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The Rationale for Nontransvenous Leads and Cardiac Resynchronization Devices

Cardiac resynchronization therapy (CRT) is an important advance in heart failure therapy for patients with ventricular conduction delay. The introduction and evolution of specialized leads and devices has facilitated a rapid transition from small-scale clinical studies to large randomized trials to regulatory and clinical acceptance of CRT. Published data indicates that CRT can improve clinical status and encourage reverse remodeling,1,2 and when coupled with an ICD, increase overall survival,3 in patients with advanced heart failure. CRT is conventionally accomplished by biventricular transvenous lead placement, one lead typically at the RV apex and a second lead on the LV epicardial surface via cannulation of the coronary sinus and its tributaries. Recent series report transvenous implantation success rates in the range of 90%,4,5 improved with the availability of over-the-wire lead technology. Lower success rates are expected until a learning curve is scaled.5 Success usually is defined in a technical sense, i.e., successful placement of a lead in a coronary sinus branch on the LV wall, regardless of location. Technical failure results from inability to cannulate the coronary sinus; occluded or atretic coronary sinus; absence of coronary sinus branches of adequate caliber, course or angulation; failure to pass or stabilize the lead in the coronary sinus branch; diaphragmatic capture; and so on. Thus, there are a variety of procedural, but also very important anatomic issues that will greatly contribute to the success or failure of a CRT procedure. Even with successful implantation, not all patients experience a favorable clinical response. For example, in the recently published MIRACLE trial, 67% of patients were described as having an improved composite heart failure score and 16% a worse score1 after successful implantation. Outcomes were better than observed in the control group, but about one third of the patients in the successfully implanted active CRT arm did not improve or worsened. If one adds the patients with unsuccessful implantations and patients whose