How does an artifical pacemaker know how fast to beat?

26 July 2009

Question

How does an artificial pacemaker know how fast the heart should beat?

Answer

We put this to Cathy Ross, Cardiac Nurse at the British Heart Foundation. The role of an artificial pacemaker is to monitor and control the heart's natural rhythm. They're implanted for many reasons and the way they work will vary according to the reasons for which they're implanted. In the case of the slow heart rate, for example, a certain number of beats per minute will be programmed into the pacemaker according to the needs of the patient. The pacemaker would then sense through a number of wires the number of beats being delivered naturally by the heart's own pacemaker, which is called the sino-atrial node. And it will only interject to deliver another beat if there is a shortfall. So the pacemaker is there only for the reason for which it has been implanted. So if it's a slow heart rate and you go running for a bus then the pacemaker will only interject if your heart rate falls below the required minimum level. Sometimes, doctors will put a maximum level on a pacemaker. So for some abnormal heart rhythms (if the heart rate went too fast) it could cause fainting or black-outs or possibly even a life-threatening rhythm and then maybe in an overriding upper level that the pacemaker will be set at but that's quite complex. They tend to be implanted with internal defibrillators so they will be the ones that are sensing for life-threatening rhythms so that the person can receive a shock if they require it.

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