DDD Pacing for Hypertrophic Cardiomyopathy
ABSTRACT & COMMENTARY
Synopsis: QRS duration is not accurate for determining the optimal AV delay and suggests that an invasive or noninvasive evaluation to determine the lowest LVOT gradient that does not reduce aortic pressure is preferable.
Source: Losi MA, et al. Cardiology 1998;89:8-13.
Sequential right atria-ventricular pacing with a short AV delay has been shown to reduce the left ventricular (LV) outflow tract (OT) gradient in patients with hypertrophic obstructive cardiomyopathy (HOCM). However, a short AV delay may reduce late atrial emptying and paradoxically reduce cardiac output in these stiffened ventricles. Thus, Losi and associates from Naples, Italy, assessed the effect of varying AV delay in 12 patients with DDD pacemakers and HOCM at cardiac catheterization. The AV delay was randomly programmed to 125, 100, and 75 ms, and hemodynamic measurements were made. Permanent pacemakers were implanted in eight patients because of improved hemodynamics, and these patients were restudied by echo-Doppler methods with AV delays of 120, 100, and 80 ms. Systemic arterial pressure was not significantly changed during the studies, but the mean LVOT gradient decreased significantly by decreasing AV delay. At baseline, all patients had LVOT gradients of more than 30 mmHg; with an AV delay of 125 ms, it was less than 30 mmHg in four patients and with 100 or 75 ms in five patients. QRS duration on the ECG increased significantly with AV delay reduction (80 ms baseline, 141 at AV 125, 161 at AV 100, and 183 at AV 75; P < 0.001), but the widest QRS was not always associated with the lowest gradient. The findings were identical in the eight patients with a permanent pacemaker on non-invasive evaluation. Losi et al conclude that QRS duration is not accurate for determining the optimal AV delay and suggest that an invasive or non-invasive evaluation to determine the lowest LVOT gradient that does not reduce aortic pressure is preferable.COMMENT BY MICHAEL H. CRAWFORD, MD
The use of DDD pacing in HOCM is controversial. Clearly, the exaggerated claims that it prevents sudden death are not tenable, but it may reduce symptoms in some drug refractory patients and avoid or delay septal myectomy surgery. These 12 patients, all with LVOT gradients of more than 30 mmHg, were still symptomatic despite drug therapy (verapamil 9, beta blockers 10, both 7). Pacing did not reduce the gradient or increased the pulmonary capillary wedge pressure in four of the 12 patients, so permanent pacemakers were not implanted. The patients were tested after drug withdrawal (> 5 half-lives), so we do not know if pacing plus drugs would have benefitted these four patients.There are some limitations to this study. They did not evaluate AV delays below 75 ms, and aortic pressure drops were not observed. Thus, we don’t know if shorter delays would have been more beneficial. However, other studies have shown that AV delays of 50 ms reduce filling and delays of 150 ms do not reduce LVOT gradient. Also, cardiac output was not measured, so we don’t know if aortic pressure is an adequate surrogate for LV output. In addition, there is no long-term follow-up data to know if the initial success is sustained, whether AV delay adjustments need to be made over time, and if this hemodynamic improvement is associated with less symptoms.
The proposed mechanism of LVOT gradient reduction is right ventricular apical septal pre-excitation that results in LVOT enlargement during much of systole since the septum is relaxing. This study and others suggest that this approach works but is limited by the resultant reduction in the atrial contribution to filling. Presumably, patients benefit if the reduction in gradient effect is greater than the effect of reduced filling, and this study suggests that this occurs at AV delays of 75-100 ms.
The optimal AV delay for DDD pacing to reduce LV gradient in HOCM is:
a. 125-150 ms.
b. 100-125 ms.
c. 75-100 ms.
d. 50-75 ms.
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