PHYSIOLOGICAL PACING IN THE TREATMENT OF HYPERTROPHIC OBSTRUCTIVE CARDIOMYOPATHY

Subaortic pressure gradient in hypertrophic obstructive cardiomyopathy (HOCM) is the consequence of a dynamic obstruction of the left ventricular outflow tract linked to the presence of a hypertrophied septum. We tried to induce an altered septal motion electrically by physiologic pacing. We studied 8 patients (6 men, 2 women, mean age 60 +/- 13 years) with symptomatic HOCM, resistant to optimal drug treatment. During a hemodynamic study, dual chamber pacing significantly reduced the preexistent subaortic pressure gradient, from 69 +/- 39 to 34 +/- 26 mm Hg (p < 0.004), without concomitant reduction of aortic pressure or cardiac output. This reduction was dependent upon a optimized AV interval A dual chamber pacemaker (PM) was then implanted and programmed to VDD mode and optimized AV delay interval (50-90 ms), warranting full ventricular capture. The follow-up of 3 to 30 months showed a significant reduction of both angina (from NYHA class 3 to 1:p < 0.009) and dyspnea (from 3 to 2:p < 0.03). An echo-doppler study in 6 patients proved the persistence of the beneficial effect of the stimulation by showing a significant reappareance of the subaortic pressure gradient after switching off the PM, from 44 +/- 29 in VDD pacing mode to 77 +/- 44 mm Hg (p < 0.02). We conclude that atrial synchronized ventricular pacing, together with an optimized AV interval, significantly reduces the outflow gradient and improves symptoms in patients with HOCM. An altered ventricular activation sequence with late septal activation is suspected to be the mechanism. This method could be an alternative therapy to surgery in some cases of HOCM refractory to drug therapy.