Studies on the pathophysiological mechanism of hypertrophic cardiomyopathy

Background Treatment options for patients with symptomatic non-obstructive HCM are limited, driving a need to develop novel treatment strategies. Objectives To investigate the effects of biventricular pacing on symptom status and exercise capacity in patients with symptomatic non-obstructive Hypertrophic Cardiomyopathy and explore the mechanism of benefit. Methods 31 patients with symptomatic, exercise limited non-obstructive Hypertrophic Cardiomyopathy were enrolled into this double blind randomised cross over study of Biventricular vs sham pacing. The primary end point was peak oxygen consumption. Results 29 patients successfully completed the study. Biventricular pacemaker therapy increased peak Oxygen consumption (1.17ml/kg/min) and improved quality of life, without effects on systolic or diastolic mechanical dyssynchrony. A subset of patients in whom left ventricular diastolic volume fell on exercise (n = 15) achieved a greater increase in peak Oxygen consumption vs. those in whom left ventricular diastolic volume increased (1.4 vs. 0.91ml/kg/min p = 0.03) and this was associated with a normalisation of the left ventricular diastolic volume response to exercise. Conclusions Severely symptomatic patients with non-obstructive Hypertrophic Cardiomyopathy may benefit from Biventricular pacing. The mechanism of benefit from this treatment modality was a profound improvement of diastolic filling on exercise potentially due to amelioration of diastolic ventricular interaction.