Dr A Röschl's picture

A common cause of pauses and bradycardia are non-conducted PACs, which generally do not require treatment. Therefore, it is important to differentiate between pauses or bradycardia that require treatment.
In this Holter ECG, the first beat on the left is a sinus node beat. The next obvious sinus beat occurs after a time of approximately 1400 ms, as does the subsequent beat. This would correspond to sinus bradycardia with a rate of just over 40 beats per minute. Upon closer examination of the T waves of QRS 1 and QRS 2, a small deflection can be seen on the T wave, which is not visible after QRS 3 (esp. middle and lower leads). These are very closely coupled PACs that cannot be conducted through the AV node because it is still refractory.
QRS number 4 is probably a conducted PAC, followed by another non-conducted one. QRS 5 is a sinus beat, and QRS 6 corresponds to QRS 4. The last QRS complex is again a conducted sinus node beat.

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