What is the appropriate management for a patient presenting with supraventricular tachycardia (SVT), characterized by specific electrocardiogram (ECG) findings including poor R waves in leads V4 and V5, abnormal Q waves in the 2nd aortic valve fistula (AVF), inverted T waves in lead V2, slight ST depression in leads V4, V5, and V6, and right axis deviation?

Management of Supraventricular Tachycardia with Concerning ECG Features

Immediate Priority: Rule Out Ventricular Tachycardia

This ECG pattern—particularly the poor R wave progression in V4-V5, abnormal Q waves, ST depression, and right axis deviation—raises critical concern that this may NOT be SVT but rather ventricular tachycardia (VT), and you must treat it as VT until proven otherwise. 1

Why This Matters

• Wide QRS morphology with poor R wave progression, abnormal Q waves suggesting myocardial scar, and right axis deviation are all highly suggestive of VT rather than SVT 1
• QR complexes (abnormal Q waves) indicate myocardial scar and are present in approximately 40% of patients with VT after myocardial infarction 1
• Right axis deviation during tachycardia is atypical for common SVTs and should raise suspicion for VT 1
• If you cannot definitively prove this is SVT despite careful ECG evaluation, you must treat the patient for VT—misdiagnosis can be fatal 1, 2

Immediate Assessment Algorithm

Step 1: Hemodynamic Stability Assessment

If the patient is hemodynamically unstable (hypotension, altered mental status, chest pain suggesting ischemia, pulmonary edema):

• Perform immediate synchronized DC cardioversion—this is the most effective and rapid means of terminating any hemodynamically unstable tachycardia regardless of mechanism 1, 3
• Have defibrillation immediately available as VT can degenerate into ventricular fibrillation 3, 4
• Do NOT delay for pharmacologic trials 3

Step 2: If Hemodynamically Stable - Confirm Diagnosis

Obtain a 12-lead ECG immediately during tachycardia—this is the single most critical step that determines all subsequent treatment decisions 2

Critical ECG features to differentiate VT from SVT:

• QRS width >140 ms with RBBB pattern or >160 ms with LBBB pattern strongly favors VT 1
• RS interval >100 ms in any precordial lead is highly suggestive of VT 1
• Negative concordance (all precordial leads showing QS complexes) is diagnostic for VT 1
• Presence of ventricular fusion beats indicates ventricular origin 1
• QR complexes indicate myocardial scar and VT 1

For true narrow QRS SVT (<120 ms):

• Pseudo r' wave in V1 and pseudo S waves in inferior leads are pathognomonic for AVNRT 5
• P waves in early ST segment suggest AVRT 1, 2
• P waves buried in QRS suggest AVNRT 1, 2

Step 3: Acute Management if Confirmed SVT and Stable

First-line: Vagal maneuvers 1, 6

• Valsalva maneuver is safer and more efficacious than carotid massage, especially in elderly patients 7
• Record 12-lead ECG during vagal maneuvers to observe response 5

Second-line: Intravenous adenosine 1, 5

• Adenosine 6 mg rapid IV push, followed by 12 mg if ineffective 6, 8
• Mean success rate of 93% for terminating SVT involving the AV node 8
• Record 12-lead ECG during adenosine administration to aid differential diagnosis 5

CRITICAL CONTRAINDICATIONS TO ADENOSINE:

• Do NOT use adenosine if pre-excitation (delta waves) is present or suspected—it can precipitate ventricular fibrillation in pre-excited atrial fibrillation 1, 4
• Contraindicated in second- or third-degree AV block, sick sinus syndrome, bronchospastic lung disease, and known hypersensitivity 4
• Use with extreme caution when diagnosis is unclear, as it may produce ventricular fibrillation in patients with coronary artery disease 1

Third-line alternatives if adenosine fails or contraindicated:

• IV calcium channel blockers (diltiazem or verapamil) 1, 6
• IV beta-blockers 1, 6

Mandatory Immediate Cardiology Referral

This patient requires urgent cardiac electrophysiology consultation based on:

• Wide complex tachycardia of unknown origin requires immediate referral—misdiagnosis as SVT when VT is present can be fatal 2
• Abnormal Q waves suggesting prior myocardial infarction with first occurrence of wide QRS tachycardia strongly indicates VT 1
• ST depression and poor R wave progression suggest underlying structural heart disease or active ischemia 3
• Right axis deviation during tachycardia is atypical and concerning 1

Critical Pitfalls to Avoid

• Automatic ECG analysis systems are unreliable and commonly suggest incorrect arrhythmia diagnoses—always perform manual interpretation 5
• Never use verapamil, diltiazem, beta-blockers, or digoxin if pre-excitation is present—they may accelerate conduction through the accessory pathway and precipitate ventricular fibrillation 3, 4
• Do not assume SVT based on rate alone—VT can present with similar heart rates 1
• Adenosine should be used with caution when diagnosis is unclear, as it may produce ventricular fibrillation in patients with coronary artery disease and atrial fibrillation with rapid ventricular rate in pre-excited tachycardias 1

Additional Workup Required

Before any definitive long-term management:

• Obtain transthoracic echocardiography to exclude structural heart disease that cannot be detected by physical examination or ECG alone 2
• Check for acute myocardial ischemia/infarction—arrhythmias in this setting require immediate correction of ischemia, pump failure, hypoxia, and electrolyte disturbances 3
• Correct hypokalemia, hypoxia, and acid-base disturbances, as these lower the threshold for ventricular arrhythmias 3

Long-Term Management After Acute Episode

Catheter ablation is first-line for long-term management of recurrent symptomatic SVT with 94.3-98.5% single-procedure success rate 2, 6

However, given the concerning ECG features in this case suggesting possible VT or underlying structural heart disease, electrophysiology study is mandatory before any ablation decision 2