Effectiveness of Calcium Channel Blockers and Adenosine in the Emergency Management of SVT

Paroxysmal Supraventricular Tachycardia (SVT) is a common cardiac emergency encountered in the Emergency Department. Both Calcium Channel Blockers (CCB) and Adenosine have been using in the Management of SVT.

Objective

This study compared the efficacy and effectiveness between slow Infusion of Calcium Channel Blockers (either Verapamil or Diltiazem) and bolus intravenous Adenosine in termination of SVT.

Methodology

This was a prospective, randomised, controlled clinical trial comparing the efficacy and effects of intravenous adenosine with slow infusion of calcium channel blockers (verapamil or diltiazem) in patients presenting with SVT to an Emergency Department. The study was approved by the hospital's Ethics Committee.

Patients of at least 10 years of age, who presented to the Emergency Department of the Singapore General Hospital with regular narrow complex tachycardia and an electrocardiographic(ECG) diagnosis of SVT that was not converted by vagal manoeuvres (Valsava manoeuvre or carotid sinus massage or both) and who were in SVT at the time of doctor attendance were included in the study.

The exclusion criteria were as follows:

• Patients with signs of impaired cerebral perfusion (e.g. altered mental state) or acute pulmonary oedema
• Patients with a subsequent diagnosis of arrhythmias other than SVT (i.e. sinus tachycardia, atrial flutter, atrial fibrillation or idiopathic ventricular tachycardia) were excluded from the analysis if they were initially enrolled
• Pregnancy by history (urine pregnancy testing was not used to actively exclude the condition in any of the female patients entered into the study).

Having selected the patients according to the criteria, they were randomly assigned into two groups: one to receive calcium channel blockers and the other, Adenosine. Within the former group, some were assigned randomly to receive Diltiazem and some to Verapamil.

Diltiazem was given at the dose of 2.5mg per minute (4ml per minute of a concentration of 0.625 mg/ml) up to a maximum of 50 mg. The dose of Verapamil was 1mg per minute (4ml per minute of a concentration of 0.25mg/ml) up to a maximum of 20mg. Both were given as a slow intravenous infusion using a Terumo infusion pump.

During intravenous infusion, the patient's vital signs, viz. heart rate and systolic and diastolic blood pressures, were monitored at two-minute intervals up to completion of infusion or conversion from SVT, whichever was the earlier. At the time of conversion to sinus rhythm, the infusion was stopped and the amount of drug infused was noted and recorded.

Regarding the Adenosine group, all the patients were administered Adenosine as a rapid bolus within 2 sec through an 18G IV cannula at an antecubital vein, followed by 10 ml saline flush and elevation of the limb. Initially 6ml bolus was given rapidly, and if there was no conversion of the SVT within 2 min, another 12 mg bolus was administered.

If SVT was not converted at the end of any of calcium channel blocker infusion, those patients were then given intravenous Adenosine as described above. Similarly, those patients who remained in SVT after first two initial boluses of Adenosine were again randomized to receive either Verapamil or Diltiazem.

This allowed four orders of treatment as follows:

• Verapamil infusion followed by Adenosine
• Diltiazem infusion followed by Adenosine
• Adenosine followed by Verapamil infusion
• Adenosine followed by Diltiazem infusion

If the tachycardia was not converted at the end of the study protocol, patients were managed either with synchronised electrical cardioversion if haemodynamically unstable or with further pharmacotherapy at the discretion of the treating physician if vital signs were stable.

Following the successful conversion, patients' vital signs were closely monitored at 1 min (immediate post-conversion), 5,10, 15 min and finally 30 min of post-conversion. If they remained stable, they were shifted to observation ward with continuous telemetric monitoring. They were eventually discharged if there were no recurrence during the period of observation and arranged a follow-up appointment at Arrhythmia Clinic one week later. Patients with the recurrence of SVT during the two-hour observation period were managed at the discretion of the treating physician.

Study end points were as follows:

• Conversion to sinus rhythm
• Withdrawal because of major adverse effects
• Completion of trial protocol without termination of tachycardia

Data on the final analysis was obtained from follow-up records of Cardiology department as well. The cost of medication used for each patient was also computed to understand the cost aspects of different regimens.

Inclusion criteria

• More than 10 years old
• Electrocardiographic diagnosis of SVT
• SVT not converted by the vagal manoeuvres

Exclusion criteria

• Signs of impaired cerebral perfusion
• Signs of pulmonary oedema
• Subsequent diagnosis of other types of arrythmias rather than SVT
• pregnancy by history