In a 32-year-old man with repaired tetralogy of Fallot who presents with a first episode of palpitations, tachycardia (115 bpm) and blood pressure 140/94 mmHg, what is the immediate assessment and management?

Immediate Management of First-Episode Palpitations in Repaired Tetralogy of Fallot

This patient requires immediate 12-lead ECG to identify the arrhythmia mechanism, followed by continuous cardiac monitoring, as arrhythmias in repaired TOF carry significant risk for sudden cardiac death and require urgent rhythm characterization. 1

Initial Assessment Algorithm

Immediate Diagnostic Steps (Within Minutes)

1. Obtain 12-lead ECG immediately to determine:

   • Rhythm type (atrial vs ventricular tachycardia)
   • QRS duration (>180 ms is high-risk marker) 1
   • Presence of sustained vs non-sustained arrhythmia

2. Place on continuous cardiac monitoring - This is non-negotiable given the TOF history 1

3. Check electrolytes (potassium, magnesium) and thyroid function despite negative review of systems

Risk Stratification for This Patient

The patient's tachycardia (HR 115) with first-time palpitations in repaired TOF requires aggressive evaluation because:

• Atrial arrhythmias occur in ~30% of repaired TOF patients and have different mechanisms than acquired heart disease 2
• Ventricular arrhythmias remain a major mortality source even in well-repaired TOF 3
• The anatomic substrate from surgical repair creates slowly conducting isthmuses that persist lifelong 4, 3

Acute Management Based on Rhythm

If Supraventricular Tachycardia (Most Likely Given Stable Hemodynamics)

First-line interventions:

• Vagal maneuvers (carotid massage, Valsalva)
• IV adenosine 6 mg rapid push (if vagal maneuvers fail)
• Non-dihydropyridine calcium channel blockers (verapamil, diltiazem) as second-line 1

Critical caveat: In repaired TOF, atrial tachycardia mechanisms include:

• Intra-atrial reentrant tachycardia (IART) - 44% of cases 2
• Cavotricuspid isthmus-dependent flutter - 37% 2
• Focal atrial tachycardia - 19% 2

If Ventricular Tachycardia (Less Likely but Higher Risk)

Immediate synchronized cardioversion if hemodynamically unstable 1

Essential Workup Within 24-48 Hours

1. Transthoracic echocardiography to assess:

   • Biventricular function (LV and RV systolic function)
   • Degree of pulmonary regurgitation
   • RV size and pressure
   • Atrial dimensions (bi-atrial dilation predicts AT) 2

2. 24-hour Holter monitor to detect:

   • Non-sustained ventricular tachycardia (correlates with inducible VT and ICD discharge risk) 1
   • Burden of atrial arrhythmias
   • Heart rate variability abnormalities (predictor of sudden death) 1

3. Consider cardiac MRI if not recently performed to evaluate:

   • RV volumes and function
   • Myocardial fibrosis/scarring (arrhythmic substrate) 5

Anticoagulation Consideration

Important pitfall: If atrial tachycardia/flutter is sustained >48 hours or duration unknown, rule out intracardiac thrombus before cardioversion regardless of duration, as CHD patients have predisposition to thrombus formation 1. This differs from standard atrial fibrillation management.

Disposition and Follow-Up

• Admit for observation if arrhythmia persists or recurs
• Urgent cardiology/ACHD specialist referral within 1 week even if rhythm converts
• Electrophysiology consultation for risk stratification, particularly if:
  • Non-sustained VT detected
  • QRS duration ≥180 ms
  • LV or RV dysfunction present 1

Long-Term Implications

This first arrhythmic event triggers need for comprehensive ACHD evaluation because:

• Arrhythmias often herald hemodynamic deterioration 6
• Multiple AT mechanisms may coexist (after ablating first AT, another was induced in 30% of patients) 2
• Prophylactic substrate ablation may be considered before future interventions like pulmonary valve replacement 4

The blood pressure of 140/94 is likely reactive to anxiety/palpitations but document baseline BP at follow-up, as hypertension can contribute to LV dysfunction in this population.