Related Experiment Videos
Hypertrophy causes delayed conduction in human and guinea pig myocardium: accentuation during ischaemic perfusion
S J Winterton1, M A Turner, D J O'Gorman
1Academic Cardiology Unit, St Mary's Hospital Medical School, London, United Kingdom.
Insights
Cardiac hypertrophy leads to delayed electrical conduction, increasing arrhythmia risk during ischemia. This study reveals how severe hypertrophy accentuates conduction delays and alters repolarization, impacting heart vulnerability.
Area of Science:
- Cardiovascular Physiology
- Cardiac Electrophysiology
- Heart Disease Research
Background:
- Cardiac hypertrophy, an enlargement of the heart muscle, is linked to increased susceptibility to arrhythmias, particularly during myocardial ischemia.
- Understanding the electrophysiological mechanisms underlying this vulnerability is crucial for developing targeted therapeutic strategies.
Purpose of the Study:
- To investigate the electrophysiological basis for increased arrhythmia vulnerability in cardiac hypertrophy during myocardial ischemia.
- To examine how aortic constriction-induced hypertrophy affects cellular electrophysiology, conduction, and refractory periods in guinea pig hearts and human subjects.
Main Methods:
- Isolated perfused guinea pig hearts underwent aortic constriction (50 and 150 days post-constriction) or sham operation.
- Cellular electrophysiology, conduction times, and refractory periods were assessed under normal and ischemic conditions (low/zero flow).
- Electrocardiograms (ECGs) were analyzed in human patients with left ventricular hypertrophy and matched controls.
Main Results:
- Severe cardiac hypertrophy (150 days) in guinea pigs demonstrated significant conduction delay and QRS widening, also observed in human subjects with left ventricular hypertrophy.
- During ischemia, hypertrophied hearts exhibited earlier ventricular arrhythmias and accentuated conduction delays.
- Ischemia-induced reductions in action potential duration were attenuated by hypertrophy, though this effect varied with ischemia severity and duration.
Conclusions:
- Delayed conduction is a key electrophysiological abnormality in severe cardiac hypertrophy in both animal models and humans.
- Cardiac hypertrophy exacerbates conduction delays and alters repolarization dynamics during ischemic events, contributing to arrhythmia susceptibility.
Objective:
The aim was to investigate why cardiac hypertrophy causes increased vulnerability to arrhythmias during myocardial ischaemia.
Methods:
The electrophysiological basis for this increased vulnerability was studied in isolated perfused guinea pig hearts obtained 50 and 150 d after aortic constriction, and in sham operated controls. Cellular electrophysiology, conduction, and refractory periods were examined during control perfusion and during low flow (coronary flow reduced to 10% of control) and zero flow ischaemia. ECGs in patients with left ventricular hypertrophy and in controls matched for age and heart rate were also studied.
Results:
Aortic constriction increased heart weight:body weight ratio by 33% at 50 d and by 69% at 150 d. Action potentials were unchanged in hypertrophied hearts. Significant conduction delay occurred in 150 d hypertrophied hearts [conduction time index 23(SEM 4) ms v 18(3) ms, p < 0.001; QRS width 40(1) ms v 35(1) ms, p < 0.01], but not in 50 d hypertrophied hearts. Conduction delay was also present in humans with left ventricular hypertrophy [QRS width 96(13) ms v 87(8) ms, p < 0.01]. Although the QTc interval was increased in humans, at 422(23) ms v 411(17) ms in controls, p < 0.05, this could be explained by the increased QRS duration. During ischaemia, ventricular arrhythmias tended to occur earlier in hypertrophied hearts. Hypertrophy was also associated with a greater increase in conduction delay. Ischaemia reduced action potential duration and refractory periods; the reduction in action potential duration was attenuated by hypertrophy (p < 0.01), although the reverse was apparent during low flow ischaemia at 50 d.
Conclusions:
Delayed conduction is an important feature of severe cardiac hypertrophy in guinea pigs and man. Hypertrophy is associated with accentuated conduction delay and altered repolarisation during ischaemia.