Tachycardia-dependent left-bundle branch block misdiagnosed as ischaemia: a case report

Rate-related left-bundle branch block (LBBB) is an uncommon conduction abnormality that can mimic ventricular tachycardia or myocardial ischaemia, and in prolonged cases may contribute to cardiomyopathy. We describe the case of a 49-year-old woman with a previous history of mitral valve annuloplasty, anomalous pulmonary vein correction, and atrial fibrillation ablation who presented with recurrent palpitations and exertional chest pain. Despite normal echocardiograms and negative investigations for ischaemia, initially; a subsequent repeat exercise-tolerance test in 2024 revealed tachycardia-induced LBBB. Tachycardia-induced LBBB may cause haemodynamic instability, chest pain ('painful LBBB syndrome'), or long-term ventricular dysfunction. Early recognition is important for avoiding misdiagnosis as ventricular tachycardia or acute coronary syndrome. Clinical management focuses on rate control, exclusion of coronary disease, and the use of implantable cardiac device therapy in refractory or cardiomyopathic cases. This case highlights the diagnostic challenges in patients with recurrent tachycardia-induced LBBB, the importance of excluding coronary artery disease, and the role of timely electrophysiology assessment to guide long-term management.