Defibrillation, the coronary venous system and the passive electrode affect

Abstract

Implantable cardioverter defibrillators are becoming an increasingly accepted treatment for primary and secondary prevention of arrhythmic death.  Key to the efficacy and future development of these devices is the defibrillation threshold (the amount of energy required to reliably terminate fibrillation).  Changing the vectors of defibrillation through lead positioning has the potential to reduce defibrillation threshold.  Current methods for the assessment of defibrillation threshold in humans lack repeatability and precision.

We undertook a program of human and porcine studies to investigate the impact on defibrillation threshold of placing electrodes in the coronary venous system.  Both actively connected and passive (adjacent, unconnected) coronary venous electrodes were studied.  We also developed and evaluated a method of assessing defibrillation threshold by delivering several test shocks following each induction.

In defibrillation from the middle cardiac vein placement of a passive electrode affect reduces defibrillation threshold by 17%.  Middle cardiac vein electrodes exert no passive electrode affect on right ventricular endocardial defibrillation.  In the pig anodes comprised of middle cardiac vein alone are equally effective as tied middle cardiac vein, right ventricular anodes.  Both these anodes decrease defibrillation threshold compared to right ventricle alone.  The novel method of defibrillation threshold assessment developed increases repeatability compared to current algorithms.  In human studies neither middle cardiac vein nor auxiliary lateral cardiac vein defibrillation decrease defibrillation threshold.

The passive electrode affect has the capacity to decrease defibrillation threshold.  There is a discrepancy between the efficacy of coronary venous defibrillation in man and pigs due to the difference in orientation of pig and human hearts and the higher impedance of the configuration in man.  A defibrillation threshold assessment algorithm delivering several test shocks after each induction may replace binary searches as gold standard in clinical studies.

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