The promise of resynchronization therapy. Who (and how many) will benefit?

It has been estimated that about 320,000 to 400,000 patients in the USA alone are possible candidates to cardiac resynchronization therapy according to the recently published AHA/ACC/NASPE guidelines for pacing and the results of the COMPANION trial. The selection of the most suitable candidate for CRT/CRTD is a crucial issue, but still a matter of debate. A large variety of clinical, invasive and non-invasive criteria have been proposed for appropriately selecting candidates for CRT. However, in all the studies the parameters have been retrospectively identified and none has reported their results in the form of a multivariate regression model. We have now well characterized the patients in sinus rhythm who most likely benefit from this non-pharmacological approach. The fact that the COMPANION trial was able to single out a specific subgroup of heart failure patients that can be treated better than what was very short time ago best medical therapy validates the large body of research that investigators worldwide have created about this therapy. Finally, the concept that any patients that require ventricular pacing, who have heart failure class II/III or IV may benefit from receiving biventricular rather than right ventricular pacing as much as the other patients with more classical indication for CRT is still open to discussion and needs to be tested in a randomized multicenter trial.