Vagal maneuvers typically will not be effective if the rhythm does not involve the AV node as a requisite component of a reentrant circuit. There is no gold standard for proper Valsalva maneuver technique but, in general, the patient raises intrathoracic pressure by bearing down against a closed glottis for 10 to 30 seconds, equivalent to at least 30 mm Hg to 40 mm Hg.82,84 Carotid massage is performed after absence of bruit has been confirmed by auscultation, by applying steady pressure over the right or left carotid sinus Another vagal maneuver based on the classic diving reflex consists of applying an ice-cold, wet towel to the ; in a laboratory setting, facial immersion in water at 10 C (50 F) has proved effective in terminating tachycardia, as well.86 One study involving 148 patients with SVT demonstrated that Valsalva was more successful than carotid sinus massage, and switching from 1 technique to the other resulted in an overall success rate of 27.7%.82 The practice of applying pressure to the eyeball is potentially dangerous and has been abandoned. I B-R 2. Adenosine is recommended for acute treatment in patients with regular SVT.42,51,83,87 92 See Online Data and 3. Adenosine has been shown in nonrandomized trials in the emergency department or prehospital setting to effectively terminate SVT that is due to either AVNRT or AVRT, with success rates ranging from 78% to 96%. Although patients may experience side effects, such as chest discomfort, shortness of breath, and flushing, serious adverse effects are rare because of the drug s very short half-life.93 Adenosine may also be useful diagnostically, to unmask atrial flutter or AT, but it is uncommon for adenosine to terminate these atrial arrhythmias.91 It should be administered via proximal IV as a rapid bolus infusion followed by a saline flush. 