Variable Unstressed Volume Keeps Normal Distributions of Canine Left Ventricular Contractility and Total Mechanical Energy under Atrial Fibrillation

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  • Mohri Satoshi
    Department of Cardiovascular Physiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences
  • Shimizu Juichiro
    Department of Cardiovascular Physiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Department of Physiology II, Nara Medical University
  • Ito Haruo
    Department of Cardiovascular Physiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Department of Physiology II, Nara Medical University
  • Yamaguchi Hiroki
    Department of Cardiovascular Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences
  • Sano Shunji
    Department of Cardiovascular Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences
  • Takaki Miyako
    Department of Physiology II, Nara Medical University
  • Suga Hiroyuki
    Department of Cardiovascular Physiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences National Cardiovascular Center Research Institute

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Abstract

We have reported that the contractility index (Emax) and the total mechanical energy (PVA) of arrhythmic beats of the left ventricle (LV) distribute normally in canine hearts under electrically induced atrial fibrillation (AF). Here, Emax is the ventricular elastance as the slope of the end-systolic (ES) pressure-volume (P-V) relation (ESPVR), and PVA is the systolic P-V area as the sum of the external mechanical work within the P-V loop and the elastic potential energy under the ESPVR. To obtain Emax and PVA, we had to assume the systolic unstressed volume (Vo) as the V-axis intercept of the ESPVR to be constant despite the varying Emax, since there was no method to obtain Vo directly in each arrhythmic beat. However, we know that in regular stable beats Vo decreases by ∼7 ml/100 g LV with ∼100 times the increases in Emax from ∼0.2 mmHg/(ml/100 g LV) of almost arresting weak beats to ∼20 mmHg/(ml/100 g LV) of strong beats with a highly enhanced contractility. In the present study, we investigated whether Emax and PVA under AF could still distribute normally, despite such Emax-dependent Vo changes. The present analyses showed that the Emax changes were only ∼3 times at most from the weakest to the strongest arrhythmic beat under AF. These changes were not large enough to affect Vo enough to distort the frequency distributions of Emax and PVA from normality. We conclude that one could practically ignore the slight Emax and PVA changes with the Emax-dependent Vo changes under AF.<br>

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