Abstract
In our opinion, the first issue is already addressed by our recommendation that the patient must have sufficient exercise capacity for the intended activities, considering the altitude-associated decline in maximum exercise capacity. It is important that there are no general rules for a particular mountain sport activity, because the amount of personal experience and the level of technical skills are important determinants of oxygen demand for a particular activity, such as rock climbing or downhill skiing (Turnbull et al., 2009). There is even a considerable variability of oxygen demand for uphill hiking for a given speed and backpack weight of 15 to 20 mL/min/kg of body weight, equivalent to about 1 to 1.5 W/kg (Knight and Caldwell 2000), depending on the economy of hiking.
Although sudden cardiac death (SCD) is the second most common cause of death at moderate to high altitude, we do not think that placing AED at strategic points will substantially reduce SCD in the mountains. It has been shown that placement of AEDs can be effective in cases of ventricular fibrillation or ventricular tachycardia (Hallstrom et al., 2004) when these devices can be reached within 60 to 90 sec to ensure an early defibrillation, since every minute of delay reduces the success of defibrillation by about 10% [American Heart Association (AHA), 2000]. In urban areas, placement of AEDs is recommended when at least 1 cardiac arrest occurs every 2 yr in an area with a radius of 100 m (Handley et al., 2005) or 1 cardiac arrest every 5 yr (Aufderheide et al., 2006).
Incidence and exact locations of SCDs in the mountains are not very well documented. Based on the data reported by Windsor and colleagues (2009), we calculate about one SCD for every 800,000 days of exposure for skiing or every 300,000 days of exposure for hiking. Based on this number for hiking and the AHA recommendation of at least 1 SCD in 5 yr, areas with a total of 60,000 visitors/yr staying over a full day in an area with a 100-m radius can be considered appropriate for placing an AED. Should there be areas in mountain environments that fulfill such criteria, we also need to consider that the risk for SCD at high altitude while resting or with very moderate exercise is to our knowledge not known. Since vigorous exercise (>6 metabolic equivalents) compared with rest is associated with a 5- to 250-fold higher risk for SCD (Albert et al., 2000), most SCD in the mountains will most likely occur during outdoor exercise and not in sufficient proximity to an AED to allow for early defibrillation. Therefore, we doubt that there are strategic points in the mountain environment that fulfill the criteria for placing an AED.