Changes in Subendocardial Viability Ratio With Acute High-Altitude Exposure and Protective Role of Acetazolamide

Abstract

Abstract-High-altitude tourism is increasingly frequent, involving also subjects with manifest or subclinical coronary artery disease. Little is known, however, on the effects of altitude exposure on factors affecting coronary perfusion. The aim of our study was to assess myocardial oxygen supply/demand ratio in healthy subjects during acute exposure at high altitude and to evaluate the effect of acetazolamide on this parameter. Forty-four subjects (21 men, age range: 24-59 years) were randomized to double-blind acetazolamide 250 mg bid or placebo. Subendocardial viability ratio and oxygen supply/demand ratio were estimated on carotid artery by means of a validated PulsePen tonometer, at sea level, before and after treatment, and after acute and more prolonged exposure to high altitude (4559 m). On arrival at high altitude, subendocardial viability ratio was reduced in both placebo (from 1.63±0.

Cardioprotection after acute exposure to simulated high altitude in rats. Role of nitric oxide

“…In both cases the effect was associated to an enhanced cytosolic NOS activity. The duration, frequency, and severity of hypoxic episodes become critical factors determining whether hypoxia could be harmful [12], or paradoxically beneficial [2,3,13].…”

Aortic stiffness and myocardial ischemia

“…Likely, this could be at least in part the consequence of the above-reported inaccuracies affecting the measurement of DPTI : SPTI ratio. Conversely, no major interferences are to be expected when considering the result of recent studies reporting significant changes in SEVR after acute exposure at high altitude [21,22], including a report on the possible link between the reduction of SEVR and the appearance of signs and symptoms of a reduced coronary reserve in this setting [22]. In these studies, in fact, only relatively young and overall healthy individuals were evaluated, in whom the contribution of isovolumic contraction time to cardiac work may be considered negligible.…”

Blood pressure at high altitude: physiology and clinical implications

“…26 This may explain why absolute BP levels achieved at peak exercise might not be much different between HA and sea level, a finding which needs to be interpreted with caution, considering the reduced maximal oxygen consumption characterizing high altitude. 27 Higher BP and heart rate, combined with a reduction in the subendocardial viability ratio (an index characterizing aortic pressure waveform, reflecting diastolic coronary perfusion and systolic energy requirements in the coronary circulation) 28 at any given level of exercise in hypoxia, may contribute to an imbalance between myocardial oxygen supply and demand in nonacclimatized exercising individuals. 29 This mechanism has been proposed to explain sporadic cases of myocardial ischemia reported in this specific setting.…”