Stimulants and drugs are often associated with cardiac effects. Caffeine, a therapeutic xanthine, has been described as a sympathomimetic and has shown to have stimulatory effects on the heart. Patients with symptomatic cardiac arrhythmias are generally informed by their physician to stop or significantly reduce caffeine intake. However, in spite of numerous reports that have reviewed the cardiac effects of caffeine, it remains unclear to what extent this stimulant may be detrimental, and what subgroups of patients may be most vulnerable. The investigators propose to evaluate the effects of caffeine in patients with previously diagnosed cardiac arrhythmias. The results of our report will provide important new information for physicians and patients regarding the effects of caffeine on symptomatic cardiac arrhythmias.

Caffeine is one of the most frequently consumed pharmacologic active substances in the world. The potential effects of caffeinated beverages and chocolate on human health remains of great interest. The increased prevalence of cardiac arrhythmias in the general population has resulted in greater concern about the potential effects of caffeine on cardiac arrhythmias. Patients diagnosed with a cardiac dysrhythmia are generally informed by their physician to restrict or even abstain from caffeine, despite a lack of evidence of this causal relationship.

Although there have been numerous reports published on the effects of caffeine on human health, there have been few reports on the relation between caffeinated beverages and chocolate in different subgroups of patients with previously diagnosed cardiac arrhythmias, including supraventricular tachycardia (SVT), atrial fibrillation (AF), atrial flutter, and ventricular arrhythmias. These patients frequently undergo interventional ablation procedures, and have a potential for a recurrence of their arrhythmia. A greater knowledge of the effects of caffeine in different subgroups of patients with cardiac arrhythmias is thus essential to properly guide patients and physicians in their treatment.

The objective of our study is to evaluate the effects of caffeine through noninvasive and/or invasive means on patients with documented symptomatic cardiac arrhythmias.

One group will consist of 80 patients with Supraventricular Tachycardia (SVT): This group will undergo Invasive testing, which will be completed in the electrophysiology laboratory prior to their ablation procedure to evaluate the electrophysiologic effects of caffeine or placebo on the human heart. This testing will include a measure of the effective refractory periods, inducibility of tachyarrhythmias, and conduction intervals during programmed electrical stimulation.

The other group will consist of up to 80 patients with Atrial Fibrillation: This group will undergo non-invasive testing, consisting of two consecutive 48-hr Ambulatory monitors while they consume caffeinated or noncaffeinated products.

Inclusion Criteria:

• Age 18-80 years.

• Document cardiac arrhythmia, consisting of either:

  i. Patients with SVT: Patients with documented narrow complex tachycardia on a twelve lead ECG or on ambulatory monitoring ii. Patients with AF, paroxysmal (self-terminating AF within 7 days), documented on a twelve lead ECG or on ambulatory monitoring

Exclusion Criteria:

• Failure to provide informed consent
• Pregnancy as determined by a pre-procedure pregnancy test, or women who are breastfeeding
• Class III or IV congestive heart failure
• Myocardial infarction within the last 6 months
• Coronary stenting or cardiac surgery within the last 6 months
• History of unstable angina
• Uncontrolled hypertension
• Intolerance to caffeinated beverages or chocolate
• Dependency on medications that may severely react with caffeine: substrate for Cytochrome P450 1A2 (CYP1A2) (tizanidine), inhibit CYP1A2 (fluvoxamine, ketoconazole, and rofecoxib), induce CYP1A2 (aminoglutethimide, carbamazepine, phenobarbital, and rifampin)
• Enrolment in another study at University of Ottawa Heart Institute (UOHI), unless approved by the Human Ethics Review Board (HREB).