Pharmacological stress myocardial perfusion scintigraphy: use of a modified adenosine protocol in patients with asthma

Abstract

Stress radionuclide myocardial perfusion scintigraphy (MPS) using adenosine pharmacological vasodilatation is the preferred method in many centres because of its convenience, safety and speed. It can, however, cause bronchospasm and hence its use is avoided in patients with known or suspected bronchospasm. Owing to service pressures, we use technologist-led adenosine stressing for patients referred for MPS studies. We use a modified adenosine infusion protocol under medical supervision for patients with asthma to prevent and minimize adenosine-induced bronchospasm. In this study, we audited our use of this modified protocol in asthmatic patients and compared the side-effect profile with the standard adenosine protocol used in nonasthmatic patients. We audited 50 consecutive patients with asthma attending our department for stress MPS. All patients were taking regular inhalers+/-oral steroids. Patients who had exacerbation of asthma requiring hospital admission during the preceding 6 months were excluded. Before commencing the infusion, two inhaled puffs of salbutamol were administered. A modified adenosine infusion protocol was used, starting initially at a rate of 70 microg/kg/min and increasing to the standard 140 microg/kg/min within 1 min and then maintained for a further 5 min. Technetium-99m tetrofosmin was injected at 3 min. Blood pressure (BP), pulse rate (PR), oxygen saturation and ECG were monitored before, during and at the end of the infusion. All side effects were recorded. Fifty-eight consecutive patients without asthma were included as controls and received the standard 140 microg/kg/min infusion over 6 min. One hundred and eight patients, 50 with asthma and 58 without asthma, were entered into the study. The test was stopped early in two patients (4%) with asthma and 11 patients (19%) without asthma (chi=5.679; P=0.017). Proportionally, more nonasthmatics developed shortness of breath (SOB) (47 of 58, 81% without asthma vs. 35 of 50, 70% with asthma); however, this did not reach statistical significance (chi=1.788, P=NS). Three out of 50 (6%) patients in the asthma group experienced severe SOB but only one of those 50 patients (2%) developed bronchospasm, manifesting as wheeze. In the nonasthma group, five of 58 patients (8.6%) experienced severe SOB but none developed a wheeze. Less flushing (16 of 50, 32% vs. 36 of 58, 62%; P=0.002), dizziness (12 of 50, 24% vs. 26 of 58, 45%; P=0.023) and neck/throat pain (5 of 50, 10% vs. 16 of 58, 28%; P=0.021) was observed in the modified infusion group with asthma compared with the standard infusion group without asthma. Statistical significance was observed in these three side effects. No significant difference in other side effects was noted. A similar decrease in mean diastolic BP, and an increase in mean PR were observed during the infusion in both asthmatic and nonasthmatic groups. The mean systolic BP decreased significantly in nonasthmatic patients (P<0.001) but not in the asthmatic group. No significant change in oxygen saturation was seen during infusion in the asthmatic group. The modified adenosine infusion protocol with salbutamol premedication can be used in patients with asthma. This protocol resulted in fewer side effects and changes in BP and PR in asthmatic patients compared with nonasthmatic patients who received the standard adenosine infusion.