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An Unusual ECG Finding during Adenosine Stress Myocardial Perfusion Imaging
Address for correspondence: Dr. Harpreet Singh, Department of Nuclear Medicine, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012, India. E-mail: harpreetsinghgem@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Wolters Kluwer - Medknow and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Adenosine is extensively utilized in myocardial stress perfusion imaging for the detection and risk stratification of coronary artery disease. It has a well-established safety profile. The majority of the undesirable effects experienced during adenosine infusion are transient (owing to its brief half-life of ~10 s) and arise from the stimulation of receptors in the atrio-ventricular (AV) node (AV block) and bronchial smooth muscles (bronchospasm). We hereby report an unusual electrocardiographic finding during adenosine stress perfusion imaging, in a patient who had previously undergone single chamber pacemaker insertion and was referred for the assessment of atypical chest pain.
Keywords
Adenosine
myocardial perfusion imaging
sinus arrest
Case Summary
A 68-year-old female presented to the cardiology department with complaints of chest discomfort for the past 1 month. The episodes were unrelated to exertion and lasted less than a minute. Apart from hypertension, the patient did not have any other risk factors for coronary artery disease. She had previously been diagnosed with infra-Hisian/mobitz II AV block and had a permanent pacemaker implanted as a treatment a year ago. All of her laboratory tests, including hemogram, serum electrolytes, liver, renal, and thyroid function tests, yielded normal results. The transthoracic echocardiogram showed no significant abnormalities, except for concentric left ventricular (LV) hypertrophy and an ejection fraction of 55%–60%.
The patient was referred for adenosine stress myocardial perfusion imaging (MPI) for assessment of inducible ischemia. A standard 6-min adenosine protocol was followed with continuous adenosine infusion at the rate of 140 μg/kg/min and radiotracer (99mTc-sestamibi) injection at 3 min. Her baseline electrocardiographic (ECG) showed some abnormal findings [Figure 1]. The baseline blood pressure (BP) was 150/76 mmHg. During the adenosine infusion, the patient reported flushing and an increase in heart rate (91 bpm); however, her BP remained stable at 150/70 mmHg. At the conclusion of the 4th min of adenosine infusion, the patient began to experience intense chest discomfort. Simultaneously, notable ECG changes were observed [Figure 2]. The adenosine infusion was promptly terminated. The chest discomfort improved gradually with a return to baseline ECG rhythm within 30 s of discontinuing the adenosine infusion. The patient remained conscious throughout the study.
Questions
Discussion
Adenosine-induced sinus arrest was the cause of the paced ventricular rhythm. The patient underwent a single chamber (ventricular) pacemaker insertion with VVIR pacing mode. VVIR is the generic code for pacemaker mode where the first 2 letters indicate the paced and sensed area, which in this case was the ventricle. The letter “I” represents the inhibitory response of the pacemaker to sensing intrinsic activity, whereas “R” signifies rate responsiveness, meaning that the pacing rate depends on the patient’s intrinsic electrical activity (R wave) detected by the sensor. When the pacemaker detects the patient’s spontaneous intrinsic electrical activity (R wave), it refrains from pacing (inhibitory response). Therefore, pacing only occurred during the bradycardia episode when the ventricular rate dropped below the base rate of the pacemaker (60 ppm).
Learning point
Although rare, sinus arrest has been reported in patients undergoing adenosine stress MPI.[1] However, most of the reported cases had either an underlying liver and/or renal failure or sinus node disease[23]
The present case highlights the need to be acquainted with the complete ECG profile of adenosine and the importance of continuous ECG/patient monitoring during adenosine stress in preventing potentially serious complications.
Patient outcome
The patient remained stable throughout the study. Poststress MPI images acquired 60 min after intravenous administration of 99mTc-sestamibi revealed normal perfusion in all the segments of the LV myocardium [Figure 3]. Since the present case’s renal and liver function tests were normal, the patient may likely have an underlying occult sinoatrial disease for which she has been advised further evaluation.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Conflicts of interest
There are no conflicts of interest.
Nil.
References
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