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Exercise Training Fails to Protect against Development of Ischemia‐Induced Ventricular Fibrillation in Isolated Rat Hearts
Author(s) -
ClementsJewery Hugh,
Radich Patricia,
Rawson Nicholas,
Hatcher Amanda Shea
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.686.6
Subject(s) - medicine , ventricular fibrillation , ischemia , cardiology , coronary artery disease , anesthesia , perfusion
Background and purpose Sudden cardiac death continues to be a major cause of mortality in the United States and beyond, with the predominant cause of death being ventricular fibrillation in the setting of ischemic heart disease. Pharmacological therapy has proven to be a limited strategy for preventing ventricular fibrillation as a consequence of the safety and efficacy of available drugs. Exercise training has been found to be effective in reducing susceptibility to spontaneous VF in a canine in vivo model (Bonila et al., 2012), but it is not known if exercise training would be effective in reducing susceptibility to ischemia‐induced VF in isolated perfused rat hearts. Methods Male and female 6 week old Sprague‐Dawley rats were separated into exercise (EX) and sedentary (SED) groups (N=15 per group). Rats in the exercise group were trained for 60 min on a treadmill 4 days/week for 8 weeks. Workloads were matched for bodyweight. Rats in the SED group were given equivalent handling time. Hearts were excised under pentobarbital anesthesia after the end of the 8‐week period in a randomized and blinded manner and perfused in the Langendorff mode using modified Krebs solution (3mM K + ). After a 10 min baseline perfusion period, regional ischemia was induced by occlusion of the left main coronary artery and maintained for 30 min. Hearts were subsequently reperfused for 10 min. The ECG was monitored for the occurrence of VF and other arrhythmias during ischemia and used for the measurement of electrocardiographic intervals. An intraventricular balloon was used to record left ventricular developed pressure (LVDP) and end diastolic pressure (EDP). Coronary flow was recorded digitally using a calibrated signal from a pump controller. Results The incidence of VF during ischemia in the EX group was 87% (13/15), which was not different from the incidence of VF in the SED group (67%; 10/15). In addition, the time to onset of VF during ischemia (950±157s vs 1035±127s in SED and EX groups respectively) as well as susceptibility to reperfusion VF (93% in the SED group vs 87% in the EX group) was similar in the two groups. There was no difference in ischemic zone size between groups. Changes in heart rate, coronary flow, EDP and LVDP with onset of ischemia were all similar in both SED and EX groups with no significant differences at any time point. Conclusions Exercise training did not confer protection against ischemia‐induced VF in an established in vitro model. Thus the protection afforded by exercise training in the canine in vivo model may indicate a species dependence of exercise training‐induced protection, or that protection is due to factors absent from isolated rat hearts such as an intact autonomic system or factors circulating in the blood. Support or Funding Information This study was supported by an intramural grant from the West Virginia School of Osteopathic Medicine.