Early and late effects of cardiac resynchronization therapy on force-frequency relation and contractility regulating...

Heart failure is associated with a reduction in left ventricular (LV) contractility as evidenced by a blunted force-frequency response (FFR) and downregulation of contractility regulating genes.

This study sought to investigate whether cardiac resynchronization therapy (CRT) is capable of reversing the blunted FFR and the downregulation of contractility regulating genes.

Twenty heart failure patients underwent echocardiographic examination during incremental AAI and DDD-CRT pacing at 70, 90, and 110 beats/min, immediately after and 4 months after CRT implantation. The FFR was determined from the ratio of the LV systolic pressure/end systolic volume index at given heart rate. In a subgroup of 6 patients with idiopathic dilated cardiomyopathy, serial LV dP/dtmax was invasively measured during both pacing modes and serial LV endomyocardial biopsies were taken to measure sarcoplasmatic reticulum calcium ATPase 2alpha (SERCA2alpha), phospholamban (PLN), sarcolemmal sodium calcium exchanger (NCX), beta1-adrenoreceptor (beta1-AR), and apelin (APL) gene expression using reverse-transcriptase polymerase chain reaction.

Acutely, DDD-CRT pacing was associated with a decrease in dyssynchrony (P <.01) and increase in diastolic filling time (P <.01) at all heart rates paralleled by an upward shift of the FFR (P <.01) without force-frequency amplification. A greater upward shift of the FFR was noticed during DDD-CRT as compared with AAI (P <.01) after 4 months. In addition, CRT was associated with a significant force-frequency amplification at follow-up as evidenced from the steeper slope of the FFR relationship (P = .039). This was associated with a significant upregulation of SERCA2alpha P = .01), PLN (P = .01), their ratio (P = .01), ratio of SERCA/NCX (P = .02), beta1-AR (P = .03), and APL (P = .01) mRNA levels.

CRT is associated with an acute upward shift in the FFR without force-frequency amplification related to restored synchronicity and increased filling time of the LV. Only chronic CRT is associated with force-frequency amplification in parallel to upregulation of contractility regulating genes.