Energy Drink-related Supraventricular Tachycardia

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To the Editor:

A 23-year-old woman with no medical history was brought to the hospital for palpitations and chest tightness shortly after consuming a GNC Speed Shot (GNC Corporation, Pittsburgh, Pa.) and a Mountain Dew (PepsiCo, Inc., Purchase, NY) soda drink.

On arrival, she looked anxious with a blood pressure of 120/55 mm Hg and heart rate of 219 beats/min. Physical examination and laboratory workup were unremarkable. Her electrocardiogram showed a narrow complex tachycardia with a ventricular rate of 219 beats/min (Figure). Carotid sinus massage and Valsalva maneuvers were unsuccessful in terminating the tachycardia. On administration of 6 mg of adenosine by rapid intravenous push, she converted to normal sinus rhythm.

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• Figure. 

  Twelve-lead electrocardiogram showing narrow complex tachycardia.

The patient was monitored in the emergency department for a few hours where she continued to remain asymptomatic and stable in sinus rhythm. She was discharged with advice to avoid caffeinated beverages and to follow up with the cardiology clinic as an outpatient.

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Discussion 

Many “energy drinks” contain excessive amounts of caffeine, sometimes several times the amount contained in a cup of coffee.¹ Caffeine is the natural alkaloid methylxanthine, which is 99% absorbed after oral ingestion.¹ The blood concentration peaks 1 to 1.5 hours after ingestion, with a half-life of 3 to 6 hours. Caffeine is metabolized by the P450 hepatic enzyme system.¹ At high serum levels, enzyme saturation occurs and elimination follows zero-order kinetics, with constant elimination regardless of serum level.¹ Caffeine increases intracellular calcium concentrations, causes noradrenaline release, and sensitizes dopamine receptors.¹ This effect causes cardiac stimulation resulting in supraventricular or ventricular tachyarrhythmias, especially with high doses.¹

The abrupt termination of this patient’s narrow complex tachycardia with adenosine narrows the differential diagnosis to atrioventricular nodal reentry tachycardia, atrioventricular reentry tachycardia, and atrial tachycardia.²

Atrioventricular nodal reentry tachycardia is the most common form of supraventricular tachycardia.² It is related to dual pathways within the atrioventricular node or close to the atrioventricular node with differential conducting properties.², ³ It is usually initiated by a premature supraventricular beat that arrives at the atrioventricular node when the fast pathway is still refractory.² It then conducts antegradely through the slow pathway and retrogradely through the fast pathway and establishes a reentry circuit that maintains the arrhythmia.² Caffeine likely precipitates this type of tachycardia by its cardiac stimulation effect causing premature atrial contractions that result in the initiation of the reentry circuit, which can commonly be terminated by adenosine.²

In this patient, atrioventricular reentry tachycardia resulting from an accessory pathway between the atria and ventricle cannot be excluded with the electrocardiogram alone because a concealed accessory pathway will still result in a normal electrocardiogram in sinus rhythm.² Atrioventricular reentry tachycardia has a mechanism of onset and termination with adenosine similar to atrioventricular nodal reentry tachycardia, except for the location of the pathways involved in the reentry circuit.² Although atrial tachycardia also can be precipitated by caffeine, the typical features of atrial tachycardia, such as p waves with a morphology similar to or different from the sinus p wave and a PR interval similar to sinus rhythm, were not seen in this patient.

The manufacturers of GNC Speed Shot specifically warn against the concomitant use of this product with other caffeine-containing products, including sodas and coffee.⁴ They also suggest that people who are naïve to the drink try half a bottle instead of a whole bottle.⁴ Our patient was not a regular user of GNC Speed Shot and ended up consuming both the energy drink and the soda Mountain Dew, which also contains caffeine, a combination that most likely precipitated the arrhythmia. It is important for the public to be more aware of the potential adverse effects of these energy drinks, alone or in combination with other caffeine-containing products, because fatal and serious events have been reported.¹

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References 

1. Cannon ME, Cooke CT, McCarthy JS. Caffeine-induced cardiac arrhythmia: an unrecognised danger of healthfood products. Med J Aust. 2001;174:520–521
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2. Delacrétaz E. Supraventricular tachycardia. N Engl J Med. 2006;354:1039–1051
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3. Denes P, Wu D, Dhingra RC, et al. Demonstration of dual AV nodal pathways in patients with supraventricular tachycardia. Circulation. 1973;48:549–555
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4. GNC Speed Shot product information. http://www.gnc.com/sm-american-body-building-speed-shot-orange-ice–pi-2508099.html2007;Accessed October 8
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