Chronic left bundle branch block does not exclude the ECG in the diagnostic process of postoperative myocardial ischaemia

An elderly female was scheduled to undergo a hip arthroplasty. Past medical history included arterial hypertension treated with nicardipine, moderate aortic stenosis with left ventricle hypertrophy and slight diastolic and systolic dysfunction (ejection fraction of 48%) due to left bundle branch block. No history of ischaemic cardiac disease was detected and functional class was not measurable. She was receiving beta-blockers for essential tremor. Preoperative ECG showed sinus rhythm (75 beats.min−1) and left bundle branch block. Slight cardiomegaly was observed on the X-ray. In the operating room, general anaesthesia was performed without incident, the patient remaining haemodynamically stable and without ECG ST-segment changes. At the end of surgery the patient was extubated and transferred to the recovery unit. Immediately after arrival, the patient complained of thoracic and epigastric discomfort highly suggestive of angina. Blood pressure was 140/80 mmHg and oxygen saturation by pulse oximetry was 89–90% despite oxygen administration (FIo2 0.5). ECG showed sinus rhythm 80 beats.min−1 with clear elevation of the ST segment in several leads. The possibility of acute coronary syndrome was confirmed by the cardiologist and sublingual nitroglycerine was administered, resulting in immediate clinical improvement and serial ECG showed progressive normalisation of ST changes similar to the pre-operative ECG. Cardiac biomarkers were negative and postoperative hemoglobin level was 9.3 g.dl−1. One unit of packed red blood cell was transfused in order to optimise oxygen carriage and secondary prophylaxis was initiated with salicylic acid, statins, transdermic nitroglycerine and beta-blockers. The patient remained stable, and was discharged to conventional ward 48 h later. Peri-operative myocardial ischaemia is a relatively common complication and it is associated with increased risk of cardiac morbidity and mortality in the surgical population with or at risk of coronary artery disease. Nowadays, several strategies have been advocated to reduce the incidence of peri-operative myocardial ischaemia including: preoperative identification of high risk patients (and revascularisation when necessary), pharmacological prophylaxis and early diagnosis and treatment [1]. Prompt detection and treatment of peri-operative myocardial ischaemia is a cornerstone in the avoidance morbid cardiac events because myocardial ischaemia lasting more than 2 h increases the risk of cardiac event more than 30-fold [2]. Classically, diagnosis of myocardial ischaemia is based on suggestive chest pain, ECG alterations (ST-T wave changes) and elevation of biochemical markers. However, in the postoperative setting, diagnosis of peri-operative myocardial ischaemia it is not always easy. Pain could be attenuated or abolished due to residual anesthesia, and cardiac biomarkers may be elevated either by previous medical disease, or surgery. In addition, cardiac biomarker elevation does not occur in acute coronary syndrome without necrosis and it may occur late at 4–6 h. Under these circumstances, the ECG may be the only reliable parameter for early detection of peri-operative myocardial ischaemia. However up to one quarter of vascular surgical patients present baseline electrocardiographic abnormalities including left bundle branch block, that can mask the ECG signs of acute myocardial injury. Recently published articles suggest that specific ECG changes could help in the diagnosis of acute coronary syndrome in presence of left bundle branch block [3-5]. The GUSTO-1 study suggests three ECG criteria to be significant of myocardial infarct in patients with chronic left bundle branch block: ST elevation greater than 1 mm concordant (in the same direction) with QRS complex, drop of ST segment greater than or equal to 1 mm in V1, V2 or V3 and elevation of ST segment greater than or equal 5 mm contrary (in the opposite direction) to the QRS complex [3]. Edhouse [4] and Kontos [5] in retrospective and prospective studies corroborated these diagnostic criteria some years later. Other studies however, have not confirmed this association [6]. We believe that our patient experienced peri-operative myocardial ischaemia based on characteristic chest pain and suggestive ST-segment alterations while pain was experienced, followed by return to the baseline ECG after nitro-glycerine administration and pain disappearance. Repeated enzyme determination ruled out the diagnosis of myocardial necrosis. It seems then, that in patients with chronic left bundle branch block with suggestive chest pain, the ECG changes are still of value for early diagnosis of peri-operative myocardial ischaemia and acute coronary syndrome. In the postoperative scenario, when a previous ECG is usually available, peri-operative myocardial ischaemia could be recognized when reversible ischaemic changes are superimposed on a pattern of chronic left bundle branch block. The ST-changes can be analysed using the criteria outlined thus helping with the diagnosis of acute coronary syndrome in the postoperative setting and probably also during anaesthesia and surgery when the ST-segment is constantly monitored.