The “R-on-T phenomenon” was first described by Smirk in as “R waves interrupting T waves”.1,2 In , Francois Dessertenne described a specific electrocardiographic form of polymorphic ventricular tachycardia (PVT) characterized by changing amplitude of the complexes with a characteristic twist around the. R on T phenomenon. Every normal QRS complex has a P wave, a QRS complex, and a T wave. The P wave represents atrial contraction; the QRS complex. R on T phenomenon refers to a premature complex interrupting the T wave. In , Horace Smirk reported that R on T can precipitate fatal arrhythmias.


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The events following a PVC are of interest. Usually a PVC is followed by a complete compensatory pause because the sinus node timing is not interrupted; one sinus P wave isn't able to reach the ventricles because they are still refractory from the PVC; the following sinus impulse occurs on r on t phenomenon based on the sinus rate.

Polymorphic VT and Torsades de Pointes (TdP)

In contrast, PACs are usually followed by an incomplete pause because the PAC usually enters the sinus node r on t phenomenon resets its timing; this enables the following sinus P wave to appear earlier than expected.

These concepts are illustrated below. Not all PVCs are followed by a pause.

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If a PVC occurs early enough especially if the heart rate is slowit may appear sandwiched in between two normal beats. This is called an interpolated PVC.

R on T syndrome

The sinus impulse following the PVC may be conducted with a longer PR interval because of retrograde concealed conduction by the PVC into the AV junction slowing subsequent conduction of the sinus impulse.

The most unusual post-PVC event is when retrograde activation of the AV junction re-enters the r on t phenomenon as a ventricular echo.

This is illustrated below. The "ladder" diagram below the ECG helps us understand the mechanism.

PVCs usually stick out like "sore r on t phenomenon, because they are bizarre in appearance compared to the normal complexes. However, not all premature sore thumbs are PVCs. The challenge, therefore, is to recognize sore thumbs for what they are, and that's the next topic for discussion!

The phenomenon comes about because of unequal r on t phenomenon of the bundle branches and critical prematurity of a supraventricular impulse see diagram of Three Fates of PACs.

With such critical prematurity, the supraventricular impulse encounters one bundle branch or fascicle which is responsive, and the other which is refractory, and is consequently conducted with a bundle branch block or fascicular block pattern. Preceding ectopic P wave i.

Analyze the compensatory pause: A complete pause favors ventricular ectopy i. An incomplete pause favors aberration i. Be aware of exceptions to this simple rule because PVCs can activate the atria retrogradely and reset the sinus node incomplete pauseand PACs can fail to reset the r on t phenomenon node complete pause.

The classical “R-on-T” phenomenon

Long-Short Rule Ashman Phenomenon: This is because the refractory period of the ventricular conduction system is proportional to cycle length or heart rate; the longer the cycle length or slower the heart rate, the longer the recovery time of the conduction system.

More precisely, the risk of TdP is determined by considering both the absolute QT interval and the simultaneous heart r on t phenomenon i. These values are then plotted on the QT nomogram below to determine whether the patient is at risk of TdP.


A QT interval-heart rate pair that plots above the r on t phenomenon indicates that the patient is at risk of TdP. Example 2 TdP secondary to hypokalaemia: Because of the preceding long QU interval, this can be diagnosed as TdP.

ECG Learning Center - An introduction to clinical electrocardiography

She had several other episodes of sustained and nonsustained TdP until transvenous temporary pacemaker was in effect. Increasing the heart rate by temporary cardiac pacing completely abolished the PVCs and TdP episodes.

Coronary angiogram showed noncritical atherosclerotic plaques and ventricular tachycardia VT was not induced with electrophysiology study. r on t phenomenon