In this Emergency Department (ED)-based study, the investigators evaluated a standardized modified Valsalva maneuver (MVM) as first-line therapy and compared intravenous (IV) adenosine with IV diltiazem among patients with persistent atrioventricular nodal re-entrant tachycardia (AVNRT)-consistent supraventricular tachycardia (SVT) after MVM, focusing on successful conversion to sinus rhythm. The investigators also assessed drug-related adverse events and clinically relevant treatment-course measures.

Supraventricular tachycardia (SVT) is a frequent cause of emergency department (ED) visits and typically presents as an abrupt-onset, regular tachycardia that can be highly symptomatic despite hemodynamic stability. Among regular narrow-complex SVTs, atrioventricular nodal re-entrant tachycardia (AVNRT) is one of the most common underlying mechanisms. Guidelines recommend modified Valsalva maneuver (MVM) as first-line therapy for hemodynamically stable regular narrow-complex SVT, followed by pharmacologic cardioversion when vagal maneuvers fail. However, while MVM has strengthened the non-pharmacologic first step, a clear emergency department (ED)-relevant comparative assessment of adenosine versus diltiazem specifically after failed MVM-with attention to conversion success, rescue therapy requirements, safety/tolerability, and clinically meaningful ED outcomes-remains warranted. This prospective, randomized, single-blind, single-center clinical trial evaluates the effectiveness of a standardized MVM and to compare the efficacy and adverse-event profiles of intravenous (IV) adenosine versus IV diltiazem among patients with persistent SVT after MVM. Consecutive adult patients with regular narrow-complex SVT consistent with AVNRT were randomized (1:1) to IV adenosine or IV diltiazem. Randomization was performed using a computer-generated sequence with allocation concealment (sequentially numbered, opaque, sealed envelopes). Treating clinicians were aware of group allocation in order to administer the assigned drug, whereas outcome assessors and the statistical team remained blinded throughout data collection and analysis. Adenosine was administered as a rapid IV push (6 mg over ~2 seconds) followed immediately by a 10-mL normal saline flush; the injected arm was briefly elevated to facilitate rapid central delivery. If tachycardia persisted and no rhythm conversion occurred within 1-2 minutes, additional doses of 12 mg and then 18 mg were administered using the same technique, per the study protocol. Diltiazem was administered intravenously as 0.25 mg/kg (maximum 20 mg) over approximately 2 minutes. If tachycardia persisted, a second dose of 0.35 mg/kg (maximum 25 mg) was administered after ~15 minutes. In patients who remained in SVT after protocolized dosing, subsequent management followed a predefined rescue algorithm based on hemodynamic status: hemodynamically stable patients received the alternative study drug (adenosine or diltiazem), whereas patients with signs of hemodynamic instability or persistent SVT despite sequential pharmacologic therapy underwent synchronized electrical cardioversion. In both groups, continuous clinical and electrocardiogram (ECG) monitoring was performed throughout the intervention period. For each eligible patient, baseline information was recorded at ED presentation, including age, sex, date/time of arrival, presenting symptoms, current medications, relevant comorbidities, and smoking and/or alcohol use history. Initial clinical and electrocardiographic data were documented, including heart rate, respiratory rate, systolic (SBP) and diastolic blood pressure (DBP), peripheral oxygen saturation (SpO2), and predefined ECG characteristics. In all patients who achieved sinus rhythm, vital signs (SBP/DBP, heart rate, and SpO2) were recorded immediately after conversion and at 10, 15, 30, and 60 minutes thereafter using standardized monitoring in the ED. The primary outcome was conversion to sinus rhythm with the allocated drug. Secondary outcomes included repeat dosing, time to conversion, adverse events, pause-related ECG events, crossover to the alternative drug, and disposition.

Inclusion Criteria:

• Age ≥ 18 years
• Presentation to the emergency department with hemodynamically stable, regular narrow-complex SVT consistent with AVNRT
• a regular narrow-complex tachycardia with QRS duration <120 ms
• no discernible P waves on the presenting rhythm strip or 12-lead ECG
• a ventricular rate of 160-220 beats/min

Exclusion Criteria:

• Contraindications to adenosine or diltiazem (known hypersensitivity to adenosine or diltiazem, prior heart transplantation, or concomitant dipyridamole/carbamazepine therapy)
• Clinical evidence of impaired cerebral perfusion (e.g., altered mental status)
• Pegnancy
• Hemodynamic instability or respiratory failure requiring emergency intubation and advanced life support

Stored in non-publicly available Available on request

Patients were randomly assigned to the adenosine or diltiazem groups using a web-based computer-generated randomization service (https://www.randomizer.org/). Allocation concealment was ensured using sequentially numbered, opaque, sealed envelopes (SNOSE). Envelopes were prepared and sealed according to the randomization list and opened sequentially after eligibility had been confirmed and written informed consent obtained.Clinicians administering the interventions were not blinded to treatment allocation but were not involved in outcome assessment or data analysis. Outcome assessors and the statistical team were blinded to treatment assignment. Treatment codes were accessible only in emergency safety situations requiring unblinding, and such cases were documented according to the study protocol. All primary analyses were conducted according to the intention-to-treat (ITT) principle, with per-protocol analyses reported as sensitivity analyses.