Alila Academy

Among the 12 leads of the ECG, lead II is most popular. This is because the net movement of the heart’s impulses is toward lead II, making it the best general view. 

Unless otherwise specified, we will be looking at lead II.

Our analysis will include heart rate, heart rhythm, P wave, PR interval, QRS complex and ST segment.

For heart rate: Identify the QRS complex, usually the biggest on an ECG; count the number of small squares between two consecutive QRS complexes and calculate the heart rate with this formula:

                                             Heart rate = 1500/number of small squares

                                  (1 small square = 40ms; 1 minute = 1500 small squares)

If this number is variable, count the number of QRS complexes on a 6-second strip and multiply by 10. A normal heart rate is between 60 and 100 beats per minute. 

For rhythm: measure the intervals between the R waves. If these intervals vary by less than 1.5 small squares, the rhythm is regular; if the variation is greater than 1.5 small squares, the rhythm is irregular.

P wave represents depolarization of the atria initiated by the SA node. 

Presence or Absence of P-wave:

- Presence of a normal P wave therefore indicates sinus rhythm. P waves are most prominent in leads II, III, aVF and V1. 

- Absence of P waves indicates non-sinus rhythms. 

- Absence of P waves and presence of irregular narrow QRS complexes are the hallmark of atrial fibrillation. The baseline may be undulating or totally flat. 

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