Outcomes of a modified Valsalva maneuver and randomized comparison of intravenous adenosine versus diltiazem after maneuver failure in patients with stable narrow-complex supraventricular tachycardia

The modified Valsalva maneuver (MVM) is recommended as first-line therapy for hemodynamically stable regular narrow-complex supraventricular tachycardia (SVT) consistent with atrioventricular nodal re-entrant tachycardia (AVNRT). Evidence comparing intravenous (IV) diltiazem regimens with IV adenosine after a failed MVM remains limited. We conducted a single-blind randomized controlled trial (July 2024–June 2025) enrolling consecutive adults presenting to the emergency department with hemodynamically stable regular narrow-complex SVT consistent with AVNRT based on clinical and surface ECG criteria. All patients underwent a standardized MVM. Patients with persistent SVT were randomized (1:1) to IV adenosine (6 mg rapid bolus, then 12 mg and 18 mg if needed) or IV diltiazem (0.25 mg/kg over 2 min; repeat 0.35 mg/kg at 15 min if needed). 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. Among 140 enrolled patients, the MVM terminated SVT in 59 (42.1%). Baseline demographics, comorbidities, and initial vital signs did not distinguish MVM responders from non-responders. The remaining 81 patients were randomized to IV adenosine ( n = 42) or IV diltiazem ( n = 39). First-drug conversion rates were similar between the adenosine and diltiazem groups (88.1% vs. 89.7%; p = 0.814). The diltiazem group required fewer repeat doses (28.2% vs. 66.7%; p = 0.001) but had a longer time to conversion (median 105.0 s vs. 5.5 s; p < 0.001) than the adenosine group. Any adverse event occurred less often with diltiazem (48.7% vs. 90.5%; p < 0.001), while hypotension was more frequent with diltiazem (10.3% vs. 0.0%; p = 0.049). Pause-related ECG events (transient asystolic pauses and sinus arrest) were more common with adenosine ( p < 0.001 and p = 0.008, respectively) than with diltiazem. Crossover to the alternative drug occurred in five patients in the adenosine group and in four patients in the diltiazem group; no synchronized cardioversion was required in either group. Ward admission did not differ between groups (14.3% vs. 10.3%; p = 0.582). A standardized MVM terminated SVT in approximately 42% of stable AVNRT-consistent presentations and should be routinely attempted before drug therapy. After a failed MVM, IV adenosine and IV diltiazem achieved similar conversion rates but with clinically relevant trade-offs: adenosine provided faster conversion with more transient symptom burden and pause-related ECG events, whereas diltiazem reduced repeat dosing and overall adverse events but increased the risk of hypotension. ClinicalTrials.gov registry no: NCT07456423; registry date: 2026-02-25 (Retrospectively registered).