Electrical dyssynchrony

Electrical dyssynchrony (wide QRS complex) is a surrogate marker of mechanical dyssynchrony, which is used to select patients for CRT. Mechanical dyssynchrony can occur between the atrium and the ventricle, between the RV and the LV (interventricular), and between the walls of a single ventricle (intraventricular). The baseline QRS dnration is a good marker of interventricular (RV-LV) dyssynchrony however snbsequent studies have shown that intraventricular (LV) dyssynchrony is a more accurate predictor of response to CRT (15) and this does not correlate with the baseline QRS dnration (25). 

Intraventricular conduction delay often leads to late activation of the left ventricular free wall with significant mechanical consequences. The mechanical consequences of abnormal electrical activation of the heart have long been recognized [58, 60, 86]. These include dyssynchrony between the atria. 

Turner MS, Bleasdale RA, Vinereanu D, Mumford CE, Paul V, Fraser AG, Frenneaux MR Electrical and mechanical components of dyssynchrony in heart failure patients with normal QRS duration and left bundle-branch block impact of left and biventricular pacing. Circulation 2004 109 2544-9. 

Disordered electrical and mechanical ventricular activation can compromise cardiac function. Pacing technology has been nsed to att pt to correct the inter- and intraventricular conduction in an effort to optimize cardiac performance. The earliest attempts were performed during surgery when epicardial leads were placed over the lateral left ventricle free wall. Later, the coronary sinus was utilized to activate the left ventricle. Cardiac-resynchronization therapy (CRT) for treatment of patients with congestive heart failure and ventricular dyssynchrony can have a remarkable beneficial effect. Use of this technology continues to evolve. 

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