Exercise or emotion sets off salvos of wide beats, each a different shape, during a sinus tachycardia, in a heart whose resting ECG is normal.
On the trace
The tracing above is a patient with CPVT during exercise. Each recording is new, so your numbers will differ a little.
- Look at the sinus beats. A sinus tachycardia of about 147 per minute: the heart rate of exercise. Each beat is narrow, with a normal PR and a normal QT (QTc about 390 ms).
- Find a salvo. Runs of wide beats, from one beat to ten or more, come straight out of the sinus rhythm.
- Compare the beats in a salvo. Each is a different shape, and the frontal axis swings from beat to beat. Some salvos alternate between two shapes, like bidirectional VT.
- Measure the R-R in a salvo. About 330 ms: about 180 per minute, faster than the sinus rate.
- See each salvo end. Sinus beats return, until the next one.
How to recognise it
| Feature | Value | On this tracing |
|---|---|---|
| Resting ECG | Normal, sometimes a sinus bradycardia | |
| Trigger | Exercise or emotion: a rising sinus rate | Sinus about 147 per minute |
| QT | Normal | QTc about 390 ms |
| Ventricular arrhythmia | Premature beats, bigeminy, bidirectional and polymorphic salvos, in that order as the rate rises | Polymorphic salvos |
| Rate in a salvo | Faster than the sinus rate | About 180 per minute |
The response to an exercise test, or to an isoproterenol infusion, is reproducible and all but diagnostic. Atrial arrhythmias, including AF, can appear with the ventricular ones.
Mechanism
CPVT is caused by mutations in the proteins that release calcium from the cell's store during each beat. The commonest (CPVT type 1, autosomal dominant) is in the ryanodine receptor, RYR2; others are in calsequestrin (CASQ2), triadin and the calmodulins.
Adrenaline loads the store and speeds its release: that is how exercise strengthens contraction. In CPVT the release channel also leaks during diastole. The leaked calcium drives an inward current, a delayed afterdepolarisation (DAD), and if it reaches threshold the cell fires a triggered beat. The faster the rate, the more the store loads, so the arrhythmias grow as the heart rate rises, and each fast triggered beat makes the next one likelier: salvos. The beats start in the conduction system, from sites that change from beat to beat, so each one has a different shape.
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Silent at rest
At rest the store is not loaded enough to leak, so the ECG is normal, apart from a slow sinus rate in some patients. The QT is normal, though it responds abnormally to a sudden change in heart rate, and large U waves can appear during exercise. CPVT can stay hidden in a cardiac arrest survivor who never has an exercise test: all the other tests, including the coronary angiogram, are normal.
Bidirectional VT
As the rate rises, two sites in the left bundle's fascicles can take turns, each beat triggering the other: bidirectional VT, the same arrhythmia as in digoxin toxicity. Faster still, polymorphic VT follows, which can reach 300 per minute and degenerate into VF.
ICD shocks
A shock is painful and frightening, and the adrenaline that follows can start the next salvo: an ICD can set off a storm of shocks. Triggered polymorphic VT often does not respond to a shock; VF does. Viskin and colleagues advise an ICD only in patients on full treatment (beta-blockers, flecainide or sympathetic denervation), programmed with a long detection time.
Clinical impact
CPVT is one cause of sudden death in the young with a normal heart. Relatives of a patient need genetic testing and an exercise test.
Management
During a storm: sedate
Sedation is essential: each episode raises adrenaline and sets off the next. Pulseless: an unsynchronised shock.
Beta-blockers at the highest tolerated dose
The cornerstone. Up to 30% of patients still have symptoms or arrhythmias on a repeat exercise test.
Add flecainide
Flecainide blocks the leaking release channel as well as the sodium current. It is highly effective added to a beta-blocker.
Then: denervation, an ICD
Left cardiac sympathetic denervation is an effective addition. An ICD only on full treatment, programmed to wait before shocking.
Differential
The same alternating axis, from digoxin toxicity: an older patient on digoxin, with AV block and a slow sinus rate, not a tachycardia.
Polymorphic with a normal QT, from acute ischaemia: chest pain, ST elevation, coronary disease. Exercise-induced ischaemia can do the same during a stress test.
Polymorphic, but on a long QT, after a pause. Congenital long QT type 1 also strikes during exercise; its QT is long.
Short runs at peak exercise or in recovery, in a healthy heart, not reproducible on repeat tests. Considered benign.
References
- Polymorphic Ventricular Tachycardia: Terminology, Mechanism, Diagnosis, and Emergency Therapy — Circulation, 2021
- Catecholaminergic polymorphic ventricular tachycardia: An exciting new era — Annals of Pediatric Cardiology, 2016
- 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death — European Heart Journal, 2022