Unusual Side Effect of Adenosine Infusion

Abstract

A 22 year old man was referred to our observation for recurrent palpitations at rest which subside after few minutes. The medical history was negative for familiar sudden death, dizziness or syncope. His body weight was 75 kg and his height was 170 cm. Physical examination revealed a blood pressure of 130/70 mmHg, clear lungs and normal heart sounds. Hematological examination, urinary analysis and thyroid function were all normal. He had no past medical history and denied taking alcohol, tobacco or any medications. Electrocardiographic (ECG) examination showed sinus rhythm of 75 beats/minute, normal atrioventricular conduction (PR: 120 ms), mild slurred QRS upstroke in leads V3-V4, no ST segment or T wave changes (Figure 1). Neither chest x-ray or color-doppler echocardiography revealed any cardiac structural or functional abnormalities. 24 hours ECG Holter monitoring and treadmill stress test did not show arrhythmias. He underwent transesophageal electrophysiological evaluation: the atrioventricular node refractory period was 240 msec. During the test it was not used any anesthesia. The patient was conscious during the entire test and its O 2 saturation, measured at pulse oximeter, was consistently 98-99%. Programmed atrial stimulation up to two extrastimuli did not induce supraventricular arrhythmias. Intravenous adenosine (12 mg) was performed for slowing of AV conduction and unmasking unapparent pathways. After a single-bolus, rapidly followed by saline flush, a sinus tachycardia at a frequency of 145 beats/min was induced. It was self-terminated in approximately 50 seconds, without change in QRS morphology (Figure 2). At the second adenosine bolus, carried out about 5 minutes later, similar effect was induced. Patient remained conscious and asymptomatic during the tachycardia. DiscussionAdenosine is an endogenous nucleoside whose actions were first investigated by Drury and Szent-Gyorgyi [1]. They described a slowing of sinus rate and a reduction of conduction through the atrioventricular node in the hearts of laboratory mammals. The adenosine test seems to have good sensitivity for unmasking pre-excitation about 76-100% in small series [2,3], because it extends the atrioventricular node refractory period favoring anterograde conduction through an accessory pathway. The electrophysiologic effects of adenosine on a specific AV bypass tract depend on the type of cell that the tract consists: nodal type cells (with decremental conduction) or atrial myocytes. In sinoatrial nodal cells, the activation of a potassium outward current results in a reduced rate of phase IV depolarization, thereby slowing sinoatrial node automaticity.In the AV node, adenosine prolongs postrepolarization refractoriness and suppresses excitability of cells in the N region of the node, resulting in AV nodal conduction block of variable degrees.Some authors reported serious adverse events related to the adenosine infusion, including supraventricular and life threatening ventricular arrhythmias [4,5]. To date, while the association betwee...