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Ventricular fibrillation does not depress postfibrillatory contractility in blood-perfused dog hearts
1Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan.
Insights
Ventricular fibrillation (VF) does not depress canine left ventricular contractility after defibrillation when coronary perfusion is maintained. Contractility initially increased, then returned to baseline levels within 30 minutes post-defibrillation.
Area of Science:
- Cardiovascular Physiology
- Cardiac Electrophysiology
- Myocardial Contractility Research
Background:
- Ventricular fibrillation (VF) is a life-threatening arrhythmia characterized by disorganized electrical activity in the ventricles.
- The impact of VF on subsequent ventricular contractility, particularly when coronary perfusion is maintained, requires clarification.
- Understanding post-arrhythmic cardiac function is crucial for developing effective resuscitation strategies.
Purpose of the Study:
- To investigate whether ventricular fibrillation (VF) depresses ventricular contractility in a blood-perfused canine heart model.
- To quantify changes in left ventricular contractility and myocardial oxygen consumption following induced VF and subsequent defibrillation.
Main Methods:
- Excised, cross-circulated canine hearts were subjected to either 20 or 40 minutes of electrically induced ventricular fibrillation (VF).
- Left ventricular pressure, volume, and myocardial oxygen consumption were measured before and at multiple time points after defibrillation.
- Ventricular contractility was assessed using the maximal pressure/volume ratio (Emax), with normal coronary perfusion pressure maintained throughout.
Main Results:
- Immediately after defibrillation, Emax increased to 116% of control levels (p < 0.05).
- Emax decreased to 84% of control levels at 10 minutes post-defibrillation (p < 0.05), then recovered to baseline by 20-30 minutes.
- Myocardial oxygen consumption changes were proportional to Emax variations; no significant difference was observed between 20 and 40 minutes of VF.
Conclusions:
- Ventricular fibrillation (VF) itself, for durations of 20 to 40 minutes, does not cause persistent depression of postfibrillatory left ventricular contractility in dogs.
- Maintained normal coronary blood perfusion is critical for preserving ventricular function after VF.
- The transient changes in contractility observed are likely related to the immediate effects of defibrillation and reperfusion.
Abstract:
We studied whether ventricular fibrillation depresses ventricular contractility in a blood-perfused heart. In 12 excised, cross-circulated dog hearts, we measured left ventricular pressure and myocardial oxygen consumption at a middle left ventricular volume as control and induced ventricular fibrillation electrically. Six hearts were subjected to 20 minutes of ventricular fibrillation (group A), and the other six hearts were subjected to 40 minutes of ventricular fibrillation (group B). Then we defibrillated the heart with direct current shock and measured left ventricular pressure, left ventricular volume, and myocardial oxygen consumption immediately, 10 minutes, 20 minutes, and 30 minutes after the defibrillation. Coronary perfusion pressure was maintained normal (around 100 mm Hg) by the arterial pressure of the support dog throughout each experiment. Ventricular contractility was quantified by the maximum value for the instantaneous pressure/volume ratio (Emax). Pooled data of both groups A and B showed that Emax immediately after defibrillation increased to 116% +/- 28% (p less than 0.05) of control level and Emax 10 minutes after defibrillation decreased to 84% +/- 17% (p less than 0.05) of control level. Then Emax recovered to the control level: 95% +/- 18% (p greater than 0.05) of control level at 20 minutes and 100% +/- 20% (p greater than 0.05) of control level at 30 minutes after defibrillation. Emax of group A was not different from that of group B at comparable measurement times after defibrillation. Changes in myocardial oxygen consumption per beat were in proportion to the changes in Emax. We conclude that ventricular fibrillation per se for 20 to 40 minutes does not depress postfibrillatory contractility when coronary blood perfusion is maintained normal in the dog left ventricle.