Absence of reverse electrical remodeling during regression of volume overload hypertrophy in canine ventricles

OBJECTIVE: Ventricular hypertrophy predisposes for cardiac arrhythmias, presumably due to prolongation of repolarization (electrical remodeling). The temporal relation between the development of hypertrophy and electrical remodeling, as well as their reversibility upon restoration of normal load, however, are poorly understood. This was investigated in the present study using volume overload hypertrophy induced by atrio-ventricular (AV) block and normalization of load by pacing. METHODS: Dogs were subjected to either 16 weeks of AV-block (CAVB group, n=9) or 8 weeks of AV-block followed by 8 weeks of right ventricular (RV) pacing at physiological heart rate (CAVB+PACE group, n=9). RESULTS: Left ventricular (LV) mass (2D-echocardiography) increased after 8 weeks of AV-block to approximately 30% above baseline and returned to 10+/-14% after 8 weeks of pacing. QT-time (surface ECG) also increased after AV-block. However, 8 weeks of pacing did not decrease QT and QTc-time (c=corrected for heart rate), neither during physiological pacing nor during temporary pacing at 100 beats/min. Lack of reverse electrical remodeling was confirmed by the absence of changes in LV and RV action potential duration (monophasic action potentials) at week 8 and 16. CONCLUSIONS: In volume overload hypertrophy due to AV-block, structural and electrical remodeling develop in parallel but restoration of physiological heart rate causes dissociation between reverse structural remodeling and reverse electrical remodeling.