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We tested the hypothesis that visualisation of defects on thallium-201 (201Tl) myocardial perfusion images (MPI) depends on the duration of the ischaemic state between 201Tl injection and the time of reperfusion of an occluded coronary artery. Praecordial imaging with a gamma camera was performed in 24 anaesthetised, open-chest dogs with transient coronary occlusion. Results indicated that if the duration of the ischaemic state after 201Tl injection was less than 3 min before reperfusion, then the MPI 5 to 15 min after 201Tl injection was falsely negative (201Tl activity in zone (IZ)/normal zone (NZ)greater than 0.85). Dogs which were ischaemic more than 5 min always had MPI defects 5 to 15 min after 201Tl injection (IZ/NZ201Tl ratio less than 0.85). MPI results (201Tl IZ/NZ) 15 min after 201Tl injection were determined by the duration of the ischaemic state after 201Tl injection (r = -0.86) because prolonged ischaemia allowed 201Tl to distribute from blood to myocardium before reperfusion: 201Tl (IZ/NZ( = 0.356 +/- 1.00 (fraction of total 201Tl remaining in blood at the end of the ischaemic state), r = 0.94.

Timing abnormalities of myocardial contractility may occur as inter- or intraventricular asynchrony. Gated blood pool scintigraphy was performed on 21 patients with a normal ejection fraction and the following electrocardiograms: six normal, six with left bundle branch block, four with right bundle branch block and five with right ventricular pacemaker rhythm. A phase and amplitude of the first harmonic of the Fourier transform was obtained for each pixel, and left and right ventricles were trisected. A mean vector phase for each region was obtained by vector summation. Regional and global values were analyzed within each group and compared with normal values.The phase differences between the entire left and right ventricles (mean ± standard deviation) were: 9 ± 3 in the normal patients, 38 ± 8 (p < 0.01) in patients with left bundle branch block, - 6 ± 7 (p < 0.05) in patients with right bundle branch block and 15 ± 9 (difference not significant) in patients with pacemaker rhythm. The phase differences between left ventricular posterolateral and septal regions were - 4 ± 2 in the normal patients, 10 ± 5 (p < 0.01) in patients with left bundle branch block, - 7 ± 10 (p < 0.05) in patients with right bundle branch block and 10 ± 5 (p < 0.01) in patients with pacemaker rhythm. Within the right ventricle, phase differences between the apical and septal segments were 14 ± 9 in the normal patients, 14 ± 10 (NS) in patients with left bundle branch block, -2 ± 3 (p < 0.01) in patients with right bundle branch block and - 22 ± 18 (p < 0.01) in patients with pacemaker rhythm.Interventricular phase differences were greatest in patients with left bundle branch block and absent or reversed in right bundle branch block. Intraventricular asynchrony occurred in the left ventricle in patients with left bundle branch block, right bundle branch block and pacemaker rhythm, while right intraventricular asynchrony occurred only in patients with right bundle branch block and pacemaker rhythm. Regional vector summation permits quantification of asynchrony within, as well as between, the right and left ventricles.

A comparison of left ventricular function data derived from a low cost, portable electrocardiographic gated scintillation probe (nuclear stethoscope) with conventional scintiangiographic data was performed in 68 patients. Ejection fraction correlation (r = 0.86, p less than 0.005) was better in patients with uniform wall motion than in those with regional asynergy (r = 0.68 p less than 0.01). Probe variables reflecting systolic emptying rates, diastolic filling rates and timing intervals, and relative volumes analyzed in combination provided 100 percent sensitivity, specificity, and predictive value in detecting abnormal left ventricular performance. The results suggest that radionuclide angiography with an electrocardiographic gated scintillation probe is a sensitive, rapid and relatively inexpensive portable method of screening for cardiac dysfunction with a yield similar to that from the more costly gamma camera derived scintiangiogram.