Craig Asher, MD

In Reply: We appreciate the interest and comments of Dr. Alraies. We would like to clarify that the patient’s baseline electrocardiogram before the nuclear stress test was normal. Second-degree atrioventricular (AV) block (Mobitz type I) was evident only during adenosine infusion before ventricular asystole. The patient was on two AV nodal blockers (labetalol and clonidine) but had no underlying conduction disease. There is no contraindication to continuing these agents before pharmacologic stress testing. In addition, the patient’s electrolyte levels were within normal ranges before testing.

We agree that the valuable teaching point for clinicians is to appreciate the contraindication to and consequences of the use of dipyridamole-containing oral medications and either adenosine or regadenoson during pharmacologic stress testing. As Dr. Alraies points out, most cardiologists may be familiar with this interaction, but a large proportion of stress tests are ordered by emergency room physicians, internists, and hospitalists who are not. Still, the overall incidence of side effects with pharmacologic stress testing is very low and comparable to that with exercise testing, with safety enhanced by following the American Society of Nuclear Cardiology (ASNC) guidelines for performing stress myocardial perfusion imaging.¹ Avoidance of this interaction may be enhanced through education, but also by using checklists and building notifications into the electronic medical record when ordering pharmacologic stress testing. Of note, according to the ASNC guidelines, the use of intravenous dipyridamole as a stress agent is a safe alternative for pharmacologic stress testing in patients taking oral dipyridamole-containing medications.

In Reply: We appreciate the interest and comments of Dr. Alraies. We would like to clarify that the patient’s baseline electrocardiogram before the nuclear stress test was normal. Second-degree atrioventricular (AV) block (Mobitz type I) was evident only during adenosine infusion before ventricular asystole. The patient was on two AV nodal blockers (labetalol and clonidine) but had no underlying conduction disease. There is no contraindication to continuing these agents before pharmacologic stress testing. In addition, the patient’s electrolyte levels were within normal ranges before testing.

We agree that the valuable teaching point for clinicians is to appreciate the contraindication to and consequences of the use of dipyridamole-containing oral medications and either adenosine or regadenoson during pharmacologic stress testing. As Dr. Alraies points out, most cardiologists may be familiar with this interaction, but a large proportion of stress tests are ordered by emergency room physicians, internists, and hospitalists who are not. Still, the overall incidence of side effects with pharmacologic stress testing is very low and comparable to that with exercise testing, with safety enhanced by following the American Society of Nuclear Cardiology (ASNC) guidelines for performing stress myocardial perfusion imaging.¹ Avoidance of this interaction may be enhanced through education, but also by using checklists and building notifications into the electronic medical record when ordering pharmacologic stress testing. Of note, according to the ASNC guidelines, the use of intravenous dipyridamole as a stress agent is a safe alternative for pharmacologic stress testing in patients taking oral dipyridamole-containing medications.

In Reply: We appreciate the interest and comments of Dr. Alraies. We would like to clarify that the patient’s baseline electrocardiogram before the nuclear stress test was normal. Second-degree atrioventricular (AV) block (Mobitz type I) was evident only during adenosine infusion before ventricular asystole. The patient was on two AV nodal blockers (labetalol and clonidine) but had no underlying conduction disease. There is no contraindication to continuing these agents before pharmacologic stress testing. In addition, the patient’s electrolyte levels were within normal ranges before testing.

We agree that the valuable teaching point for clinicians is to appreciate the contraindication to and consequences of the use of dipyridamole-containing oral medications and either adenosine or regadenoson during pharmacologic stress testing. As Dr. Alraies points out, most cardiologists may be familiar with this interaction, but a large proportion of stress tests are ordered by emergency room physicians, internists, and hospitalists who are not. Still, the overall incidence of side effects with pharmacologic stress testing is very low and comparable to that with exercise testing, with safety enhanced by following the American Society of Nuclear Cardiology (ASNC) guidelines for performing stress myocardial perfusion imaging.¹ Avoidance of this interaction may be enhanced through education, but also by using checklists and building notifications into the electronic medical record when ordering pharmacologic stress testing. Of note, according to the ASNC guidelines, the use of intravenous dipyridamole as a stress agent is a safe alternative for pharmacologic stress testing in patients taking oral dipyridamole-containing medications.