Importance of LV Lead Placement for CRT
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville
Source: Singh JP, et al. Left ventricular lead position and clinical outcome in the multicenter automatic defibrillator implantation trial-cardiac resynchronization therapy (MADIT-CRT) trial. Circulation 2011;123:1159-1166.
In this paper, Singh and his colleagues from the MADIT-CRT study looked at the influence of left ventricular lead position on responses to therapy in that trial. MADIT-CRT was a randomized clinical trial of patients with indications for an ICD New York Heart Association (NYHA) class I or II heart failure and a QRS duration > 130 msec. All subjects were randomized to receive either a standard ICD or an ICD with resynchronization capability. This paper looked at the 799 patients with analyzable data who received a left ventricular (LV) lead. At implantation, coronary sinus venograms were obtained in two orthogonal (RAO and LAO) views. In the RAO view, the LV was divided into basal, midventricular, or apical segments. In the LAO view, the segments were anterior, anterolateral, lateral, posterolateral, and posterior. Final lead position could then be classified into 15 possible positions. The primary endpoints in MADIT-CRT were death and heart failure hospitalization. Multivariate Cox proportional hazards regression analysis was used to evaluate the impact on LV lead location on these endpoints. Prespecified variables considered in the analysis included: gender, ischemic status, QRS duration, type of bundle branch block. Other variables considered were LV ejection fraction, right bundle branch block, BUN, heart rate smoking status, diabetes, and blood pressure.
Among the 799 patients included in this analysis, the LV lead was located on the lateral wall in 59%, the posterior wall in 22%, and the anterior in 19%. In the long axis, the distribution was as follows: apical (14%), basal (23%), and mid-ventricular (63%). There were no significant differences in baseline characteristics when the groups were divided into anterior, lateral, and posterior wall positions or apical and non-apical lead positions. A total of 116 patients reached the primary heart failure or mortality endpoint. When patients were subdivided by apical vs non-apical LV lead location, there were 24 primary endpoints (21.8%) in the apical lead location compared to 92 primary endpoints (13.3%) in the non apical lead position. The increased hazard ratio (HR) for heart failure deaths in patients with an apical lead position was 1.64 (95% CI, 1.05 to 2.58; P = 0.003). The apical lead position was also associated with an increased HR for death (HR = 2.91). Apical lead positions were associated with worst clinical outcomes compared to other lead positions in patients with left bundle branch block and nonischemic cardiomyopathy among men, but not among women. Further analysis showed that patients with left ventricular ejection fractions below 25% and those with a prior history of NYHA class greater than class II symptoms did worse with apical lead positions.
The authors conclude that LV lead placement is an important determinant of success of CRT. In particular, LV lead positions in the apical region were associated with an unfavorable clinical outcome. These data suggest that physicians should avoid the apical position when possible.
Commentary
This paper is very helpful to those who implant CRT devices. Most implanters try to target a posterolateral or lateral coronary sinus branch but a suitable vessel in these locations may not be available. One of the alternatives is the middle cardiac vein but to achieve a stable position, it's often necessary to advance the lead quite far down into the apex. This paper suggests that this is not an optimal strategy. Basal or midventricular positions, even if they are more anterior, may yield better results.
Other methods for choosing LV lead position have been proposed. In patients with left bundle branch block, the posterolateral wall is usually the latest LV segment activated and this is the target for most implants. A careful pre-procedure echo can localize the area of latest activation more accurately. In patients with prior infarctions, one should also try to avoid areas of dense scarring that can be detected with cardiac magnetic resonance imaging. Unfortunately, the coronary sinus venous anatomy still is the biggest obstacle to ideal placement and many patients provide limited choices, since only one site may allow a stable and effective lead position.