Case: A 75-year-old man with syncope

A 75-year-old man was admitted after experiencing syncope during intense physical exertion. He had no warning signs or prodromal symptoms before the episode. On admission, he was in sinus rhythm.

Several years earlier, the patient had received an ICD (implantable cardioverter-defibrillator) following a cardiac arrest. The evaluation at that time revealed no obvious underlying cause, and the event was classified as a primary arrhythmia. It is important to note that it is not uncommon for the cause of a cardiac arrest to remain unidentified.

During this admission, ICD interrogation revealed that the patient had developed rapidly conducted atrial fibrillation during physical activity, without noticing any symptoms. This progressed into a more organized rhythm with a ventricular rate of around 250 beats per minute, consistent with ventricular fibrillation (VF), leading to syncope. The ICD quickly recognized VF and initiated anti-tachycardia pacing (ATP) while preparing to deliver a shock. ATP was effective, and VF was terminated. The patient converted back to atrial fibrillation and regained consciousness spontaneously shortly thereafter.

 What is ATP (Anti-Tachycardia Pacing)?

ATP is a function in ICDs that attempts to interrupt a rapid, regular ventricular tachycardia by delivering short sequences of rapid electrical impulses to the heart—faster than the pathological rhythm. The goal is to “take over” the rhythm and terminate the arrhythmia painlessly, avoiding the need for a shock. In this case, ATP was effective, and VF was terminated before a shock was delivered.

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 Learning points

• Atrial fibrillation can be life-threatening in patients at risk for ventricular arrhythmia.

• Rapidly conducted atrial fibrillation can trigger ventricular fibrillation in susceptible individuals.

• In patients with a history of cardiac arrest, cardiomyopathy, or structural heart disease, atrial fibrillation should be managed more aggressively.

• Atrial fibrillation is common, but not necessarily benign, and should always be treated appropriately.