NASVAL-SVT: Nasal Swab Versus Modified Valsalva for Supraventricular Tachycardia (NASVAL-SVT)

BACKGROUND:

Supraventricular tachycardia (SVT) encompasses re-entrant arrhythmias dependent on the atrioventricular node, including atrioventricular nodal re-entry tachycardia (AVNRT) and atrioventricular re-entry tachycardia (AVRT). Vagal maneuvers increase parasympathetic tone via the vagus nerve, slowing atrioventricular conduction and terminating these re-entrant circuits. The modified Valsalva maneuver (REVERT protocol) achieves termination in approximately 43% of cases, making it the most effective non-pharmacological approach currently available.

The trigeminocardiac reflex (TCR), also termed the nasocardiac reflex, involves mechanical stimulation of the nasal mucosa and nasopharynx activating the trigeminal nerve (V1/V2 branches) → pterygopalatine ganglion → trigeminal nucleus → dorsal vagal nucleus → cardiac inhibitory parasympathetic output → bradycardia. This reflex has been documented in nasoendoscopy studies (observed in approximately 30% of patients) and was reported to cause syncope during COVID-19 nasopharyngeal swab collection. Hooker and Liebman (2023) reported SVT termination within 10 seconds of nasal swab insertion in a patient refractory to other vagal maneuvers and adenosine. Cinpolat et al. (2025) reported a mean 28% decrease in heart rate and 22% decrease in systolic blood pressure during nasopharyngeal swab procedures, explicitly suggesting SVT as a potential application.

STUDY DESIGN:

Two-phase prospective single-center randomized controlled superiority trial.

• Phase 1 (pilot): 30 participants per arm (n=60 total). Primary aim: feasibility assessment.
• Phase 2 (main): Sample size recalculated from actual pilot-phase conversion rates.

RANDOMIZATION: Computer-generated blocked randomization (block sizes 4 and 6, randomly mixed) stratified by SVT subtype (probable AVNRT / probable AVRT / indeterminate). Allocation concealment using sequentially numbered, sealed, opaque envelopes.

BLINDING: Open-label for participants and care providers; outcome assessor (30-minute satisfaction survey) and statistician are blinded.

INTERVENTIONS:

• Arm 1 (Nasal Swab): Standard nasopharyngeal swab inserted through the right nostril, parallel to the nasal septum, to the nasopharyngeal vault. Held for 10 seconds with gentle rotation, then withdrawn. Patient in 45-degree semi-recumbent position.
• Arm 2 (mVM/REVERT): Forced expiration for 15 seconds into 10 mL syringe barrel, immediately followed by rapid supine repositioning and 45-degree passive leg elevation for 15 seconds.

OUTCOMES: Primary: sinus rhythm conversion at 1 minute (T=60 seconds post-procedure). Secondary: conversion at 3 and 5 minutes; rescue adenosine requirement; procedural discomfort (VAS 0-10); treatment satisfaction (5-point Likert); re-preference; SVT recurrence at 24 hours and 30 days; adverse event profile.

STATISTICAL ANALYSIS: Chi-square or Fisher's exact test for the primary outcome. Results reported as absolute risk difference with 95% CI. Intention-to-treat analysis as the primary; per-protocol analysis as a sensitivity analysis. Benjamini-Hochberg correction for secondary outcomes. Multiple imputation (MICE) for missing data between 5-20%.

SAFETY STOPPING RULES: Immediate procedure termination and rescue therapy for hemodynamic deterioration, arrhythmia worsening, patient request, or serious adverse event. Pilot phase safety stopping rule: ≥3 serious adverse events in either group triggers protocol review.

PILOT FEASIBILITY GO/NO-GO CRITERIA:

• Monthly enrollment rate: ≥5 patients/month
• Protocol adherence rate: ≥85%
• Missing data rate: ≤10%
• 30-day follow-up completion: ≥70%