Study Design

Study Design:

Patients Enrolled: 42 (25 analyzed)
NYHA Class: III, IV
Mean Follow Up: 6 Months
Mean Patient Age: 47-67
Female: 48
Mean Ejection Fraction: LVEF was 22% +/- 7% (mean +/- SD) at baseline and 26% +/- 9 (mean +/- SD) after 6 months.

Patient Populations:

1. Dilated cardiomyopathy of either ischemic or idiopathic etiology 2. NYHA Class III or IV 3. Sinus rhythm >55 bpm 4. QRS complex duration >120 msec in at least 2 surface ECG leads 5. PR interval >150 msec

Exclusions:

1. Major cardiovascular event such as MI, CABG or major surgical procedure within 6 months of study entry 2. Primary valve dysfunction or valve repair or replacement 3. Heart failure equiring inotropic medication 4. Unexplained syncope 5. Sustained ventricular arrhythmias requiring antiarrhythmic medications or an implantable cardioverter defibrillator 6. Atrial fibrillation or flutter within the last 6 months 7. Sinus node dysfunction 8. Atrioventricular block greater than Mobitz I or arrhythmias requiring pacemaker implantation 9. Hypertrophic obstructive cardiomyopathy 10. Life expectancy <6 months 11. Clinically significant renal or hepatic disease, uncontrolled diabetes or chronic alcoholism

Primary Endpoints:

Oxygen consumption at peak exercise and at anerobic threshold during cardiopulmonary exercise test and 6-minute walk distance

Secondary Endpoints:

Changes in New York Heart Association dunctional class, hospitalization frequency and quality of life.

Drug/Procedures Used:

Patients received an implantable pacemaker system with te ability to switch from univentricular to biventricular pacing capability. At the time of the initiation of this study, this necessitated implantation of two pulse generators. The patient was then randomized to univentricular or biventricular pacing. The optimal pacing site and AV delay when pacing the right, left, or right and left ventricles were determined using a computer generated protocol. Patients were paced for 4 weeks followed by 4 weeks without pacing, and finally crossed over the the other modality (biventricular or univentricular) of pacing for 4 weeks. Quality of life was assessed using the Minnesota Living with Heart Failure Questionnaire. Changes in ejection fraction, chamber sizes and filling pattern were obtained by echocardiography.

Concomitant Medications:

Of the 25 patients evaluated, 96% receive angiotensin converting enzyme inhibitors, 88% received digitalis, and 44% received nitrates. 14 patients were initially taking beta-blockers. At 6 months, 9 had constant dosage. The dose was reduced in two and increased in three after 6 months. Of the 24 patients taking diuretics, the dosage was increased in two, decreased in 10 and kept constant in 12.