Differential Diagnosis for ECG Findings

The provided ECG findings in a 17-year-old male suggest an abnormality in the QRS complex, which may indicate a conduction disturbance. Here's a differential diagnosis based on the given information:

• Single Most Likely Diagnosis

  • Incomplete Right Bundle Branch Block (IRBBB): The presence of a deep, broad S wave in V1/V2 without a clear second positive deflection (R′) and a QRS duration of 123 ms, which is slightly prolonged but not meeting the full criteria for complete RBBB (>140 ms in adults), suggests IRBBB. The morphology described, with a broad monophasic R in lateral leads and deep terminal S in right precordials, further supports this diagnosis.

• Other Likely Diagnoses

  • Left Anterior Fascicular Block (LAFB): Although less likely given the specific findings, LAFB could potentially cause alterations in QRS morphology, particularly in the lateral leads. However, it typically presents with left axis deviation, which is not mentioned.
  • Non-specific Intraventricular Conduction Delay: This could be considered if the QRS prolongation is not specifically localized to the right bundle branch. However, the morphology described leans more towards a right-sided conduction delay.

• Do Not Miss Diagnoses

  • Wolff-Parkinson-White (WPW) Syndrome: Although the described morphology does not classically suggest WPW, it's crucial to consider this diagnosis due to its potential for serious complications, such as supraventricular tachycardia. The absence of a delta wave and the specific QRS morphology makes this less likely but not impossible.
  • Cardiac Sarcoidosis or Other Infiltrative Diseases: These conditions can cause various conduction abnormalities, including bundle branch blocks. While less common, they are critical to consider due to their potential impact on cardiac function and the need for specific treatment.

• Rare Diagnoses

  • Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): This condition can lead to abnormalities in the right ventricular conduction and structure, potentially mimicking or causing RBBB patterns on ECG. However, it's a rare condition and would typically be associated with other clinical and diagnostic findings.
  • Myocardial Bridging: Although more commonly associated with ischemic changes, in rare cases, it could potentially affect conduction, leading to ECG abnormalities. However, this would be an unusual presentation and not a primary consideration based on the provided ECG findings alone.