Evaluation of Resynchronization Therapy for Heart Failure

Heart failure is a major health problem in Canada. Recent advances in medical and device therapy have helped to reduce the morbidity and mortality of patients with this problem. Among these treatments, cardiac resynchronization therapy (CRT) has very recently been shown to be effective to improve functional class, quality of life and exercise tolerance of the patients with the most severe symptoms of heart failure and a prolonged duration of the QRS on the 12-lead Electrocardiography (ECG).

Resynchronization of the failing ventricle is currently achieved by pacing the left and right ventricles simultaneously with specialized electrodes and a cardiac stimulator. However, controversy persists concerning the optimal configuration for cardiac pacing in these patients. Right ventricular pacing alone has been shown to be deleterious in some patient populations. The benefits of biventricular pacing in heart failure patients may be due primarily to left ventricular stimulation and may, in some patients, be decreased by the presence of simultaneous RV stimulation. Preliminary data from our own animal work suggest that in the majority of cases, LV stimulation alone is better than RV stimulation, and that BiV stimulation represents an intermediary situation between LV and RV stimulation.

Eligibility Criteria:
Inclusion Criteria:

* The patients are eligible if they undergo an ICD implantation or replacement
* They have a documented LVEF ≤ 35% measured in the previous 6 months (without major clinical subsequent event, such as heart surgery, since the LVEF measurement)
* If measured by echocardiography, the LV end-diastolic diameter must be ≥ 60 mm
* The duration of the QRS is \< 120 ms
* They are in sinus rhythm
* They cannot walk more than 400 meters during the screening 6-minute walk test (the patients must be limited by heart failure symptoms)

Exclusion Criteria:

* Patients with an indication for permanent ventricular pacing or with chronotropic insufficiency defined as follow:

  * Any condition where the treating physician believes it would not be acceptable for the patient to have his device NOT programmed with the SENSOR at ON for the duration of the study
  * Second or third degree AV block, either persistent or intermittent
  * Patients with a pacemaker or an ICD who are paced in the ventricular chamber more than 5% of the time
* Patients with LV dysfunction associated with a reversible cause such as post-partum cardiomyopathy, tachycardia induced cardiomyopathy, acute myocarditis or acute toxic cardiomyopathy (including acute alcoholic)
* Patients who had a myocardial infarction within the past 6 weeks\* defined by 2 of the 3 following conditions:

  * Prolonged chest pain
  * ECG changes suggesting of AMI
  * Cardiac enzymes elevation more than twice the local upper limit of normal)
* Patients who had cardiac surgery within the past 6 weeks\*
* Patients with moderate or severe cardiac valve stenosis (aortic, mitral, pulmonary or tricuspid)
* Patients with an inability or a limitation to walk for reasons other than heart failure symptoms (e.g., angina, intermittent claudication, severe lung condition or arthrosis)
* Patients with severe coexisting illnesses making survival \> 6 months unlikely
* Patients who are pregnant and/or nursing.
* Patients with inability or unwillingness to consent or comply with follow-up requirements
* Patients participating in another study

The 6-week period is calculated prior to the beginning of the baseline evaluation and not the implant procedure itself. This difference comes from the fact that the protocol includes a delay of 2 to 8 weeks between the implant procedure and the actual beginning of the patient's evaluation.