ABC | Volume 115, Nº1, Suplement, July 2020

Case Report Idiopathic Left-Bundle Branch Block and Unexplained Symptom At Exercise: A Case Report Guilherme Veiga Guimarães 1 e Edimar Alcides Bocchi 1 Universidade de São Paulo Instituto do Coração,1 São Paulo, SP – Brasil Introduction The presence of a left bundle branch block (LBBB) in the apparent absence of any other heart disease raises questions and concerns about the stratification of the risk of subsequent cardiovascular events or symptoms. 1-5 The detection of LBBB in asymptomatic adults, including athletes, is estimated to range between 0.1% and 0.8%, which is more likely to represent a structural heart disease rather than a physiological response to exercise. 6-8 On the other hand, some studies have shown that the mortality risk of patients with LBBB and heart disease varies between 2.4% and 11% per year. 9 Although several studies have suggested that exercise- induced LBBB is usually associated with cardiovascular disease and, particularly, coronary artery disease, there are contrasting studies showing an association between exercise-induced LBBB and normal coronary arteries. 6,7,9 However, exercise- related cardiovascular adverse effects in LBBB with normal resting cardiac function remains poorly defined. This case report examined the relationship between exercise, LBBB, symptoms and exercise capacity in a younger woman, with typical LBBB and without history of cardiovascular disease, who reported sudden anxiety and shortness of breath during vigorous exercise, which can be suggestive of cardiac disease, being referred for exercise stress testing. Case Report A healthy 42-year-old woman with LBBB, who reported sudden anxiety and shortness of breath during vigorous exercise, and was referred for cardiopulmonary exercise testing (CPX) to evaluate the unexplained symptoms. She was not taking any medication and had no significant medical history. She had no previous symptoms suggestive of cardiac disease (chest discomfort, palpitations, fainting and angina). She had no history of neuromuscular or pulmonary disease. She did not smoke or drink alcohol. There was no family history of cardiac disease or heart attack. Over the previous 6 months, she had been exercising three times a week at the gym. The exercise program consisted of sessions of at least 60 min of regular activity at moderate intensity, including aerobic, muscle-strengthening, flexibility, and balance-strengthening exercises. Her physical examination was considered normal, her BMI was 21.5 kg/m 2 and her resting blood pressure was 110/70 mmHg. The resting electrocardiogram (ECG) showed a sinus rhythm (SR) and heart rate (HR) of 70 bpm, with the dominant feature of intraventricular block: prolonged QRS complex (≥0.12s) due to delayed activation of the left ventricle, accompanied by a characteristic morphology of the QRS complex. 6 Coronary computed tomography angiography (CTA) was performed, which showed no deposits of calcium and fatty material in the coronary arteries and no stenotic coronary arteries. A complete blood count showed normal results: her fasting glucose was 78 mg/dL, low-density lipoprotein cholesterol (LDL-C) was 168 mg/dL, high- density lipoprotein cholesterol (HDL-C) was 81 mg/dL, total cholesterol was 159 mg/dL, lipoprotein(a) [Lp(a)] was 7 mg/dL, triglycerides were 49 mg/dL and creatine phosphokinase (CPK) was 26 U/L. The magnetic resonance imaging (MRI) of the heart showed normal biventricular function, a left ventricular ejection fraction of 65% and preserved dimensions, except for an abnormal septal motion. She underwent CPX on a treadmill. Throughout the CPX phases, the 12-lead ECG showed a SR (Figure 1). Blood pressure measurements were in the normal range: at rest (126/82 mmHg), peak exercise (160/90 mmHg) and recovery stages (120/90 mmHg). She stopped the exercise due to fatigue (RER=1.29). Peak oxygen consumption (VO 2peak = 27.1 ml/kg/min) and maximum heart rate (HRmax = 176 bpm) values obtained from CPX were normal for age and gender, 95% and 102%, respectively. (https://www. ahajournals.org/doi/10.1161/01.CIR.91.2.580 ) From stage 14 of the modified Balke protocol until test termination, the CPX identified a decrease in VO 2 and in O 2 pulse (VO 2 / HR, ml/bpm), and an increase in HR and dead space to tidal volume ratio (Vd/Vt) (Figure 2). From this event, the minute ventilation/carbon dioxide production relationship slope (VE/ VCO 2 slope) increased abruptly and was not accompanied by hypoxia (Figure 2). Discussion To the best of our knowledge, we report for the first time a younger woman with LBBB without apparent cardiomyopathy and with unexplained symptoms during vigorous exercise (decreased VO 2 , during CPX), which is suggestive of impaired cardiac function in the face of cardiovascular stress. There were no ECG abnormalities except for a LBBB. Heart rate reserve and blood pressure were normal throughout the CPX test. Mailing Address: Guilherme Veiga Guimarães • Universidade de São Paulo Instituto do Coração – Av. Dr. Eneas de Carvalho Aguiar, 44. Postal Code 05403-000, São Paulo, SP – Brazil E-mail: gvguima@usp.br Manuscript received June 05, 2019, revised mansucript July 25, 2019, accepted September 10, 2019 Keywords Bundle Branch Block; Exercise; Physical Activity; Oxygen Consumption/physiology; Cardiovascular Diseases/prevention and control. DOI: https://doi.org/10.36660/abc.20190363 10