Age-related arrhythmogenesis on ascent and descent: "autonomic conflicts" on hypoxia/reoxygenation at high altitude?

PURPOSE: To discern whether arrhythmogenesis at high-altitude (HA) may differ depending on ascent or descent, as well as on age. METHODS: Male subjects (37.9±12.0 SD y, n=33) were separated into a young (Y) group (29.6±5.73 SD y, n=18) and an older (O) one (47.9±9.83 SD y, n=15). All subjects were monitored by Holter electrocardiography while successively ascending (41.2±7.51 SD min) and descending (38.7±6.68 SD min) between 2950 and 5050 m as car passengers on a 25 km road in Northern Chile. Arrhythmic events (AE) ensued when the difference between two consecutive RR intervals exceeded 0.16 sec. RESULTS: From 311 AE registered, 29% occurred on ascent and 71% on descent, the sinusal type predominating in both age groups. AE incidence, RR interval duration, and heart rate variability (HRV) in the time domain (RMSSD) increased during descent, as compared to ascent, in the Y group (p<0.05), but not in the O one. Independently of age, AE incidence along descent associates with the time previously spent at 5050 m (p<0.001). CONCLUSIONS: Rapid transitions at HA favor arrhythmogenesis, the latter becoming evident particularly in the Y group on descent. Age-dependent changes of autonomic activity appear to be involved in arrhythmogenesis on transitions at HA.

Visualizing the electrocardiogram through orbital transform.

The purpose of this work is to present a new electrocardiogram (ECG) visualization technique through a mathematical transform applied to one lead ECG signal. This transform, called orbital transform (OT) in this work, consists of a remapping of the ECG signal to a spatial curve represented by a three dimensional phase portrait. With this spatial curve it is possible to observe the evolution of changes in the QRS complex, which are not always clear to distinguish by a simple visual inspection of the temporal ECG signal. Moreover, using the projection of this curve in one of the 2D planes it is possible to easily calculate variation ranges of several ECG parameters such as maximal and minimal waves amplitudes and maximal and minimal wave slopes.