Tailor-CRT: Better Application of Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) is an established treatment for heart failure (HF) patients with severe left ventricular (LV) systolic impairment and delayed electrical impulse conduction through the ventricles, such as left bundle-branch block (LBBB). Since initial approval of the therapy over 10 years ago, there have been hundreds of thousands of implants worldwide. In The Netherlands, currently more than 2000 CRT devices are implanted each year. In a heart with LBBB, electrical activation of the lateral LV free wall is delayed, which leads to dyssynchronous and inefficient LV mechanical contraction and compromised LV pump function. The positive impact of CRT on LV pump function is attributed to paced pre-excitation of the delayed activated lateral LV wall. CRT is most commonly applied by pacing the right ventricle (RV) and LV lateral wall (almost) simultaneously. This corrects the abnormal LV electrical activation and resynchronizes LV mechanical contraction, which in turn results in improved LV pump function.

Despite the striking effectiveness of CRT, 30-50% of apparently suitable patients show little or no improvement. Previous studies have shown that the response to CRT can be improved by tailoring LV lead placement and programming of atrioventricular (AV) and inter-ventricular (VV) stimulation intervals to the individual patient. In clinical practice, echocardiographic techniques are the most widely employed for CRT optimization. However these techniques are subject to large measurement errors and inter- and intra-observer variability. A more accurate technique is invasive assessment of acute hemodynamic response to CRT, with the most widely used invasive hemodynamic parameter being the maximum rate of LV systolic pressure rise (LVdP/dtmax). However, the invasive and time-consuming nature of this approach limits its use in clinical practice. Thus, the best strategy to optimize lead positioning and device programming still remains to be established.

Earlier work in our research group suggests that the vectorcardiogram (VCG) can be used to determine the optimal LV lead position and AV- and VV-intervals, and pilot studies showed the feasibility to derive a VCG-like signal (D-VCG) from the implanted pacing electrodes. Other studies have suggested that the best position for the LV electrode is the region of latest electrical activation. The region of latest electrical activation can be identified by measuring the electrical delay on the LV lead (LVLED) during implantation. Validation of these techniques for tailoring LV lead positioning and AV- and VV- stimulation intervals to the individual patient, will provide non-invasive and easy methods to optimize CRT application and improve response rate.

The objective of this study is to investigate whether D-VCG can be used to determine the optimal AV- and VV-interval and whether VCG and LVLED can be used to determine the optimal LV lead position. Validation of these techniques for tailoring LV lead positioning and AV- and VV- stimulation intervals to the individual patient, will provide non-invasive and easy methods to optimize CRT application and improve response rate.

Inclusion criteria

• Chronic heart failure with NYHA functional class II-IV
• Left ventricular ejection fraction (LVEF) < 35%
• Left bundle-branch block (LBBB) with QRS duration > 120 ms
• In sinus rhythm

Exclusion criteria

• Atrial fibrillation
• ≥4 premature ventricular complexes on standard 12-lead ECG
• Age <18 years or > 80 years
• Incapable of giving informed consent
• Moderate to severe aortic valve stenosis