Excerpt

A 61-year-old man with left ventricular ejection fraction of 25% was referred for cardiac resynchronization therapy. He had undergone percutaneous coronary intervention to right coronary artery (RCA) for inferior wall myocardial infarction 3 years ago. Electrocardiography (ECG) showed complete left bundle branch block with QRS duration of 174 ms (Fig. 1a). Coronary angiography confirmed patent stent in RCA. Left bundle branch pacing (LBBP) was done using C315 sheath and 3830 Selectsecure™ lead (Medtronic, Minneapolis, MN) [1] (Fig. 2a). Nonselective to selective capture of left bundle could be demonstrated at near pacing threshold value. Paced ECG showed rSR pattern in lead V1 with QRS duration of 108 ms (Fig. 2b) and peak left ventricular activation time of 65 ms. Inferior leads showed resurgence of Q wave (> 40 ms) corresponding to the old inferior wall myocardial infarction(Fig. 1b and 2b). ECG diagnosis of myocardial ischemia during right ventricular pacing and native left bundle branch block can be difficult as non-physiological activation would result in masking of pathological Q waves and ST segment changes [2]. LBBP restores the physiological activation of the ventricle thereby unmasking the pathological Q waves.

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