Effect of trimetazidine on 99Tcm-tetrofosmin uptake in patients with coronary artery disease

Technetium-99m Radiopharmaceuticals for Ideal Myocardial Perfusion Imaging: Lost and Found Opportunities

The favorable nuclear properties in combination with the rich coordination chemistry make technetium-99m the radioisotope of choice for the development of myocardial perfusion tracers. In the early 1980s, [^99mTc]Tc-Sestamibi, [^99mTc]Tc-Tetrofosmin, and [^99mTc]Tc-Teboroxime were approved as commercial radiopharmaceuticals for myocardial perfusion imaging in nuclear cardiology. Despite its peculiar properties, the clinical use of [^99mTc]Tc-Teboroxime was quickly abandoned due to its rapid myocardial washout. Despite their widespread clinical applications, both [^99mTc]Tc-Sestamibi and [^99mTc]Tc-Tetrofosmin do not meet the requirements of an ideal perfusion imaging agent due to their relatively low first-pass extraction fraction and high liver absorption. An ideal radiotracer for myocardial perfusion imaging should have a high myocardial uptake; a high and stable target-to-background ratio with low uptake in the lungs, liver, stomach during the image acquisition period; a high first-pass myocardial extraction fraction and very rapid blood clearance; and a linear relationship between radiotracer myocardial uptake and coronary blood flow. Although it is difficult to reconcile all these properties in a single tracer, scientific research in the field has always channeled its efforts in the development of molecules that are able to meet the characteristics of ideality as much as possible. This short review summarizes the developments in ^99mTc myocardial perfusion tracers, which are able to fulfill hitherto unmet medical needs and serve a large population of patients with heart disease, and underlines their strengths and weaknesses, the lost and found opportunities thanks to the developments of the new ultrafast SPECT technologies.

Placebo or trimetazidine (99m)Tc tetrofosmin myocardial SPECT and low-dose dobutamine echocardiography in hibernating myocardium

BACKGROUND

Trimetazidine (TMZ) improves (99m)Tc sestamibi uptake in myocardial single photon emission tomography (SPECT). This study compared TMZ (99m)Tc tetrofosmin SPECT and low-dose dobutamine echocardiography (LDDE) as predictors of functional recovery of hibernating myocardium after coronary revascularization.

METHODS

Thirty-one patients with prior myocardial infarction and left ventricular dysfunction underwent coronary angiography, LDDE, placebo SPECT and TMZ SPECT. Echocardiographic follow-up was obtained at 2/6 months; the clinical follow-up lasted 2 years.

RESULTS

Twenty-three (74.2%) patients (195 dysfunctioning left ventricular segments) were revascularized. TMZ improved (99m)Tc tetrofosmin uptake (p = 0.0001) as well as LVEF at gated SPECT (p = 0.04). At 2-months, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated (LDDE 71.9, 78.7, 71, 79.5; placebo SPECT 66.2, 75.6, 65.4, 76.3; TMZ SPECT 79.2, 67.7, 61.6, 83.3, respectively). The specificity improved in placebo and TMZ SPECT (82.1 and 78.7%) at 6-months follow-up. Two patients (2/23) with hibernating myocardium treated with revascularization and three (3/4) treated medically died a cardiac death (p = 0.0016, log rank 12.89). None (0/4) without viability died during the 2-year follow-up (p = 0.6, log rank 0.28).

CONCLUSIONS

The addition of TMZ to (99m)Tc tetrofosmin SPECT improved diagnostic accuracy. The importance of hibernating myocardium revascularization was confirmed.

The acute administration of trimetazidine modified myocardial perfusion and left ventricular function in 31 patients with ischaemic ventricular dysfunction

Trimetazidine (TMZ) increases the mithocondrial oxidative metabolism and improves Tc-99m sestamibi uptake in myocardial single photon emission tomography (SPECT). The aim of this study was to evaluate whether the acute administration of TMZ improved myocardial perfusion and modified left ventricular ejection fraction (LVEF) in ischaemic left ventricular impairment.

METHODS

Thirty-one patients (23 males, age 66 years) with prior myocardial infarction (>6 months) and echocardiographic LVEF < or = 45% underwent coronary angiography, rest basal myocardial SPECT (after 3-day placebo administration) and rest TMZ myocardial SPECT [after 3-day TMZ administration (60mg/die)]. The left ventricle was analysed in 16 segments. The summed placebo score (SPS) and the summed TMZ score (STS) were calculated with a 5-point scale (from 0 = normal uptake to 4 = absent uptake) by two blinded operators. The GATED Tc-99m SPECT was always provided.

RESULTS

After TMZ administration GATED LVEF improved from 26.5+/-9.7% to 29.1+/-11.3% (p = 0.04) and left ventricular end-systolic volume (LVESV) was reduced from 90.2+/-40.7 to 85.6+/-39.2 ml/mq (p = 0.006). Similarly the addition of TMZ to myocardial SPECT significantly reduced the STS compared to SPS (21.5+/-11 vs. 26.6+/-10.5 p = 0.0001). Eleven patients (35.5%) had an echocardiographic LVEF < or = 30%; in these patients who had severe ventricular dysfunction, GATED LVEF and LVESV did not change after TMZ (20.2+/-5.7% vs. 21+/-6.9% p =0.6; 116.7+/-35.3 ml vs. 112.6+/-32.3 ml p = 0.08, respectively).

CONCLUSION

In comparison with placebo, the addition of TMZ to myocardial Tc-99m tetrofosmin SPECT improved myocardial perfusion and LVEF, reducing LVESV. These effects were lost in patients with more severe ventricular dysfunction.

Irbesartan has a masking effect on dipyridamole stress induced myocardial perfusion defects

BACKGROUND AND AIM

The angiotensin II type 1 (AT1) receptor antagonist irbesartan is used for the treatment of hypertension, but its anti-ischaemic effect is not yet known. Our aim was to assess the effect of irbesartan administration on the diagnostic yield of 99mTc sestamibi single photon emission computed tomography (SPECT) in patients with coronary artery disease (CAD) after dipyridamole stress.

METHODS

Our study group consisted of 13 patients (11 men and two women; mean age, 53.3 +/- 10.6 years; body mass index, 26.9 +/- 3.3 kg x m(-2)) with angiographically documented CAD. All patients underwent SmTc sestamibi SPECT studies at rest, before (STRESS-1) and 2 weeks after irbesartan (150 mg daily) administration (STRESS-2) at dipyridamole stress. The extent and severity of defects were analysed by using visual and quantitative 99mTc sestamibi SPECT.

RESULTS

The mean summed stress score was significantly higher during the STRESS-1 study than the STRESS-2 study (13.2 +/- 7.4 vs. 11 +/- 7.4, P=0.003). The mean size of perfusion defects at stress was significantly larger for the STRESS-1 group than the STRESS-2 group (17.8% +/- 2.85% vs. 15.3% +/- 2.95%, P=0.01).

CONCLUSION

Our study showed that the AT1 receptor blocker irbesartan reduces the extent and severity of 99mTc sestamibi perfusion defects after dipyridamole stress in patients with CAD. Irbesartan may alter coronary blood flow reserve. The continued use of irbesartan before stress myocardial perfusion SPECT has a masking effect on stress induced myocardial perfusion defects. For this reason AT1 receptor blockers must be stopped before stress myocardial perfusion scintigraphic examinations.