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

Area of Science:

• Cardiology
• Cardiac Electrophysiology
• Heart Failure Research

Background:

• Ventricular hypertrophy is linked to cardiac arrhythmias, potentially due to repolarization changes (electrical remodeling).
• The precise timing of hypertrophy and electrical remodeling development and their reversibility are not fully understood.
• This study investigates these processes using a canine model of volume overload hypertrophy induced by atrioventricular block.

Purpose of the Study:

• To examine the temporal relationship between structural and electrical remodeling in volume overload hypertrophy.
• To assess the reversibility of hypertrophy and electrical remodeling after restoring normal cardiac load via pacing.
• To understand the dissociation between reverse structural and electrical remodeling.

Main Methods:

• Canine model with complete atrioventricular block (CAVB) for 16 weeks (n=9).
• A separate group underwent 8 weeks of CAVB followed by 8 weeks of right ventricular (RV) pacing (n=9).
• Measurements included 2D-echocardiography for left ventricular (LV) mass, surface ECG for QT and QTc intervals, and monophasic action potentials for action potential duration.

Main Results:

• LV mass increased by ~30% after 8 weeks of AV-block and normalized after 8 weeks of pacing.
• QT and QTc intervals prolonged after AV-block but did not decrease with pacing.
• Action potential duration remained unchanged, indicating a lack of reverse electrical remodeling.

Conclusions:

• In AV-block-induced volume overload hypertrophy, structural and electrical remodeling occur concurrently.
• Restoring physiological heart rate leads to reverse structural remodeling but not reverse electrical remodeling.
• This dissociation highlights distinct mechanisms governing structural and electrical adaptation in the hypertrophied heart.