What are the next steps for a patient whose Zio patch detected a borderline wide‑complex rhythm lasting 21 beats and 21 supraventricular tachycardia (SVT) episodes, with the longest run of 14 beats?

Immediate Cardiology Referral with Electrophysiology Study Consideration

The patient requires prompt cardiology referral for comprehensive evaluation, including 12-lead ECG during any recurrent symptoms, echocardiography to assess for structural heart disease, and strong consideration for electrophysiology study given the borderline wide-complex rhythm that could represent either ventricular tachycardia or SVT with aberrancy 1.

Critical Diagnostic Clarification Needed

The "borderline wide complex rhythm" lasting 21 beats is the most concerning finding and demands immediate attention. This represents a diagnostic dilemma that fundamentally changes management:

• If ventricular tachycardia: Requires risk stratification for sudden cardiac death, possible ICD consideration, and antiarrhythmic therapy
• If SVT with aberrancy: May be amenable to curative catheter ablation with excellent outcomes
• If pre-excited tachycardia: Represents high-risk accessory pathway requiring ablation

The distinction cannot be made reliably from ambulatory monitoring alone 2, 3. Wide-complex tachycardias should be presumed ventricular tachycardia until proven otherwise, as misdiagnosis carries significant mortality risk 3.

Immediate Next Steps

1. Cardiology Referral (Urgent - Within 1-2 Weeks)

The patient needs:

• 12-lead ECG in sinus rhythm to assess for:

  • Pre-excitation (short PR, delta waves suggesting WPW syndrome)
  • Baseline QRS duration and morphology
  • Structural abnormalities (Q waves, bundle branch blocks)

• Echocardiography to evaluate:

  • Left ventricular function (reduced EF suggests VT more likely)
  • Structural heart disease
  • Cardiomyopathy assessment

2. Electrophysiology Study Consideration

Given 21 beats of wide-complex tachycardia, EP study is strongly indicated 1, 2:

• Definitive diagnosis of the wide-complex rhythm mechanism
• Risk stratification for sudden death if VT
• Potential for curative ablation if SVT with aberrancy or accessory pathway
• The 2019 ESC guidelines significantly upgraded catheter ablation to preferential first-line status for symptomatic recurrent SVT 4

3. Management of the SVT Episodes

The 21 episodes of narrow-complex SVT (longest 14 beats) are less immediately concerning but still warrant treatment:

• If symptomatic and recurrent: Catheter ablation should be offered as first-line therapy per current guidelines 1, 4
• If infrequent/minimally symptomatic: Conservative management with "pill-in-pocket" approach or scheduled antiarrhythmic drugs
• Beta-blockers or calcium channel blockers for rate control if needed acutely 5, 6

Common Pitfalls to Avoid

1. Assuming wide-complex = VT without EP confirmation: While VT should be presumed for safety, SVT with aberrancy (including AVNRT) can present identically 2. The case report demonstrates an 81-year-old with wide-complex tachycardia ultimately diagnosed as AVNRT with aberrancy via EP study.

2. Delaying evaluation: Even asymptomatic or minimally symptomatic wide-complex rhythms require evaluation, as they may represent life-threatening arrhythmias

3. Treating empirically without diagnosis: The management differs dramatically based on mechanism—adenosine is appropriate for SVT but potentially dangerous in pre-excited AF; amiodarone treats VT but is downgraded for routine SVT management 5

Risk Stratification Factors

Higher-risk features requiring more urgent evaluation:

• Symptoms during arrhythmia (syncope, presyncope, chest pain)
• Structural heart disease or reduced ejection fraction
• Family history of sudden cardiac death
• Very rapid rates (>200 bpm) suggesting accessory pathway

The patient should avoid activities with risk of sudden incapacitation (driving, swimming alone, heights) until the wide-complex rhythm is definitively characterized 1.