Effects of Adaptation to Intermittent High Altitude Hypoxia on Ischemic
Ventricular Arrhythmias in Rats
G. ASEMU, J. NECKÁŘ, O. SZÁRSZOI, F. PAPOUŠEK, B. OŠŤÁDAL,
F. KOLÁŘ
Department of Developmental Cardiology, Institute of Physiology, Academy of
Sciences of the Czech Republic, Prague, Czech Republic
Received April 4, 2000
Accepted May 3, 2000
Summary
We compared the effects of adaptation to intermittent high
altitude (IHA) hypoxia of various degree and duration on ischemia-induced
ventricular arrhythmias in rats. The animals were exposed to either relatively
moderate hypoxia of 5000 m (4 or 8 h/day, 2-3 or 5-6 weeks) or severe hypoxia of
7000 m (8 h/day, 5-6 weeks). Ventricular arrhythmias induced by coronary artery
occlusion were assessed in isolated buffer-perfused hearts or open-chest
animals. In the isolated hearts, both antiarrhythmic and proarrhythmic effects
were demonstrated depending on the degree and duration of hypoxic exposure.
Whereas the adaptation to 5000 m for 4 h/day decreased the total number of
premature ventricular complexes (PVCs), extending the daily exposure to 8 h
and/or increasing the altitude to 7000 m led to opposite effects. On the
contrary, the open-chest rats adapted to IHA hypoxia exhibited an increased
tolerance to arrhythmias that was even more pronounced at the higher altitude.
The distribution of PVCs over the ischemic period was not altered by any
protocol of adaptation. It may be concluded that adaptation to IHA hypoxia is
associated with enhanced tolerance of the rat heart to ischemic arrhythmias
unless its severity exceeds a certain upper limit. The opposite effects of
moderate and severe hypoxia on the isolated hearts cannot be explained by
differences in the occluded zone size, heart rate or degree of myocardial
fibrosis. The proarrhythmic effect of severe hypoxia may be related to a
moderate left ventricular hypertrophy (27 %), which was present in rats adapted
to 7000 m but not in those adapted to 5000 m. This adverse effect can be
overcome by an unknown protective mechanism(s) that is absent in the isolated
hearts.
Key words
High altitude · Chronic hypoxia ·
Rat heart · Ischemia ·
Arrhythmias
Reprint requests
Dr. F. Kolář, Institute of Physiology, Academy of
Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague 4, Fax: +420
2 475 2125, e-mail: kolar@biomed.cas.cz
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