ABSTRACT
Objective - To assess the changes in ventricular evoked responses (VER) produced by the decrease in left ventricular outflow tract gradient (LVOTG) in patients with hypertrophic obstructive cardiomyopathy (HOCM) treated with dual-chamber (DDD) pacing. Methods - A pulse generator Physios CTM (Biotronik, Germany) was implanted in 9 patents with severe drug-refractory HOCM. After implantation, the following conditions were assessed: 1) Baseline evaluation: different AV delay (ranging from 150ms to 50 ms) were sequentially programmed during 5 to 10 minutes, and the LVOTG (as determined by Doppler echocardiography) and VER recorded; 2) standard evaluation, when the best AV de lay (resulting in the lowest LVOTG) programmed at the initial evaluation was maintained so that its effect on VER and LVOTG could be assessed during each chronic pacing evaluation. Results - LVOTG decreased after DDD pacing, with a mean value of 59 + 24 mmHg after dual chamber pacemaker, which was significantly less than the gradient before pacing (98 + 22mmHg). An AV delay > 100ms produced a significantly lower decrease in VER depolarization duration (VER(DD)) when compared to an AV delay =100ms. Linear regression analyses showed a significant correlation between the LVOTG values and the magnitude of VER (r=0.69; p<0.05) in the 9 studied patients. Conclusion - The telemetry obtained intramyocardial electrogram is a sensitive means to assess left ventricular dynamics in patients with HOCM treated with DDD pacing.