Introduction Painful left bundle branch block (LBBB) syndrome is a rare condition characterised by chest pain associated with intermittent LBBB, in the absence of significant coronary artery disease. Its prevalence, mechanism and management are not well described in the literature . An ischaemic substrate has been postulated but largely disregarded in favour of a ‘ventricular dyssynchrony’ theory . Nevertheless, most described cases occur on exertion , with only a single case of the condition occurring at rest being described . Pacing has been used to successfully treat the condition via a range of modalities, including right ventricular pacing , cardiac resynchronisation therapy  and His-bundle pacing (HBP) . We present a further patient who experienced the syndrome at rest, and successfully treated with HBP.
Case Presentation A 64 year old lady presented to the emergency department reporting acute onset cardiac sounding chest pain. An ECG revealed evidence of LBBB. Blood tests were performed but the results were not available before further investigations. The patient was immediately taken to the cardiac catheter lab for primary percutaneous coronary intervention. An angiogram revealed no significant coronary artery disease and no percutaneous intervention was performed. A CT-aorta was unremarkable. Her troponin was normal on serial measurements and the remainder of her blood tests were unremarkable. A repeat ECG when she was pain free revealed sinus rhythm with narrow QRS complexes and first degree heart block. An echocardiogram showed normal cardiac structure and function.The patient was moved to the coronary care unit and placed on cardiac monitoring. Over the next 24 hours the nursing staff observed and documented around 20 episodes of LBBB that coincided abruptly with the patient’s reports of chest pain. During periods when her heart rate was less than 60 beats per minute (bpm) she had a narrow QRS interval, but when her heart rate increased to over 60bpm, she developed LBBB. Her chest pain was debilitating and difficult to manage. Her baseline hypotension (90/50) and borderline bradycardia (45-55bpm) limited the use of chronotropic medications.
The diagnosis of painful LBBB syndrome was made and after considering the available literature, the decision was made to offer the patient a DDDR pacemaker with His-bundle pacing, an intervention that has been recognised to offer effective symptomatic relief . A DDDR pacemaker with HBP was implanted, achieving non-selective His-bundle pacing. Electrophysiology studies performed at the time revealed a narrow QRS complex at rates less than 60bpm with no chest pain. This was also achieved during non-selective His-bundle pacing at rates greater than 60bpm. However, when AAI pacing was performed at rates above 60bpm, LBBB was induced and the patient complained of chest pain.
The procedure was successful and afforded the patient immediate and persistent relief. She was discharged the next morning and at her one month follow up these positive results persisted.DiscussionThis case of painful LBBB syndrome is only the second described occurring at rest and offers further evidence against an ischaemic aetiology. Treatment options for this syndrome include negatively chronotropic medications and patient education to avoid the heart rate exceeding the threshold at which LBBB develops. However, this was not feasible in our case due to a resting bradycardia and the condition occurring at rest. Theoretically, using HBP to correct LBBB appears counterintuitive, as it is pacing proximal to the point of abnormal conduction. Despite this, it has a proven success rate in the treatment of LBBB  and does appear to be a management option that can offer a striking resolution of symptoms in select patients with this unusual and still poorly understood condition.
Conflict of Interest None
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