Predictors of response to cardiac resynchronization therapy: the holy grail of electrophysiology
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Cardiac Resynchronization Therapy (CRT) has been found to improve quality of life, reduce heart-failure related hospitalizations, and prolong survival in patients with New York Heart Association (NYHA) class III or IV heart failure and electrocardiographic evidence of ventricular dyssynchrony [1, 2]. CRT is currently an indispensable mode of treatment for the increasing number of eligible persons with severe heart failure [3, 4]. Although there is significant success of CRT, there are a significant number of patients who do not show improvement with CRT [2, 5, 6, 7]. It is reported in many clinical trials such as the Multicenter InSync Randomized Clinical Evaluation (MIRACLE) that 34% of individuals eligible for CRT did not benefit based on a heart failure clinical composite score [2, 5, 7, 8, 9]. These so called “non-responders” have spurred research into identifying potential responders to CRT before device implantation. Important echocardiographic parameters measuring ventricular dyssynchrony using tissue doppler imaging (TDI) among other methods, as well as important parameters such as device lead placement and level of scar formation are important when determining ideal patients for CRT [8, 9, 10, 11, 12, 13, 14, 15, 16]. Several single-center studies have established different echocardiographic parameters to distinguish CRT responders from non-responders. Furthermore, in the multicenter study of Predictors of Response to CRT (PROSPECT), echocardiographic measures of ventricular dyssynchrony such as left ventricular end-systolic volume (LVESV) and septal-posterior wall motion delay (SPWMD) were used to predict responsiveness to CRT . It was shown that despite promising data from small single-center studies, echocardiographic measures of ventricular dyssynchrony fail to have enough predictive clinical merit to be established as selection criteria for CRT .
In the current report by Pavlopoulos and Nihoyannopoulos, the authors review both echocardiographic and clinical parameters for predicting response to CRT. This review article highlights the point that besides echo based parameters, perhaps clinical parameters such as the medical history of whether atrial fibrillation exists, or ischemic versus non-ischemic cardiomyopathy may help. Furthermore, incorporating more advanced imaging modalities such as cardiac magnetic resonance imaging may help overcome certain limitations of echocardiography. It has been shown in the multicenter study PROSPECT that echo-based dyssynchrony is not sufficient and failed to predict responsiveness to CRT. Therefore, it is imperative in the future as the current paper proposes, that an overall and complete approach combining not only echo parameters of dyssynchrony but also clinical and other imaging modality parameters be undertaken to evaluate and predict responsiveness to CRT because there are many more important variables besides electrical dyssynchrony that appear to contribute to outcomes in these patients. Therefore, the search for the holy grail of prediction of responsiveness to CRT continues!
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