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 Carotid massage is performed after absence of bruit has been confirmed by auscultation, by applying steady pressure over the right or left carotid sinus for 5 to 10 seconds.83,84 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 nonpregnant 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 C-LD 2. Adenosine is recommended for acute treatment in pregnant patients with SVT.516 See Online Data Supplement 20. When vagal maneuvers fail to terminate SVT, adenosine is a first-line drug option for pregnant patients.516 Adverse effects to the fetus would not be expected, given that it is unlikely the drug will reach the fetal circulation because of adenosine s short half-life.517 Maternal side effects, such as chest discomfort and flushing, are usually transient. The initial dose for adenosine is 6-mg rapid bolus IV. If this is ineffective, up to 2 subsequent infusions of 12 mg may be administered. 