Sunday, October 19, 2008

Seasons of the heart - bradycardia, arrhythmias and sudden death

A younger colleague stopped me over the weekend and asked my opinion of an young otherwise healthy individual with a resting heart rate of 40/min. I had to admit to pausing for while before answering. The normal range for a normal heart rate is probably about 60-100/min. Quite often we do see individuals with heart rates between 50-60, especially if they are aerobically quite fit. But 40/min is a bit of a stretch below the normal range especially considering that the atrial and nodal pacemakers start to kick in. Marathon runners can drop their heart rates down to 40. But here the individual wasn't quite a marathon runner...merely borderline fitness. He had a heart rate of 40, no escape rhythms (ECG done), and otherwise cardiovascularly normal.

I passed him as normal.

But it made me think a bit more about the heart. Amazing organ. At an average heart rate of 72/min, with a lifespan of 80 years, the heart would have beaten over 3 billion times. Isn't that incredible?
And all this while, the complex movement of Na+, K+ and Ca++, through intricately regulated ion channel activities, maintain appropriate heart rhythms that allow us to function normally through extreme ranges of physical activities. It's just such a miracle that we don't all seize up and die. When you think about it, we wouldn't really require a myocardial infarct to die of ventricular fibrillation. Yet most of us will live through this uncertainty.

Perhaps the sudden death cases that we read about in young people ...or crib deaths in infants....are nothing more than the random occurrences of electrical convulsions of the heart? Intrinsic risks of life.
Food for thought.

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