Bradycardia and Tachycardia


Chapter 27

Bradycardia and Tachycardia



Terry Mahan Buttaro



Bradycardia


Definition and Epidemiology


Absolute bradycardia is defined as a heart rate of less than 60 beats per minute. Athletes, older adults, and other individuals may have normally slow heart rates, and bradycardia may not be pathologic during sleep or after a Valsalva maneuver or other vagal stimulation.1 Relative bradycardia occurs when the heart does not respond as expected to trauma, hypovolemia, or an infectious process.1 Lyme borreliosis, malaria, and dengue fever are other possible causes.2


Numerous medications, cardiac disease, hypothyroidism, electrolyte abnormalities, sleep apnea, infections, increased intracranial pressure, hypothermia, hypoxemia, acidemia, and other disease states can also produce bradycardia. Asymptomatic bradycardia does not require urgent intervention. However, careful monitoring and therapy are indicated if the bradycardia causes symptoms (e.g., angina, change in mental status, dizziness associated with hypotension, hypertension, heart failure, or syncope) or if the bradycardia is related to type II second-degree (Mobitz type II) or third-degree atrioventricular (AV) block.


imageImmediate emergency department referral or physician consultation is indicated for patients with symptomatic bradycardia or Mobitz type II or third-degree heart block.



Pathophysiology


Bradycardia may result from sinus node dysfunction or AV block.3 Sinus node dysfunction can be a result of increased vagal tone, as seen in athletes or conditioned young people or in older adults as the result of underlying disease processes, medications, or toxicity.4 AV block is also associated with various disease processes, including myocardial infarction, coronary artery spasm, digitalis toxicity, cardiac mesotheliomas, and infectious processes. Medications, particularly beta blockers and calcium channel blockers, may induce either sinus node or AV dysfunction.



Clinical Presentation


Some symptoms may be nonspecific, but dizziness, fatigue, and syncope are complaints commonly identified with bradycardia.3 Nausea, vomiting, and confusion have also been correlated with bradycardia. Any bradyarrhythmia associated with chest pain, shortness of breath, exercise intolerance, decreased level of consciousness, hypotension, seizure, congestive heart failure, or myocardial infarction is considered a prearrest condition. A careful symptom analysis and review of the patient’s medical history, including allergies and prescribed and over-the-counter medications, is necessary to discern the cause of the bradycardia so that appropriate treatment can be initiated.



Physical Examination


Although associated symptoms will often guide the physical examination, a focused history and physical examination are necessary. The patient’s level of responsiveness and vital signs (including temperature, blood pressure, pulse, respiratory rate, and oxygen saturation) are significant and should be continually reassessed. Hypotension, ventricular arrhythmias, and pulmonary congestion are serious signs indicating the need to identify the cardiac rhythm and to institute rapid, appropriate treatment.



Diagnostics


An electrocardiogram (ECG) is necessary for rhythm analysis and appropriate management. Further diagnostics are guided by the history and physical examination but can include drug levels, electrolyte values, glucose concentration, blood urea nitrogen (BUN) level, creatinine concentration, complete blood count (CBC), creatine kinase muscle-brain (CK-MB) fraction, troponin T or troponin I level, thyroid studies, and chest x-ray studies.




Differential Diagnosis


Determination of the bradyarrhythmia and associated disease is essential for treatment. Herbals and medications can be a common cause of bradycardia, but infections, vasovagal syncope, myocardial infarction, digitalis toxicity, sick sinus syndrome, bradycardia-tachycardia syndrome, hypothyroidism, and other disease states are also possible reasons.3




Initial Stabilization and Management


The American Heart Association recommends cardiac monitoring, intravenous access, and continuous assessment of the patient (including airway, breathing, vital signs, oxygen saturation, and supplementary oxygen) when indicated It is crucial to differentiate the symptoms caused by the bradycardia from those not related to the slow rate. No intervention is necessary if the patient is stable and asymptomatic, but continued monitoring is indicated to ensure the patient’s well-being.


For correct identification of the cardiac rhythm, a 12-lead ECG is necessary. Patients with suspected myocardial infarction should be treated for acute coronary syndrome according to the 2010-2015 American Heart Association guidelines (with oxygen, if indicated; aspirin [162 to 325 mg chewed, if not aspirin allergic]; nitroglycerin; morphine; and, if appropriate, reperfusion therapy).5


Symptomatic patients with worsening clinical symptoms or prearrest conditions related to the bradycardia may require urgent intervention before a definitive underlying condition is identified. For adult patients with symptomatic bradycardia, especially if the bradycardia is associated with Mobitz type II second-degree heart block or third-degree heart block, the American Heart Association recommends atropine, 0.5 mg intravenously every 3 to 5 minutes (up to a total dose 3 mg), until a transcutaneous or transvenous pacer (class I intervention) is available.5 However, atropine can induce cardiac ischemia, precipitate ventricular tachycardia (VT) or fibrillation, and be deleterious for patients with a history of cardiac transplantation.5 In the presence of Mobitz type II second-degree heart block or third-degree heart block associated with wide-complex ventricular escape beats, atropine should be avoided and treatment with a transcutaneous or transvenous pacer applied as soon as possible.5 Some defibrillator monitors may also have a transcutaneous pacer component.


If the bradycardia is drug induced (e.g., beta blocker or calcium channel blocker overdose), a pacer is not available, atropine is contraindicated, or the patient is unresponsive to atropine or pacing, intravenous epinephrine 2 to 10 µg/min can be used to treat critical bradycardia.5 A dopamine infusion of 2 to 10 µg/kg/min can also improve cardiac output and increase blood pressure and may be used alone or in conjunction with an epinephrine infusion.5



Disposition and Referral


Patients experiencing signs and symptoms related to bradyarrhythmias require constant reassessment and definitive management in an emergency department. Immediate transfer to an emergency center is required.



Prevention


Prevention, when possible, may avert complications or serious injury. Patients who complain of syncope, fatigue, or other symptoms that may be related to bradycardia require diag­nostic assessment. A permanent pacemaker may be indicated for bradycardia associated with sinus node dysfunction and certain heart blocks (e.g., fascicular block or acquired AV block).3,5,6



Patient and Family Education


Patients should understand the importance of calling their health care provider if they experience syncope, lightheadedness, or a slow heart rate that hinders activities. In addition, patients and caregivers should know how to activate the emergency medical system (911) if these symptoms occur with chest discomfort or shortness of breath.


Careful explanation and supportive therapy will enhance patient and family understanding. These measures will also help allay the anxiety inherent in an emergent situation. Medication regimens, if associated with the bradyarrhythmias, should be reviewed to prevent misinterpretation.

Only gold members can continue reading. Log In or Register to continue

Oct 12, 2016 | Posted by in CRITICAL CARE | Comments Off on Bradycardia and Tachycardia

Full access? Get Clinical Tree

Get Clinical Tree app for offline access