Question

A 32-year-old man with no significant past medical history presented with dyspnea, palpitations, feelings of anxiety, and dizziness, all of which occurred earlier in the morning following a brisk walk. He denied any prior episodes, illicit drug use, alcohol or cigarette use, skipping meals, or caffeine intake. He further denied fever, chills, chest pain, history of murmurs, cough, edema, rashes, syncope, headache, psychiatric, or focal neurological complaints. The physical examination demonstrated a fast, regular pulse with a constant-intensity first heart sound, but was otherwise normal. An EKG was performed, which revealed a short PR interval plus a slurred upstroke at the beginning of the QRS complex.

What is the most likely mechanism responsible for this patient's presentation?

1. Conduction delay in the proximal part of the right or left branches
2. Pre-excitation occurring via an atrio-His bundle
3. Spontaneous ectopy from muscular sleeves of pulmonary veins
4. Early excitation due to accessory pathways between the atria and ventricles
5. Inappropriately enhanced automaticity of sinus node pacemaker cells

Answer 1

The patient's symptoms and EKG findings suggest an accessory pathway between the atria and ventricles, such as seen in Wolff-Parkinson-White (WPW) syndrome, which causes early ventricular excitation.

Step-by-step explanation:

The most likely mechanism responsible for the patient's presentation of dyspnea, palpitations, feelings of anxiety, dizziness, along with the EKG findings of a short PR interval and a slurred upstroke at the beginning of the QRS complex (characteristic of a delta wave), is indicative of an accessory pathway between the atria and ventricles. This is a hallmark sign of Wolff-Parkinson-White (WPW) syndrome, which involves an abnormal, extra electrical pathway or accessory pathway that bypasses the normal route. It leads to early excitation of the ventricles due to the impulse reaching them prematurely.

Other options, such as conduction delay in the branches of the heart's conduction system, pre-excitation via the atrio-His bundle, or spontaneous ectopy from the pulmonary veins, do not correspond to the EKG findings presented in the question. Enhanced automaticity of sinus node pacemaker cells would also not account for a short PR interval with a delta wave.