Biventricular ICDs: A Dual Approach to Heart Failure Management

The aging of the population in the next few decades will bring the need for increases in facility manpower and the challenge of creating enhanced technology. It is estimated that the number of Americans over the age of 65 will soon double.¹ This graying of the population comes with an increase in the incidence of coronary artery disease and congestive heart failure. It is estimated that 550,000 new cases of heart failure are diagnosed each year in the U.S., and heart failure is attributed for 287,000 deaths annually. The heart failure population is at high risk for sudden cardiac death episodes, and this risk increases as heart failure severity increases. The use of devices in the heart failure population has taken two distinct paths. One path has been via primary prevention of sudden cardiac death (SCD) through the implantation of ICDs. The other path has been the development of cardiac resynchronization therapies (CRT) to resynchronize the pumping of the left ventricle. This article will briefly look at these two therapy approaches and then discuss the marriage of the two ideas: the biventricular ICD. In 1999, there were 728,743 cardiac disease-related deaths in the U.S., of which 462,349 (63.4%) were due to SCD.² In the mid 1990s, clinical trials of ICD implantation for patients at high risk for SCD were initiated. The first of these, the Multicenter Automatic Defibrillator Implantation Trial (MADIT),³ enrolled patients who had sustained a myocardial infarction (MI) at least three weeks prior, had episodes of nonsustained ventricular tachycardia (VT), and left ventricular ejection fraction (LVEF) of 4,5 enrolled patients with coronary artery disease, nonsustained VT, and LVEF 120 ms.⁷ This decision was considered controversial in that it allowed payment for ICD implantation as a primary prevention for SCD, but limited that payment to those with a defined QRS width, a variable not examined in any of the pivotal studies. A widening of the QRS to > 120 ms is seen in approximately one-third of all patients with left ventricular systolic dysfunction.⁸ As a result, these patients experience a ventricular dyssynchrony or a lack of synchronization between the left and right ventricle. This dyssynchrony results in functional changes that ultimately lead to an increase in mortality. These changes include suboptimal ventricular filling and a resultant decrease in cardiac output. In addition, there is a reduced left ventricular contractility, mitral regurgitation occurs during a greater portion of the cardiac cycle, and there is a paradoxical septal wall motion. All of these abnormalities add up to decreased output and further enhancement of heart failure symptoms.^9-12 The theory behind CRT was that a more synchronous contraction of the left ventricle should improve cardiac output. In addition, it was believed that the shortening of the activation time for the left ventricle may add to the time available for myocardial perfusion, thus increasing coronary blood supply. Biventricular pacing seemed to make these goals a reality. The Multicenter InSync Randomized Clinical Evaluation (MIRACLE) trial^13,14 enrolled 453 patients with moderate to severe heart failure associated with a LVEF = 130 ms. These patients were randomized to resynchronization therapy with biventricular pacing or control, with control patients crossing over to biventricular pacing at 6 months. Patients underwent baseline and 3- and 6-month evaluations of quality of life, 6-minute hall walk test, treadmill testing, and a functional class assessment. At one year, New York Heart Association (NYHA) class improved by one class, and sustained improvement was seen with the 6-minute hall walk test and the quality of life scores. This trial was pivotal in the acceptance of CRT as a therapy in heart failure management. The CRT implant procedure includes routine pacemaker implantation with the placement of an additional lead in the coronary sinus. An injection of dye into the coronary sinus allows the physician to visualize the coronary venous anatomy and select an appropriate vein for lead placement. The right ventricular and coronary sinus leads should be placed as distant from each other as possible, in order to enhance the resynchronization effect. During the procedure, 12-lead ECGs are generally obtained to document the patient s native QRS, right ventricular (RV) paced QRS, left ventricular (LV) paced QRS, and the biventricular QRS. This serves as a template for future 12-lead assessments of proper lead positioning. A wide QRS will be seen in the native RV and LV tracings, but a narrowed version should be present when biventricular pacing is occurring. After implantation, the physician may choose to utilize AV optimization to fine tune the hemodynamics of the device. AV optimization is echo-guided programming of the pacing AV interval to optimize the left atrial contribution to LV filling. A 12-lead ECG may be obtained as well as a chest x-ray to document lead placement. The development of multisite pacing has resulted in the need to revise the NASPE Code for pacing. Table 1 contains the current pacing designations. Position V is now used for the multi-site pacing designation.¹⁵ The improved functional capacity, which CRT provides, was joined with SCD prevention to provide a truly innovative and efficacious tool for heart failure management. Two major trials have examined the use of biventricular ICDs in the heart failure population: MIRACLE ICD (Medtronic, Minneapolis, Minnesota) and CONTAK CD (Guidant, Indianapolis, Indiana).^16-17 The data from these trials led to device approvals in 2002. Patients who qualify for the implantation of a biventricular ICD have: Evidence of life-threatening arrhythmias (these devices provide ventricular anti-tachycardia pacing and ventricular defibrillation) The presence of moderate to severe heart failure (NYHA classes III and IV) Left ventricular ejection fraction of = 130 ms (Medtronic), or > 120 ms (Guidant) These patients are also currently on optimum medical therapy but are having continued symptoms Contraindications to device implantation include: The presence of ventricular tachyarrhythmias that are of a transient or reversible nature The presence of incessant VT or VF (rapid battery depletion would result if a device were implanted) The presence of a unipolar pacemaker (enhanced pacing signal would be sensed as a ventricular event by the defibrillator, thus double counting ventricular rate and possibly delivering tachycardia therapies erroneously) Two devices are currently available. These include the INSYNC MARQUISTM 7277 (Medtronic) and the CONTAK ® RENEWAL (Guidant). The implant procedure includes the insertion of the extra coronary sinus lead, as in the biventricular pacemaker implantation plus the normal testing performed for ICD implantation. Patients are generally seen 7-10 days after implantation, in order to assess the wound site and examine sutures. This is an excellent time to review activity and care instructions. Because of the stressors of hospitalization and the effect of medications, patients often do not remember information told prior to discharge. Therefore, this follow-up visit provides an opportunity to fill informational gaps. Videotapes and printed materials are helpful as well. Patients should be seen thereafter at about three-month intervals. Visits should be coordinated efforts between the heart failure and electrophysiology staff. Elements of follow-up include recent history, physical assessment focusing on heart failure status, interrogation of the device, and in some cases an echocardiogram to assess potential reprogramming needs. Device interrogation provides information on a multitude of arrhythmic problems. The heart rate variability information collected by the devices assists in risk stratification for sudden cardiac death in addition to indicators of functional improvement. The status of SA nodal function is available, as is information about atrial fibrillation, atrial flutter and the potential need to institute anticoagulation therapy. In addition, episodes of sustained and nonsustained ventricular tachycardia will be stored within the device s memory. The percentage of ventricular pacing should be checked as well, along with an evaluation of battery s life. Device testing will include: Sensing tests Testing for biventricular pacing threshold LV/RV pacing threshold (ventricular output should be based on the higher of the RV and LV thresholds) Possibly AV optimization with echocardiography Upper tracking rate should be programmed to ensure a device rate above the patient s inherent rate through a wide range of daily activity levels to ensure that resynchronization therapy will be consistently delivered Programming issues include avoiding situations in which inappropriate therapy is delivered and an avoidance of possible electrical resets of the device, thus sources of magnetic and electromagnetic radiation should be avoided. As the functional status of the patient improves, medication dosages may be changed. Emergency care providers must be instructed that transthoracic defibrillation paddles cannot be placed directly over the device. Elements of patient education for this population include: lifestyle modification; information about signs of mild heart failure; information about diet, especially salt intake and volume management; ICD and pacemaker education; stress management; and information about medications. These patients would benefit from participation in both heart failure and ICD support groups. Patients should be instructed to avoid any source of magnetic or electromagnetic radiation. This includes MRI, diathermy and electrosurgical units. The use of biventricular pacing combined with ICD capabilities offers an opportunity to make a major impact on the care of heart failure patients. The challenge to the professional is in the integration of expertise from the heart failure realm with the intricacies of device therapy. The future will surely continue to make this an exciting area for practice and bring hope to our patients.