Atropine

Cardiovascular

In a classic study, more than a generation ago, of patients given atropine sulfate intravenously as premedication in a total dose of 1 mg, dysrhythmias occurred in over one-third of the subjects, and in over half of those younger than 20 years.

In adults, atrioventricular dissociation was common and in children atrial rhythm disturbances [ ]. In volunteers, atropine in doses of 1.6 mg/70 kg/minute causes episodes of nodal rhythm with absent P waves on the electrocardiogram [ ]; the episodes occurred before the heart rate had increased under the influence of the drug. In healthy men being anesthetized for dental surgery a dose of only 0.4 mg atropine intravenously 5 minutes before induction caused reductions in mean arterial pressure, stroke volume, and total peripheral resistance [ ].

Second- or third-degree heart block occurred in three of 23 male heart transplant recipients given intravenous atropine [ ]. The mechanism is unknown but it appears that particular caution is needed when atropine is used in this group of patients.

The use of atropine in myocardial infarction to increase the heart rate succeeds as a rule, but in some patients with second-degree heart block the ventricular rate is slowed by atropine, resulting in bradycardia. In contrast, other patients can have tachycardia, and even ventricular fibrillation has been seen, occasionally even in doses as low as 0.5 mg [ ].

Possible precipitation of acute myocardial infarction has been discussed by two American emergency medicine specialists [ ].

• A 62-year-old woman developed chest pain and sinus bradycardia (41/minute). She had third-degree heart block and was given atropine 1 mg intravenously. Three minutes later, her chest pain increased and the electrocardiogram now showed an acute inferior myocardial infarction, confirmed by serum markers. Angioplasty recanalized the right coronary artery.

The authors discussed the possibility, suggested by others, that atropine can precipitate acute myocardial infarction in an ischemic setting. They concluded that while this may be true, on the whole the advantages of successfully correcting bradycardia outweigh the risks of this rare complication.

Respiratory

Atropine increases the rate and depth of respiration, probably as a reaction to the increase in the dead space resulting from bronchodilatation [ ].

Sensory systems

Transient central blindness has followed an intravenous injection of atropine 0.8 mg in the course of spinal anesthesia; blink reflex and pupillary response to light and accommodation were lost; vision returned slowly after some hours after the instillation of pilocarpine [ ].