ELECTROPHYSIOLOGY AND OTHER CATHETER-BASED PROCEDURES OVERVIEW

Cardiac EP is the medical specialty devoted to the diagnosis and treatment of abnormal heart rhythms. It involves diagnostic electrophysiology testing, radiofrequency catheter ablation, and implantation of antiarrhythmic devices such as pacemakers and cardio-defibrillators.

Advanced medical research, new technology, an aging population, and the prolonged survival of very ill patients have added to the complexity of procedures performed and management of patients requiring EP therapies.^1–4 The anesthesiologist is frequently consulted in both the cardiac catheterization and electrophysiology laboratories to help manage patients with severe coronary, valvular, and vascular diseases. Patients can experience hemodynamic perturbations secondary to arrhythmias, poor baseline ventricular function, or procedurally related iatrogenic myocardial perforation and tamponade. Anesthesiologists are called upon not only to maintain patient comfort during these procedures but also to be available to resuscitate the patient should hemodynamic or airway complications present.¹ Consistent guidelines have yet to be established regarding the nature of procedures and the complexity of patients which warrant the involvement of the anesthesia team.

Procedures that might involve the anesthesia team include:

a. Coronary artery stenting is used in the treatment of ST-elevation myocardial infarction, in-stent restenosis, stenting of saphenous vein grafts, and treatment of chronic coronary artery occlusions. Most of these procedures are performed under moderate sedation given by the nursing staff of the catheterization laboratory. Involvement of the anesthesia team typically is requested when the patient is hemodynamically unstable or there is a need for emergent airway management.⁵

b. Percutaneous ventricular assist devices (VADs): Until recently, intra-aortic balloon contrapulsation with inotropic support was the main therapeutic option for supporting the failing ventricle. Implantable ventricular assist devices have been and are being used now as “bridge to recovery or to transplantation” for the failing ventricle. Implantable VADs are placed in the cardiac surgery operating room. However, during the past few years a number of percutaneous designs have appeared which can be placed in the catheterization laboratory to provide emergent support for the failed heart.
Two percutaneous ventricular assist devices (PVAD) that can be placed in the cardiac catheterization laboratory are the TandemHeart (Cardiac Assist, Inc., Pittsburg, PA) and the Impella Recover LP 2.5 and 5.0 (Abiomed Inc., Danvers, MA). Both of these devices can be placed with moderate sedation; however, general anesthesia is preferred to secure the airway and to facilitate the use of TEE should it be required during PVAD placement.⁵

c. Percutaneous closure of septal defects: Increasingly closure of atrial septal defects has been accomplished through the placement of a variety of catheter-delivered occluding devices. A similar device is under development to treat postmyocardial infarction ventricular septal defects. Most of those devices are placed under general anesthesia with transesophageal echocardiography guidance for device positioning.

d. Percutaneous valve repair and replacement: Percutaneous valvuloplasty or valvotomy has been performed for decades, but new interventions now focus not only on opening stenotic valves but also on actual percutaneous valve repair and replacement.

The introduction of nonsurgical catheter-based approaches to the management of valvular disease is in a phase of rapid development. Initially, the patient population considered suitable for percutaneous aortic valve replacement was that thought high risk for surgery or nonsurgical candidates with significant comorbidities. Although early mortality with this approach was high, rapid improvements continue to better the patient outcomes. The initial approach to the aortic valve was accomplished via passage of the catheter-based valve from the femoral vein to the right atrium and then trans-septally to the left atrium, left ventricle, and into the aortic root. As this approach has yielded poor outcomes in a significant number of patients, more recently the valve has been placed into the aortic position via the femoral artery, or antegrade, via a small chest incision, and puncture of the left ventricular apex.⁶

Catheter-based approaches to the mitral valve are quite complex as there is no single therapeutic approach for repair for every etiology of mitral regurgitation.⁷

Catheter-based treatments for mitral regurgitation include clipping together the anterior and posterior leaflets of the mitral valve at the midpoint yielding a double-barrel mitral orifice. Alternatively, a device can be placed in the coronary sinus to tighten the mitral annulus. These procedures are completed using echocardio-graphic and fluoroscopic guidance.

EP PROCEDURES

Indications for EP studies include:

1. Determine the precise mechanism of tachyarrhythmia.

2. Perform catheter ablation for treatment of a medically refractory arrhythmia.

3. Evaluate the need for placement of implantable defibrillators in patients with or at risk of life-threatening ventricular arrhythmias.

4. Risk stratification for sudden cardiac death syndrome (SCD).

EP procedures include percutaneous catheter-based therapy/ablation for atrial and ventricular arrhythmias, pacemaker, and/or defibrillator implantation.

Electrophysiology studies are performed in specialized EP laboratories, equipped with a fluoroscopy (x-ray) machine. During an EP study peripherally inserted catheters are advanced into the heart to identify areas of altered cardiac electrical conduction.

Intracardiac measurements of electrical activity are recorded at different parts of the heart at baseline or following administration of chronotropic agents.

During an EP procedure, two to four temporary electrode catheters are inserted and positioned into the heart chambers (with the x-ray guidance) via a large vein either in the groin or in the neck.

These wires permit electrical stimulation and recording of electrical responses. An important part of the EP study is to induce the arrhythmia in order to locate the abnormal circuit.

Treatment options for cardiac arrhythmias include the following^2,3:

1. Antiarrhythmic drug therapy

2. Catheter ablation therapy

3. Implantable device therapy (pacemakers, defibrillators)

The decision of choosing one option over another depends on the severity of cardiac arrhythmia and the impact of therapy options upon the patient’s quality of life.

Catheter-Based Ablation

Until 20 to 25 years ago, the only viable treatment for most arrhythmias was medication. On rare occasions open-heart surgeries with mapping and ablation or high-energy direct current internal ablation were performed.

In the 1990s, radiofrequency (RF) catheter ablation was developed. Catheter ablation has evolved over the past two decades to become first-line therapy for many cardiac arrhythmias. Catheter ablation often eliminates the need for chronic drug therapy and can result in significant long-term cost savings.^8,9

Tachyarrhythmias amenable to RF catheter ablation include:

AV nodal reentrant tachycardia

AV reciprocating tachycardia (WPW syndrome)

Some forms of atrial tachycardia and flutter

Selected patients with paroxysmal atrial fibrillation (AF)

Some of the ventricular tachycardias

Catheter ablation in the setting of reentrant supraventricular tachycardia (SVT) and atrial flutter is associated with both low complication and high success rates. It can be safer, more effective, and less expensive than chronic medical therapy for all age groups. Catheter ablation has expanded to include the treatment of more complex arrhythmias such as atrial fibrillation (AF), unstable ventricular tachycardia (VT), and epicardial VT.

Catheter-based EP studies first identify the area responsible for arrhythmia generation. Using radio frequency (RF) energy the small focus of heart tissue responsible for initiating the arrhythmia is ablated. Catheter-based ablation is limited by: inability to precisely localize (map) the area responsible, difficulty in positioning the catheter tip at the critical site, or inability to deliver adequate energy to the target.

Catheter ablation procedures are tripartite by nature involving:

1. Placement of electrode catheters inside the heart through veins and arteries

2. Performance of an EP study to detect the mechanism of arrhythmia and localize the responsible area

3. Performance of the actual RF ablation to destroy the target tissue

Atrial fibrillation is one of the more common arrhythmias successfully treated by RF catheter ablation and is the most common sustained cardiac rhythm disturbance associated with an increased risk of stoke, heart failure, and death.

The pulmonary veins (PV) have been demonstrated to play an important and mischievous role in generating atrial fibrillation. Because of their critical role in AF, a variety of surgical and catheter ablation techniques are used to isolate the PV within the left atrium.¹⁰

Before the procedure, computerized tomography (CT) scan of the heart with three-dimensional reconstruction is performed in order to define the anatomy of the pulmonary veins.

The procedure involves positioning a catheter in the right atrium via the femoral vein. The patient is anticoagulated with heparin and transeptal catheterization of the left atrium is achieved after systemic anticoagulation to a target activated clotting time (ACT) of 250 to 350 seconds. Angiograms of the four pulmonary veins are performed. Once identified, pulmonary vein isolation is performed by the delivery of RF energy at the pulmonary vein’s ostium for a target temperature of 52°C and a maximum power of 30 to 35 W for 30 to 45 seconds. Elimination of all ostial pulmonary vein potentials and complete entrance block into the pulmonary veins are considered indicative of complete PV electrical isolation.

Potential limitations of PV ablation include technical failure due to variations in anatomy and difficulty in mapping the focus. The procedure may result in complications, including pulmonary vein stenosis (up to 45%), hemopericardium (1%), and chronic thromboembolic events (1%).^9,10

Most ablative procedures can be performed with moderate sedation and standard monitoring. However, some of the percutaneous ablation procedures can be very lengthy (6-8 h). Also, coughing or partial airway obstruction with abdominal paradoxical motion can interfere with the procedure, so moderate to deep sedation or even general anesthesia with controlled respiration might be required. In patients with compromised ventricular function, inotropic/pressor support with invasive monitoring might be necessary.

Implantation of Cardioverter Defibrillators (ICD/Biventricular Pacemakers)

The placement and testing of ICDs has increased exponentially in recent years, mostly secondary to an expanded list of indications. Biventricular pacing and cardiac resynchronization therapy (CRT) permits better timing of global left ventricular depolarization and improves mechanical contractility and mitral regurgitation in selected patients with heart failure. Many clinical trials have shown that CRT results in improved quality of life,¹¹ lower mortality rate, and improved functional class in heart failure patients.¹²

Standard indications for ICD therapy include^4,12,13:

1. Primary prevention of sudden cardiac death (SCD) for patients who have not yet sustained a clinical event, but who are at risk for SCD:

a. Prior myocardial infarction with left ventricular ejection fraction (LVEF) of less than 35% (by cardiac imaging, echocardiography, nuclear study, or cardiac catheterization)

b. Nonischemic cardiomyopathy (CMP) with LVEF less than 35%

c. Hypertrophic cardiomyopathy and risk for sudden cardiac death (SCD)

d. Primary electrical disorders (long QT, Brugada syndrome)

2. Secondary prevention of SCD for patients who have already had a clinical event:

a. Survived cardiac arrest due to ventricular tachycardia (VT) or ventricular fibrillation (VF)

b. Sustained VT

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