Is that the right split? Using the physical examination to diagnose right bundle branch block (RBBB)

Learning Objective 1: Use the physical examination to diagnose RBBB
Learning Objective 2: Describe the differential diagnosis of a widely split S1

Case: A 47-year-old woman presented with 3 unexplained episodes of chest pain. The first episode occurred 6 months prior while she was making dinner. The second occurred 4 months prior while she walked in her home after work. The third occurred 10 days prior to the office visit and woke the patient from sleep. She described the pain as a gripping sensation under her left breast. The pain was pleuritic and resolved after an hour. There was no chest pain with exertion, dyspnea, palpitations, syncope, heartburn or feelings of anxiety or panic. Past medical history was remarkable for anemia and hypothyroidism. Medications included levothyroxine. Family history was significant for sudden cardiac arrest in her mother and maternal grandfather in their late 60s due to myocardial infarction. She worked as an attorney, had never smoked, drank 2 drinks per week and did not use drugs. On physical examination, cardiac exam revealed regular rate and rhythm S1, S2 without murmur rub or gallop, BP 152/78, pulse 64. There was an additional sound following S1, felt to be a widely split first heart sound. The remainder of the examination was normal. EKG showed sinus bradycardia with heart rate=56 and an incomplete RBBB. Echocardiogram revealed mild tricuspid regurgitation. Stress echocardiogram and lipid profile were normal.

Discussion: Although RBBB is often first identified on EKG, it may also be diagnosed on physical examination. RBBB results in an electrical delay in RV contraction, causing delayed closure of the pulmonary and tricuspid valves. Delayed closure of the pulmonary valve causes splitting of S2 that increases with inspiration and remains auscultable on expiration. Delayed closure of the tricuspid valve results in increased splitting of S1 best heard in the tricuspid region, as was seen in our patient. RBBB is the most common cause of increased splitting of S1. LV ectopic or paced beats may also present with prominent splitting of S1. Atrial septal defects cause a widely split S1 due to increased blood flow across the tricuspid valve delaying its closure. Ebstein anomaly (associated with RBBB) can also present with wide splitting of S1 due to delayed tricuspid valve closure due to ballooning of the leaflets during systole. Mimickers of a widely split S1 include an S4, ejection sound and systolic click. Auscultation of a widely split S1 and/or S2 on physical examination may necessitate an EKG as it indicates a potential RBBB. Although most patients with incomplete RBBB are asymptomatic, it is important to consider the possibility of underlying cardiac disease, as RBBB may result from structural heart disease, be rate-related or iatrogenic.