Optimal Pacing Site for Resynchronization Therapy In Heart Failure Patients
Abstract & Commentary
Synopsis: LV free wall pacing resulted in better systolic performance as compared to anterior wall stimulation in heart failure patients undergoing resynchronization therapy.
Source: Butter C, et al. Circulation. 2001;104: 3026-3029.
Butter and colleagues performed a study which systematically evaluated the acute hemodynamic response to biventricular and left ventricular pacing in patients with heart failure. Butter et al enrolled 43 patients scheduled for implantation of a biventricular pacemaker. In 30 of these patients, the left ventricular electrode could be successfully positioned in both an anterior wall position and a left ventricular free wall position via the coronary sinus. The group included 18 patients with dilated cardiomyopathy and 12 patients with coronary artery disease. They had New York Heart Association class II or greater heart failure with a mean QRS width of 152 ± 17 msec. Their ejection fraction was 23 ± 8%. At the time of their pacemaker implant, the left ventricular pacing electrode was placed either in the free wall region via the lateral or posterior vein or in the anterior region via the great cardiac vein. Micromanometer dual transducer catheters were inserted into the heart to provide right ventricular, aortic, and left ventricular pressures. Data were obtained during univentricular left ventricular pacing, and biventricular pacing for each possible configuration. A VDD stimulation mode was used with 4 preset AV delays. Changes in dP/dt and pulse pressure were calculated for each type of pacing.
Free wall stimulation and anterior wall stimulation increased left ventricular dP/dt over a wide range of AV delays. However, in 9 of the 30 patients, discordant results between free wall stimulation and anterior wall stimulation were observed with increases noted in the former and decreases in the latter. There was no difference in the pattern of response between dilated cardiomyopathy patients and CAD patients. Pulse pressure increased 8% during free wall stimulation compared to 4% during anterior wall stimulation. In 13 of 30 patients, biventricular resynchronization from the free wall was better than from the anterior wall. There was a greater intrinsic conduction delay to the free wall as compared to the anterior wall site. The magnitude of the conduction delay difference was positively correlated with changes in dP/dt observed during free wall and anterior wall stimulation. Butter et al concluded that LV free wall pacing resulted in better systolic performance as compared to anterior wall stimulation in heart failure patients undergoing resynchronization therapy.
Comment by John P. DiMarco, MD, PhD
Biventricular pacing has emerged as a promising therapy for patients with heart failure and intraventricular conduction delays. The theory has been that delays in activation of the left ventricle produce dyssynchronous ventricular contraction with negative effects on ventricular function and hemodynamics. In theory, cardiac resynchronization therapy should eliminate the conduction delay between the right and left ventricles by pacing both ventricles simultaneously.
Unfortunately, at the present time, the lead systems used for placement of the left ventricular lead via the coronary sinus are difficult to use. Coronary venous anatomy is also variable. For this reason, it is often difficult to achieve a stable position at any desired place in the left ventricle. These data, however, suggest that an anterior wall site should not be accepted until attempts to find a free wall site have been made. This may not always be technically feasible. The implanting physician must use judgment and weigh the relative risks of greatly prolonging an already difficult procedure vs. accepting a suboptimal pacing site. v
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