Survenue d’une extrasystole ventriculaire pendant la période vulnérable du potentiel d’action (sommet de l’onde T du QRS précédent) à l’origine d’une arythmie ventriculaire sévère.
Le phénomène R sur T peut s’observer en cas d’intervalle QT normal et donner lieu à TV polymorphe ou une fibrillation ventriculaire. Dans ce cas, l’ESV est à couplage court (Cf ESV malignes).
Il peut s’observer en cas d’intervalle QT long et donner lieu à une torsade de pointes [1]. Dans ce cas, l’ESV (“complexe particulier de Dessertenne”) est à couplage long (Cf. Torsade de pointe).
Voir ci-dessous une TV polymorphe catécholergique.
[1] Oksuz F, Sensoy B, Sahan E, et al. The classical “R-on-T” phenomenon. Indian Heart J. 2015;67(4):392–394 (téléchargeable)
–-> The polymorphic ventricular tachycardia (PVT) is uncommon arrhythmia with multiple causes and has been classified according to whether they are associated with long QT interval or normal QT. Whereas “Torsade de pointes (TdP)” is an uncommon and distinctive form of PVT occurring in a setting of prolonged QT interval, which may be congenital or acquired (congenital or acquired), “PVT with normal QT” is associated with myocardial ischemia, electrolyte abnormalities (hypokalemia), mutations of the cardiac sodium channel (Brugada syndrome), and the ryanodine receptor (catecholaminergic PVT). This distinction is crucial because of the differing etiologies and management of these arrhythmias. Moreover, the PVT in the setting of acute MI generally occurs during the hyperacute phase, is related to ischemia (“ischemic PVT”) and is not associated with QT prolongation. It is triggered by ventricular extrasystoles with very short coupling interval (the “R-on-T” phenomenon) and is not pause-dependent.
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