Title of Trial
Multicenter Pacing Therapy (M-PATHY) Trial

Date and Citation of Primary Publication(s) or References
Maron BJ, Nishimura RA, McKenna WJ et al. Assessment of dual-chamber pacing as a treatment for drug refractory symptomatic patients with obstructive hypertrophic cardiomyopathy: A randomized, double-blind, crossover study (M-PATHY). Circ 1999; 99: 2927-33.

Purpose of the Trial
Evaluate the effects of pacing therapy with short AV delays for patients with hypertrophic cardiomyopathy.

Study Category
Pacing

Patient Population
Inclusion Criteria
Severe drug refractory hypertrophic cardiomyopathy. Left ventricular outflow gradient > 50 mmHg without provocation.

Exclusion Criteria
Atrial fibrillation, left bundle branch block, end stage hypertrophic cardiomyopathy, prior septal myotomy/myectomy.

Study Design
Randomized double blind parallel controlled trial. Patients were randomized to 3 months of dual chamber pacing or backup AAI pacing mode (30 bpm) and crossed over to the alternate pacing mode for another 3 month period. After the six month blinded and randomized portion of the study, the patients were followed for an additional six months of unblinded pacing.

Primary Endpoints
Death and nonfatal stroke

Secondary Endpoints
Peak oxygen consumption, exercise time (Chronotropic Assessment Exercise Protocol)

Baseline Characteristics
Patient number: 48 patients initially enrolled and 44 patients completed the randomized crossover portion of the study.
Mean Age: 53 ± 17 years
Gender: 32% female
Other characteristics:
Average gradient at baseline: 82 ± 32 mm Hg, exercise duration at baseline: 9.2 ± 4 min, and peak O2 consumption at baseline: 16.2 ± 5 ml/min/kg.

Time to Follow-up
Two blinded three-month crossover periods. 32 patients completed the study to 12 months.

Results
Dual chamber pacing reduced the outflow gradient by 40% from 82 ± 32 mmHg to 48 ± 32 mm Hg. However, no change in objective measures of symptoms (NYHA functional class, quality-of-life scores) or exercise capacity (treadmill exercise time, peak oxygen consumption) could be detected. A significant placebo effect was noted. A small retrospectively identified group of 6 elderly patients (65-75 years old) showed modest improvements in functional capacity.

Trial Status: Completed