Nitroglycerin-augmented 201T1 reinjection enhances detection of reversible myocardial hypoperfusion. A randomized, double-blind, parallel, placebo-controlled trial

Sublingual glyceryl trinitrate given during adenosine sestamibi myocardial perfusion imaging causes apparent transient ischaemic dilation in a propensity-matched analysis

OBJECTIVES

Administration of sublingual glyceryl trinitrate (GTN) prior to resting radiotracer injection during myocardial perfusion imaging (MPI) has been advocated to aid detection of viable myocardium and increase the extent of reversible perfusion defects. However, GTN is also known to reduce resting left ventricular volume and could thus increase the transient ischaemic dilation (TID) ratio, independently of severe or extensive coronary artery disease. We aimed to determine if GTN administration causes an increase in the TID ratio.

METHODS

Causal inference using propensity score matched analysis was used to assess the effect of GTN on TID ratios in subjects undergoing adenosine sestamibi MPI.

RESULTS

From 597 consecutive patients undergoing MPI, we selected a treatment group of 51 who received 400 μg of sublingual GTN before resting sestamibi injection and 51 propensity score matched controls. Mean TID ratios were 1.24 in treated subjects and 1.10 in controls (mean difference 0.15; 95% CI, 0.05-0.25; P  = 0.0018). The mean difference in TID ratio fell progressively in each quartile of time elapsed between GTN administration and image acquisition. The proportion with TID ratios equal and greater than an abnormal threshold of 1.39 was 17.6% among the treated and 0% in controls ( P  = 0.0010). The effect on TID ratio was not restricted to those with moderate-to-severe stress perfusion defects or accompanied by greater reversible perfusion defects.

CONCLUSIONS

There is evidence of a cause-and-effect relationship between administering GTN before resting sestamibi injection and increased TID ratio on MPI. This may be a source of misleading false positive TID findings.

Myocardial viability assessment and utility in contemporary management of ischemic cardiomyopathy

Background

In clinical practice, we encounter ischemic cardiomyopathy (ICM) with underlying viable, dysfunctional myocardium on a regular basis. Evidence from the Surgical Treatment for Ischemic Heart failure (STICH) and its Extension Study is supportive of improved outcomes with coronary revascularization, irrespective of myocardial viable status. However, Dobutamine stress echocardiography (DSE) and single‐photon emission computed tomography (SPECT), used in STICH to assess myocardial viability may fail to distinguish hibernating myocardium from scar due to suboptimal image resolution and poor tissue characterization.

Hypothesis

Cardiac magnetic resonance (CMR) and positron emission tomography (PET) can precisely quantify myocardial scar and identify metabolically active, viable myocardium respectively. Unlike DSE and SPECT, CMR and PET allow examining myocardial status as a contiguous spectrum from viable to partially viable myocardium with varying degrees of subendocardial scar and nonviable myocardium with predominantly transmural scar, the therapeutic and prognostic determinants of ICM.

Methods

Under the guidance of CMR and PET imaging, myocardium can be distinguished viable from partially viable with subendocardial scar and predominantly transmural scar. In ICM, optimal medical therapy and coronary revascularization of viable/partially viable myocardium but not transmural scar may improve outcomes in patients with acceptable procedural risk.

Results

Coronary revascularization of partially viable and viable myocardial territory may improve clinical outcomes by preventing future ischemic, infarct events and further worsening of left ventricular remodeling and function.

Conclusions

When deciding if coronary revascularization is appropriate in a patient with ICM, it is essential to take a patient‐tailored, comprehensive approach incorporating myocardial viability, ischemia, and scar data with others such as procedural risk, and patient's comorbidities.

1.

Viability of myocardium is assessed by different imaging modalities, probing different characteristics of the living myocyte – uptake of radioactive isotope, TC‐99m or Tl‐201 (SPECT MPI), contractile reserve (Dobutamine stress imaging, echo or CMR), metabolic properties (FDG uptake on PET), absence of scar (CMR).

2.

Dysfunctional, viable myocardium as compared to nonviable myocardium carries a better prognosis with appropriate therapy.

3.

Dysfunctional myocardium may not be simplified into a binary state of viable or not. It can be a continuum process, with a myocardial segment in a hybrid state with an intermix of viable myocytes in early to late phases of hibernation and fibrosis.

4.

Nonviable myocardium on Dobutamine Stress Echocardiography or SPECT Nuclear imaging may be partially viable (with varying degrees of fibrosis) or viable with no scar, on CMR.

5.

Coronary revascularization of partially viable or viable myocardium should be considered if the procedural risk is acceptable, as it improves long‐term outcomes by preventing further myocardial ischemia/infarction and possibly improving left ventricular function and remodeling.

Analysis of Myocardial (18)F-FDG Uptake by PET/CT in the Patients with Different Dialectically Classified Coronary Heart Diseases (CHD)

To quantify myocardial glucose metabolism by (18)F-FDG PET/CT in patients that have coronary heart disease (CHD) according to traditional Chinese medicine classification. Ninety patients with CHD were enrolled and were categorized into three groups. All patients underwent PET-CT examination for (18)F-FDG uptake quantification. In group A, the radioactive signals were weak in multiple segments in 27 cases (90 %). One case had no visualization and two had normal visualization (mean SUV = 4 ± 0.6). In group B, the radioactive signals were in some local areas in eight cases (26.7 %). Twenty cases had an overall increase in signal density (SUV ≥ 8) (66.7 %). One case had no visualization, and one case had normal visualization (mean SUV 4 ± 0.6). In group C, 23 cases had no visual or a weak visual (SUV ≤ 2 ± 0.3) (76.7 %). Seven cases had segmental weak signals or signal defects. Different types of CHD demonstrate different metabolisms of myocardium glucose. It is necessary to dialectically classify CHD and apply differential treatment.

Nitrate-augmented myocardial perfusion imaging for assessment of myocardial viability: recent advances

Nitrate-augmented myocardial perfusion imaging has been demonstrated to improve the detection of myocardial viability and accurately predicts recovery of left ventricular (LV) function in patients with severe coronary artery disease and LV dysfunction. Recently, several studies showed the prognostic utility of nitrate imaging in evaluation of event-free survival in ischemic LV dysfunction. Furthermore, the diagnostic power of nitrate imaging compared with positron emission tomography or MRI, as well as the mechanism of nitrate-enhanced imaging, were also studied. We describe recent studies using nitrate-augmented myocardial perfusion imaging for the assessment of myocardial viability.

Coronary collaterals during single-vessel coronary angioplasty: effects of nitroglycerin

BACKGROUND

Although the protective role of collaterals in coronary artery disease (CAD) is well known, the influence of drugs on collateral function remains controversial.

HYPOTHESIS

We aimed to investigate prospectively the prevalence of spontaneously visible and recruitable coronary collaterals in consecutive patients with single-vessel CAD and the effect of systemic administration of nitroglycerin on these types of collaterals during percutaneous transluminal coronary angioplasty (PTCA).

METHODS

Ipsi- and contralateral coronary artery contrast injections were performed before and during PTCA. Simultaneously with balloon occlusion, we measured coronary artery occlusion pressure via the balloon catheter. All measurements were repeated after administration of 0.5 mg of nitroglycerin intravenously.

RESULTS

Of 101 consecutive patients, 24% had spontaneously visible and 30% had recruitable collaterals. Contralateral collaterals were five times more frequent than ipsilateral collaterals. Presence of collaterals was highly associated with the degree of coronary stenosis. Coronary occlusion pressure was higher in patients with than in those without collaterals. Collaterals prevented pain and ischemia during PTCA, and in this respect spontaneously visible collaterals were more effective than recruitable collaterals. There was no effect of systemic administration of nitroglycerin on appearance or occlusion pressure of coronary collaterals.

CONCLUSION

Coronary collaterals were found in more than half of patients with single-vessel CAD, as the prevalence of recruitable collaterals was slightly higher than that of spontaneously visible collaterals. Nitroglycerin did neither recruit nor augment coronary collaterals.

Imaging techniques in nuclear cardiology for the assessment of myocardial viability

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with ischemic cardiomyopathy. Although revascularization may be considered in patients with sufficient viable myocardium, patients with predominantly scar tissue should be treated medically. Patients with left ventricular dysfunction who have viable myocardium are the patients at highest risk because of the potential for ischemia but at the same time benefit most from revascularization. It is important to identify viable myocardium in these patients, and radionuclide myocardial scintigraphy is an excellent tool for this. Single-photon emission computed tomography perfusion scintigraphy (SPECT), whether using (201)thallium, (99m)Tc-sestamibi, or (99m)Tc-tetrofosmin, in stress and/or rest protocols, has consistently been shown to be an effective modality for identifying myocardial viability and guiding appropriate management. Metabolic and perfusion imaging with positron emission tomography (PET) radiotracers frequently adds additional information and is a powerful tool for predicting which patients will have an improved outcome from revascularization. New techniques in the nuclear cardiology field, like attenuation corrected SPECT, dual isotope simultaneous acquisition (DISA) SPECT and gated FDG PET are promising and will further improve the detection of myocardial viability. Also the combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and non-invasive coronary angiography to myocardial perfusion imaging and quantification. Evaluation of the clinical role of these creative new possibilities warrants investigation.

Stress echocardiography versus myocardial SPECT for risk stratification of patients with coronary artery disease

PURPOSE OF REVIEW

Diagnostic testing using noninvasive imaging has become an integral part of risk stratification in patients with coronary artery disease. It is important to understand the integral strengths and weaknesses between the different modalities of stress testing and to apply accurately the type of test the clinical scenario demands.

RECENT FINDINGS

There have been tremendous advances made in the field of cardiac imaging. Both myocardial perfusion imaging and stress echocardiographic techniques continue to evolve and play an important role in the assessment of patients with coronary artery disease.

SUMMARY

In this review the authors discuss the relative merits of both stress echocardiography and myocardial single photon emission computed tomographic imaging for diagnosis and risk stratification of patients with coronary artery disease.

Association of myocardial viability on nitrate-augmented technetium-99m hexakis-2-methoxylisobutyl isonitrile myocardial tomography and intermediate-term outcome in patients with prior myocardial infarction and left ventricular dysfunction

Seventy-eight patients with prior myocardial infarction and left ventricular dysfunction who underwent nitrate-augmented myocardial tomography were followed for 23 +/- 14 months. Event-free survival was 100% in 34 patients with myocardial viability who underwent coronary artery bypass grafting (CABG) and 53% in those who received medical therapy (p = 0.0008). Of the 44 patients without myocardial viability, event-free survival was not significantly different between patients who underwent CABG and those who received medical therapy (96% vs 90%, p = NS).

The non-invasive assessment of hibernating myocardium in ischaemic cardiomyopathy--a myriad of techniques

Heart failure is placing an ever-increasing burden on society. Many subjects with heart failure and underlying coronary artery disease have a significant amount of akinetic but viable myocardium that is able to contract should myocardial perfusion improve (hibernating myocardium). Non-randomised studies have shown prognostic benefit in subjects with hibernating myocardium undergoing revascularisation. Several non-invasive techniques have been developed to assess the presence or absence of hibernating myocardium. This review will examine the epidemiology and underlying pathogenesis of hibernating myocardium; evaluate the non-invasive techniques for diagnosing hibernating myocardium, and look at therapeutic intervention in subjects with hibernating myocardium.

Myocardial viability assessment using nuclear imaging

Myocardial assessment continues to be an issue in patients with coronary artery disease and left ventricular dysfunction. Nuclear imaging has long played an important role in this field. In particular, PET imaging using 18F-fluorodeoxyglucose is regarded as the metabolic gold standard of tissue viability, which has been supported by a wide clinical experience. Viability assessment using SPECT techniques has gained more wide-spread clinical acceptance than PET, because it is more widely available at lower cost. Moreover, technical advances in SPECT technology such as gated-SPECT further improve the diagnostic accuracy of the test. However, other imaging techniques such as dobutamine echocardiography have recently emerged as competitors to nuclear imaging. It is also important to note that they sometimes may work in a complementary fashion to nuclear imaging, indicating that an appropriate use of these techniques may significantly improve their overall accuracy. In keeping these circumstances in mind, further efforts are necessary to further improve the diagnostic performance of nuclear imaging as a reliable viability test.

Value of linsidomin in assessing myocardial viability with thallium-201 SPECT

Myocardial viability can be assessed with rest/24 h redistribution (201)Tl myocardial single photon emission computed tomography (SPECT). The intravenous injection of vasodilators induces an early redistribution of (201)Tl and shortens the total examination time. The aim of this study was to compare the images after injection of linsidomin with the 24 h images. We studied 51 consecutive patients (38 males, 13 females), aged 66+/-11 years, referred for assessment of myocardial viability after acute myocardial infarction. SPECT acquisition at rest (30 projections over 180 degrees, 30 s per projection) was performed 20 min after injection of (201)Tl. A second acquisition (same parameters) was performed 2 min after intravenous injection of linsidomin (2 mg). A delayed acquisition was performed on the following day (50 s per step). Myocardial perfusion at rest was normal in 111 of 255 segments. For the 144 other segments, 24 h images were similar to the images acquired after the injection of linsidomin in 94% of cases (136 of 144 segments). The 24 h images showed partial redistribution that was not present after linsidomin in only eight segments (6%). Injection of linsidomin after rest acquisition can provide a reliable and more rapid assessment of myocardial viability. This very simple protocol (rest/linsidomin (201)Tl myocardial SPECT) can be performed in less than 1 h.

Accuracy of biphasic response, sustained improvement and worsening during dobutamine echocardiography in predicting recovery of resting myocardial dysfunction after revascularization: comparison with thallium-201 SPECT

To evaluate the accuracy of various types of wall motion response during dobutamine echocardiography (DE) in predicting functional recovery after revascularization, we studied 30 patients with stable coronary disease and left ventricular dysfunction by simultaneous DE and (201)Tl reinjection SPECT. Among 480 segments (16 segments/patient), 199 had abnormal wall motion at baseline and 167 were revascularized. The predictive value for recovery of function was 72% for a biphasic response, 61% for sustained improvement, 77% for worsening, and 27% for no change (p < 0.01 vs. each). Biphasic response had a sensitivity of 40% and specificity of 85%. Combining biphasic, sustained improvement and worsening responses, the sensitivity, specificity and accuracy were 76%, 65% and 71%, respectively. For (201)Tl SPECT, they were 90%, 65% and 78%, respectively. Thus, a biphasic response alone is of low sensitivity. Combination of biphasic, sustained improvement and worsening responses gives an accuracy rate comparable to that of (201)Tl reinjection SPECT in assessing functional recovery.

[Nuclear cardiology: technical bases and clinical applications]

Although the role of nuclear cardiology is currently well consolidated, the addition of new radiotracers and modern techniques makes it necessary to continuously update the requirements, equipment and clinical applications of these isotopic tests. The characteristics of the radioisotopic drugs and examinations presently used are explained in the first part of this text. In the second, the indications of them in diagnostic and prognostic evaluation of the different coronary diseases are presented.

Improved detection of myocardial perfusion reversibility by rest-nitroglycerin Tc-99m-MIBI: comparison with TI-201 reinjection

BACKGROUND

The role of nitroglycerin (NTG) in Tc-99m-methoxyisobutil isonitrile (MIBI) studies to improve the assessment of myocardial viability in patients with coronary artery disease and its comparison with TI-201 reinjection has not yet been clarified. This study aimed to test whether sublingual administration of NTG could improve the capability of Tc-99m-MIBI to detect reversibility in exercise-induced perfusion defects and to compare it with the TI-201 stress-redistribution-reinjection protocol.

METHODS AND RESULTS

Thirty-eight patients (33 men, 5 women; mean age 49.3 +/- 8.2 years with previous myocardial infarction [mean evolution 7.1 +/- 3.9 months]) underwent exercise, redistribution, and reinjection TI-201 imaging, as well as exercise, rest, and NTG MIBI myocardial scintigraphy (3-day protocol). A total of 494 myocardial segments were assessed by quantitative analysis. Of the 136 myocardial segments with fixed defects on exercise-rest sestamibi imaging, 109 (80%) did not change after NTG MIBI study, and 27 (20%) demonstrated enhanced uptake. In the 140 myocardial segments with fixed defects on exercise-redistribution thallium imaging, 112 (80%) did not improve after TI-201 reinjection study, and 28 (20%) showed increased activity. The observed agreement on reversibility detection between NTG MIBI and TI-201 reinjection, with the 210 segments with perfusion defects used for this analysis on both studies, was 78%, with a significant kappa = .56 +/- .07 SE.

CONCLUSION

Our data suggest that the use of an NTG MIBI protocol results in an incremental improvement for detecting exercise-induced perfusion defect reversibility and achieves results similar to those from a TI-201 reinjection protocol.

Prognostic utility of myocardial viability assessment

Myocardial viability assessment is useful in patients with severe coronary artery disease and severe left ventricular dysfunction. Whereas most studies have focused on recovery of regional function, there are emerging data on patient outcome. Review of these data suggests that patients with chronic ischemia, cardiomyopathy, and viable myocardium who are treated medically have a worse, outcome than those treated with coronary revascularization. However, there are no prospective randomized trials. We present perspectives for future studies.