LONG-TERM EFFECTS OF DUAL-CHAMBER PACING IN PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY WITHOUT OUTFLOW TRACT OBSTRUCTION AT REST

Background Atrioventricular-synchronous pacing is beneficial in patien ts with hypertrophic obstructive cardiomyopathy. The effects of pacing in patients without significant left ventricular outflow tract obstru ction at rest are, however, less well explored. This study compares th e long-term outcome of pacing patients with and without significant le ft ventricular outflow tract obstruction at rest. Methods Forty-one pa tients with hypertrophic obstructive cardiomyopathy were studied, 19 w ith a left ventricular outflow tract gradient <40 mmHg at rest: but ex ceeding 50 mmHg during provocation with isoproterenol (group A), and 2 2 with a left ventricular outflow tract obstruction >40 mmHg at rest ( group B). Before the implantation of a permanent pacemaker, the patien ts were studied according to a temporary pacing protocol. This include d graded isoproterenol provocation of the left ventricular outflow tra ct obstruction, which was assessed by echo Doppler. Following permanen t pacemaker implantation, the patients were regularly followed up with echo Doppler, exercise testing and monitoring of the clinical conditi on. Results Isoproterenol provocation was reproducible and the techniq ue did not cause any clinically important side effects. Left ventricul ar outflow tract gradient reduction after chronic pacing did not diffe r between the two groups. In group A, it decreased from 98 +/- 30 mmHg in sinus rhythm to 42 +/- 26 mmHg during pacing. The corresponding va lues in group B were 87 +/- 40 mmHg to 36 +/- 24 mmHg. The clinical co ndition improved similarly in the two groups. Exercise capacity increa sed significantly and perceived dyspnoea and angina pectoris were sign ificantly lower at submaximal levels of exercise after 6 months of pac ing. Conclusion Hypertrophic obstructive cardiomyopathy patients who o nly exhibit significant left ventricular outflow tract obstruction dur ing provocation benefit as much from pacemaker treatment as do patient s who already have significant obstruction at rest. Isoproterenol is a safe and reproducible method for pre-pacing evaluation of hypertrophi c obstructive cardiomyopathy patients.