Cardiac resynchronization therapy (CRT), achieved by simultaneously pacing the RV and LV, has assumed prominence in patients with advanced heart failure and refractory symptoms. Specific candidates include patients with a prolonged QRS duration > 120 milliseconds.

A prolonged QRS, typically manifested as left bundle branch block in patients in cardiomyopathy is associated with poor prognosis. In several large clinical trials, lengthening of the QRS was independently associated with poor survival. In addition, several deleterious hemodynamic consequences arise in the presence of bundle branch block including shortening of the diastolic filling period, aggravation of mitral regurgitation, and abnormal systolic wall motion. The overall result is a typical and sometimes dramatic deterioration in cardiac performance.

Most clinical trials have demonstrated that about two-thirds of patients will have a clinical response to CRT. Clinical responses include improvement in New York Heart Association functional class, improved exercise capacity, a decreased need for diuretic, reduced hospitalization for heart failure management, and the like. Unfortunately, about one-third of patients do not respond, and approximately 15% of patients can actually have a worsened clinical outcome.

No clinical trial has determined that CRT improves survival. The recently concluded COMPANION study, not yet published but presented at the NASPE meetings, has found that CRT tended to improve survival but without statistical significance. When CRT was combined with an implantable defibrillator, there was a large reduction in death rates: deaths were reduced more than 40% if CRT-ICD was used. Presumably, the ICD prevented the large number of sudden deaths that occur in heart failure patients.

Finding the Target Area 

Crucial to successful CRT is deployment of the left ventricular lead. This is typically accomplished by passing the LV lead through the coronary sinus into one of its venous tributaries overlying the epicardial left ventricular surface. Conventional target sites are the posterior and lateral myocardium. In principle, the target should be the latest site of left ventricular mechanical contraction. Although this is predicted to be in the posterior-lateral region, the actual site tends to be rather variable and difficult to predict in the individual patient.

Along these lines, tissue Doppler imaging, a sophisticated echocardiographic technique, allows visualization of individual myocardial segments and their contraction patterns, and has allowed online visualization and analysis of segmental wall motion. It has been observed that up to 50% of patients may have the left ventricular lead (when placed in a conventional fashion) pacing a zone that does not correspond to the latest myocardial contraction segment, i.e. mismatched between the desired target and the actual target. Moreover, it was only those patients in whom a ³match² occurred between the paced segment and the target zone was a clinical response observed (only in about 50% of patients). This likely explains why there is a lower than desired clinical response rate to CRT.

Complications of CRT and New Techniques for Combatting Them 

In clinical practice, approximately 90% of transvenous CRT procedures are technically successful, although as described above, in a substantial number of these ³successes², leads end up being placed in areas that may not ultimately benefit the patient. In addition, some of the transvenous leads may become non-functional, may dislodge, may pace the diaphragm, etc., in all cases making them unavailable for use in the CRT system.

What is the current practice for patients who fail transvenous CRT lead placement? We have designed an epicardial transvenous lead implantation technique that uses a robotic thoracoscopic approach in collaboration with our cardiac surgical staff. We have now performed over 25 such procedures. The robotic system requires tiny incisions in the patient¹s thorax through which robotic arms, controlled by the surgeon from a sophisticated console, are advanced to identify the appropriate myocardial target segment.

OOnce attached, the LV leads are tunnelled to a subclavicular pocket where they are connected to the conventional CRT device, pacemaker or defibrillator. We have had a 100% successful implantation rate, and the current robotic procedure lasts only just over 40 minutes. There have been only two perioperative complications. Of great interest, we have seen an 80% clinical response rate after the epicardial lead implantation, compared to a 50% overall response rate in patients with transvenous implants. We hypothesized that this may be due to a greater degree of flexibility in selecting myocardial target sites not limited by anatomic or technical constraints that hamper conventional lead placement.

We are in the midst of developing a randomized clinical trial that will compare epicardial lead implantation with transvenous lead implantation in patients who are eligible for CRT systems. At the present time, we are continuing to use the robotic system for patients who have failed coronary sinus implants.