Clinical paperSlow infusion of calcium channel blockers compared with intravenous adenosine in the emergency treatment of supraventricular tachycardia*
Introduction
Paroxysmal supraventricular tachycardia (SVT) is a common cardiac emergency presenting to the Emergency Department (ED). Since the 1970s intravenous verapamil has been the drug of choice1, 2 for the treatment of SVT. The 1986 American Heart Association guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Care recommended that verapamil be given as a 2.5–5 mg intravenous bolus over 2 min and 5–10 mg over 2 min to be given after 15–30 min of the first dose if the SVT persisted3 or recurred and if blood pressure remains acceptable. For the 1992 American Heart Association Guidelines, adenosine was recommended as the initial drug of choice for haemodynamically stable paroxysmal SVT. The sequence of agents recommended was adenosine twice (6 mg followed by 12 mg). If the blood pressure had not dropped and the SVT persisted up to two doses of verapamil (2.5–5 mg) intravenous over 2 min followed by 5–10 mg over 2 min could be given. When treating the elderly or when blood pressures were within the lower range of normal, smaller doses (2–4 mg) of verapamil over a longer period (3–4 min) were recommended for the first dose.4 The main reason given for adenosine as the first choice drug was that adenosine does not cause hypotension to the same degree as verapamil because adenosine has a very short half-life (<10 s).
A previous randomized controlled trial (161 patients) by our group compared intravenous verapamil and intravenous diltiazem5 given as slow infusions (verapamil at a rate of 1 mg per minute and diltiazem at a rate of 2.5 mg per minute). This showed a conversion rate of more than 97% with only one patient (1%) developing hypotension. This finding suggests that the haemodynamic instability previously attributed to verapamil may be related to the speed of verapamil administration.
There are few studies directly comparing the effectiveness of adenosine and calcium channel blockers. Most of these studies recruited subjects with laboratory-induced SVT.6, 7, 8 In addition, they used a rapid bolus of intravenous calcium channel blocker given over 15 s (except for the study by Hood and Smith).7 These studies generally conclude that adenosine and verapamil are both highly effective in the termination of SVT.
There has been no previous large prospective, randomized controlled trial comparing the usefulness of intravenous adenosine vs. slow-infusion calcium channel blockers in a clinical patient-care environment. The aim of this study was to compare the efficacy and safety of bolus intravenous adenosine with the slow infusion of verapamil or diltiazem, in the termination of spontaneous SVT in the ED.
Section snippets
Methods
This was a prospective, randomized, controlled clinical trial in patients presenting with SVT to an ED. The study was approved by the hospital Ethics Committee.
Results
From 1st January 1997 to 31st March 1999, over a 27-month period, a total of 236 patients with regular narrow complex tachycardia not converted by vagal maneuvers were treated by, the Singapore General Hospital ED. Of these, none were pregnant by clinical history, and 3 had signs of impaired cerebral perfusion or heart failure. All three had concomitant medical problems and all were converted with 6 mg IV bolus of adenosine. The remaining 233 patients were enrolled into the trial.
Twenty-seven
Discussion
Verapamil, diltiazem and adenosine compounds exert their maximum effect on the AV node by lengthening intranodal conduction time significantly.10, 11 The effect of calcium channel blockers on paroxysmal SVT has been best studied with verapamil. Early studies suggest that adequate dosage of verapamil resulting in an initial plasma concentration exceeding 72 ng/ml is needed to effect conversion.12 These concentrations were then achieved by giving bolus doses of verapamil at 0.075–0.15 mg/kg body
Conclusion
Calcium channel blockers administered as a slow infusion offer an alternative to adenosine in the emergency treatment of stable SVT patients. In our study slow calcium channel blocker infusions were more effective than bolus IV adenosine 6 mg followed by 12 mg in converting stable spontaneous SVT. Calcium channel blockers are safe and affordable for healthcare systems where the availability of adenosine is limited.
Conflict of interest statement
We hereby declare that there is no conflict of interest in conducting this randomized clinical trial.
Acknowledgement
We wish to acknowledge the Department of Clinical Research, Singapore General Hospital for funding of adenosine and diltiazem.
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2009.01.017.