Skipping A Beat- Literally!!!

Ever wondered how your heart skips a beat each time you encounter a scary or an exciting situation? Even though ‘skipping a beat’ is used as an idiom, there is a simple physiological cause underlying it. Our heart, the vital pumping organ of our body, can perform its function only if it receives electrical signals (called impulses). Our heart also has a resting period (called refractory period) within which it doesn’t pump blood even on arrival of an impulse.

Sometimes, when we’re scared or excited, it so happens that our heart receives extra unexpected impulses apart from the normal ones. These unexpected impulses supplement a normal impulse to increase the vigour of the heart beat and prolongs the pumping activity such that the heart’s refractory period coincides with the arrival of the next normal impulse, causing a period of inactivity. The heart doesn’t respond to the next impulse due to the prolonged pumping activity causes by the extra impulse.

Thus the heart literally ‘skips a beat’ which was supposed to occur under normal circumstances. In medical terms, this phenomenon is called extrasystole or ectopic beat and the comparatively long pause of inactivity (due to the unexpected impulse) is called compensatory pause.

To compensate for this loss, the heart pumps the next beat with a slightly greater energy (by an intrinsic mechanism) as compared to a normal beat, which can sometimes be felt as a palpitation. This is called post-extrasystolic potentiation.

 

1

 

To explain this interesting phenomenon graphically, assume that the normal heart function is shown in (a). The peaks correspond to the vigour (amplitude) of the heart beat while the flat, horizontal lines correspond to the refractory period. A heart beat consists of two small peaks, one large peak and a flat line following one small peak.

 

normal ecg (a)

 

In (b), we can see that the large peak following the arrow pointing to ‘extrasystole’ has a very high amplitude as compared to other beats. This is the combined effect of an unexpected and a normal impulse. One can also observe that the flat line succeeding this high- amplitude beat is longer that the flat lines of other beats. This corresponds to the prolonged period of inactivity, the compensatory pause. After the pause, we see that the large peak following the pause has a slightly greater amplitude than other normal beats. This is post-extrasystolic potentiation to compensate for the ‘lost’ beat.

 

Extrasysyole(b)

So, having said all this, the heart does undergo a sea of changes when it skips a beat and also compensates for the skipped beat in a very efficient manner. The next time you come across the idiom ‘skipping a beat’, I know you’ll be more than able to explain how it exactly works.

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