Introduction and objectives: Atrial synchronized ventricular pacing has shown to be an alternative to surgery in the therapeutic management of obstructive hypertrophic cardiomyopathy. Our purpose is the analysis of the hemodynamic mechanisms associated with the reduction of left ventricular outflow tract gradient and the changes in left ventricular diastolic function induced by dual-chamber pacing.
Patients and methods: We studied twenty patients (age range 40-78 years; mean 63 +/- 10), who were evaluated while receiving their current medication with cardiac catheterization and angiography, at baseline and under dual-chamber pacing.
Results: The atrioventricular delay was 127 +/- 26 ms. The subaortic gradient was reduced from 96 +/- 38 to 36 +/- 28 mmHg (p < 0.001), the ejection period index was shortened from 523 +/- 26 to 491 +/- 30 ms (p < 0.001) and the left ventricular end-diastolic pressure fell from 22 +/- 6 to 13 +/- 5 mmHg (p < 0.001). There was no remarkable change in cardiac output. The median wedge pressure decreased from 17 +/- 5 to 12 +/- 2.5 mmHg (p < 0.01), the pulmonary systolic pressure from 39 +/- 15 to 30 +/- 10 mmHg (p < 0.01), the pulmonary diastolic pressure from 19 +/- 5 to 13 +/- 4 mmHg (p < 0.01) and the right ventricular end-diastolic pressure from 7 +/- 3 to 5 +/- 3 mmHg (p < 0.05). The left ventricular ejection fraction was reduced from 79 +/- 6 to 72 +/- 6 per cent (p < 0.001). The initial ejection fraction diminished from 49 +/- 13 to 34 +/- 13 per cent (p < 0.01), the early diastolic filling increased from 39 +/- 11 to 52 +/- 10 per cent (p < 0.001) and the atrial contribution was reduced from 36 +/- 10 to 24 +/- 10 per cent (p < 0,001). The degree of mitral regurgitation changed from 1.4 +/- 1.2 to 0.7 +/- 0.9 (p < 0.01).
Conclusions: There is an obstruction in the left ventricular outflow tract in patients with obstructive hypertrophic cardiomyopathy that is relieved with dual-chamber pacing. The reduction in the intraventricular pressure seems to improve the ventricular relaxation and the diastolic function. The decrease in the degree of mitral regurgitation and the improvement in diastolic function diminish pulmonary capillary and right circuit pressures.