#KYJ - Why are ECG waves called PQRST and not ABCDE

#KYJ -Why are ECG waves called PQRST and not ABCDE?

In short, the first ecg was ABCD.

So to answer the question we need to go back to the late 1800s. Electricity was a new thing and we were still understanding ways to measure it.

The first ECGs waves were measured by a Lippmann capillary electrometer device that measured current in liquid mercury rising and falling in a fine glass tube.   There were actually only 4 waves and rightly called ABCD.

But the mercury was heavy and subject to friction in the glass tubes where it fluctuated with current, so Einthoven in 1895, devised the precursor of today’s ECG.

He used a more sensitive technology called a String Galvanometer, that demonstrated a more mathematically correct 5 distinct waves.  Naturally these were different to the Mercury Glass system and the ABCD needed to be replaced.

So why PQRST?

These go back historically to Descartes.  Where a set of variables were grouped XYZ if there was 3 ; ABCD if there was 4, or PQRST if there were 5.

Einthoven therefore named his 5 ecg waves of the normal sinus rhythm, PQRST.

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