Arrhythmix archive
Every past rhythm strip puzzle, with the vignette, the rhythm and how to read it. Newest first.
6 past puzzles, up to Thursday 5 November 2026. Today’s and future puzzles are never shown here.
November 2026
#6 · Thursday 5 November 2026 Hard
A 63-year-old woman has had 40 minutes of heavy central chest pain spreading to her jaw. She is sweaty and nauseated. 12-lead ECG:
Rhythm: Inferior STEMI
Explanation: ST elevation in II, III and aVF with reciprocal ST depression and T inversion in aVL (and I): an inferior STEMI. Elevation in III greater than II points to the right coronary artery. Reciprocal change argues strongly against pericarditis. Right-sided leads (V4R) look for right ventricular involvement.
- ST elevation in II, III and aVF (III > II)
- Reciprocal ST depression and T inversion in aVL and I
- Early Q wave forming in III
Pearl: Reciprocal depression in aVL is often the first clue to an inferior STEMI, sometimes before the inferior elevation is obvious.
Play this puzzle#5 · Monday 2 November 2026 Medium
A 34-year-old woman ran the New York City Marathon yesterday and is having a routine check with her sports doctor. She feels well; her resting pulse is slow and a little irregular. Lead II rhythm strip:
Rhythm: Second-degree AV block, Mobitz I (Wenckebach)
Explanation: The PR interval lengthens with each beat (about 190, 290, then 340 ms) until a P wave fails to conduct; the cycle then resets with the shortest PR. That gives grouped beating. The block is usually in the AV node, so it is often benign in athletes, during sleep and with high vagal tone, though drugs and inferior MI can cause it too.
- Progressive PR prolongation
- Then a non-conducted P wave (dropped QRS)
- Shortest PR straight after the pause; grouped beating
Pearl: Compare the PR just before and just after the dropped beat. Different: Wenckebach. Identical: think Mobitz II.
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October 2026
#4 · Thursday 29 October 2026 Medium
World Stroke Day. A 74-year-old woman with high blood pressure and type 2 diabetes says her smartwatch keeps flagging an irregular pulse.
Rhythm: Atrial fibrillation
Explanation: An irregularly irregular narrow-complex rhythm with no identifiable P waves and a wavy fibrillatory baseline: atrial fibrillation. Fitting for World Stroke Day: AF raises stroke risk around five-fold, and about one in four strokes is linked to it. Age, high blood pressure and diabetes all add to that risk, which is why scores like CHA₂DS₂-VA exist.
- Irregularly irregular R-R intervals
- No P waves; fine fibrillatory baseline
- Narrow QRS, rate about 100/min
Pearl: Irregularly irregular with no P waves is AF until proven otherwise. MAT is also irregular, but it has P waves in at least three different shapes.
Play this puzzle#3 · Monday 26 October 2026 Easy
A 63-year-old man with a heart attack two years ago has palpitations and feels light-headed. BP 92/60.
Rhythm: Ventricular tachycardia
Explanation: A regular broad-complex tachycardia at about 175/min with identical QRS complexes. With a past MI, a broad-complex tachycardia is VT until proven otherwise. Clues to AV dissociation clinch it: P waves marching through at their own slower rate, and capture or fusion beats.
- Rate about 175/min, regular
- Broad QRS (about 165 ms), all the same shape
- Dissociated P waves visible here and there
Pearl: Assume any broad-complex tachycardia is VT until proven otherwise. After a previous MI, the vast majority are.
Play this puzzle#2 · Thursday 22 October 2026 Medium
An 82-year-old woman feels exhausted and dizzy. Pulse 38 and regular.
Rhythm: Complete heart block
Explanation: P waves march through regularly at about 88/min, broad QRS complexes march at about 38/min, and the PR interval is random because nothing conducts. That is complete (third-degree) heart block with a ventricular escape rhythm. A narrow escape would suggest a higher, junctional escape, which is faster and more reliable.
- P waves regular at about 88/min
- Broad escape QRS regular at about 38/min
- No consistent PR: complete AV dissociation
- P waves hide in QRS and T waves
Pearl: In complete heart block the atria beat faster than the ventricles. If the ventricles are faster, think of another cause of AV dissociation, such as VT.
Play this puzzle#1 · Monday 19 October 2026 Easy
A 19-year-old woman felt her heart start pounding suddenly while bending to tie her shoelaces. She is otherwise well.
Rhythm: Supraventricular tachycardia (AVNRT)
Explanation: A regular narrow-complex tachycardia at about 185/min with no visible P waves (they are buried in or just after the QRS). Sudden onset and offset in a young, well person fits AV nodal re-entrant tachycardia, the commonest regular SVT, and one that is more common in women.
- Rate about 185/min, perfectly regular
- Narrow QRS
- No P waves visible before the QRS
Pearl: In AVNRT, look for a 'pseudo-r′' in V1 or 'pseudo-S' in the inferior leads: the retrograde P wave hiding at the end of the QRS.
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