It is unknown whether electrophysiological data from zoo lions is indicative of their wild counterparts since little is known about ECGs in wild lions. A known difference between the two groups is that zoo lions adapt to diurnal routines of their human zookeepers, compared to nocturnal lifestyle of their wild cousins. It is not known if this impacts the heart rate and ECG presentation of the two groups of lions. In a recent study, ECG was measured in wild lions and compared to zoo lions. The purpose was to establish a baseline so it would be possible to estimate cardiac response to changes in the surroundings and impact of human activities.

Heart rate or ECG measured every 2 minutes for 14 days
A group of scientists from Denmark, Germany, Northern Ireland and South Africa studied 9 captive and 15 wild African lions. The captive group was part of population management in zoos, and were euthanized after ECG measurements were performed under anesthesia. The group implanted 15 wild lions with Star-Oddi DST milli-HRT or DST centi-HRT data loggers. The loggers measured heart rate every 2 minutes, and a 3-7.5 sec ECG was stored every 8 minutes. During anesthesia of the wild lions due to implantation, an ECG was also taken to compare to the anesthetized captive group. The loggers were retrieved from the wild lions after 14 days.

Zoo lions have significantly shorter QT intervals compared to wild lions
The QT interval represents the time of the ventricular contractions (depolarization) and the consecutive relaxation (repolarization). The QT interval was found to be significantly shorter in zoo lions compared to their wild counterparts. Two comparisons were made, first: ECG from conscious and anesthetized wild African lions. Then ECGs from anaesthetized zoo lions were compared to anaesthetized wild African lions. As the loggers were measuring heart rate 24h of the day it was possible to determine the QT interval during a wide range of heart rates. Furthermore, the data loggers revealed a higher heart rate during nocturnal activities in the wild lions.

Fig: 5c QT intervals from wild lions at matched heart rates compared to anesthetized zoo lions.

Impact of physical fitness
The significance of the shorter QT intervals shows the plasticity of cardiac electrophysiology of lions and suggests functional differences of the heart in zoo-kept and wild lions. This may be significant when reintroducing captured lions to the wild and can impact veterinary treatments in zoo-kept lions, taking into consideration a shorter QT interval could suggest that zoo lions face a higher risk of sudden cardiac death.
 
Further results can be read in the article published in Experimental Physiology.