Hello, I'm Andres Enriquez, Cardiac Electrophysiologist from Queen's University, and I would like to talk today about the use of the ECG to predict the site of origin of ventricular arrhythmias. So several ECG features are useful for PVC localization. The curious axis has a vertical dimension which is best reflected by leads 2 and 3. A positive 2 and 3 suggests an origin in the superior aspect of the ventricles, including the outflow tracts and the superior aspect of the mitral and tricuspid valves, while a negative 2 and 3 indicates an origin in the inferior aspect of the ventricles. And we have the horizontal dimension which is best reflected by lead 1. A positive lead 1 suggests an origin rightward from midline and the opposite when lead 1 is negative. Second, we have the bundle branch block pattern. PVCs with a right bundle pattern arise in the left ventricle and PVCs with a left bundle pattern may arise in the right ventricle or the septum. Third, we have the QRS duration. Septal PVCs have narrower QRS durations than PVCs originating on the free wall of both ventricles. And finally, we have the precordial transition. In PVCs with a right bundle pattern, transition becomes later as the site of origin moves from apex to base. And on the other side, in PVCs with a left bundle pattern, transition becomes later as the origin moves from the septum to the right ventricular free wall. This slide shows the value of the frontal plane axis and precordial transition for localization of outflow tract PVCs. Here we see that the RVOT is actually located anterior and leftward relative to the LVOT. If lead 1 is positive, the origin is on the right side of the midline. And here we have the posterior RVOT, the right coronary cusp, the tricuspid valve and the parachesial region. If lead 1 is negative, the origin is on the left side of the midline. And here we have the anterior RVOT and all the LVOT structures with exception of the right cusp. Second, we look at precordial transition. The free wall of the RVOT is the most anterior structure and as we move toward the mitral annulus, the precordial transition gets progressively earlier and the left bundle branch block transform into a right bundle branch block. Thus, when transition occurs at V4 or later, the origin is in the RVOT. When transition occurs at V2 or earlier, the origin is in the LVOT. However, when transition occurs at V3, differentiation is more difficult as the site of origin can be in the septal RVOT but also in the right cusp. Different algorithms have been proposed to differentiate RVOT versus LVOT origin in these cases. One of them from UPenn compares the precordial transition during PVC and sinus rhythm. When the PVC transition occurs later than sinus rhythm, the origin is in the RVOT with high specificity. If PVC transition occurs at or earlier than sinus rhythm, we measure the V2 transition ratio, which is the percentage R-wave during PVC divided by the percentage R-wave during sinus rhythm. A ratio of 0.6 or more predicts an LVOT origin. Finally, some key morphological features may suggest a particular site of origin. Just to mention a few examples, parahysian PVCs have a narrow QRS with lead II taller than III and most importantly a positive AVL, something that we don't see in outflow tract PVCs. Early transition with a multiphasic pattern in V1 suggests an origin from the left cusp. A QS in V1 with a notch in the downward deflection has been described in PVCs from the right left cusp commissure and PVCs from the anterolateral mitral annulus usually have positive precordial concordance with a monophasic R-wave in V1.

electrocardiogram

ventricular arrhythmias

QRS duration

precordial transition

morphological features