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

A Randomized Controlled Trial Comparing Nasal Swab and Modified Valsalva Maneuver for the Treatment of Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is a common heart rhythm disorder seen in emergency departments, causing a rapid heartbeat (typically 150-250 beats per minute). The current best non-drug treatment, the modified Valsalva maneuver (mVM), successfully restores normal rhythm in about 43% of cases. When these maneuvers fail, intravenous adenosine is used, which, while effective, can cause brief but distressing side effects such as chest tightness, shortness of breath, and intense anxiety.

During the COVID-19 pandemic, some patients briefly fainted during nasal swab collection. This happens because inserting a swab into the back of the nasal cavity (nasopharynx) stimulates the trigeminal nerve, which then activates the vagus nerve and slows the heart - a phenomenon called the trigeminocardiac (or nasocardiac) reflex. One published case report described a patient whose SVT was terminated within 10 seconds using a nasal swab.

This study compares the nasal swab technique with the modified Valsalva maneuver in patients presenting to the emergency department with SVT. Patients are randomly assigned to one of two groups. The primary outcome is whether a normal heart rhythm is restored within 1 minute of the procedure. Patient comfort and satisfaction are also measured.

The study is conducted in two phases. The first (pilot) phase (30 patients per group) will assess whether the study can be successfully conducted and collect data to finalize the required sample size. The second (main) phase will use the pilot phase's actual data to determine the final number of participants needed.

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%

Inclusion Criteria:

• Age 18 years or older
• Electrocardiographically confirmed supraventricular tachycardia (SVT): narrow QRS complex (≤120 ms), regular rhythm, rapid ventricular rate, documented on 12-lead ECG or continuous cardiac monitoring
• Hemodynamic stability, defined as ALL of the following simultaneously present:
• Systolic blood pressure ≥90 mmHg
• Diastolic blood pressure ≥60 mmHg
• Alert and oriented mental status (GCS 15)
• No signs of acute end-organ dysfunction
• Ability and willingness to provide written informed consent

Exclusion Criteria:

• Age younger than 18 years
• Pregnancy (known or suspected)
• Inability to confirm SVT diagnosis by ECG criteria
• Delta wave or pre-excitation pattern on ECG (Wolff-Parkinson-White syndrome or asymptomatic pre-excitation) - due to risk of ventricular fibrillation with vagal maneuvers
• Wide QRS tachycardia (QRS ≥120 ms) where ventricular tachycardia cannot be excluded
• Absolute contraindication to modified Valsalva maneuver (inability to assume supine position or passive leg elevation)
• Contraindication to nasal swab (nasal surgery within 30 days, active epistaxis, visible nasal polyp or mass)
• Hemodynamic instability requiring immediate synchronized cardioversion
• Prior enrollment in this study (re-presentation with SVT)
• Refusal to participate