Atrioventricular block during adenosine thallium imaging

Intravenous adenosine and lidocaine in patients with acute myocardial infarction

OBJECTIVES

A pilot study was designed to assess the safety of combined intravenous adenosine and lidocaine in patients with acute myocardial infarction and to estimate the likelihood of a beneficial effect on final infarct size.

BACKGROUND

Adenosine plus lidocaine reduces infarct size in animals, but the safety and efficacy in human beings is unknown.

METHODS AND RESULTS

Adenosine (70 microg/kg per minute intravenous infusion) plus lidocaine (1 mg/kg intravenous bolus injection and 2 mg/kg per minute infusion) was given to 45 patients with acute myocardial infarction. Patients underwent immediate balloon angioplasty without preceding thrombolytic therapy. Myocardial perfusion defects were measured with serial technetium 99m sestamibi studies. One patient developed persisting hypotension in conjunction with a large inferolateral myocardial infarction. Transient hypotension in three other patients resolved with a reduction in adenosine. Advanced atrioventricular block was never observed. Other adverse events (including atrial fibrillation, ventricular tachyarrhythmia, bradycardia, and respiratory distress) occurred at low frequencies, as expected for patients with acute myocardial infarction. An initial median perfusion defect of 45% of the left ventricle (60% for anterior infarction, 17% for nonanterior infarction) was observed. At hospital discharge (mean +/- SD = 4.3 +/- 2.1 days) the median value was 12%, and at 8 +/- 4 weeks it was 3% (7% for anterior infarction, 0% for nonanterior infarction); 14 patients had no measurable follow-up. Compared with historical control patients, prehospital discharge measurements were not different but late perfusion defects were improved.

CONCLUSIONS

Treatment with intravenous adenosine and lidocaine during acute myocardial infarction has sufficient safety and potential for improved myocardial salvage. Randomized studies are justified.

Thallium-201 myocardial tomography with intravenous infusion of adenosine triphosphate in diagnosis of coronary artery disease

OBJECTIVES

The purpose of this study was to evaluate the feasibility, safety and diagnostic accuracy of thallium-201 myocardial tomography with intravenous adenosine triphosphate (ATP) infusion in patients with suspected coronary artery disease.

BACKGROUND

Both ATP and adenosine are potent coronary vasodilators with a very short half-life. Several studies have confirmed that the diagnostic accuracy of adenosine thallium-201 scintigraphy is comparable to that with exercise. However, a high incidence of side effects, including atrioventricular (AV) block, has also been reported. Because the appropriate infusion rate for ATP has not yet been determined, this agent has not been tested in combination with myocardial scintigraphy.

METHODS

The study group included 253 consecutive patients who underwent thallium-201 myocardial tomography with ATP infusion (0.16 mg/kg body weight per min for 5 min). The occurrence of adverse effects was carefully monitored. Of the 120 patients with coronary angiography, 76 had significant coronary artery disease. Tomographic images were assessed visually and by computer-quantified polar maps, and they were compared with the results of coronary angiography.

RESULTS

Although 56% of the patients had some adverse effects, they were transient and mild. In all patients, the ATP infusion protocol could be completed, and no patient required aminophylline; AV block occurred in only 2% of the patients. The sensitivity and specificity were 88% and 80%, respectively, by visual analysis and 91% and 86%, respectively, by computer quantification.

CONCLUSIONS

Thallium tomography with ATP is feasible and has a diagnostic value similar to that with adenosine for detecting coronary artery disease. In addition, it may have fewer side effects than adenosine myocardial tomography.

Adenosine combined with dynamic exercise for myocardial perfusion imaging

OBJECTIVES

This study investigated whether combining exercise with adenosine would reduce the adverse effects of adenosine vasodilation.

BACKGROUND

Adenosine vasodilation is effective for perfusion imaging but causes frequent unpleasant noncardiac adverse effects, high noncardiac tracer uptake and occasional arrhythmias.

METHODS

Of 500 consecutive patients referred for thallium-201 myocardial perfusion imaging, 407 were randomized to three study groups: 6 min of adenosine infusion alone; 6 min of adenosine with submaximal exercise; or symptom-limited exercise with continuous adenosine. Minimal detectable differences are presented; a significance level of 0.05 with a power of 80% is assumed.

RESULTS

There was no difference among the three groups in sensitivity and specificity (overall 96% and 78%, minimal detectable differences 5.5% and 11%, respectively) for detection of coronary artery disease or stenosis in individual coronary arteries. There was a trend toward improved sensitivity in the combined exercise groups compared with that in the adenosine-only group (98% vs. 93%, p = 0.07, minimal detectable difference 6%). Noncardiac side effects were reduced by 43% in the exercise groups (p < 0.0001), and major arrhythmias were reduced by 90% (p < 0.0001). There was no effect on minor arrhythmias (25% vs. 22%, p = 0.6, minimal detectable difference 12%). The heart/background ratios were higher in the exercise groups (all p < 0.02). Each ratio was correlated with the exercise level achieved (all p < 0.001). The reversibility score increased with exercise (p = 0.04), as did the number of patients and segments with reversible defects (both p = 0.03).

CONCLUSIONS

Combining exercise with adenosine infusion reduced the noncardiac side effects of vasodilation and major arrhythmias while improving redistribution and heart/background ratios. These findings may be clinically important. Although maximal exercise with adenosine infusion produced optimal results, the improvement over the submaximal exercise protocol was minor, and this has the advantage of being simple and achievable within the normal 6-min duration of the adenosine infusion.

Safety of single-site adenosine thallium-201 scintigraphy

The diagnostic accuracy, safety and tolerance of adenosine thallium scintigraphy have been reported using a 2-site intravenous infusion with either a titrated or fixed-dose protocol. A single-site infusion would considerably simplify the test procedure, but its safety must be established before it can be recommended. Accordingly, 400 consecutive patients who had adenosine and thallium-201 administered through the same intravenous line were classified into 2 groups. Group I (n = 201) patients received a 7-minute titrated intravenous infusion of adenosine, with an initial dose of 50 micrograms/kg/min that increased at 1-minute intervals to a maximum of 140 micrograms/kg/min. Group II (n = 199) patients received a fixed dose of adenosine at 140 micrograms/kg/min for 6 minutes. Adenosine significantly (p < 0.001) increased heart rate and decreased systolic blood pressure by similar amounts in both groups. Adverse effects occurred more often (88 vs 71%, p < 0.001) and started earlier (2.8 vs 3.6 minutes, p < 0.001) in group II. There was no significant difference in the occurrence of second- and third-degree atrioventricular block between the 2 groups (4.0 vs 5.0%); however, chest pain, flushing and nausea were all more frequent in group II. Severe side effects were seldom seen in either group and occurred in 9 group I and 8 group II patients. Scintigraphic findings were similar in both groups. Transient perfusion defects were seen more often in patients with than without second- or third-degree atrioventricular block (42 vs 21%, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic stress testing: mechanism of action, hemodynamic responses, and results in detection of coronary artery disease

Pharmacologic stress testing may be used in the diagnosis of coronary artery disease and risk assessment. The stress agents may be divided into those that produce primary coronary vasodilation (dipyridamole, adenosine, or adenosine triphosphate) and those that produce secondary vasodilation as a result of increase in myocardial oxygen demand (dobutamine and arbutamine). Assessment of myocardial perfusion and function can be made by single-photon imaging, positron emission tomography, two-dimensional echocardiography, magnetic resonance imaging, and contrast angiography. For assessment of myocardial perfusion, either thallium 201-labeled or technetium-labeled perfusion imaging agents may be used. This article will focus on the mechanisms of action, hemodynamic responses, and results of pharmacologic imaging in detecting coronary artery disease. The use of pharmacologic stress testing in risk assessment will be discussed in a separate article.

Side effects during adenosine thallium imaging with single-port or double-port infusion protocols

The double-port infusion protocol during adenosine thallium imaging involves the use of two infusion systems, one for adenosine and one for thallium. The single-port infusion protocol, on the other hand, uses one infusion system; both adenosine and thallium are injected via a "Y" connection. This study examined the possibility that the single infusion system, by displacing a column of blood filled with adenosine, may be responsible for a greater incidence of side effects. In a parallel study, 140 patients underwent adenosine thallium imaging with the single-port system (group 1) and 140 patients underwent imaging with the double-port system (group 2). Both groups were comparable in age (67 +/- 10 years vs 64 +/- 11 years), gender (men comprised 56% of patients in group 1 and 64% in group 2), resting heart rate, and systolic blood pressure. More patients in group 1 had chest pains (57% vs 44%; p = 0.03), ST-segment depression (25% vs 9%; p = 0.005), nausea (11% vs 4%; p = 0.04), and second- or third-degree atrioventricular block (11% vs 5%; p less than 0.08) than did patients in group 2. The other side effects were similar, and peak heart rate and peak systolic blood pressure were also similar. The thallium images that used single-photon emission computed tomography were abnormal in 61% of patients in group 1 and in 65% of patients in group 2 (p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)