Author + information
- Yeruva Madhu Reddy, MD and
- Dhanunjaya Lakkireddy, MD⁎ ()
- ↵⁎Center for Excellence in Atrial Fibrillation/Complex Arrhythmia Management, Bloch Heart Rhythm Center at University of Kansas Hospital, Electrophysiology Research, KU Cardiovascular Research Institute, 3901 Rainbow Boulevard, MS 4023, Kansas City, Kansas 66160-7200
We read with great interest the TARGET (Targeted Left Ventricular Lead Placement to Guide Cardiac Resynchronization Therapy) study by Khan et al. (1), a randomized controlled trial with targeted left ventricular (LV) lead placement to guide cardiac resynchronization therapy. The results of the study are promising and do emphasize the importance of the location of the LV lead in relation to the latest segment of contraction. However, many conventional variables have not been identified in the study, and more data are needed to support the conclusions of the study.
Morphology of the QRS complex (left bundle branch block vs. right bundle branch block vs. nonspecific intraventricular conduction delay) has not been reported in the study. Many previous studies have consistently shown that QRS morphology is one of the most important predictors of response (2). The distribution of left bundle branch block between both groups should be identified as it can potentially influence the results.
It will be interesting to see if there is a correlation between the QRS morphology and axis with the latest segment of contraction in this study. It is postulated that QRS morphology and frontal axis can predict the latest segment of activation; whether it would predict the latest segment of mechanical contraction is unknown (3). Khan et al. (1) do have the unique opportunity to evaluate this concept in their study population. Nearly one-half (47%) of the patients in the control group ended up having a concordant LV lead location in relation to the segment of latest contraction. It would be very helpful to identify the surface electrocardiogram characteristics (QRS morphology and axis) of this subgroup and compare them with those of patients in whom the LV lead was not concordant. If it is possible to predict the area of latest contraction, with reasonable accuracy, using surface electrocardiogram morphology, it would make the concept of “targeting LV lead” much easier and widely acceptable, without the use of the more sophisticated radial strain measurement.
Total scar burden, an important variable in predicting outcomes in cardiac resynchronization therapy (4) has not been reported in this study. Patients with higher scar burden are intuitively more likely to have a scar at the LV lead site and are less likely to have a concordant LV lead (more remote or adjacent location), thereby significantly influencing the results. The mean total scar burden in both groups should be reported in the study to support the conclusions.
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