Biventricular Pacing for Heart Failure: The Guidant Companion Study

This growth appears to be related to the aging population, and also because of the successful treatment of many cardiac conditions with medications, interventions and devices. Nearly one million patients are discharged from the hospital annually with the diagnosis of heart failure, an increase of 159.4% from 1979 to 1998. The total cost of managing heart failure was estimated to be approximately $56 billion in 1999. Another common problem associated with heart failure is sudden cardiac death (SCD). Sudden cardiac death accounts for nearly 300,000 deaths per year which is half of all cardiac-related deaths (Figure 2). Aggressive identification of high-risk patients is critical, since 95% of patients who experience a SCD episode die before reaching the hospital. Patients with heart failure are at a high risk for SCD, anywhere from six to nine times the rate of the general population. Multiple drug therapy is most often used to treat heart failure. Various combinations and frequent dosing modifications are often necessary for treatment. Listed below are the typical drugs used for heart failure treatment: Ace inhibitors: Angiotensin-converting enzyme (ACE) inhibitors. Depresses circulatory levels of angiotensin I and markedly elevates plasma renin activity, and with interfering with the breakdown of bradykinin, which increases the circulating level of this vasodilator. These drugs act on both the arterial and venous beds. Digoxin: Positive inotropic affect on cardiac muscle that increases the force and velocity of contraction. Beta blockers: These are used to treat high blood pressure and decrease the workload on the heart by decreasing the heart rate; thus, decreasing the hearts oxygen demands. Beta blockers are shown to decrease overall mortality in Class II and III heart failure patients. Diuretics: Diuresis excessive fluid, despite a low glomerular filtration rate, promotes venodilation and reduces preload volumes. Spironolactone: Antihypertensive agent used in the management of edema associated with excessive aldosterone excretion. These medications, alone or in combinations, can be very effective in treating heart failure. One of the drawbacks is patient compliance. The Merck study looked at patient compliance, and defined it by the patient refilling 80% of the prescriptions on time and continuing them for more than one year. This study found that only 46% of patients with heart failure remained compliant. The previous standard of pacing the left ventricle was by affixing an electrode to the LV epicardial surface by means of a transthoracic, subxyphoid, or the open-chest procedure. Many concerns arise regarding this type of invasive procedure. The risks associated with this include infection, risk with general anesthesia and risks with the procedure itself. Coronary venous access allows for implantation of a left ventricular lead. The coronary veins lie on the epicardial surface of the left ventricle. Leads placed in the coronary vein can stimulate the myocardium through the coronary vein wall. Benefits of this type of implantation include a reduction in surgical risk, less invasive, shorter recovery time, and not necesitating the need for general anesthesia. The development of over-the-wire angioplasty catheters revolutionalized interventional cardiology, and this same technology is utilized to place the left ventricular leads in the coronary venous system. The coronary sinus os is typically 18-24 French (Fr) in size, while the distel segments taper to as small as 4-5 Fr. The placement of the lead is not only dependant of the distal diameter, but also on the tortousity of the vessel itself. Axial stiffness of the lead is required to the proximal portion of the lead body to allow forward passage through the guidewire and coronary vein, but must also remain flexible enough to conform to the shape of the heart as it contracts and relaxes. The LV lead is secured by using a tined lead with an atraumatic tip. It has been shown through animal studies that there is a low incidence of erosion of the coronary vein, as well as a low incidence of dislodgement. The most beneficial sites to be paced appear to be in the mid-lateral to the inferior regions of the left ventricle. The Guidant Companion clinical study is designed to compare the long-term results of patients who are receiving the current standard-of-care (optimal pharmacologic therapy or OPT) to those receiving OPT with resynchronization pacing therapy to those receiving OPT with resynchronized pacing therapy with an implantable cardioverter defibrillator (ICD) backup. The enrollment goal for the study is to enroll Several studies have shown that bi-ventricular resynchronization therapy has had a positive affect on systolic function (Figure 6). When bi-ventricular pacing patients for heart failure with a left bundle branch block and prolonged QRS complex at rest, it has been shown that there is an increase of 45% of stroke work and a 40% increase in stroke volume. In that same patient population there was a negligible affect if there was RV pacing alone. Guidant registered and enrolled 1000 consecutive patients, who received either a CONTAK TR bi-ventricular pacemaker or a CONTAK CD bi-ventricular pacemaker with ICD backup utilizing an EASYTRAK (Figure 4) over-the-wire left ventricular lead. These implants were carried out at 249 different centers by 323 different implanters. If the lead was successfully placed in the CS, the success rate was 95% (Figure 5). The most common problems were inappropriate thresholds, unstable positions, phrenic nerve stimulation, and subendothelial dissection. The most common problem was the inability to cannulate the coronary sinus, which led to the overall implant success rate of 86%. Bi-ventricular pacing with optimized atrioventricular delay has been proven to improve quality of life and functional capacity in a subgroup of congestive heart failure patients. Congestive heart failure remains the leading cause of death with patients having ICDs. It is speculated that combining bi-ventricular pacing with an ICD could lead to improvements in mortality, improved quality of life and less hospital admissions for heart failure. Current and ongoing studies will show if these speculations are true.