In a 63-year-old man with prior anterior myocardial infarction presenting with one hour of palpitations and severe weakness, what is the most likely diagnosis?

Ventricular Tachycardia

In a 63-year-old man with prior anterior myocardial infarction presenting with palpitations and severe weakness, ventricular tachycardia (VT) is the most likely diagnosis (Answer B).

Clinical Reasoning

The combination of prior anterior MI + acute palpitations + severe weakness creates a high-probability scenario for VT. Here's why:

Why Ventricular Tachycardia is Most Likely:

• Substrate exists: Prior anterior MI creates myocardial scar tissue, which forms the anatomical substrate for reentrant ventricular arrhythmias 1
• Hemodynamic compromise: The "severe weakness" suggests hemodynamically significant arrhythmia, which is characteristic of sustained VT 1
• Timing and presentation: Sustained VT in post-MI patients typically presents with palpitations and symptoms of poor perfusion (weakness, lightheadedness, near-syncope) 2

Why Other Options Are Less Likely:

Atrial fibrillation (A): While AF occurs in 15-20% of MI patients, it typically causes less severe hemodynamic compromise unless the rate is extremely rapid. AF is more commonly associated with heart failure symptoms rather than acute severe weakness 2. The prior anterior MI makes VT far more probable.

Sinus tachycardia (C): Would not cause "severe weakness" in isolation and represents a physiologic response rather than a primary arrhythmia. The acute onset of palpitations argues against this 1.

Pulmonary embolism (D): Could cause palpitations and weakness, but the specific history of anterior MI makes VT the primary concern. PE would typically present with dyspnea as a prominent feature.

Acute coronary syndrome (E): While possible, the presentation of palpitations as the primary symptom with severe weakness is more consistent with an arrhythmic event. ACS typically presents with chest pain/pressure, though atypical presentations occur.

Key Clinical Pearls:

• Monomorphic VT at rates >150 bpm is the typical post-MI arrhythmia pattern 1
• Anterior MI carries higher risk for VT than inferior MI due to larger scar burden 2
• Sustained VT (>30 seconds or causing hemodynamic compromise) requires immediate intervention 1
• Distinguish true VT from accelerated idioventricular rhythm (rate <120 bpm), which is benign and often represents reperfusion 2

Immediate Management Approach:

1. If hemodynamically unstable (which "severe weakness" suggests):

   • Immediate synchronized cardioversion: 100 J for monomorphic VT >150 bpm 1
   • Unsynchronized 200 J if polymorphic/uncertain 1

2. If hemodynamically stable (brief window):

   • Lidocaine: 1.0-1.5 mg/kg bolus, then 2-4 mg/min infusion 1
   • Alternative: Amiodarone 150 mg over 10 minutes 1
   • Beta-blockers if not contraindicated 2

3. Do not delay cardioversion if patient deteriorates during medication trial 1

The ECG would be essential to confirm the diagnosis, but the clinical scenario strongly points to VT as the culprit arrhythmia requiring urgent recognition and treatment.