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tons wrote: What is the
upper limits of normal for the PR interval in a giraffe or large whale?
Best, Michael Teuton
Michael: Thanks for an interesting
discussion. I don't have data on the upper limits of the PR intervals,
but I do have some readings which I assume indicate rough averages.
The resting heart rate of an anesthetized giraffe is 70 beats per minute
with a PR interval of 0.18 sec. Some lost soul actually did an EKG
on a humpback whale (trapped in a net on the ocean's surface), 10 meters
long with a weight of 30,000kg, and whose estimated heart weight was 150
to 180kg. The heart rate was 30 to 35 beats/min and the PR interval
did not exceed 0.4 sec. For those who don't know what a PR interval
is, it is a measurement found on EKGs that represents the time it takes
for the electrical impulse generated by the heart's pacemaker (sinoatrial
node) to travel through the atria, into the atrioventricular node, and
down the vetricular conduction system into the muscle (myocardium) of the
ventricles. In humans it ranges from 0.14 to 0.22 sec.--Ken Clay,
M.D.
1. Rossof A.H. An electrocardiographic study of the giraffe. Am Heart J 1972 Jan;83(1):142-3. |