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Assoc Prof Harry Mond
December 2, 2024
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This ECG was reported as complete heart block.
What do you think?It sure looks like it, but the ventricular response is irregular.Look closer.
I have now identified the P waves and they follow two patterns:4:3 Wenckebach AV block (solid red with dropped beat stippled)All dropped beats (stippled blue)This rhythm is referred to as alternating Wenckebach AV blockThe features are:
How do we explain this?
Here is another example:
This is a 3:2 Wenckebach AV block and the sequences terminate with two dropped beats (highlighted).Alternating Wenckebach AV block can occur with other situations such as atrial tachycardia.
This innocuous looking ECG was reported as sinus rhythm 95 bpm, but the tech thought better! The PR intervals varied.Let us look more closely.
There is a pattern to AV conduction consistent with alternating Wenckebach AV block, but of course this patient doesn’t need a pacemaker. Note again the 2 sequential dropped P waves terminating a sequence (highlighted).When you look for it you find it! This one appeared a few weeks later.
There are other variations of the multi-level AV block phenomenon.
Here are two Wenckebach AV blocks, a few minutes apart. There is a typical Wenckebach sequence below and above is an AV Wenckebach sequence within atrial bigeminy.There are other examples including Wenckebach AV block with sino-atrial Wenckebach and even Wenckebach at the ectopic myocardial junction, but those are different stories.
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Harry Mond
October 29, 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.Â
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