Multicenter Pacing Therapy - M-PATHY


Dual chamber pacing for symptomatic hypertrophic cardiomyopathy.


Dual chamber pacing for symptomatic hypertrophic cardiomyopathy.

Study Design

Study Design:

Patients Screened: Not given
Patients Enrolled: 48
Mean Follow Up: 12 months
Mean Patient Age: 52

Patient Populations:

Unequivocal diagnosis of hypertrophic cardiomyopathy on 2-dimensional echocardiography.
Severe refractory symptoms causing important functional disability despite standard drug therapy.
Basal outflow tract obstruction (≥50 mmHg rest gradient) on continuous wave Doppler.

Primary Endpoints:

Subjective/objective measures of symptoms and exercise capacity, including functional class, quality of life (QOL) scores, treadmill exercise time, and peak oxygen consumption with exercise.

Drug/Procedures Used:

Randomization to 3 months of dual chamber pacing (DDD) or backup mode (AAI-30) followed by crossover to the alternative mode for another 3 months. This was followed by 6 months of unblinded DDD pacing.

Principal Findings:

The first 6 months of the study conformed to a randomized, double-blind, crossover design. Specifically, patients were randomized to either 3 months of DDD pacing or to an AAI-30 back-up mode. All patients were subsequently crossed over to the alternative mode for the next 3 months. Finally, patients underwent 6 additional months of DDD pacing in an uncontrolled/unblinded fashion. Patients completing this 12-month protocol experienced a total of 9 months of DDD pacing.

Of the 48 patients originally enrolled, 4 did not participate in the cross over. The remaining 44 constitute the primary study group. Twelve of these 44 patients deviated from the protocol design, including 8 who elected for early and unscheduled crossover from AAI-30 to DDD. One patient, age 67, died unexpectedly after 8.5 months. Thus, 32 patients completed the original protocol.

Symptomatic improvement was the same for patients randomized between DDD and AAI-30. In the uncontrolled phase of DDD pacing, quality-of-life scores were significantly improved compared to baseline, but the scores were no different from those recorded during AAI-30.

None of the objective measures analyzed, including treadmill exercise duration, peak oxygen consumption during treadmill exercise, and outflow gradient, improved significantly with DDD pacing.

Some modest hemodynamic benefit was achieved in most patients. In a small subset of older patients (>65 years), a significant clinical response was seen, suggesting that DDD pacing could be a viable therapeutic option for elderly patients.


Permanent dual chamber (DDD) pacing has been proposed as an alternative to septal myotomy/myectomy surgery for reducing symptoms in severely symptomatic patients with obstructive hypertrophic cardiomyopathy (HCM). M-PATHY is the first controlled test of this hypothesis. The similarity results from DDD and control (AAI-30) pacing modes suggests a substantial placebo effect. On the other hand, it is difficult to obtain sufficient sample sizes in this area to control type II error. Investigators could not confirm prior claims that chronic pacing produces left ventricular remodeling in HCM. They concluded that overall, pacing should not be regarded as a primary treatment for patients with obstructive HCM, and previous uncontrolled results should be interpreted with caution.


1. Circulation 1998;98(Suppl I):I-506. Preliminary results

Keywords: Echocardiography, Doppler, Cross-Over Studies, Oxygen Consumption, Placebo Effect, Dichlorodiphenyldichloroethane, Cardiomyopathy, Hypertrophic, Ventricular Remodeling, Hemodynamics

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