Effect of pacing rate in pacing therapy in hypertrophic obstructive cardiomyopathy.

The effects of dual-chamber pacing therapy in patients with hypertrophic obstructive cardiomyopathy (HOCM) have been reported in short- and long-term studies. Almost all of these studies have reported that the key factor in pacing therapy is the setting of the atrioventricular (AV) interval. However, studies focusing on the effects of pacing rate on the hemodynamic state are rare. In this study, cardiac catheterization was performed in 2 patients during temporary pacing at various rates and AV intervals. When the pacing rate was increased slightly (to 70-90/min), AV sequential pacing decreased peak subaortic pressure gradient and increased systolic aortic pressure without increase in pulmonary capillary wedge pressure, left ventricular end-diastolic pressure, and the time constant of isovolumetric relaxation. In another case, of a patient who became refractory to AV sequential pacing therapy at an optimum AV interval, pacing at a slightly higher rate relieved syncope. Thus, AV sequential pacing therapy performed at a slightly higher rate than normal in a patient with HOCM may lead to a decreased subaortic pressure gradient and relief of symptoms without noticeable deterioration in cardiac function.