HCM is a heterogeneous disease genotypically, phenotypically, pathophysiologically, clinically, and therapeutically. In decisions on the management of these patients, it is important to recognize this heterogeneity and to direct therapy at the predominant abnormalities.

Hypertrophic Cardiomyopathy Clinical Spectrum and Treatment

BACKGROUND Patients with obstructive hypertrophic cardiomyopathy (HCM) with symptoms refractory to drugs (beta-blockers or verapamil) are candidates for cardiac surgery (left ventricular septal myectomy or mitral valve replacement). The present study examines prospectively the ability of dual-chamber (DDD) pacing to improve symptoms and relieve left ventricular outflow obstruction in such patients. METHODS AND RESULTS Forty-four consecutive patients with obstructive HCM who had failed to benefit from pharmacotherapy underwent treadmill exercise tests, echocardiography, and cardiac catheterization before and 1.5-3 months after implantation of a DDD pacemaker. Symptoms (angina, dyspnea, palpitations, presyncope, and syncope), New York Heart Association functional class status (1.7 +/- 0.7 versus 3.4 +/- 0.5, p less than 0.00001), and exercise durations were improved at follow-up evaluation. This was associated with significant reduction in left ventricular outflow tract gradient (38 +/- 38 versus 87 +/- 43 mm Hg, p less than 0.0001) and significant increases in cardiac output and systemic arterial pressures. Notably, when pacing was discontinued and comparisons were made in sinus rhythm, treadmill exercise durations were greater and left ventricular outflow tract gradients were less at the follow-up evaluation compared with the baseline study. CONCLUSIONS DDD pacing is an effective alternative to surgery in most patients with obstructive HCM with drug-refractory symptoms. The beneficial effects of pacing continue to be evident when pacing is acutely discontinued.

Impact of dual-chamber permanent pacing in patients with obstructive hypertrophic cardiomyopathy with symptoms refractory to verapamil and beta-adrenergic blocker therapy.

The pacemaker syndrome is a complex of clinical signs and symptoms related to the adverse hemodynamic and electrophysiologic consequences of ventricular pacing in the absence of other causes. Neurologic symptoms or those suggesting low cardiac output or congestive heart failure, temporally related to the onset of ventricular pacing, are indicative of the pacemaker syndrome. The evolution of a clinically recognized syndrome, an analysis of possible mechanisms and clinical manifestations, and diagnostic approaches and their implications for management are discussed.

The Pacemaker Syndrome

In contrast to asynchronous ventricular pacing (VOO, VVI), atrial synchronized ventricular pacing (VAT, VDD, DDD) maintains the normal sequence of cardiac chamber activation and permits a chronotropic response to exercise, thereby improving exercise performance. To assess the separate contributions of these two factors to improved work capacity, 14 patients with implanted programmable VAT pacemakers were exercised according to the Bruce protocol, in three different pacing modes, selected in a random order and on a double blind basis: (a) VAT; (b) chest wall stimulation triggered ventricular (V-CWS-T) pacing, during which the pacemaker was programmed to VAT mode but driven externally using chest wall stimulation at rates fractionally above the patients' atrial rate, thereby providing a chronotropic response to exercise without atrioventricular synchronization; and (c) VOO mode at 70 beats per minute. There was a significant improvement in exercise performance in all patients during both VAT and V-CWS-T pacing as compared to VOO mode; the average increase in work capacity being similar: VAT: 44 +/- 31, (range, 12 to 140) percent and V-CWS-T; 40 +/- 24 (range, 5 to 85) percent. It is concluded that in patients with adaptive pacing systems, the chronotropic response is the major determinant of any improvement in exercise performance.

Atrial synchronized ventricular pacing: contribution of the chronotropic response to improved exercise performance.

The effect of atrialventricular versus ventricular pacing and contraction were studied in seven open-chest dogs. Cardiac output, left ventricular, left atrial, right atrial and pulmonary artery pressures were recorded. The right or left ventricular apical areas were consistently superior as ventricular pacing sites.



Appearance of cannon A waves within the pre- or ejection period produced a significant decrease in left ventricular and systemic blood pressure, and cardiac output with a concomitant increase in right atrial, ventricular and pulmonary pressures. Prominent “v” waves were also observed during these periods.



Reducing the basic driving cycle length from 400 to 300 msec caused a marlted deterioration of all hemodynamic parameters with the appearance of mechanical alternans. Random VA conduction or ventricular pacing in the presence of com-plete AV and VA heart block appeared to offer a more favorable hemodynamic result than constant 1:1 VA conduction. It is concluded that maintenance of a physiologic AV interval permitting atrial contraction to appear outside of pre- or ejection period of ventricular systole is an important determinant or ventriculor function during cardiac pacing.

Hemodynamic consequences of atrioventricular and ventriculoatrial pacing.

Hypertrophic Subaortic Stenosis Complicated by High Degree Heart Block: Successful Treatment with an Atrial Synchronous Ventricular Pacemaker

https://www.annalsthoracicsurgery.org/article/S0003-4975(10)62217-5/pdf

Pat O. Daily

Papers

Hypertrophic Subaortic Stenosis Complicated by High Degree Heart Block: Successful Treatment with an Atrial Synchronous Ventricular Pacemaker

Sonomicrometry: Its Application as a Routine Monitoring Technique in Cardiac Surgery