Simpler Is Better

ardiac resynchronization therapy (CRT) can have a profound therapeutic impact on appropriately selected patients. However, even when the current clinical guidelines for CRT 1 are rigorously applied, the response rate is 70%. Nearly a third of patients who undergo implantation of a CRT device are clinical nonresponders and more may be "remod- eling nonresponders." An extensive body of literature reports on a wide variety of methods that can be better used to identify potential responders by measurement of mechanical dyssynchrony. Factors responsible for nonresponse include comorbid conditions, cardiac substrate, left ventricular (LV) lead location, and device programming. Comorbid conditions such as obstructive sleep apnea, right-sided heart failure, and type of intraventricular conduction delay should be consid- ered at the preprocedural stage. Device programming may help minimize the number of nonresponders. Prediction of responders by invasive hemodynamic assessment is imprac- tical for daily clinical practice. Cardiac magnetic resonance imaging is too expensive for routine use and is not an option for many patients who already have devices and need upgrades. The appeal of echocardiography for predicting responders by identifying mechanical dyssynchrony has been dampened by its limited reproducibility and poor predictive value. 2 It is also impractical to perform echocardiography during implantations. The prolonged QRS duration (QRSd; electric dyssynchrony), as measured on a standard 12-lead ECG, remains the best method for identifying candidates for CRT. In an elegant and important study reported in this issue of Circulation, Sweeney and colleagues3 use the 12-lead ECG and show that, despite its apparent simplicity, analysis of the standard 12-lead ECG can yield both pitfalls and impressive rewards. Article see p 626