the muscle before contraction (preload). Sarcomere contraction occurs when thin, double-helix actin is exposed to thick myofilament myosin. Contraction as well as relaxation is controlled by calcium ion (Ca2+) release from the sarcoplasmic reticulum. When intracellular Ca2+ is increased, it binds to the contraction regulatory protein troponin, which causes a conformational change in tropomyosin that exposes actin to myosin. In the presence of adenosine triphosphate (ATP), linkages between actin and myosin are rapidly made and broken, causing the actin to slide along the myosin filaments. This process generates muscle tension and ultimately myocyte contraction. A decrease in intracellular Ca2+ by sarcoplasmic reticulum reaccumulation reconforms the troponin-tropomyosin complex in such a way that myosin and actin linkages are broken, allowing sarcomere relaxation. Intracellular ionic calcium is thus the principal mediator of the inotropic state of the heart and is mainly stored and regulated by the sarcoplasmic reticulum. Most positive inotropic agents, including digitalis and catecholamines, act by increasing availability of intracellular calcium. On the downside, increased intracellular calcium reduces diastolic relaxation.



Cardiac Physiology


The normal cardiac index is 2.5 to 4.0 L/min/m2 at rest. It is determined by contractility, preload, afterload, and HR. In normal hearts, the collective force of contraction of the cardiac chamber is the sum of forces generated by individual myocytes. Myocyte force is in turn a function of the ability of contractile proteins to generate power (inotropic state or contractility) as well as degree of sarcomere stretch at the start of contraction (preload). Stretching the sarcomere progressively toward its optimal length of 2.2 µm increases the force of contraction by allowing the maximum number of actin-myosin myofilament interactions. This forms the basis of the Frank-Starling relation, which states that within physiologic limits, force of ventricular contraction is directly related to end-diastolic length of the myofibril. Contractility may be affected by a host of factors. Multiple physiologic depressants (e.g., hypoxia, hypercarbia, acidosis, ischemia) and pharmacologic depressants (e.g., antidysrhythmic agents, calcium channel blockers, beta-blockers, alcohol) decrease myocardial contractility. Correcting physiologic myocardial depressant factors and discontinuing unnecessary medications with negative inotropic properties are important first steps in managing HF. Inotropic agents enhance contractility and may improve hemodynamics both acutely, such as with catecholamines, and chronically, as with cardiac glycosides.


Preload is the amount of force stretching the myofibril before contraction. In the intact ventricle, preload is produced by venous return into the chamber, resulting in stretch of the myofibrils constituting the chamber walls. The volume filling the chamber also results in development of pressure that can be measured in either ventricle. The pressure measured within a chamber is determined by both the volume stretching the chamber wall and compliance characteristics of the muscle. For this reason, ventricular pressure is only an indirect reflection of preload. Changes in compliance may occur acutely with ischemia or chronically with hypertrophy and may substantially alter the relationship between chamber volume, pressure, and preload (Fig. 81-2).



Optimal preload is the filling pressure that stretches ventricular myofibrils maximally and leads to greatest stroke output per contraction. The actual optimal preload is unique for each patient because it is affected by LV loading conditions and compliance characteristics. For example, patients with acute myocardial infarction (AMI) tend to have a stiffer, less compliant left ventricle. In these patients, optimal LV pressure ranges are higher. Despite the inotropic state of the ventricle, optimizing preload results in the maximum stroke output for that ventricle (Fig. 81-3). Ventricles with normal compliance accommodate larger volumes before the chamber pressure rises. Accordingly, if pressure is used to estimate preload, the normal ventricle has more dramatic increases in stroke output for similar increases in filling pressure (steeper Starling curve). The risk of pulmonary edema increases when LV end-diastolic pressure rises significantly above normal ranges (6-12 mm Hg). In patients with low colloid osmotic pressures secondary to hypoalbuminemia, pulmonary edema may occur at even lower filling pressures.



Afterload, for clinical purposes, can be thought of as the pressure against which the heart must pump to eject blood. Blood pressure (BP) is determined by the product of cardiac output (CO) and systemic vascular resistance (SVR) (BP = CO × SVR). Hypertension is a major contributor to HF in about 75% of cases.27 Patients with HF and low CO tend to maintain BP through peripheral vasoconstriction mediated mainly by endogenous catecholamines and the RAAS. Afterload represents the mural tension on myocardial cells during contraction and is determined by the total peripheral vascular resistance and the cardiac chamber size. The peripheral resistance is affected by the total cross-sectional area of the circulation, the blood viscosity, and other factors. The arterioles are the major resistance vessels in the circulation. Flow is directly proportional to the fourth power of the vessel radius (Poiseuille’s law). The larger the ventricular cavity, the more mural tension and thus myocardial work is required during contraction (law of Laplace).


Failing ventricles have difficulty overcoming increases in peripheral resistance, instead dilating further, increasing end-diastolic volume to maintain SV, even with decreasing EF (preload reserve). Failing hearts are therefore extremely afterload sensitive, and modest vasodilation can dramatically increase CO, particularly in those most compromised (Fig. 81-4). Afterload reduction may be beneficial because it allows conversion of pressure work into flow work. When BP is decreased, CO increases as long as preload is maintained. Because flow work is proportionally less oxygen demanding, afterload reduction therapy has the additional benefit of decreasing myocardial oxygen demand.



HR and rhythmic contraction are important determinants of optimal CO (CO = HR × SV). As HR increases to the range of 150 to 160 beats/min in the adult, CO increases progressively. Tachycardia above this level compromises diastolic filling time and may lead to decreased CO. Coronary perfusion, which occurs only during diastole, also becomes impaired by severe tachycardia. SV is maximized when atrial contraction “primes” the ventricular pumps before they contract. Therefore any derangement of intracardiac conduction or dysrhythmia can reduce SV. Loss of atrial priming (e.g., in AF) can lead to marked deterioration in CO, especially in diseased, stiffer hearts that require high filling pressures to optimize preload. Synchronized contraction of myocardial tissue and chambers is now a focus of therapeutic intervention.



Primary Disease Processes Resulting in Heart Failure


HF can result from primary disease of coronary arteries, myocardium, cardiac valves, pericardium, peripheral vessels, or lungs. Frequently the cause is multifactorial. Often, determination of the causes of HF is simpler early in its course than during later stages.



Coronary Artery Disease


In developed countries, atherosclerotic coronary artery disease remains the leading cause of HF, present in almost 70% of patients in multicenter HF trials.28 Acute coronary thrombosis leads to focal myocardial necrosis, with resultant fibrosis and scarring. This process leads to areas of dyskinesis that result in decreased EF. Aneurysmal dilation of infarcted areas with paradoxical motion during systole may disproportionately decrease EF. When approximately 40% of the LV muscle mass is acutely infarcted, cardiogenic shock ensues. Transient loss of contractile function may result from episodes of myocardial ischemia that do not cause frank necrosis, or from an ischemic zone surrounding the infarct. This “myocardial stunning” may persist for several days. Owing to improved treatment of acute coronary syndromes, the rates of secondary death and HF are decreasing.29


Chronic coronary insufficiency leads to a more diffuse myocardial fibrosis termed ischemic cardiomyopathy. Revascularization of ischemic but not infarcted myocardial tissue provides a survival benefit in patients with HF related to ischemic LV systolic dysfunction.30 Diseases affecting the coronary microcirculation, such as vaso-occlusive sickle cell anemia and diabetes mellitus, result in similar pathology. Compensatory mechanisms may occur after large MI and progressive cardiac disease, which are collectively termed ventricular remodeling. They include cardiac dilation, reactive hypertrophy, progressive fibrosis, and changes in wall conformation. These may result from elevated chamber filling pressures as well as neurohumoral adaptive responses.




Valvular Heart Disease


Cardiac valvular disease is the third leading cause of HF, after ischemic heart disease and dilated cardiomyopathy. Most acute valvular dysfunction involves either the mitral or the aortic valve, and usually results in severe regurgitation. Acutely stenotic lesions are predominantly restricted to mechanical catastrophes of prosthetic valves. These patients may be in extremis with fulminant pulmonary edema. Valvular disease is discussed in Chapter 83.


Mitral insufficiency and aortic stenosis are most commonly associated with chronic HF. Knowledge of the precise valvular pathology may have important implications for emergent HF therapy. For example, patients with decompensated aortic stenosis should generally not receive vasodilator agents, as flow cannot increase across a fixed obstruction. These patients may become hypotensive owing to reduced preload, with resultant decreased systemic and coronary perfusion. On the other hand, patients with mitral regurgitation benefit greatly from vasodilators, which improve antegrade flow by reducing afterload.




Pulmonary Disease


Chronic obstructive pulmonary disease (COPD), which has a prevalence of 20 to 30% in HF, may obscure recognition of HF.31 Pulmonary dysfunction reduces myocardial oxygen supply while CO must be increased because tissue is being perfused with suboptimally oxygenated blood. Hypoxia leads to pulmonary arteriolar vasoconstriction, reducing lung vascular bed area and elevating pulmonary artery pressures. Chronic increases in pulmonary arterial pressure lead to right ventricular (RV) hypertrophy and dilation. When compensatory mechanisms fail, the patient develops right-sided HF (cor pulmonale), usually with LV output preserved, at least at rest. Causes of acute cor pulmonale, such as a large pulmonary embolus, may precipitate sudden systemic hypotension and death, partly because of decreased LV priming.


Distinguishing primary pulmonary disease causing predominantly right-sided HF from LV failure with secondary right-sided dysfunction is clinically challenging. Wheezing or rhonchi may be seen in both entities. The chest radiograph may be difficult to interpret because both presentations cause interstitial changes. Hyperinflation depresses the diaphragm, which elongates the cardiac silhouette and may mask cardiomegaly. Competition for intrathoracic space reduces lung capacity in patients with chronic HF.32 Natriuretic peptide levels are only slightly elevated in primary pulmonary disease compared with much higher levels in LV failure.31,33,34



Compensatory Mechanisms in Heart Failure



Physiologic Mechanisms





Development of Cardiac Hypertrophy


Development of cardiac hypertrophy is the primary chronic adaptation of the heart to compensate for pump failure. This hypertrophy occurs mainly by increasing the number of myofibrils per cell, as the heart has very limited ability to produce new cells (hyperplasia). New myofibrils arrange in series in response to an increase in chamber volume (leading to dilation over time) and in parallel when responding to higher pressure loads (leading to increased chamber wall thickness). In addition to myofibril hypertrophy, mitochondrial mass expands, leading to additional ATP provision for the expanded myofibril mass.


Initially, hypertrophy leads to improved function of each myocardial cell but at a higher energy cost. Hypertrophy is associated with myosin synthesis shifts from V1 to V3 isoforms, however, with related slowing of contraction, prolongation of time to peak tension, and reduced rate of relaxation.35 With the continued influence of volume overload, myofibril mass expands more than mitochondrial mass. Relative capillary blood flow is reduced, leading to progressive myocyte death with fibrosis and increased stress on the remaining myocytes. Thus the hypertrophic response, if allowed to continue, eventually becomes maladaptive, accelerating myocyte death and reducing pump function. This process gradually occurs as a normal part of aging.36



Neurohormonal Modulation


Neurohormonal mechanisms maintain BP and vital organ perfusion and are activated by LV dysfunction. Regrettably, these neurohormonal mechanisms also increase the hemodynamic burden and oxygen consumption of the failing ventricle and are counterproductive on a chronic basis.




Central and Autonomic Nervous System Neurohormonal Response


The heart and great vessels contain sensory receptors that detect changes in perfusion. Metabolic receptors in muscles also exert inhibitory and excitatory influences on brainstem vasomotor neurons. Arginine vasopressin (antidiuretic hormone) is released from the pituitary gland in response to decreases in perfusion. Elevated vasopressin levels in HF increase volume overload while decreasing osmolality. This adversely affects hemodynamics and cardiac remodeling while potentiating effects of angiotensin II and norepinephrine.37


HF results in a generalized stimulation of sympathetic activity and inhibition of parasympathetic tone. Increased sympathetic outflow results in release of epinephrine and norepinephrine from the adrenal glands and norepinephrine at peripheral sympathetic nerve endings. These elevated catecholamine levels stimulate surface receptors in the heart and blood vessels, increasing cardiac contractility, HR, and vascular tone. The resulting increased vascular tone augments preload through venous contraction as well as afterload by arterial vasoconstriction. Acutely, arterial BP is improved and CO increased by catecholamines. Chronically, a decrease in the number and affinity of surface catecholamine receptors occurs in myocardial tissue, reducing responsiveness to epinephrine and norepinephrine. Elevated catecholamines adversely affect myocardial perfusion, leading to progressive apoptosis and cardiac fibrosis.



Renal Neurohormonal Response


Decreased glomerular perfusion results in reduced renal excretion of sodium. Renal arteriolar and adrenergic receptors stimulate renin release by the juxtaglomerular apparatus. Renin facilitates the conversion of angiotensinogen to angiotensin I, which is further converted to angiotensin II by angiotensin-converting enzyme (ACE). Angiotensin II is a potent vasoconstrictor and an important stimulus for aldosterone release by the adrenal cortex. Aldosterone increases renal sodium retention and potassium excretion. Renal adaptation to hypoperfusion occurs mainly through production of vasodilatory hormones such as prostacyclin, along with prostaglandins PGI2 and PGE2. Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) interfere with prostaglandin synthesis by inhibiting cyclooxygenase. Therefore, except for the useful antiplatelet effect of aspirin, NSAIDs optimally should be avoided in patients with chronic HF because they may contribute to acute renal insufficiency with concomitant salt and water retention.



Vascular Endothelial Neurohormonal Response


Endothelial function locally regulates vasomotor tone. A family of ETs is produced by endothelial and smooth muscle cells as well as neural, renal, pulmonary, and inflammatory cells. This occurs in response to hemodynamic stress, hypoxia, catecholamines, angiotensin II, and many inflammatory cytokines. ET-1 is the most important ET and the most potent vasoconstrictor known.38 It exerts its main vascular effects, vasoconstriction and cell proliferation, through specific ETA and ETB receptors on vascular smooth muscle cells. ETA receptor activation causes vasoconstriction, whereas ETB receptor stimulation increases prostacyclin and nitric oxide (NO) release, causing vasodilation. ET-1 plasma levels are elevated in HF, correlate with symptoms as well as hemodynamic stress, and are associated with adverse prognosis.


NO is produced in almost all tissues and plays a critical role in the homeostasis of cardiac function.39 NO exerts its biologic signaling through production of cyclic guanosine monophosphate (cGMP), which is broken down by cyclic nucleotide phosphodiesterases (PDEs).40 Reduced synthesis or increased degradation of NO at the endothelial level is detrimental in HF. NO-mediated endothelial dysfunction may represent the earliest stage of target organ damage, which ultimately leads to hypertensive heart disease and HF.41



Classification of Heart Failure


Many different methods of classifying HF exist, including acute versus chronic, systolic versus diastolic, right sided versus left sided, and high output versus low output. Early in HF, these may be useful clinical descriptors suggesting particular causes and treatment strategies. Late in the disease process, these distinctions blur.




Systolic versus Diastolic Dysfunction


Systolic dysfunction refers to impairment of contractility, with stroke output reduced and forward flow compromised. Systolic dysfunction is typically caused by myocyte damage such as in MI or myocarditis. Asymptomatic LV systolic dysfunction in patients 45 years of age or older has an estimated prevalence of 6% and is much more common than symptomatic systolic HF.43,44 Most cases of systolic dysfunction also involve some degree of diastolic dysfunction.


Diastolic dysfunction indicates a primary problem with ability of the ventricles to relax and fill normally.45 In many cases, normal or even supernormal systolic function is preserved. Echocardiographic and nuclear imaging techniques demonstrate that 40 to 50% of patients with congestive symptoms have normal EFs and experience diastolic dysfunction,46,47 also termed heart failure with normal ejection fraction.48 The proportion of HF that is primarily diastolic increases with age, from about 45% in patients younger than 45 years to almost 60% in patients older than 85 years. Asymptomatic diastolic dysfunction is much more common than asymptomatic systolic dysfunction. Diastolic dysfunction is the predominant pathophysiology in hypertrophic and restrictive cardiomyopathies, valvular aortic stenosis, and, most important, hypertension.


Diastolic dysfunction occurs predominantly as a result of one of three mechanisms: impaired ventricular relaxation, increased ventricular wall thickness, or accumulation of myocardial interstitial collagen. Impaired lusitropic capacity of the myocardium leads to higher ventricular filling pressure, resulting in congestive symptoms. Myocardial relaxation is an active, energy-requiring process. Failure of myocytes to relax may be secondary to low intracellular energy stores. Physiologic stresses causing increased cardiac demands can precipitate lusitropic abnormalities. In chronic renal disease, mortality is higher in diastolic than systolic HF.49 In addition, systolic contractile dyssynchrony occurs in one third of diastolic HF patients, whereas diastolic dyssynchrony is present in more than half, with therapeutic implications.50,51


As with the other classification schemes, most patients with HF have components of both systolic and diastolic dysfunction, with the predominant type allowing specific treatment strategies. For example, patients with predominantly diastolic dysfunction have the advantage of intact myocardial contractile function. Stiffer hearts, however, have steep pressure-volume curves. Therefore small reductions in diastolic filling volume, as may occur with aggressive vasodilator or diuretic therapy, may markedly decrease ventricular filling and compromise stroke output (see Fig. 81-3).



Right-Sided versus Left-Sided Heart Failure


The notion that one cardiac chamber can fail independently of the others is somewhat artificial. The right and left circulations are connected and, over time, output from the two sides must be equal. Furthermore, the right and left ventricles share an interventricular septum, and dysfunction in one chamber may have an immediate impact on the other. For example, acute right-sided HF from pulmonary hypertension secondary to acute respiratory failure causes bulging of the interventricular septum into the LV chamber. This so-called “septal shift” results in decreased LV preload and low CO that is volume responsive. Chronic left-sided HF leads to pulmonary hypertension with resultant right-sided HF. In addition, cardiac biochemical changes such as an abnormal catecholamine response affect all chambers.


Nonetheless, the terms have usefulness in identifying the predominant clinical presentation. Fluid accumulation “behind” the involved ventricle is responsible for many of the clinical manifestations of HF. For example, LV failure leads primarily to pulmonary congestion with symptoms mostly of dyspnea and orthopnea. Patients with right-sided HF have symptoms of systemic venous congestion, such as pedal edema and hepatomegaly.


When previously healthy patients have acute pathology, the concept of left- versus right-sided HF may be clinically useful. Patients with acute MI may have APE; yet unlike patients with chronic HF, they may not have jugular venous distention or pedal edema because central venous pressure may remain within normal limits. A chest radiograph reveals evidence of pulmonary venous congestion, interstitial edema, and, in fulminant cases, alveolar edema. Because there has not yet been time for cardiac dilation, the cardiac shadow is often of normal size.


Acute RV infarction is an important cause of hypoperfusion with jugular venous distention and absent pulmonary congestion. There is often evidence of ST segment elevation or depression in the V1 lead, and right-sided leads may provide further evidence of RV infarction. Approximately one third of patients with acute inferior infarction have significant RV involvement, leading to inadequate pulmonary perfusion and low LV priming (decreased preload). These patients have right-sided HF with hypotension that is often symptomatic. Aggressive crystalloid resuscitation, followed by inotropic support with norepinephrine, may be required for adequate LV preload and restoration of BP.



High-Output versus Low-Output Failure


High-output failure refers to a hyperdynamic state with supranormal CO and low arteriovenous oxygen difference (decreased oxygen extraction ratio). The hyperdynamic state may result from increased preload (e.g., renal retention of salt and water, or excess mineralocorticoids), decreased SVR (e.g., arteriovenous fistulas, pregnancy, cirrhosis, severe anemia, beriberi, thyrotoxicosis, Paget’s disease, or vasodilator medications), increased beta-sympathetic activity, or persistent tachycardia. A persistent hyperdynamic state results in myocardial damage over time. Early recognition of the hyperdynamic state may allow effective therapy of the underlying condition, thus avoiding development of HF. As the condition progresses, myocardial dysfunction with circulatory overload is superimposed on this background, and symptoms progress. At some point, CO becomes normal or even low, indistinguishable from classic HF.


Low-output failure is the more typical variety of HF and occurs as a result of entities such as ischemic heart disease, dilated cardiomyopathy, valvular disease, and chronic hypertension. Low CO (systolic dysfunction), high filling pressures (diastolic dysfunction), and an increased systemic oxygen extraction ratio (widened arteriovenous oxygen difference) characterize this more commonly encountered form of HF.



Clinical Evaluation of Patients with Suspected Heart Failure



Precipitating Causes of Heart Failure and Exacerbating Factors


When cardiac decompensation occurs because of an acute precipitating cause, intervention can focus on the precipitating factor(s), and the prognosis is much better than when there is simply progression of intrinsic cardiac failure. Causes of acute cardiac decompensation are provided in Box 81-1.



Iatrogenic causes of HF should also be considered, especially in patients who have recently received intravenous fluids. Patients with known renal insufficiency most often experience pulmonary edema as a consequence of salt and fluid overload, as well as missed dialysis. In chronic HF, the most common cause of decompensation is inappropriate decrease in intensity of treatment, including drug therapy, dietary sodium restriction, limited physical activity, or a combination of these measures.







Dysrhythmia


Both tachydysrhythmias and bradydysrhythmias can severely affect CO, especially when acute. Tachydysrhythmias compromise diastolic filling time, reduce CO, and impair coronary perfusion as well as myocardial oxygen delivery. The tachycardia also results in increased myocardial oxygen demand. These factors may precipitate ischemia, which may further impair contractility and exacerbate HF.


The prevalence of AF in patients with HF increases from less than 10% in New York Heart Association (NYHA) functional class I to approximately 50% in NYHA functional class IV.57 Neurohormonal alterations, electrophysiologic changes, and mechanical factors create an environment in which HF predisposes to AF and AF exacerbates HF. New-onset AF or other dysrhythmias that affect coordinated atrial priming of the ventricular pump may seriously reduce preload, especially in disease states with reduced ventricular compliance. Significant bradydysrhythmias may also reduce CO simply by reducing the number of systolic ejections per minute (CO = SV × HR).



Acute Hypoxia and Respiratory Problems


Both COPD exacerbations and respiratory tract infections are very important precipitating factors for HF exacerbation.58 Pulmonary infection, which is more common in patients with pulmonary vascular congestion, may add hypoxia to the metabolic stressors of fever, tachycardia, and increased tissue perfusion requirements.



Anemia


With chronic anemia, oxygen delivery to tissues is maintained by increased CO (isovolumic hemodilution). Anemia increases in prevalence with increasing severity of HF, especially with declining renal function and increasing age. Anemia is associated with poorer survival in HF,5961 with greater disease severity, greater LV mass index, and higher hospitalization rates. Abrupt exacerbations of anemia increase systemic perfusion demands and, especially if coupled with reduced coronary oxygen delivery, may prompt onset or exacerbation of HF.









Pharmacologic Complications


Beta-blocking and calcium channel blocking agents have negative inotropic effects and may precipitate overt HF with excessive administration. Many antidysrhythmic agents have similar effects. Glucocorticoids, NSAIDs, vasodilator medications, and others may result in sodium retention with substantial increases in plasma volume that may precipitate HF.63 NSAIDs in particular interfere with prostaglandin synthesis through cyclooxygenase inhibition, thereby impairing renal homeostasis in patients with HF. They also interfere with the effects of diuretics and ACE inhibitors. Nonadherence to medication regimens for hypertension, HF, or ischemia is the most common pharmacologic cause of HF decompensation.



Evaluation of Heart Failure


The NYHA classification system is a time-honored categorization for patients with chronic HF based on degree of activity causing symptoms (Box 81-2).64 Careful consideration of the differential diagnosis of HF is symptom based. The most common manifestation of acute HF is respiratory distress caused by pulmonary edema. Therefore the differential diagnosis includes exacerbation of COPD or asthma, pulmonary embolus, pneumonia, anaphylaxis, and other causes of acute respiratory distress. Hypoperfusion may be caused by some of these as well as by sepsis syndrome, hypovolemia, hemorrhage, cardiac tamponade, and tension pneumothorax.




History


The presence and character of dyspnea, chest pain, previous heart disease, cardiac catheterization, surgery, current medications (and adherence), and possible intercurrent illness should be explored.


Paroxysmal nocturnal dyspnea results from pulmonary congestion precipitated by plasma volume expansion that occurs during recumbency as interstitial edema is reabsorbed into the circulation. Orthopnea occurs through the same mechanism, with the supine position causing rapid increases in diastolic filling pressure. Symptoms abate after the patient stands or props up the trunk and venous return decreases. Nocturia results from the same pathophysiologic process. Many historical features increase the likelihood of HF. Most predictive is a past history of HF or paroxysmal nocturnal dyspnea, and the absence of dyspnea on exertion reduces the likelihood of chronic HF.65



Physical Examination


Most HF patients are hypertensive, which is prognostically preferable to normal or low BP. Clammy, vasoconstricted patients with a thready pulse and delayed capillary refill may have systemic hypoperfusion despite adequate BP, which is maintained by intense vasoconstriction. Noninvasive assessment of BP in the vasoconstricted patient with low CO can be inaccurate.66 If available, intra-arterial pressure monitoring may more accurately reflect the systemic hemodynamic state and guide the choice of inotropic or vasoconstrictor therapy in hypotensive HF patients.


Most patients with APE are diaphoretic because of intense sympathetic activation. Patients with pulmonary congestion secondary to HF develop interstitial and alveolar pulmonary edema, causing reduced pulmonary compliance and decreased functional residual capacity. Clinical findings include diffuse moist rales, which may be absent with decreased ventilation in more agonal patients. Peribronchial edema may cause wheezing or rhonchi, which can mimic bronchospastic disease (“cardiac asthma”). A positive response to bronchodilator therapy does not exclude HF. Jugular venous distention is present in approximately 50% of cases, and one third of patients have peripheral edema. An S3 gallop may be present in up to 25% but is often difficult to hear.


These common clinical findings of chronic HF are prevalent among patients with APE because most patients have acute exacerbations superimposed on chronic underlying disease. Jugular venous distention, pedal edema, and cardiomegaly may be absent in previously healthy individuals with pulmonary edema resulting from an initial episode of acute HF. The presence of a third heart sound significantly increases the likelihood of HF, whereas absence of rales decreases the likelihood.65 Physical examination of patients with APE resulting from acute MI may identify surgically correctable lesions such as acute mitral regurgitation or ventricular septal defect.



Diagnostic Testing in Heart Failure


An upright chest radiograph helps distinguish cardiogenic pulmonary edema from other causes of dyspnea. An enlarged cardiac silhouette is seen in 70% of cases. A normal heart size suggests acute cardiogenic pulmonary edema in a patient without prior HF, diastolic dysfunction, COPD, or noncardiogenic pulmonary edema. An early ECG for arrhythmia recognition and management is important, as well as for identification of acute coronary syndrome. Absence of cardiomegaly on chest radiography and a normal ECG greatly decrease the likelihood that HF is causing the presentation.65 Obtaining a complete blood count (CBC) to evaluate for anemia and a basic metabolic panel to determine electrolyte status as well as renal function is generally useful. Cardiac biomarkers help evaluate for ongoing myocyte injury, which may be clinically silent.


In most cases, and particularly when the diagnosis of HF is unclear, natriuretic peptide levels should be obtained. Pre-proBNP is synthesized in the ventricles in response to myocyte stretch, then released and enzymatically cleaved to NH2-terminal–proBNP (NT-proBNP) and BNP. NT-proBNP and BNP levels help identify patients with HF and may improve management of patients in the ED with dyspnea.6769 The “breathing not properly” BNP Multinational Study was a prospective evaluation of patients who came to the ED with acute dyspnea. BNP levels above 500 pg/mL were highly associated with HF (likelihood ratio [LR] 8.1), and levels of 100 to 500 pg/mL were generally indeterminate (LR = 1.8). A low BNP level (<100 pg/mL) indicated that HF was highly unlikely (LR = 0.13).70,71 ED use of BNP and NT-proBNP assays aids diagnosis of HF and can reduce admission rates and length of hospitalization in acute dyspnea.72


Natriuretic peptide levels correlate with ventricular function, NYHA classification, and prognosis.7376 Results of large clinical trials confirm that BNP levels are the strongest predictor of outcome in HF compared with other neurohormones and clinical markers.77 There is often a disconnect between the perceived severity of HF by clinicians and the degree of BNP elevation, yet BNP levels are better predictors of 90-day outcome than physician judgment.78 High predischarge BNP and NT-proBNP levels are strong, independent predictors of death or rehospitalization after decompensated HF.79,80


NT-proBNP– and BNP-guided therapy reduces all-cause mortality and provides a strong measure of therapeutic response in chronic HF compared with usual care.8183 Mildly elevated BNP levels may also be seen in right-sided HF related to cor pulmonale or pulmonary embolism. BNP levels are only slightly elevated in patients with end-stage renal disease, and in this setting marked elevation reflects ventricular dysfunction.84 Admission BNP and troponin levels are independent predictors of in-hospital mortality in acute decompensated HF.85 Increased concentrations of these and other biochemical markers of myocyte injury in the absence of discrete ischemic events in HF help identify patients most likely to have adverse outcomes.86 Plasma levels of cardiac troponins in stable HF also predict adverse outcomes.87,88


The ESCAPE trial demonstrates that pulmonary artery catheterization in severe symptomatic HF increases anticipated adverse effects but does not affect overall mortality or duration of hospitalization.89 Noninvasive impedance cardiography appears to be an effective and developing technology to measure CO and other hemodynamic variables in HF and may obviate the need for a pulmonary artery catheter, although it cannot reliably measure LV filling pressures.90,91


Bedside ultrasound can be an important ED screening tool in HF, with attention to wall motion abnormalities, EF, and valvular function, as well as exclusion of cardiac tamponade. Echocardiography is similarly useful and can provide detailed measures of LV function and determine structural heart disease.92,93 Multidetector computed tomography coronary angiography can distinguish ischemic from other forms of cardiomyopathy but is rarely useful in acute HF.94 Radionuclide imaging and cardiac magnetic resonance imaging have an expanding role in evaluating chronic HF but no utility in the acute setting.



Treatment of Acute Heart Failure


Of patients with HF in the ED, about 20% are experiencing their first episode of HF, and 80% have had prior hospital visits for the same condition.42 The approach focuses on (1) determining underlying cardiac pathology, (2) identifying the acute precipitant, and (3) mitigating the acute decompensation. The immediate therapeutic goals are to improve respiratory gas exchange, maintain adequate arterial saturation, and decrease LV diastolic pressure while maintaining adequate cardiac and systemic perfusion.


The acute congestive state can be controlled by (1) reducing cardiac workload through decreased preload and afterload, (2) controlling excessive retention of salt and water, and (3) improving cardiac contractility. Patients may have a wide spectrum of symptoms and signs ranging from mild dyspnea on exertion to full-blown cardiogenic shock with hypotension and concomitant respiratory failure.



Acute Heart Failure


Pulmonary edema is classified clinically into cardiogenic and noncardiogenic forms. Most patients in the emergency setting with pulmonary edema have the acute cardiogenic variety, resulting mainly from elevated LV end-diastolic pressure, forcing a protein-sparse plasma ultrafiltrate across the pulmonary capillary membrane into the pulmonary interstitium. Large amounts of edema accumulate, leading to alveolar flooding. Volumes as large as 1 or 2 L may leave the plasma over a short time and create serious respiratory compromise. Most commonly, cardiogenic pulmonary edema occurs with acute myocardial ischemia or infarction, cardiomyopathy, valvular heart disease, or hypertensive emergencies.


Patients with acute cardiogenic pulmonary edema have substantially lower plasma volumes than control patients. These changes are reflected by initial hemoconcentration as evidenced by higher hematocrits and colloid osmotic pressures. Despite the presence of pulmonary congestion, concomitant hypotension may require fluid challenge to rapidly restore preload, CO, systemic perfusion, and BP. Thus careful volume infusion with aliquots of normal saline is appropriate initial resuscitation for the hypoperfusing patient with acute-onset cardiogenic pulmonary edema.


In contrast, noncardiogenic pulmonary edema generally results from an alteration in the permeability characteristics of the pulmonary capillary membrane. The alteration may have such diverse causes as septic shock, inhalation injuries, drugs or toxins, aspiration syndromes, fat emboli syndrome, neurogenic causes, and high altitude.



Acute Heart Failure with Adequate Perfusion


Many patients with acute HF demonstrate adequate systemic perfusion with elevated BP because of activation of various compensatory mechanisms. The ability of the left ventricle to generate normal or elevated systolic pressures indicates the presence of considerable myocardial reserve and is associated with lower mortality in both acute and chronic HF.95 These patients should be quickly distinguished from those with pulmonary edema and evidence of hypoperfusion. Hypertensive pulmonary edema is easier to manage because afterload reduction with vasodilators is extremely effective.


Therapeutic interventions should decrease both preload and afterload. Excessive preload reduction may result in an abrupt decrease in CO, however, which could cause hypotension. This occurs more readily in patients with less compliant hearts. Fluid challenge generally restores BP. Therapy for APE with adequate perfusion should begin with upright positioning, supplemental oxygen, nitrates, morphine sulfate, and loop diuretics (Fig. 81-5). This allows prompt improvement in most of these patients.


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Jul 26, 2016 | Posted by in ANESTHESIA | Comments Off on Heart Failure

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