Cardiology · Conduction Abnormalities
The facts most likely to be tested
The QRS duration is prolonged to ≥ 120 milliseconds in a complete right bundle branch block.
The V1 and V2 leads demonstrate a classic rsR' pattern often described as rabbit ears.
The lateral leads (I, aVL, V5, V6) exhibit a wide, slurred S wave representing delayed terminal activation of the left ventricle.
A new-onset RBBB in the setting of acute chest pain is highly suggestive of an acute pulmonary embolism or acute myocardial infarction.
The secondary T-wave inversion in the right precordial leads is a normal repolarization finding and does not indicate myocardial ischemia.
An incomplete RBBB is defined by a QRS duration between 100 and 119 milliseconds with the characteristic rsR' morphology.
Right bundle branch block is frequently an incidental finding in healthy individuals but can be associated with atrial septal defects or cor pulmonale.
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A 68-year-old male presents to the emergency department with sudden onset of shortness of breath and pleuritic chest pain. His medical history is significant for hypertension and hyperlipidemia. On physical examination, he is tachycardic and tachypneic with an oxygen saturation of 91% on room air. An ECG reveals sinus tachycardia with a QRS duration of 130 ms, an rsR' pattern in V1, and a wide, slurred S wave in lead I.
Which of the following is the most likely underlying cause of this patient's new conduction abnormality?
Acute pulmonary embolism
The patient presents with classic signs of right heart strain; a new-onset RBBB in the context of acute dyspnea and tachycardia is a high-yield indicator of acute pulmonary embolism.
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High yield triage
Etiology / Epidemiology
Common in structural heart disease or idiopathic degeneration. Associated with congenital defects like ASD.
Clinical Manifestations
Often asymptomatic. Wide QRS >0.12s with rsR' pattern in V1-V2.
Diagnosis
12-lead ECG is the gold standard. Look for terminal S wave in leads I and V6.
Treatment
Treat underlying cause. No specific therapy for isolated RBBB. Avoid unnecessary pacing.
Prognosis
Generally benign. New-onset RBBB warrants investigation for pulmonary embolism or ischemia.
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Epidemiology & Etiology
Prevalence increases with age, often reflecting degenerative conduction system disease. Frequently seen in patients with coronary artery disease, hypertension, or cor pulmonale. In younger patients, consider atrial septal defect or other congenital anomalies.
Pertinent Anatomy
The right bundle branch travels through the interventricular septum to the right ventricle. Because it is a single fascicle, it is highly susceptible to ischemic injury or mechanical stretch from right ventricular overload.
Pathophysiology
Delayed activation of the right ventricle occurs because the impulse must travel through the left bundle and cross the septum. This results in prolonged QRS duration and altered sequence of ventricular depolarization. The left ventricle depolarizes normally, but the right ventricle is activated late, creating the characteristic rsR' morphology.
Clinical Manifestations
Patients are typically asymptomatic and diagnosed incidentally. Physical exam may reveal a wide, fixed split S2 if associated with an ostium secundum ASD. Red flags include syncope or dyspnea, which suggest underlying structural heart disease or transient ischemia.
Diagnosis
12-lead ECG is the diagnostic tool of choice. Criteria include QRS duration ≥0.12s, an rsR' pattern in V1/V2, and a wide, slurred S wave in leads I, aVL, and V6. Always compare with prior ECGs to determine if the block is new-onset.
Treatment
Isolated RBBB requires no specific treatment. Management focuses on identifying and treating the underlying etiology, such as hypertension or myocardial ischemia. Avoid prophylactic pacing as it provides no mortality benefit in asymptomatic patients.
Prognosis
Isolated RBBB has a favorable prognosis in healthy individuals. However, new-onset RBBB in the setting of acute chest pain is a marker for myocardial infarction and requires immediate cardiac evaluation.
Differential Diagnosis
Brugada Syndrome: coved ST elevation in V1-V2
Ventricular Tachycardia: AV dissociation or fusion beats
WPW Syndrome: delta wave and short PR interval
Left Ventricular Hypertrophy: high voltage criteria
Hyperkalemia: peaked T waves and wide QRS