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Assoc Prof Harry Mond
February 23, 2026
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There has been some difficulty understanding the different types of compensatory pauses following an atrial ectopic.A premature atrial ectopic will usually be propagated retrograde toward the sinus node. If it invades and depolarizes the sinus node, resetting of the sinus cycle will occur. Consequently, the cycle length after a premature atrial ectopic is longer than the basic sinus cycle, creating what is called a partial compensatory pause.
In this illustration, the sinus cycle is 1350 ms (44 bpm). The premature atrial ectopic, highlighted in red, has no obvious P wave, because it is concealed and resets the sinus cycle, so the next P wave does not occur (blue stippled arrow). The sinus cycles with the embedded atrial ectopic are only 2000 ms apart rather than the 2700 ms without an atrial ectopic; hence the term partial compensatory pause.If however, the sinus node is not depolarized, the next sinus cycle results in a concealed sinus P wave and a full compensatory pause.
The premature atrial ectopic, highlighted in red, has a P wave preceding it. The next sinus cycle falls in the refractory period of the conducting system (red stippled arrow) and is not conducted. Now there is a full compensatory pause.On occasion, resetting the sinus node results in a prolonged suppression of sinus activity (greater than a full compensatory pause). This is referred to as a long compensatory pause resulting from an abnormal or prolonged sinus node recovery time, indicative of sinus node dysfunction.
The absence of a compensatory pause is referred to as interpolation.
In the presence of long sinus cycles or sinus bradycardia, a premature atrial ectopic may conduct to the ventricle leaving enough time for the atrioventricular conduction to at least partially recover before the next sinus beat. This next sinus P wave will conduct to the ventricles, albeit usually with a prolonged PR interval or marked first degree AV block. Because of the prematurity, the atrial ectopic as well as the next sinus beat may be conducted with aberration.
The three ECGs above are from the same patient. The first (left) shows an atrial ectopic with a compensatory pause and no aberration. In the next two ECGs (right), the sinus rate is slower and the atrial ectopics are more premature with the P waves buried in the T waves of the previous sinus cycle. This results in interpolation with degrees of aberration. The next sinus complex has first degree AV block.
Assoc Prof Harry Mond
October 28, 2026
As its name implies, AVNRT is a reentrant junctional or supraventricular tachyarrhythmia which involves the fast and slow pathways within the AV node creating a self-perpetuating circus movement. It can be divided into typical (slow-fast) or atypical (fast-slow) as well as several rarer forms related to more than one slow or fast pathway with similar electrophysiological properties. On the ECG, they can be identified and differentiated by the positioning of the P wave in relation to the QRS complex, which in turn is related to the direction of the re-entrant AV nodal circuit. However, in about 60% of cases, the P wave is buried in the QRS/T and cannot be identified on the surface ECG.
October 16, 2026
Retrograde conduction is defined as conduction from an ectopic site to the atrium via the AV node or accessory pathway and referred to as VA conduction. II results in a P wave configuration which differs from an anterograde P wave, and in most ECG leads is inverted. The site from where the impulse originates can be the AV node, Bundle of His, distal conducting system or the body of the ventricles including ventricular pacing. On the ECG, the QRS complex usually precedes the inverted retrograde P wave but on occasion may follow it.
October 1, 2026
In 1970, I commenced work as a “novice” cardiologist at The Royal Melbourne Hospital. Training at that time was learning how to recognise the diastolic murmur of mitral stenosis and making sure the ECG and chest x-rays were the correct way up. As this was prior to coronary artery surgery, stenting and echocardiography, the ECG was a highly respected tool for the diagnosis of many conditions. I was fortunate to befriend a number of the gurus of ECG interpretation who taught me to look into the soul of an ECG. Today, even though the ECG is the first investigation performed by a cardiologist, the art of ECG interpretation has been lost because we depend on the new tools for cardiac diagnosis.
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