Assoc Prof Harry Mond
February 23, 2026
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Referred for opinion regarding heart block
What do you think?
There is sinus rhythm (arrows) and a ventricular ectopic (red highlight).
Embedded in the terminal portion of the T wave is a sinus P wave (blue arrow). Because of the timing of ventricular ectopic, the P wave falls within the refractory period of the ventricle and therefore is not conducted.
With ventricular ectopics, a sinus P wave is usually concealed (blue highlight) within the ectopic and obviously does not conduct, unlike the other P waves (red arrows).
A poorly understood feature of ventricular ectopics is that the non-conducted sinus P wave (blue arrow) may not be concealed within the ectopic QRS (yellow highlight).
With appropriate timing (including sinus rate, ectopic prematurity) as well as QRS width and shape, the sinus P wave may emerge from the tail of the QRS or even the T wave.
Left ECG: The sinus rate is ~60 bpm (blue highlight) and the non-conducted sinus P wave (blue arrow) lies at the end of the T wave.
Right ECG: The sinus rate is ~50 bpm (blue highlight) and the non-conducted sinus P wave is later (blue arrow), but still within the refractory period of the ectopic. This mimics second degree AV block. I call this pseudo AV block and remember it is physiologic and dependent on the timing.
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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