Sympathetic stimulation increases dispersion of repolarization in humans with myocardial infarction
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Key result
Direct sympathetic stimulation with isoproterenol and reflex stimulation with nitroprusside significantly increased regional differences and dispersion of repolarization in patients with postinfarct cardiomyopathy compared to structurally normal hearts.
Why the study?
Does sympathetic stimulation (direct and reflex) increase regional dispersion of repolarization in patients with postinfarct cardiomyopathy compared to structurally normal hearts?
Population
10 patients total: 5 with postinfarct cardiomyopathy and recurrent ventricular arrhythmias referred for…
Comparison
Direct sympathetic stimulation with… vs Baseline measurements and patients with…
Design
Other
Authors
Discussion
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Overview
Suggests heightened arrhythmic vulnerability during sympathetic stress post-MI; leaves open whether modulation alters clinical events.
Structured PICO
Does sympathetic stimulation (direct and reflex) increase regional dispersion of repolarization in patients with postinfarct cardiomyopathy compared to structurally normal hearts?
P
Population
10 patients, including 5 with postinfarct cardiomyopathy and 5 with structurally normal hearts, undergoing electrophysiological study to assess the effects of sympathetic stimulation on ventricular repolarization.
I
Intervention
Direct sympathetic stimulation with isoproterenol infusion (to increase heart rate by ≥20 beats/min) and reflex sympathetic stimulation with nitroprusside infusion (to decrease systolic blood pressure by ≥20 mmHg).
C
Comparator
Baseline measurements (intra-patient control) and patients with structurally normal hearts (inter-patient control).
O
Outcome
Activation recovery interval (ARI) and ARI dispersion (a surrogate for action potential duration) measured from unipolar intracardiac electrograms in normal, scar, and border zone regions.surrogate
Main Result
p-value: p=0.015
Direct and reflex sympathetic stimulation significantly increases regional repolarization heterogeneity in postinfarct cardiomyopathy, providing a mechanistic basis for ventricular arrhythmogenesis in these patients.
Limitations
- Small number of patients enrolled in the study
- Many patients with ischemic cardiomyopathy were on amiodarone and beta-blockers, which have sympatholytic effects
- Repolarization measurements in scar can be difficult to obtain due to low T waves
- Nitroprusside can reduce wall strain, potentially complicating the effect of the reflex sympathetic nervous system
- Potential underestimation of responses due to heterogeneity of perfusion
- Mapping was limited to electrodes feasible under the approved protocol
- Heterogeneity in remodeling of adrenergic signaling pathways could not be controlled for
Cite This Study
Vaseghi et al. (2012) studied Postinfarct cardiomyopathy (n=10). Isoproterenol and nitroprusside infusion vs. Baseline (within-patient) and structurally normal hearts was evaluated on Change in activation recovery interval (ARI) and ARI dispersion (p=0.015). Direct sympathetic stimulation with isoproterenol and reflex stimulation with nitroprusside significantly increased regional differences and dispersion of repolarization in patients with postinfarct cardiomyopathy compared to structurally normal hearts.
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