Effect of cardiac resynchronization therapy on left atrial electromechanical function

Abstract

Background: Cardiac resynchronization therapy (CRT) is effective in improving cardiac function and symptoms in patients (pts) with advanced heart failure (HF) and ventricular conduction abnormalities. These results are thought to be secondary to reduction in ventricular dyssynchrony and mitral regurgitation (MR). However, effects of CRT on left atrial (LA) function and interatrial conduction (IAC) are unknown. LA dysfunction and prolonged IAC are associated with decreased left ventricular (LV) filling and atrial fibrillation (AF). Accordingly, we studied the effects of CRT on LA function and IAC. Methods: Fifty-six pts (39m, 17f, 67 10 yr) with NYHA III-IV CHF, LV ejection fraction 35%, a QRS interval 130 msec on optimal medical therapy for HF underwent CRT (Medtronic InSync or Guidant Contak CD). P max (maximum P wave duration on any lead) and P disp (difference between P max and minimum P wave duration) were measured on a 12-lead ECG at baseline and at 6 months post CRT. Echocardiograms were recorded in a subset of 27 pts at baseline and at 6 months post CRT. Using the biplane area-length method, LA volumes at mitral opening, onset of P wave and mitral closure were determined. Based on Simpson’s formula, LA stroke volume (LASV), ejection fraction (LAEF) and kinetic energy (LAKE) were calculated. Peak A wave velocity (Avel) and A wave acceleration time (At) were also measured. Results: While LA volumes, At and Avel were similar at baseline and post CRT, there was a marked reduction in P max (143 23 msec vs. 132 27 msec, p 0.01)) and P disp (35 13 msec vs. 22 13 msec, p 0.01) 6 months post CRT. There was also a significant improvement in LASV (7.5 4 ml vs. 20 15 ml, p 0.01), LAEF (19 6% vs. 29 20%, p 0.01) and LAKE (28 20 Kdyne/cm/s vs. 70 40 Kdyne/cm/s, p 0.01) at 6 months. Conclusions: CRT results in marked reduction in IAC delay and significant improvement in LA systolic function. Although LA volumes did not change, LASV, LAEF, and LAKE improved at 6 months. Enhanced LA electromechanical function may result in improved LV filling and contribute to the hemodynamic and symptomatic improvement observed with CRT and has implications for reduction in the propensity for AF.