Differential Diagnosis for a 30-year-old Man with Intermittent Episodes of a Racing Heart

• Single most likely diagnosis:
  • Wolff-Parkinson-White (WPW) syndrome: This condition is characterized by the presence of an accessory electrical pathway between the atria and the ventricles, which can cause the heart to beat too quickly. The patient's symptoms of intermittent episodes of a racing heart and the absence of other significant past medical history make WPW syndrome a plausible diagnosis. The ECG would typically show a delta wave (a slurred upstroke in the QRS complex) and a short PR interval, which are hallmarks of WPW syndrome.
• Other Likely diagnoses:
  • Atrial flutter: This is a type of supraventricular tachycardia characterized by a rapid but regular atrial rhythm. It could present with symptoms of a racing heart, although the ECG would typically show a sawtooth pattern of P waves, which may not be evident if the patient is not in an episode at the time of the ECG.
  • Multifocal atrial tachycardia (MAT): MAT is characterized by an irregular atrial rhythm with P waves of at least three different morphologies. It could cause symptoms of a racing heart, but the ECG during an asymptomatic period might not capture the diagnostic features.
• Do Not Miss diagnoses:
  • First-degree atrioventricular (AV) block: While often asymptomatic and not typically causing a racing heart sensation, it's crucial to identify any conduction abnormalities. However, first-degree AV block is characterized by a prolonged PR interval on the ECG, which might not directly explain the symptoms of intermittent tachycardia.
  • Idioventricular rhythm: This is a rare condition where the ventricles beat on their own without input from the atria, typically seen in severe heart disease or after myocardial infarction. It's less likely given the patient's age and lack of past medical history but is a condition that would not be missed due to its potential severity.
• Rare diagnoses:
  • Other supraventricular tachycardias (SVTs): These include AV nodal reentrant tachycardia (AVNRT), AV reentrant tachycardia (AVRT), and others. They can cause episodes of a racing heart but might not be captured on a single ECG if the patient is not experiencing an episode at the time of the test.
  • Ventricular tachycardia: Although less common in a young individual without structural heart disease, it's a diagnosis that needs consideration, especially if there are any signs of structural heart disease or significant electrolyte imbalances.