The ECG before the procedure shows advanced right bundle branch block and negative T waves in leads aVF and III.
Figure 1 shows first-degree atrioventricular block and QRS of 120ms with anterior-superior fascicular block and prominent anterior QRS forces (PAF), ST-T depression (upward arrows), and ST-T elevation in aVR (downward arrows), and repolarization changes resulting from the ischemia.
The differential diagnosis for PAF includes pre-excitation via a left lateral accessory pathway (option 2 incorrect, long PR), inferolateral infarction (option 3 incorrect, diffuse changes in repolarization point to left coronary artery or multivessel disease), right ventricular growth, and left septal fascicular block (LSFB).1 Acute pulmonary embolism, unlike chronic pulmonary hypertension, does not present with a monophasic R wave in the right precordial leads (option 1, incorrect).
The transient nature of PAF, along with the clinical context and presence of LSFB criteria (figure 2),2 supported the final diagnosis (option 4, correct). LSFB develops mainly due to proximal obstruction of the left anterior descending artery, before the first septal perforating branch.
