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Prolonged bradyasystole and seizures following intravenous adenosine for supraventricular tachycardia

Atrioventricular-nodal-reentry tachycardia (AVNRT) is a form of supraventricular tachycardia (SVT) that is relatively common in the emergency department (ED). It is rarely indicative of underlying electrical or structural pathology.

This review evaluates the literature and controversies concerning treatment of AVNRT in the ED.

For treatment of narrow-complex tachycardia, Advanced Cardiovascular Life Support guidelines recommend the use of vagal maneuvers, followed by adenosine. Recent literature suggests that nondihydropyridine calcium channel blockers, such as verapamil and diltiazem, may be as effective as adenosine, without the negative short-term side effects. Multiple studies have demonstrated that although adenosine is rapid acting, there is no statistically significant difference in conversion rate between adenosine and calcium channel blockers. Both medications result in a conversion rate above 90%, but there are significantly more minor adverse effects, such as flushing or chest discomfort, with adenosine. Calcium channel blockers are a viable option for treatment for AVNRT, especially in refractory states. Beta-blockers have been evaluated but should not be used routinely due to lower efficacy. AVNRT is the most common tachydysrhythmia in pregnancy, and vagal maneuvers and adenosine are first line. Electrical cardioversion should be utilized for hemodynamically unstable patients. Most patients with AVNRT may be discharged with appropriate follow-up.

Several studies demonstrate that nondihydropyridine calcium channels (verapamil and diltiazem) are equally as efficacious as adenosine in converting AVNRT to sinus rhythm, without the negative (albeit short-lived) side effects. If given over 20 min, the risk for hypotension is low.

We present an unusual case of maternal death following medical treatment of paroxysmal supraventricular tachycardia (PSVT) in late gestation.

A 30-year-old woman, gravida 1, para 0, came to the outpatient clinic of our obstetrics and gynecology department at 35 weeks of gestation. She had suffered from palpitation and shortness of breath that lasted 3 days. Electrocardiographic examination revealed PSVT. Although intravenous administration of verapamil (5 mg) and adenosine (36 mg) effectively prevented the relapse of PSVT, the patient lost consciousness 30 minutes after her last dose of adenosine with sudden-onset convulsions. Despite immediate administration of advanced cardiac life support, she showed no signs of improvement and died.

PSVT in late gestation can be associated with maternal death even following conversion to sinus rhythm using medical treatment. Clinical use of adenosine for PSVT should alert the clinician to the potential risk of administering a high dose of adenosine to a pregnant woman, which can lead to maternal mortality in late gestation. Administration of a high dose of adenosine was, in our opinion, partially responsible for the maternal death and intrauterine fetal demise in this case.

Study objective: To determine the effect of the addition of adenosine, as a standing-order medication, on the prehospital management of supraventricular tachycardia (SVT) in a large urban emergency medical services (EMS) system. Design: Prospective observational case series with historical controls. Setting: Large urban municipal EMS system staffed by paramedics and emergency medical technicians trained to operate automatic or semiautomatic defibrillators (EMT-Ds). Participants: We observed a consecutive sample of prehospital patients who presented with an initial ECG rhythm of SVT, as interpreted by the treating paramedics, between July 1 and December 31, 1993. We used patients from the same 6-month period in 1992 as our control group. Indications for treatment were chest pain, evidence of myocardial ischemia, or shock. Adenosine had been introduced as a first-line medication to be used under standing orders in cases of unstable SVT before a physician was contacted for medical control options. Results: We studied 239 cases and 228 controls. Acceptable call reports with pretreatment and posttreatment ECGs were available for 140 (59%) of the study cases and 104 (46%) of the controls. The two groups were similar in terms of age, sex, and initial vital signs. In the control group, 75 patients had indications for treatment, and 16 were treated (21%). In the study group, 127 had indications for treatment and 103 (81.1%) were treated (odds ratio, 15.83; 95% confidence interval, 7.38-34.4). Conclusion: The introduction of adenosine as a standing-order medication into an urban EMS system increased the proportion of patients who received advanced life support treatment. Paramedics were able to accurately diagnose and begin treatment of SVT with adenosine without direct medical supervision. [Lozano M Jr, McIntosh BA, Giordano LM: Effect of adenosine on the management of supraventricular tachycardia by urban paramedics. Ann Emerg Med December 1995;26:691-696.]

Adenosine has become the preferred treatment for common types of supraventricular tachycardia because it is extremely effective and rarely associated with serious side effects. It has also been advocated as an intervention for diagnostic use to assess uncommon types of tachycardia. Evidence is shown in this report that adenosine was associated with dangerous worsening of arrhythmia in patients with atrial flutter. In two patients, adenosine precipitated acceleration of ventricular response, in one case necessitating emergent cardioversion. Both patients had atrial flutter with 2 to 1 atrioventricular block that evolved into 1 to 1 atrioventricular conduction. In three other patients, adenosine was associated with prolonged bradyasystole and hypotension. In each of the five patients, adenosine was given in a standard fashion (6 or 12 mg). In summary, adenosine should be recognized as a potentially dangerous intervention in patients with atrial flutter. If it is used for diagnostic purposes, resuscitative equipment should be readily available.