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Related Experiment Videos

Ventricular rate determines early bradycardic electrical remodeling.

Fumiaki Suto1, Wei Zhu, Sean A Cahill

  • 1Cardiovascular Research Programme, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.

Heart Rhythm
|April 27, 2005
PubMed
Summary

Chronic bradycardia causes ventricular electrical remodeling, increasing QT intervals and risk of arrhythmias. Maintaining a near-physiologic heart rate prevents these changes, independent of structural remodeling.

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Area of Science:

  • Cardiology
  • Electrophysiology
  • Molecular Cardiology

Background:

  • Chronic bradycardia can lead to ventricular repolarization delay, increasing the risk of potentially lethal tachydysrhythmias.
  • Prolonged QT intervals and torsades de pointes are linked to reduced ventricular myocyte delayed rectifier potassium (K+) currents.

Purpose of the Study:

  • To determine if chronic slow heart rate (bradycardia) is the primary driver of early ventricular electrical remodeling.
  • To investigate the impact of bradycardia on ventricular repolarization and ion channel function.

Main Methods:

  • Rabbits underwent transcatheter AV node ablation and were paced at either 140 bpm or 280 bpm.
  • ECG QT intervals were measured, and ventricular myocyte repolarizing currents (I(Kr), I(Ks), I(to), I(K1)) were assessed using whole-cell patch clamp.

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Main Results:

  • Bradycardic rabbits showed significantly increased QT intervals and down-regulated I(Kr) and I(Ks) currents.
  • These electrical remodeling changes were not observed in rabbits paced at 280 bpm.
  • One bradycardic rabbit developed pause-dependent torsades de pointes; no heart failure or hypertrophy was noted.

Conclusions:

  • Bradycardic ventricular electrical remodeling occurs independently of structural changes, heart failure, or AV synchrony.
  • Maintaining a near-physiologic ventricular rate prevents bradycardia-induced electrical remodeling.