Please note that, while “supraventricular tachycardia (SVT)” is a term that can be used more broadly to refer to any tachyarrhythmia originating above the ventricles, I use its more conventional meaning here to describe AVnRT and AVRT. LITFL has a good summary of narrow-complex tachycardias.
SVT is a narrow complex tachycardia commonly seen in the emergency department. In hemodynamically stable patients the first-line treatment is vagal stimulation, usually the Valsalva maneuver. However, success rates for this approach are low, with data citing success rates of around 5-25%1,2. The modified Valsalva maneuver was recently developed and trialled with successful conversions in 43% of patients, compared to 17% with the standard Valsalva maneuver. No serious adverse outcomes were described. This is a safe, simple, and low-resource technique that can be taught to emergency physicians, prehospital care providers, and even to patients themselves. Use of this technique can minimize the use of costlier, resource-heavy, and uncomfortable treatments, such as adenosine or electrical cardioversion.
So, what exactly is the modified Valsalva maneuver?
The standard Valsalva maneuver is usually performed by having patients “bear down” to stimulate the Vagus nerve. This can be done either by instructing them to push like they’re having a bowel movement or having them blow into a syringe with the plunger in place. The modified Valsalva maneuver more precisely describes this procedure and adds a passive leg raise. This is designed to stimulate vagal tone through a different mechanism (baroreflex activation). To remember the steps of the modified Valsalva maneuver just think of “SVT”:
S = Strain (just enough to make the plunger of a 10cc syringe move, equal to 40mmHg)
V = Venous return (supine with passive leg raise)
T = Time (15s at each stage)
Video from the original Lancet publication
This post was copyedited by Anton Nikouline (@anikoul).
Reviewing with the Staff
Vagal maneuvers are considered the initial treatment modality for patients presenting with hemodynamically stable AV nodal reentry tachycardia (AVNRT). By performing a vagal maneuver the Vagusvagal nerve is stimulated to slow the electrical conduction at the AV node, in the hopes of terminating the AVNRT. Vagal maneuvers include carotid artery massage, ice submersion or the more frequently used Valsalva maneuver. The Valsalva maneuver is a safe and easy to perform technique, where the patient is asked to perform attempted exhalation against a closed airway. Unfortunately, this maneuver has a low success rate of about 1 in 5. In failed cases adenosine can be attempted to terminate the arrhythmia. Despite the excellent safety profile of adenosine the side effects are unpleasant, where patients often experience a brief feeling of dying. Even though the sensation is short lived it is definitely something that we should try to avoid if at all possible. It also requires IV line placement, with its own discomfort and potential complication risk.
The modified Valsalva maneuver was developed in an attempt to increase the success rate of the traditional Valsalva maneuver. The patient is asked to blow into a sphygmomanometer at a pressure of 40 mmHg for 15 seconds (alternatively, the patient is asked to blow into a syringe in an attempt to move the plunger), then to lie back flat with the legs elevated to increase venous return in the relaxation phase, thereby increasing vagal nerve stimulation.
The REVERT trial was designed to assess the efficacy and safety of the modified technique. 433 patients with AVRNT were enrolled and randomized to either the modified or the traditional Valsalva maneuver. The primary outcome of return to sinus rhythm after 1 minute was achieved in 43% of patients with the use of the modified Valsalva maneuver, compared to 17% in those who underwent the traditional technique. The absolute risk reduction was 26.2% (p<0.001), with a number needed to treat of 3.8. There was a slight increase in adverse events in the modified technique group, however, all of these were considered to be mild and there were no serious adverse events in either groups.
In summary, the REVERT trial provides data to support for the use of the modified Valsalva maneuver for patients in AVNRT.
The SVT mnemonic is a quick and easy way for novice practitioners to memorize the modified Valsalva maneuver.