Arrhythmic risk evaluation during exercise at high altitude in healthy subjects: role of microvolt T-wave alternans.
BACKGROUND
Altitude-induced sympathetic hyperactivity can elicit rhythm disturbances in healthy subjects, in particular during exercise.


OBJECTIVE
To asses the real susceptibility of healthy myocardium to malignant ventricular arrhythmias during exercise at high altitude using microvolt T-wave alternans (MTWA).


METHODS
We evaluated eight healthy trained participants (one female, 42 +/- 9 years) during a mountain climbing expedition on Gashembrum II (Pakistan, 8,150 m). MTWA and heart rate variability (HRV) were measured in each subject at sea level and at high altitude, both under rest conditions and during exercise. MTWA was determined with the modified moving average method. HRV was expressed as root mean square of successive differences.


RESULTS
Rest HRV at high altitude was significantly lower compared to rest HRV at sea level (36 +/- 5 vs 56 +/- 9 ms, P = 0.003). HRV during exercise was significantly lower with respect to rest condition both in normoxia (46 +/- 7 vs 56 +/- 9 ms, P = 0.0001) and hypoxia (27 +/- 4 vs 36 +/- 5 ms, P = 0.005). Moreover, HRV was significantly lower during exercise at high altitude compared to exercise at sea level (27 +/- 4 vs 46 +/- 7 ms, P = 0.0002) and arrhythmias were more frequent during exercise in hypoxia. Nevertheless, MTWA was absent under rest conditions both at sea level and at high altitude and minimally evoked during exercise in both conditions (22 +/- 3 microV and 23 +/- 3 microV, respectively, P = 0.2).


CONCLUSIONS
In spite of an enhanced sympathetic activity, MTWA testing during exercise at high altitude was negative in all participants. Healthy trained subjects during exercise under hypoxia seem to be at low risk for dangerous arrhythmias.
Gibelli
Giuseppe
G
Division of Cardiology, Clinical Institute San Carlo, Paderno Dugnano, Milano, Italy.
Fantoni
Cecilia
C
Anzà
Claudio
C
Cattaneo
Paolo
P
Rossi
Andrea
A
Montenero
Annibale S
AS
Baravelli
Massimo
M
D000328:Adult; D000531:Altitude; D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000503:physiopathology*; D004569:Electroencephalography / Q000379:methods*; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D005082:Physical Exertion; D018570:Risk Assessment