Assoc Prof Harry Mond
February 23, 2026
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I was shown this ECG this week.
There are two ectopic beat configurations labelled “S” for supraventricular and “V” for ventricular. The issue with the referring doctor was that they were mislabelled because the broad QRS is labelled supraventricular and the narrow QRS, ventricular.
What do you think?
A conundrum exists when in the same tracing, an atrial ectopic is broader than a ventricular ectopic.
Sinus rhythm with a bundle branch block (red highlight). An atrial couplet has the same broad configuration (yellow highlight, “S”).However, an ectopic with a narrow configuration is most likely a ventricular ectopic. The focus may be in or very close to a fascicle and the wave of depolarization avoids the block in the bundle branch, which is probably very proximal.
The labelling is correct.
A fascicular ectopic as its name implies has its focus in left bundle branches of the His-Purkinje system. The QRS therefore, has aRBBB-like morphology with either a superior or inferior axis, depending on whether the focus is in the posterior or anterior fascicles. These ectopics have a relatively narrow QRS and the initial forces are abrupt and not slurred asthe early conduction is within the conducting system. Ventricular ectopics arising from the right bundle branch and bundle of His also occur.
Harry Mond
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.
September 18, 2026
Dr Thura Thant asked for an opinion on this confusing ECG. By using arrows and highlight, the ECG bared its soul and gave me an answer. See if you can work it out? What do you think?
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