Background: Electrophysiological studies always remained essential to differentiate the type of pre-excitation syndrome in
arrhythmia. We explore mahaim fibers’ role instead of a bundle of his in the accessory pathway to diagnose left bundle branch block.
Case presentation: A asymptomatic 51-year-old man was present in the outpatient department with a history of myocardial
infarction over several years. The classical pre-excitation syndrome remains classical without delta waves. Trans-esophageal atrial
pacing was induced using electrocardiogram and intracardiac electrogram (IEGM) to study further morphological changes of QRS
in all directions.
Diagnosis: The evaluated accessory pathway before and after ablation at anterolateral bypass potentially synchronous the
transitional R wave at the electrical axis, recording the positive and negative sign readings. The morphology pattern closer to the
left bypass’s origin at the frontalis concludes the left bundle branch block, which was misdiagnosed earlier with the right bundle
Conclusion: This is the first case report which elaborated the importance of retrograde study in uni-directional stimulus that
significantly identified the maximum QRS terminal vector changes in rhythm disorder.