BACKGROUND

Supraventricular tachycardia (SVT) is a group of tachycardic arrhythmias with an incidence of approximately 35 in 100,000 people per year.Reference Orejarena, Vidaillet and DeStefano ² A number of methods exist for cardioversion in patients with acute SVT, though all with varying and limited rates of success.Reference Ferguson and DiMarco ^{3 ,} Reference Mehta, Ward and Wafa ⁴ The Valsalva maneuver is a safe and recommended first line treatment for SVT, but with cardioversion rates to sinus rhythm of less than 20%.Reference Smith, Morgans and Boyle ^{5 -} Reference Members, Blomström-Lundqvist and Scheinman ⁸ Patients who have remained in SVT after Valsalva are most often treated with adenosine, which is commonly associated with adverse and frightening effects for patients and requires IV access.Reference Innes ⁹ Modifications to the standard Valsalva that increase relaxation phase venous return and vagal stimulation may improve cardioversion effectiveness but have not yet been tested in controlled trials.Reference Appelboam, Gagg and Reuben ^{10 -} Reference Walker and Cutting ¹²

POPULATION STUDIED

Investigators enrolled patients older than 18 years with SVT confirmed by 12-lead electrocardiogram (ECG) as a regular narrow complex tachycardia (QRS<120 ms). Exclusion criteria included unstable patients with systolic blood pressure less than 90 mm Hg or with indication for immediate cardioversion. Patients in atrial fibrillation and atrial flutter were also excluded. Additional exclusion included any contraindication to Valsalva (aortic stenosis, recent myocardial infarction, glaucoma, or retinopathy), inability to perform the maneuver, to lie flat, or to have legs lifted, third trimester pregnancy, or previous inclusion in the study.

STUDY DESIGN

The study was a randomized, multicentre parallel group trial conducted in 10 EDs in southwest England between January 1, 2013 and April 30, 2015. Patients were randomly assigned to either a standard or modified Valsalva. For both groups, the Valsalva strain was standardized to 40 mm Hg for 15 seconds by single forced expiration as monitored by an aneroid manometer. The interventions were disguised from patients by using descriptive terms for each Valsalva maneuver. In the standard “stay sitting Valsalva” patients were positioned semi-recumbent at 45° and instructed to perform the strain and then remain in the same position for 60 seconds before assessment of cardiac rhythm by 3-lead ECG. The modified Valsalva maneuver was described as “lying down with leg lift Valsalva.” Participants performed the same standard Valsalva strain but immediately after were laid flat with their legs raised at an angle of 45° for 15 seconds. They were then returned to the semi-recumbent position for 45 seconds before their cardiac rhythm was reassessed using a 3-lead ECG. In either arm, if sinus rhythm was not restored, participants were able to do one additional attempt using their allocated Valsalva maneuver. A 12-lead ECG was recorded 1 minute after the final Valsalva maneuver.

OUTCOMES MEASURED

The primary outcome was the presence of sinus rhythm 1 minute after the Valsalva maneuver, as recorded by the treating physicians and confirmed by ECG. In cases where the ECG was missing, an endpoint committee confirmed outcomes. Secondary outcomes were the use of adenosine, the use of any emergency treatment for SVT, the need for and reason for admission to hospital, the length of time spent in the emergency department (ED), and adverse events.

COMMENTARY

The rates for conversion of acute SVT to sinus rhythm using non-pharmacologic therapies in clinical settings have historically been less than 20%.Reference Lim, Anantharaman and Teo ^{6 ,} Reference Smith, Fry and Taylor ¹³ A study published in 2010 by Walk and Cutting showed the highest rate of acute cardioversion in a clinical setting (31%) using a modified Trendelenberg version of Valsalva, where patients place their heads between their knees.Reference Walker and Cutting ¹² The 43% of participants who cardioverted using the postural modification of Valsalva described in this controlled trial was substantially higher than with any other reported technique for emergency treatment of SVT. The authors noted that the proportion of participants who converted using the control Valsalva was larger than that in most observational studies, although was within the range of routine practice.

Modification of the standard Valsalva using supine positioning with legs raised has long been postulated to augment conversion of SVT.Reference Mehta, Ward and Wafa ⁴ The principle of the posture is that it increases venous return to the heart and thus stimulates vagal tone during the relaxation phase of Valsalva that follows the cessation of strain. This increased cardiac parasympathetic tone slows atrioventricular node conduction sufficiently to interrupt the circuitous electrical activity of SVT and allow the underlying sinus node to reemerge.Reference Wong, Taylor and Bailey ¹¹

A major benefit of the modified Valsalva maneuver is its ability to be performed outside of the hospital and without specialist equipment. Rather than using a manometer to ensure a consistent 40 mm Hg strain, a 10 mL syringe blown to just move the plunger can be used to generate a similar pressure. The modified maneuver is cost-effective, safe, and can be easily taught to patients after their first episode of SVT to perform independently and in low-resource settings. The technique could further be incorporated into established EMS treat and release protocols for uncomplicated SVT that aim to decrease the burden on EDs.Reference Minhas, Vogelaar and Wang ¹⁴ The maneuver can thus prevent many individuals with SVT from requiring future hospital care or treatment with pharmacologics such as adenosine.

A major limitation of the REVERT trial is that practicing physicians and patients were unable to be blinded to treatment allocation due to the nature of the treatment. However, patients were kept unaware of which treatment was the control versus study intervention by using descriptive terms for the maneuvers and disguising trial paperwork. The authors further mitigated this limitation by implementing a stringent concealed randomization procedure and by using the objective primary outcome of conversion to sinus rhythm on ECG and confirmed by an independent cardiologist masked to the treatment.