Imaging of adenosine bolus transit following intravenous administration: insights into antiarrhythmic efficacy

Abstract

Objective: To study the effects of the site of intravenous injection of adenosine and to assess the site of action of adenosine in the heart by correlating cardiac effects with bolus transit.

Methods: Ten patients undergoing routine technetium (Tc-99m) gated blood pool ventriculography consented to the coadministration of intravenous adenosine. The dose of adenosine required to produce heart block during sinus rhythm was determined following antecubital vein administration. This dose (6-18 mg) was mixed with Tc-99m and given first into the same antecubital vein (proximal injection) and then repeated into a hand vein (distal injection). The ECG was recorded and the transit of the bolus was imaged using a gamma camera.

Results: Heart block occurred in all 10 patients (second degree in seven, first degree in three) at (mean (SEM)) 17.5 (1.0) seconds after the proximal injection of adenosine. Distal injection produced heart block in six patients (second degree in two, first degree in four) at 21.9 (4.4) seconds (p < 0.01). In eight of 10 patients the electrophysiological effects were less with distal injection. The onset of heart block was close to the time of peak bolus Tc-99m activity in the left ventricle. Peak bolus activity was delayed (by about three seconds) and the duration of bolus activity in the left ventricle was increased with distal injection compared with proximal injection, at 17.2 (4.2) v 9.2 (3.1) seconds, p < 0.01.

Conclusions: The lesser electrophysiological effects of adenosine following distal intravenous injections were associated with delay in transit time and dispersion of the bolus. The correlation of adenosine induced heart block with bolus activity in the left heart indicated dependence on coronary arterial delivery of adenosine to the atrioventricular node.

Figure 1

Activity of adenosine/technetium-99m bolus imaged during transit from (A) left upper arm and shoulder through (B) right ventricle, (C) pulmonary artery and lungs to (D) left ventricle and aorta. The totalised image from frames captured during the transit is shown in (E) and the four regions of interest—left upper arm, left shoulder, right ventricle, and left ventricle—are shown (F).

Figure 2

Activity-time curves at the four regions of interest following (A) the proximal injection and (B) the distal injection.

Figure 3

ECG responses produced by the proximal and distal injections of adenosine.

Figure 4

ECG recordings following (A) proximal injection of adenosine, showing second degree AV block, and (B) distal injection of adenosine in the same patient, which did not produce AV block. Adenosine was given 16 seconds before beginning these recordings. Marker deflections on the tracings correspond to the patient's reporting of systemic symptoms. (Surface ECG leads II and aVF, 25 mm/s.)

Figure 5

Time to peak bolus activity (mean and standard error bars) at each of the four regions of interest for patients who had AV block with (A) the proximal injection, n = 10, and (B) the distal injection, n = 6. The mean time of AV block following each injection is indicated by the thick horizontal lines and standard errors are shown as the thin lines.

Figure 6

Time to peak bolus activity (mean and standard error bars) at each of the four regions of interest for patients who had sinus slowing with (A) the proximal injection, n = 6, and (B) the distal injection, n = 5. The mean time of sinus slowing following each injection is indicated by the thick horizontal lines and standard errors are shown as the thin lines.

Figure 7

Correlation between the duration of AV block produced by adenosine injection (proximal) and the duration of bolus activity in (A) the right ventricle and (B) the left ventricle.