Exercise myocardial perfusion scintigraphy with technetium-99m methoxy isobutylisonitrile: a comparative study with thallium-201.

The evaluation of technetium-99m methoxy isobutylisonitrile for the diagnosis of coronary artery disease requires comparative validation against thallium-201, the established perfusion imaging agent. We have compared myocardial and lung uptake of both radiotracers following maximal exercise in 52 patients: 40 with angiographically proven coronary disease. Qualitative and quantitative image analysis showed the diagnostic sensitivity of technetium-99m methoxy isobutylisonitrile to compare favourably with that of thallium-201 as reflected by the mean number of ischaemic segments identified: 5.6 +/- 2.5 vs 4.8 +/- 2.1 by qualitative analysis, and 5.7 +/- 3.2 vs 5.0 +/- 2.6 segments by quantitative analysis. More reversibly ischaemic segments per patient were identified with technetium-99m methoxy isobutylisonitrile than with thallium-201: 3.6 +/- 2.3 vs 1.8 +/- 1.9. There was a higher exercise myocardial to background count ratio with technetium-99m methoxy isobutylisonitrile: 3.16:1 vs 2.58:1, and the mean exercise lung uptake normalised to left ventricular uptake ('lung index'), was lower for technetium-99m methoxy isobutylisonitrile than for thallium-201 (36 +/- 8% vs 40 +/- 10%). Five of the six patients with abnormal elevation of the thallium-201 exercise lung index also had elevation of the technetium-99m methoxy isobutylisonitrile exercise lung index, and all had extensive coronary artery disease. These results indicate that technetium-99m methoxy isobutylisonitrile is at least as effective as thallium-201 for detecting exercise induced myocardial ischaemia. However, technetium-99m methoxy isobutylisonitrile provides a better image quality and may be a more sensitive marker of defect reversibility. For both radiotracers lung uptake is increased with extensive coronary artery disease and measurement of this variable provides prognostic information.

The localization of myocardial ischaemia with technetium-99m methoxy isobutyl isonitrile and single photon emission computed tomography.

Thirty-two patients with suspected coronary artery disease were studied by single photon emission computed tomography (SPECT) imaging with oblique reconstructions of the myocardium following the intravenous administration of technetium-99m methoxy isobutyl isonitrile at peak exercise. All patients also underwent three-vessel coronary angiography. The SPECT technique produced very detailed images allowing easy delineation of localized myocardial defects. Segmental myocardial uptake defects were compared with diseased vessels as shown at angiography. A good correlation was shown between right coronary artery (RCA) disease and mid and proximal inferior segments and between left circumflex (LCx) artery disease and mid and proximal lateral segments, allowing accurate localization of a defect to one of these two vessels' territories. Sensitivity and specificity of detection of disease of the RCA and LCx artery were high. Defects associated with a lesion of the left anterior descending vessel were more variable.

Coronary angioplasty and left ventricular function in single vessel coronary artery disease.

Left ventricular function was investigated in 86 patients with single vessel coronary artery disease before and three to six months after successful angioplasty. Before angioplasty thallium-201 perfusion scintigraphy and technetium-99m gated equilibrium ventriculography in most patients showed that stress testing (exercise and ice water stimulation and isometric handgrip respectively) induced myocardial perfusion defects that were associated with a mean (SD) drop in left ventricular ejection fraction from 64 (6)% to 56 (7)%. After angioplasty there was residual coronary stenosis of less than or equal to 20% of the diameter of the vessel in 78 patients (group 1) and of between 20 and 50% in eight patients (group 2). After the procedure the perfusion defects seen during stress resolved in 86% of group 1 and in 87% of group 2. Despite the apparent improvement in myocardial perfusion left ventricular dysfunction persisted in group 2--that is during stress the left ventricular ejection fraction fell from 65% (6) to 56% (5). In group 1, on the other hand, the improvement in myocardial perfusion was associated with significant improvement in left ventricular function with a normal increase in ejection fraction from 63 (5) at rest to 67 (6) during stress. Radionuclide studies, one to six weeks after angioplasty in 30 group 1 patients showed continuing left ventricular decompensation during stress in nine (30%) of them despite correction of perfusion defects. But reinvestigation three to six months after the procedure showed recovery of left ventricular function with an increase in ejection fraction from 66 (5) at rest to 69 (7) during stress. These data indicate that coronary angioplasty procedures that give a residual stenosis of

The evaluation of ventricular function using gated myocardial imaging with Tc-99m MIBI.

Left ventricular function is an important prognostic indicator in patients with coronary artery disease. We have assessed a method of providing this information as an adjunct to myocardial perfusion imaging using Tc-99m MIBI (2-methoxy-2-methyl-isopropyl-1-isonitrile). Two separate studies, at rest and during exercise, were performed following an injection of 400-600 M Bq of Tc-99m MIBI in 62 patients. Cardiac gating permitted excellent myocardial edge definition during the cardiac cycle. Radionuclide fractional shortening (RFS) was calculated from the anteroposterior (AP) and the septum to lateral wall (SL) axes in diastole and systole. Results were compared with echocardiographic fractional shortening (EFS) and the ejection fraction (EF) obtained from the gated equilibrium blood pool using Tc-99m-labelled red blood cells. The RFS in the AP axis correlated closely with echocardiographic FS (r = 0.89, P less than 0.001). The RFS in both axes was averaged to provide a global RFS. Global RFS correlated closely with LV radionuclide EF (r = 0.83, P less than 0.001). Inter- and intra-observer reproducibility studies have shown a variability for the procedure of less than 10%. In conclusion, gated perfusion imaging with Tc-99m MIBI, provides useful functional information as an adjunct to perfusion imaging.

Captopril versus placebo in congestive heart failure: effects on oxygen delivery to exercising skeletal muscle.

The effects of captopril versus placebo on oxygen consumption in the exercising leg have been examined using Doppler measurements of femoral flow and arteriovenous oxygen difference. Twenty patients with heart failure were randomized to captopril 25 mg (N = 10) or placebo (N = 10). Maximal supine exercise of one leg was performed before treatment and again 1 h and 4 h afterwards. Systemic haemodynamic variables were unaffected by placebo, but captopril increased stroke index at peak exercise from 26 +/- 3 to 34 +/- 3 ml beat-1 m-2 and reduced pulmonary artery wedge pressure from 26 +/- 3 to 16 +/- 3 mmHg (P less than 0.05). Despite the captopril-induced improvement in left ventricular function, exercise duration did not increase significantly and peak values for femoral flow (1059 +/- 178 to 938 +/- 134 ml min-1, P = NS), and oxygen consumption (134 +/- 26 to 111 +/- 18 ml min-1, P = NS) in the exercising leg were unaffected. Cutaneous flow, as reflected by skin temperature (27.5 +/- 0.4 to 27.6 +/- 0.4 degrees C, P = NS), was also unaffected. In the patients randomized to captopril, the acute improvement in left ventricular function was abbreviated and, after 4 h, all variables had returned towards baseline. Moreover, when the invasive studies were repeated after four weeks chronic treatment responsiveness to converting enzyme inhibition had attenuated and there were no detectable differences between the captopril and placebo groups. These data have demonstrated an acute captopril-induced improvement in left ventricular function in patients with congestive heart failure. Nevertheless the beneficial acute response was abbreviated predicting the development of early tolerance. Oxygen delivery to the exercising leg showed no tendency to increase either acutely when left ventricular function was significantly improved, or chronically when systemic responsiveness had attenuated. Thus irrespective of its effects on left ventricular function, captopril does not increase nutritive flow to exercising skeletal muscle in congestive heart failure.

Reversible occlusion of a side branch and the left anterior descending coronary artery following angioplasty.

A 61-year-old man with unstable angina underwent emergency angioplasty of a proximal left anterior descending coronary stenosis. This was successful but a major first septal branch involved in the stenosis was occluded following the procedure. Recovery was uncomplicated, however, without chest pain or other evidence of myocardial infarction. Predischarge treadmill stress testing was negative for ischaemia but two hours afterwards abrupt coronary occlusion required a second emergency angioplasty procedure. Recanalization of the left anterior descending artery was achieved and the first septal branch was shown to be fully patent. Spasm probably accounted for the side branch occlusion which complicated the first procedure but the mechanism of the abrupt coronary occlusion following stress-testing is unclear.

Pulsed Doppler ultrasound compared with thermodilution for monitoring cardiac output responses to changing left ventricular function.

To determine the responsiveness of the pulsed Doppler technique to pacing and drug induced changes in left ventricular function 125 simultaneous cardiac output measurements by pulsed Doppler ultrasound and thermodilution were compared in 12 patients. The Doppler velocity frequencies were analysed using a signal averaging process and the validity of this method first tested in vitro. This showed almost perfect linearity of pulsed Doppler and electromagnetic flow determinations in a test rig. Although data points showed greater scatter in the clinical study, a highly significant linear relation between cardiac output measurements by pulsed Doppler and thermodilution was confirmed by regression analysis (r = 0.88, p less than 0.001). Certain mean values for cardiac output by the two techniques differed, however, by up to 0.9 litre.min-1. Despite this, changes in cardiac output in response to pacing, inotropic stimulation with dobutamine, and vasodilatation with nitrates were directionally similar, indicating a useful role for the pulsed Doppler technique in monitoring responses to treatment in the intensive care unit. Pulsed Doppler also provided a simple measure of left ventricular contractile function. Thus the inotropic response to dobutamine produced a significant rise in peak aortic flow velocity, and this variable was unaffected by either pacing or nitrate induced vasodilatation.