Correlating QLV Interval to Left Ventricular (LV) Lead Position in Patients Receiving Cardiac Resynchronization Therapy.

This is a prospective clinical trial to determine the optimal QLV interval during implantation to achieve the best possible response from cardiac resynchronization therapy for heart failure patients.

Heart failure is a growing epidemic in the United States. Heart failure is associated with shortness of breath, reduced exercise tolerance, and manifestations of peripheral fluid retention. As the disease progresses, there is development of cardiac dyssynchrony (failure of the heart to act as one unit) in the electrical and mechanical functions of the myocardium. During implantation of a cardiac resynchronization therapy defibrillator (CRT-D) device, three electrical wires are placed in the right atrium (RA), right ventricle (RV) and coronary venous system that drains blood from the left ventricle (LV). The LV lead is placed in the posterolateral tributaries of the coronary venous system using special delivery tools. Pacing therapies to resynchronize the heart have been shown to improve functional class and mortality in patients with severe heart failure i.e. New York Heart Association (NYHA) class III and IV functional status. Current indications for cardiac resynchronization therapy (CRT-D) include severe cardiomyopathy (Ejection Fraction \< 35%), with shortness of breath at rest or minimal exertion (NYHA class II, IV), prolonged QRS \> 130ms on surface echocardiogram (ECG) and life expectancy more than one year. CRT-D therapy results in decrease of heart failure admissions and improvements in quality of life. Response to CRT is associated with improvement in functional status by one NYHA functional class schema or by evidence of reverse remodeling (decrease in end systolic LV dimension by 15%). However across clinical trials, a third of the patients are non-responders to CRT therapy. Non-ischemic etiology of heart failure and presence of electrical dyssynchrony on surface ECG suggested by QRS \>150ms are associated with better response with CRT. Non response to CRT can be due to inappropriate patient selection, inappropriate device programming, and inappropriate lead placement. However, inappropriate lead placement is the factor that can be changed during device implantation. Adverse changes in morality and heart failure can occur with sub-optimal position of the LV lead. Most echocardiographic parameters to predict responders were not clinically useful. Appropriate positioning near the area of the heart with latest activation (usually posterolateral segment of the left ventricle) is associated with better response. Inter-ventricular delay as measured by the time delay between the two leads in the left and right ventricles (RV-LV delay) was shown to be a better predictor of response. Interval from the first deflection of the surface ECG to the bipolar electrogram (QLV interval) can be used as a surrogate to identify the delayed segments of the left ventricle. Preliminary studies have shown better response using this approach of lead placement in the regions of latest activation. SMART AV study which used a similar algorithm in assessing delay also showed a trend for better response using QLV interval. However, the fluoroscopic lead position was not correlated with QLV interval for that study. We plan to measure this area of delayed activation to target effective lead placement and map the coronary veins to target the longest QLV interval in each patient. For this study, medical history and demographic information will be collected from patients as well as clinical information from the procedure. The QLV measurements will be collected prior to implant of LV lead. The QLV interval is defined as the measurement from the onset of the QRS width of the surface ECG to the first large positive or negative peak of the LV electrogram (EGM) during a cardiac cycle. QLV EGM will be taken from either the LV pacing lead and/or .014 wire. QLV EGM's will be measured at three distinct points (basal, mid, and distal) within each target vessel. Each data point will be the average of four to six beats to allow for respiratory variance, and recorded using the Bard mapping system. The final lead position will be the area of vein that has the longest QLV interval with appropriate sensing and pacing thresholds. The QLV measurements will be conducted, in addition to all standard of care procedures for CRT-D implantation for patients enrolled in the clinical trial.