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Acute exposure to extreme altitude increases arterial stiffness by activation of the sympathetic and endothelin system as well as hypoxia-induced reactive oxygen species production. Beyond a certain individual threshold, these physiological adaptations represent a relevant cardiovascular risk factor. In this pilot study we investigated to what extent temporary exposure to moderate altitude, as present during hiking, skiing or in aeroplanes, leads to changes in vascular tone. Pulse wave parameters of 8 healthy individuals were assessed with a BR-102 plus pulse wave analyser (Schiller, Germany) at baseline (521 m) and after 24 h exposure to moderate altitude (2650 m). We identified a significant increase in heart rate (61 vs. 68/min, p  = 0.021) as well as changes in central (35.6 vs. 41.4 mmHg, p  = 0.024) and peripheral pulse pressure (44.7 vs. 52.6 mmHg, p  = 0.006). Amplitudes of forward (21.6 vs. 25.4 mmHg, p  = 0.012) and backward pulse waves (15.3 vs. 17.6 mmHg, p  = 0.043) were significantly elevated. Pulse wave velocity showed no significant change from 5.8 m/s at baseline to 6.1 m/s at moderate altitude ( p  = 0.056). We show that temporary exposure to moderate altitude leads to mild changes in vascular tone reflected by pulse pressure and pulse wave amplitude in healthy adults. Although the observed effects were mild in our study, it indicates that adaptation capacity is of crucial importance and any restrictions by disease or simply with the process of ageing demand increased awareness, even in moderate altitude.

Background: Periodic repolarization dynamics (PRD) is a novel electrocardiographic phenomenon that refers to sympathetic activity-associated low-frequency modulations of cardiac repolarization. Retrospective post-myocardial infarction (MI) studies revealed that increased PRD indicates an increased risk of subsequent death., Objective: This is the first prospective study to validate PRD in patients after MI receiving up-to-date treatment., Methods: Four hundred fifty-five survivors of MI (age ≤80 years) in sinus rhythm were enrolled. PRD was assessed from 20-minute electrocardiographic recordings (2048 Hz) and prospectively dichotomized at 5.75 deg 2 . Primary and secondary end points were total mortality and cardiovascular mortality, respectively. Multivariable analyses additionally included Global Registry of Acute Coronary Events score (dichotomized at >140), left ventricular ejection fraction (dichotomized at ≤35%), diabetes mellitus, and deceleration capacity of heart rate (dichotomized at ≤2.5 ms). The prognostic power of PRD was evaluated using receiver operating characteristic curve analysis, Cox regression analysis, and the integrated discrimination improvement index., Results: During a median follow-up period of 27 months, 47 patients died. Twenty-three of these deaths were classified as cardiovascular. Increased PRD was significantly associated with both end points, yielding areas under receiver operating characteristic curves of 69.3% (60.2%-77.8%) and 79.1% (69.7%-86.7%) for total mortality and cardiovascular mortality, respectively (P < .001 for both). In multivariable analysis, increased PRD indicated a 2.2- and 9.5-fold risk of total mortality and cardiovascular mortality (P = .024 and P = .003, respectively). Addition of PRD to the models significantly improved the integrated discrimination improvement index for total (P = .047) and cardiovascular mortality (P = .007)., Conclusion: PRD is a strong and independent predictor of total mortality and cardiovascular mortality in patients after MI treated with contemporary therapy., (Copyright © 2019 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Hamm, Wolfgang, Lukas von Stülpnagel, Mathias Klemm, Monika Baylacher, Konstantinos D. Rizas, Axel Bauer, and Stefan Brunner. Deceleration capacity of heart rate after acute altitude exposure. High Alt Med Biol 19:299-302, 2018., Background: The autonomic nervous system plays a crucial role in adaptive changes after high-altitude exposure. Deceleration capacity (DC) of heart rate is an advanced marker of heart rate variability (HRV) that predominantly reflects the vagal activity of the cardiac autonomic nervous system. The impact of high-altitude exposure on DC has not been investigated yet., Methods: In eight healthy individuals we performed a high-resolution digital 30-min electrocardiography in Frank leads configuration at baseline (521 m altitude), immediately after ascent to the Environmental Research Station Schneefernerhaus (UFS) at Zugspitze (2650 m altitude) and after a sojourn of 24 hours at this altitude. DC of heart rate was assessed using customized software. In addition, standard parameters of HRV were assessed., Results: DC decreased significantly from 10.2 ± 0.8 ms to 8.9 ± 1.0 ms (p < 0.05) after acute altitude exposure. After a sojourn of 24 hours at high altitude, DC remained low at 8.6 ± 1.2 ms. There were no significant changes in standard parameters of HRV., Conclusion: Our findings show for the first time a decrease of DC of heart rate providing a novel insight into the dysbalance of autonomic nervous system at high altitude.

Aims: Twenty-four-hour deceleration capacity (DC24h) of heart rate is a strong predictor of mortality after myocardial infarction (MI). Assessment of DC from short-term recordings (DCst) would be of practical use in everyday clinical practice but its predictive value is unknown. Here, we test the usefulness of DCst for autonomic bedside risk stratification after MI., Methods and Results: We included 908 patients after acute MI enrolled in Munich and 478 patients with acute (n = 232) and chronic MI (n = 246) enrolled in Tuebingen, both in Germany. We assessed DCst from high-resolution resting electrocardiogram (ECG) recordings (<30 min) performed under standardized conditions in supine position. In the Munich cohort, we also assessed DC24h from 24-h Holter recordings. Deceleration capacity was dichotomized at the established cut-off value of ≤ 2.5 ms. Primary endpoint was 3-year mortality. Secondary endpoint was 3-year cardiovascular mortality. In addition to DC, multivariable analyses included the Global Registry of Acute Coronary Events score >140 and left ventricular ejection fraction ≤ 35%. During follow-up, 48 (5.3%) and 48 (10.0%) patients died in the Munich and Tuebingen cohorts, respectively. On multivariable analyses, DCst ≤ 2.5 ms was the strongest predictor of mortality, yielding hazard ratios of 5.04 (2.68-9.49; P < 0.001) and 3.19 (1.70-6.02; P < 0.001) in the Munich and Tuebingen cohorts, respectively. Deceleration capacity assessed from short-term recordings ≤ 2.5 ms was also an independent predictor of cardiovascular mortality in both cohorts. Implementation of DCst ≤ 2.5 ms into the multivariable models led to a significant increase of C-statistics and integrated discrimination improvement score., Conclusion: Deceleration capacity assessed from short-term recordings is a strong and independent predictor of mortality and cardiovascular mortality after MI, which is complementary to existing risk stratification strategies.