Supraventricular tachycardia
Algorithm
Narrow QRS complex tachycardia
Hemodynamic instability
No
Yes
If Ineffective
If Ineffective
If Ineffective
Modified Valsalva Maneuver

To perform this maneuver, start with the patient in a semi-recumbent position and have them exhale into a 10cc syringe for 15 seconds. Next, place the patient supine with their legs raised to a 45-degree angle and hold this position for another 15 seconds. This procedure aids in improving venous return and increasing vagal tone.

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Adenosine
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Drug of choice: an endogenous purine nucleoside
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6-18 mg i.v. Rapid bolus with immediate saline flush via Large, centrally located (e.g., antecubital) veins.
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Dosing should be incremental, starting at 6 mg in adults, then 12 mg.
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The initial dose should be less (3 mg) for patients with central venous catheters, heart transplant recipients, or dipyridamole patients.
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Mediated through cardiac adenosine A1 receptors.
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Prolongation of AV conduction [Effects on the atrial-His (AH) interval, and none on the HV interval], culminating in transient AV block.
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Adenosine has a very short plasma half-life due to enzymatic deamination to inactive inosine achieved in seconds, with end-organ clinical effects complete within 20-30 s. Repeat administration is safe within 1 minute of the last dose.
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Bronchoconstriction is rare in patients receiving intravenous adenosine for SVT. In clinical experimental studies, intravenous administration did not impact the airways.

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Calcium channel blockers (Verapamil/Diltiazem i.v. ) and betablockers (e.g. esmolol and metoprolol i.v.)
Verapamil [0.075 - 0.15 mg/kg i.v. (average 5 - 10 mg) over 2 min]
Diltiazem [0.25 mg/kg (average 20 mg) over 2 min]
(SVT termination 64-98%, but is associated with a risk of hypotension)
Avoided in patients with hemodynamic instability, HF with reduced LV ejection fraction (<40%), a suspicion of VT, or pre-excited AF.
Esmolol (0.5 mg/kg i.v. bolus or 0.05 - 0.3 mg/kg/min infusion)
Metoprolol tartate (2.5-15 mg given i.v. over several minutes)
(Likely reducing the tachycardia rate than in terminating it)
Beta-blockers are contraindicated in patients with decompensated HF.
Adenosine response
v(' -')v
No Effect
Inadequate dose/ delivery High septal VT

Sudden termination
AVNRT AVRT Sinus nodal re-entry Triggered focal AT (DADs)

Gradual slowing then reacceleration
Sinus tachycardia Automatic focal AT Junctional ectopic tachycardia

Persisting atrial tachycardia with transient high-grade AV block
Atrial flutter Micro-re-entrant focal AT

References
1) Brugada J, Katritsis DG, Arbelo E, Arribas F, Bax JJ, Blomström-Lundqvist C, Calkins H, Corrado D, Deftereos SG, Diller GP, Gomez-Doblas JJ, Gorenek B, Grace A, Ho SY, Kaski JC, Kuck KH, Lambiase PD, Sacher F, Sarquella-Brugada G, Suwalski P, Zaza A; ESC Scientific Document Group. 2019 ESC Guidelines for the management of patients with supraventricular tachycardiaThe Task Force for the management of patients with supraventricular tachycardia of the European Society of Cardiology (ESC). Eur Heart J. 2020 Feb 1;41(5):655-720. doi: 10.1093/eurheartj/ehz467. Erratum in: Eur Heart J. 2020 Nov 21;41(44):4258. doi: 10.1093/eurheartj/ehz827. PMID: 31504425.
2) Appelboam A, Reuben A, Mann C, Gagg J, Ewings P, Barton A, et al. Postural modification to the standard Valsalva manoeuvre for emergency treatment of supraventricular tachycardias (REVERT): a randomised controlled trial. The Lancet. 2015 Oct 31;386(10005):1747–53.
3) Raviña T, Raviña P, Suárez ML. Adenosine-Induced Atrial Instability. Revista Española de Cardiología (English Edition). 2004;57(6):487–601.