The goal of this randomized double blind controlled trial is to learn about the effects of calcium when it is given prior to diltiazem for patients with atrial fibrillation ( a type of irregular heart beat) who have rapid ventricular response ( a pulse over 100 beats per minute). Normally diltiazem 0.25mg/kg (max 20mg) is given to slow the heart rate. We will give Placebo versus Calcium Gluconate 2gm given prior to diltiazem.

The main questions it aims to answer are:

• Does calcium decrease the incidence of low blood pressure (a side effect of diltiazem)?
• How does calcium effect the action of diltiazem? Does it interfere with the desired decrease in heart rate?

Participants will receive either placebo or calcium immediately prior to the administration of diltiazem. Their blood pressure and pulse will be measured:

• prior to study drug administration
• post study drug and prior to diltiazem administration
• 3 minutes post start of diltiazem
• 5 minutes post start of diltiazem
• 10 minutes post start of diltiazem
• 20 minutes post start of diltiazem
• 30 minutes post start of diltiazem

Researchers will compare the placebo group to the calcium group to see if there is a difference in the blood pressure and pulse.

Diltiazem, a calcium channel blocker is the standard of care for treatment of stable patients with atrial fibrillation and rapid ventricular response. Many emergency physicians opine that calcium, the "antidote" for calcium channel blockers, when given prior to diltiazem administration, mitigates the common adverse effect of hypotension.

In order to obtain evidence related to this belief, we will study the effects of placebo (normal saline 50ml) versus calcium gluconate (2 grams in normal saline 50ml). Hemodynamically stable patients in afib with rvr will be identified on their arrival to the emergency department. Those who consent to the study will be enrolled and the pharmacy will be contacted to provide a blinded study sample to the patient's bedside. After initial vital signs are recorded the study sample will be infused via pump over a 10 minute period. Vitals will be recorded on its completion and a diltiazem bolus (0.25mg/kg, max 20mg) will be administered. Vitals will be recorded at 3, 5, 10, 20 and 30 minutes post start of diltiazem bolus.

The primary outcome of hypotension will be calculated using rates (frequencies). The rate of hypotension will be compared between the two groups using Chi square analysis. The groups will be compared for similarity using means(sd) and frequencies(percentages). Any variables that differ by group will be controlled for with a multiple logistic regression analysis.

A 35% rate of hypotension is estimated for the placebo group and a hypothesized 22% in the treatment group (a relative 37% decrease). This will require a minimum total sample size of 378 (184/ group) . We may terminate the study earlier if we achieve power.

Inclusion Criteria: Diagnosis of atrial fibrillation with rapid ventricular response (ventricular rate over 100 bpm) due to an electrophysiologic etiology.

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Exclusion Criteria:

1. Unstable, requiring electric cardioversion -hypotensive

   • altered mental status
   • myocardial infarction
   • pulmonary hypertension

2. Patients at risk of hypercalcemia - renal failure

3. Know cardiac valvular disease

4. Allergic to calcium gluconate or diltiazem

5. Underlying cardiac disease - sick sinus syndrome

   • 2nd/3rd degree atrial ventricular block
   • cardiogenic shock
   • recent IV beta blocker administration
   • accession bypass tract (WPW, short PR)

Each formulation is masked by the pharmacy department.