ALTERED CARDIAC HEMODYNAMIC AND ELECTRICAL STATE IN NORMAL SINUS RHYTHM AFTER CHRONIC DUAL-CHAMBER PACING FOR RELIEF OF LEFT-VENTRICULAR OUTFLOW OBSTRUCTION IN HYPERTROPHIC CARDIOMYOPATHY

Dual-chamber (DDD) pacing relieves left ventricular (LV) outflow tract obstruction in patients with hypertrophic cardiomyopathy. The reduction in LV outflow gradient persists in some patients after cessation of pacing. Twelve-lead and signal-averaged electrocardiograms were obtained before and after 12 weeks of DDD pacing in 18 patients with obstructive hypertrophic cardiomyopathy to determine whether the altered hemodynamic state after chronic pacing is accompanied by electrical changes. Hemodynamic studies were performed at baseline and at follow-up. Signal-averaged electrocardiograms were obtained using a Corazonix Predictor and bidirectional filters at 25 Hz to a noise level of <0.5-mu-V. At follow-up, LV outflow tract gradients were reduced significantly during DDD pacing and with cessation of pacing in sinus rhythm by 56 +/- 10 and 47 +/- 10 mm Hg, respectively (p <0.001). There was no simple relation between changes in LV outflow tract gradient and in the electrocardiogram. For example, amplitude of the R wave in V5,6 was reduced by greater-than-or-equal-to 0.5 mv in 4 patients, unchanged in 12 and increased in 2. Similarly, the S wave in leads V1,2 was reduced in 7 patients, unchanged in 7 and increased in 4. The T wave became more negative (greater-than-or-equal-to 0.1 mv) in leads II, III, aVF and V5,6 in 13 patients and more positive in leads I and aVL in 12. The QRS was also altered by signal-averaged electrocardiographic criteria; duration of the total QRS and root-mean-square voltage of the QRS of the filtered Y axis increased (106 +/- 12 to 112 +/- 13 ms [p = 0.036] and 170 +/- 82 to 195 +/- 102-mu-V [p = 0.059], respectively). In conclusion, chronic DDD pacing significantly reduces obstruction to LV outflow, and after discontinuation of chronic DDD pacing, there is evidence of altered mechanical as well as electrical myocardial state.