Cardiac Rhythm Management
Articles Articles 2013 August


John Day, MD, FHRS, FACC

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John Day, Editor-in-Chief

Dear Readers,

The theme of our Journal this month could appropriately be called, “first do no harm” when it comes to cardiac resynchronization therapy (CRT). Indeed, this month we have a total of three articles that all highlight some of these pitfalls of CRT. Of these three articles, I would like to focus my thoughts and comments to an excellent article by Dr. Bomb and colleagues from the University of Missouri-Columbia entitled “QRS Prolongation Following Cardiac Resynchronization: Incidence, Predictors, and Outcomes”.

Unfortunately, we are all very well aware that approximately one in three of our patients who meet current criteria for CRT do not appear to benefit clinically. This is very frustrating as these are our patients that are often struggling the most. At the various meetings around the world I attend, this is a common topic. Generally, the same things are discussed such as appropriate selection, AV delays, V-V timing, maximizing the percentage of biventricular pacing, ideal left ventricular lead placement, etc. Interestingly, surprisingly little is ever discussed about something so simple as QRS narrowing or widening with CRT implantation.

In this article by Bomb and colleagues, they take things a step further and look to analyze not just the “non-responders” but also those rare patients who actually get worse with CRT. Too often, I suspect we often blame further deterioration of their underlying heart failure status as the cause. However, in some of these cases could the problem actually be CRT? Could our therapy designed to improve their heart failure symptoms actually sometimes be making things worse?

Over the years of my career I have watched with great interest the rise and fall of echo markers of dyssynchrony. Not too long ago, this concept was very popular and received a great deal of attention at the meetings. Many advocated using echo at the time of implantation to adequately reverse left ventricular dysynchrony. Unfortunately, no clear echo assessment of dyssynchrony could ever be shown to reliably predict clinical outcomes and we are now left with again using ECG parameters to determine which patients are most likely to benefit from CRT.

We have now come to understand that probably the best predictor of CRT outcomes is the left bundle branch block (LBBB) with a QRS width greater than 150 ms. Fortunately, for most CRT patients, the QRS narrows with biventricular pacing. While there have been a handful of studies over the years which have shown that QRS narrowing with CRT placement predicts who will ultimately respond clinically to this therapy, unfortunately, in modern times these studies have received little attention.

Could QRS widening with CRT implantation be a predictor of a worse clinical outcome? Intuitively, it makes sense. If the QRS widens with CRT are we causing further deterioration of the electrical dyssynchrony and making the patient’s heart failure worse?

In this article of the Journal, Bomb and colleagues retrospectively analyze 100 consecutive CRT patients. Fortunately, only 8% had clinical deterioration with CRT. Of these patients who got worse with CRT, they found that their QRS duration had increased by a mean of 33 ms with CRT. CRT non-responders had a mean QRS widening of 5 ms with CRT and CRT responders were found to have a mean QRS narrowing of -15 ms.

Interestingly, they found that the traditional optimal lead placement site, the lateral wall, was most likely to correlate with QRS narrowing. In addition, the traditional worst site for left ventricular lead placement, the anterior or anterolateral wall, was most likely to correlate with QRS widening with CRT.

These important data are in complete harmony with a study published last year in the Heart Rhythm Journal by Niraj Varma and colleagues from the Cleveland Clinic. 1 Their study was also a retrospective study. Similarly, they found in 856 patients that QRS widening with CRT is associated with a deterioration in clinical function.

It really amazes me that something so simple as simply ensuring that you get adequate QRS narrowing with CRT implantation has really not been studied very much in the literature. It has often been said that the best solutions are the simplest ones. Could it be that with the problem of CRT non-responders the best solution is really quite simple. Ensure that at the time of CRT implantation you get adequate QRS narrowing?

This really is not hard to do. It simply means having the patient continuously hooked up to a 12-lead ECG during the time of CRT implantation. It needs to be a 12-lead ECG as the precordial leads are an important in assessing QRS narrowing or widening with CRT. To the unaccustomed eye, seeing all of the ECG wires during implantation could be distracting, however, with experienced implanters this should not be a problem.

Logistically, it would also mean that there would likely need to be a dedicated ECG machine in the device implantation lab. This should not be an insurmountable problem for most hospitals as ECG machines have become quite affordable and smaller in size over the years.

Dr. Bomb and colleagues should be commended for this excellent study. I hope that studies like the ones mentioned in this letter will stimulate the need for a randomized multicenter trial to evaluate the true role of QRS narrowing or widening with CRT implantation.

I am confident that this Journal will continue to be valuable to you and your patients and I look forward to hearing from you on this important topic. Do you regularly use real time 12-lead data to evaluate whether or not you have good left ventricular lead placement at the time of implantation? What has been your experience with this approach?

Warm regards,

John Day, Editor-in-Chief
John Day, MD, FHRS, FACC
The Journal of Innovations in Cardiac Rhythm Management
Director of Heart Rhythm Services
Intermountain Medical Center
Salt Lake City, UT



  1. Rickard J, Jackson G, Spragg D, Cronin E, Baranowski B, Tang W, Wilkoff B, Varma N. QRS prolongation induced by cardiac resynchronization therapy correlates with deterioration in left ventricular function. Heart Rhythm - October 2012 (Vol. 9, Issue 10, Pages 1674-1678, DOI:
    CrossRef: 10.1016/j.hrthm.2012.05.013)