Left bundle branch area pacing: Electrocardiographic features

FIGURE 1. (A) Fluoroscopic RAO 30 degree and LAO 40 degree projection showing relative position of the pacing lead (yellow arrow) and the His Bundle catheter, (B) From left to right showed baseline ECG of complete AV block with narrow QRS complex, unipolar pacing at basal septum before penetration and unipolar pacing at LBB area

FIGURE 2. Ventricular activation during LBB area pacing: LV depolarization is rapid as a result of rapid downstream stimulation via native conduction system from the pacing site. RV gets depolarized by 2 wave‐fronts: (a) slow conduction wave from the LV through septal myocardium, and (b) from the pacing site conduction wave goes retrogradely through the native conduction system to reach the distal HB where it is recorded as “retro” His in a prepositioned EP catheter. From there the impulse reaches the RBB through slower conducting transverse connections (may be slower conducting sometimes). Although relative contribution of each one is unknown. Now the impulse reaches the RV myocardium by rapid conduction through the native RBB. Solid red arrow indicates faster conduction and curved red arrow indicates slower conduction. HB, His bundle; LBB, left bundle branch; LV, left ventricle; RBB, right bundle branch; RV, right ventricle

FIGURE 3. Different paced QRS morphologies in lead V1 during LBB area pacing

FIGURE 4. (A) Baseline ECG showed LBBB with QRS duration of 145 ms, (B) Dual‐chamber pacing with ventricular pacing from LBB area with a short AV interval showing QRS duration of 110 ms, (C) Dual‐chamber pacing in the same patient with an optimum AV delay showed paced QRS interval of 100 ms with LBBB corrected without overt RBBB

FIGURE 5. Effects of LBB area pacing in 2 patients with baseline RBBB. In case 1 left anterior hemiblock persisted after LBB area pacing which indicated the probable location of the pacing lead in the left posterior fascicle. In case 2 left posterior hemiblock got corrected which indicated the probable lead location in the main left bundle branch or in the posterior fascicle

FIGURE 6. A method to prove engagement of left bundle branch in patients with LBBB. Usually, in patients with baseline, LBBB the LBB potential is not recordable from pacing lead tip positioned at the LBB area. However, if a retro His potential is recorded from the prepositioned HB catheter during LBB area pacing it is possible to prove the engagement of the LBB by the pacing lead. The distance from the pacing spike to retro His plus pacing spike to the beginning of earliest surface QRS if was equivalent to baseline His to the beginning of earliest surface QRS interval, indicated evidence of LBB engagement

FIGURE 7. Measurement of different intervals in a patient with LBB area pacing