Duration of abnormal SPECT myocardial perfusion imaging following resolution of acute ischemia: an angioplasty model

Noninvasive cardiac imaging in suspected acute coronary syndrome

Noninvasive cardiac imaging has an important role in the assessment of patients with acute-onset chest pain. In patients with suspected acute coronary syndrome (ACS), cardiac imaging offers incremental value over routine clinical assessment, the electrocardiogram, and blood biomarkers of myocardial injury, to confirm or refute the diagnosis of coronary artery disease and to assess future cardiovascular risk. This Review covers the current guidelines and clinical use of the common noninvasive imaging techniques, including echocardiography and stress echocardiography, computed tomography coronary angiography, myocardial perfusion scintigraphy, positron emission tomography, and cardiovascular magnetic resonance imaging, in patients with suspected ACS, and provides an update on the developments in noninvasive imaging techniques in the past 5 years.

The Localization and Characterization of Ischemic Scars in relation to the Infarct Related Coronary Artery Assessed by Cardiac Magnetic Resonance and a Novel Automatic Postprocessing Method

Aims. The correspondence between the localization and morphology of ischemic scars and the infarct related artery (IRA) by use of cardiac magnetic resonance imaging and a novel automatic postprocessing method. Methods and Results. Thirty-four patients with one-year-old single IRA myocardial infarction were examined. Endocardium, epicardium, and the point where right and left ventricles are coinciding were manually marked. All measurements were automatically assessed by the method. The following are results with manual assessments of scar properties in parenthesis: mean scar size (FWHM criterion): 7.8 ± 5.5 as %LV (17.4 ± 8.6%); mean endocardial extent of infarction: 44 ± 26° (124 ± 47°); mean endocardial extent of infarction as %LV circumference: 9.7 ± 7.0% (34.6 ± 13.0%); and mean transmurality: 52 ± 20% of LV wall thickness (77 ± 23%). Scars located in segments 1, 2, 7, 8, 13, and 14 by use of the automatic method were 96-100% specific for LAD occlusion. The highest specificities of RCA and LCX occlusions were segment 4 with 93% and segment 6 with 64%, respectively. The scar localization assessed automatically or manually was without major differences. Conclusion. The automatic method is applicable and able to assess localization, size, transmurality, and endocardial extent of ischemic scars.

Role of imaging for acute chest pain syndromes

Acute chest pain suggestive of ischemic cardiac origin, with a normal or nondiagnostic electrocardiogram and negative initial cardiac markers for myocardial necrosis represent a significant diagnostic dilemma for clinicians. Multiple imaging modalities play a pivotal role in early diagnosis and safe discharge of these patients. In this review, we compare the current imaging modalities available for these patients including their diagnostic accuracy, feasibility, and cost effectiveness. Acute rest myocardial perfusion imaging significantly improves the clinical outcome in these patients and reduces the overall cost when incorporated into the decision making pathway. The choice of imaging modality recommended should be based on local institutional expertise and the overall clinical presentation. The imaging modality with high diagnostic accuracy and negative predictive value will provide for precise risk stratification which is important to clinical decision making, including patients who require admission to the hospital and those who can be safely discharged.

Imaging strategies for acute chest pain in the emergency department

OBJECTIVE

Echocardiography, radionuclide myocardial perfusion imaging (MPI), and coronary CT angiography (CTA) are the three main imaging techniques used in the emergency department for the diagnosis of acute coronary syndrome (ACS). The purpose of this article is to quantitatively examine existing evidence about the diagnostic performance of these imaging tests in this setting.

CONCLUSION

Our systematic search of the medical literature showed no significant difference between the modalities for the detection of ACS in the emergency department. There was a slight, positive trend favoring coronary CTA. Given the absence of large differences in diagnostic performance, practical aspects such as local practice, expertise, medical facilities, and individual patient characteristics may be more important.

Correspondence between the 17-segment model and coronary arterial anatomy using contrast-enhanced cardiac magnetic resonance imaging

OBJECTIVES

The purpose of this study was to investigate the correspondence between the coronary arterial anatomy and supplied myocardium based on the proposed American Heart Association 17-segment model.

BACKGROUND

Standardized assignment of coronary arteries to specific myocardial segments is currently based on empirical assumptions.

METHODS

A cardiac magnetic resonance study was performed in 93 subjects following acute myocardial infarction treated with primary percutaneous coronary intervention. Two observers blindly reviewed all angiograms to examine the location of the culprit lesion and coronary dominance. Two additional observers scored for the presence of cardiac magnetic resonance hyperenhancement (HE) on a 17-segment model. Segments were divided based on anatomical landmarks such as the interventricular grooves and papillary muscles.

RESULTS

In a per-segment analysis, 23% of HE segments were discordant with the empirically assigned coronary distribution. Presence of HE in the basal anteroseptal, mid-anterior, mid-anteroseptal, or apical anterior wall was 100% specific for left anterior descending artery occlusion. The left anterior descending artery infarcts frequently involved the mid-anterolateral, apical lateral, and apical inferior walls. No segment was 100% specific for right coronary artery or left circumflex artery (LCX) occlusion, although HE in the basal anterolateral wall was highly specific (98%) for LCX occlusion. Combination of HE in the anterolateral and inferolateral walls was 100% specific for a LCX occlusion, and when extended to the inferior wall, was also 100% specific for a dominant or codominant LCX occlusion.

CONCLUSIONS

Four segments were completely specific for left anterior descending artery occlusion. No segment can be exclusively attributed to the right coronary artery or LCX occlusion. However, analysis of adjacent segments increased the specificity for a given coronary occlusion. These findings bring objective evidence in the appropriate segmentation of coronary arterial perfusion territories and assist accurate assignment of the culprit vessel in various imaging modalities.

Myocardial microinfarction after coronary microembolization in swine: MR imaging characterization

PURPOSE

To use first-pass perfusion and delayed-enhanced (DE) magnetic resonance (MR) imaging for the detection of the early effects of coronary microembolization on myocardial perfusion and viability.

MATERIALS AND METHODS

Approval was obtained from the institutional committee on animal research. A hybrid x-ray and MR imaging system was used to guide the endovascular catheter and quantify the left anterior descending coronary artery (LAD) perfusion territory before microembolization and ischemic myocardium and microinfarction after microembolization. The embolic agent was selectively delivered in the LAD in six pigs. First-pass perfusion MR imaging was performed 1 hour and 1 week after microembolization. Microinfarction was measured on DE MR images in beating and nonbeating hearts (high-spatial-resolution sequence) by using extracellular and blood pool MR contrast media and after death. The Wilcoxon signed rank test and correlation analysis were used.

RESULTS

The LAD perfusion territory was 35% of left ventricular (LV) mass +/- 2 (standard error of the mean). Microembolization caused perfusion deficit in 15.7% of LV mass +/- 2.6 compared with that of LAD territory (P = .03). At 1 week, perfusion parameters improved and the extent of hypoperfused territory declined (4.6% of LV mass +/- 1.4, P = .03). Microinfarction size expanded from 1.4% of LV mass +/- 0.2 at 1 hour to 7.5% of LV mass +/- 1.2 at 1 week. In nonbeating hearts and at triphenyltetrazolium chloride staining at 1 week, microinfarction size was 7.6% of LV mass +/- 1.4 and 7.2% of LV mass +/- 1.5, respectively. There was no correlation between the ejection fraction and the extents of microinfarction or hypoperfused territory. Histopathologic findings confirmed the presence of patchy microinfarction.

CONCLUSION

Coronary microembolization caused persistent decline in myocardial perfusion at first-pass perfusion imaging. DE MR imaging has the potential to help reliably quantify subacute microinfarction. The magnitude of LV dysfunction is not related to the extents of microinfarction or hypoperfused territory.

Effect of percutaneous coronary intervention on coronary blood flow at rest in myocardial sites remote from the intervention site in patients with stable angina pectoris

Little is known about changes in myocardial perfusion of myocardial regions supplied by angiographically normal or near-normal coronary arteries after percutaneous coronary intervention (PCI) of the target lesion. The purpose of this study was to assess the effect of PCI on coronary blood flow at rest in sites remote from the PCI. We studied 85 patients who underwent successful elective PCI for stable angina. We used the Thrombolysis In Myocardial Infarction frame count to provide a simple continuous index of coronary flow and myocardial perfusion in the target and nontarget arteries. Coronary artery diameters of nontarget vessels did not significantly differ before and after PCI and at 6 months' follow-up. At baseline, the greater the percent diameter stenosis in the target artery, the slower the flow in the target (r = 0.22, p <0.01) and nontarget arteries (r = 0.28, p <0.01). Relief of stenosis using PCI did not account for simultaneous changes in epicardial coronary blood flow of the nontarget artery. After 6 months, coronary blood flow improved in both the target (p <0.05) and nontarget arteries (p = 0.007). In conclusion, this study provided evidence of a functional link between coronary blood flow in diseased and nondiseased arteries. Relief of a significant stenosis using PCI globally improved regional and global myocardial blood flow at rest in patients with stable angina. Flow improvement was not apparent at the time of revascularization, but at 6 months' follow-up. Late upturn of the microcirculation may account for delayed recovery of myocardial perfusion.

Myocardial perfusion imaging after transient balloon occlusion during percutaneous coronary interventions

BACKGROUND

Myocardial perfusion imaging (MPI) is highly sensitive in detecting rest ischemia when the radiotracer is injected during the episode of ischemia. The frequency of abnormal MPI results after resolution of ischemia is not well defined. The aim of this study was to determine how long MPI results remain abnormal after transient coronary artery occlusion.

METHODS AND RESULTS

Patients undergoing single-vessel percutaneous coronary intervention were injected with technetium 99m sestamibi at 30 to 60 minutes (group 1) (n = 20) or 90 to 120 minutes (group 2) (n = 10) after the last balloon inflation and 24 hours later. There were 30 men aged 59 +/- 8 years. The culprit vessel was the left anterior descending artery in 14 patients and the right coronary artery in 13. The diameter stenosis was reduced from 76.1% +/- 8.7% to 3.0% +/- 6.4% (P < .001). The duration of balloon inflation was 40.3 +/- 12.5 seconds. Chest pain or ST shifts occurred in 66% of patients. A perfusion defect in the territory of the culprit artery was detected in 3 of 20 patients (15%) in group 1 and in 0 of 10 patients (0%) in group 2 (P = .3). One of those three patients had a perfusion defect on MPI done 24 hours later, along with a regional wall motion abnormality on the 2 sets of images.

CONCLUSIONS

Abnormal perfusion is seen in a small percentage of patients at 30 to 60 minutes and in none at 90 to 120 minutes after a brief transient balloon occlusion. These results might have important implications in patient care.

Elective percutaneous coronary intervention immediately impairs resting microvascular perfusion assessed by cardiac magnetic resonance imaging

BACKGROUND

Percutaneous coronary intervention (PCI) is known to induce atherosclerotic plaque rupture, which may affect resting distal microvascular perfusion either through distal microvascular spasm or through embolization. We evaluated the effect of PCI on resting microvascular flow.

METHODS

We performed cardiovascular magnetic resonance imaging to assess left ventricular systolic function and microvascular perfusion in 15 patients with stable coronary artery disease before and within 24 hours after PCI and in 10 control subjects without obstructive coronary artery disease on a clinical 1.5-T CMR scanner. Microvascular perfusion was evaluated at rest after injecting a bolus of gadolinium-diethylenetriamine pentaacetic acid (0.1 mmol/kg) by calculating the time to 50% maximum myocardial enhancement (T50% max), as well as the relative upslope, of the myocardial signal intensity curve. Regional perfusion and systolic thickening were evaluated using a 16-segment left ventricular model with the slice locations matched anatomically pre-PCI and post-PCI. The relative contrast delay in the region of myocardium subtended by the PCI artery was calculated by subtracting the T50% max of a remote region from the PCI region.

RESULTS

In subjects with coronary artery disease, PCI resulted in a regional contrast delay (mean delay 0.6 +/- 0.2 seconds post-PCI vs 0.0 +/- 0.2 seconds pre-PCI, P < .05) and a reduction in the relative upslope (8.6 +/- 0.5 post-PCI vs 10.1 +/- 0.7 pre-PCI, P = .02), consistent with reduced microvascular perfusion. This was unaccompanied by any change in regional systolic thickening (54% +/- 7% pre-PCI vs 53% +/- 5% post-PCI, P = NS).

CONCLUSIONS

The data show PCI-induced impairment of resting microvascular perfusion in the area of myocardium subtended by the treated artery after PCI, a likely consequence of iatrogenic atherosclerotic plaque rupture.

Imaging in the evaluation of the patient with suspected acute coronary syndrome

Over the last decade, major advances have been made in the treatment of acute coronary syndromes (ACSs). However, effective implementation of these treatments requires timely and accurate identification of the high-risk patient among all those presenting to the emergency department (ED) with symptoms suggestive of ACS. The opportunity for improving outcomes is time-dependent, so that early identification of the patient who has true ACS is essential. This necessity further increases the need for rapid triage tools, especially in the current setting of ED and hospital overcrowding that has become the norm in large urban centers.

Acute resting myocardial perfusion imaging in patients with diabetes mellitus: results from the Emergency Room Assessment of Sestamibi for Evaluation of Chest Pain (ERASE Chest Pain) trial

BACKGROUND

Resting myocardial perfusion imaging (MPI) improves the triage of patients presenting to the emergency department (ED) with symptoms suggestive of acute cardiac ischemia (ACI). In the ED setting the presence of diabetes mellitus (DM) is a predictor of ACI and hospitalization, but the role of resting MPI in patients with DM is unknown.

METHODS AND RESULTS

A secondary data analysis of a prospective, multicenter, randomized, controlled trial of ED evaluation strategies in patients with symptoms suggestive of ACI and normal or nondiagnostic electrocardiograms was performed. In the main trial 2475 patients were randomized to receive either the usual ED evaluation strategy (n = 1260) or the usual strategy supplemented by results from resting MPI by use of single photon emission computed tomography (SPECT) technetium 99m sestamibi (n = 1215). Patients with diabetes (n = 341) were evaluated separately. Imaging results, final diagnoses, effect on triage, and prognostic value of the SPECT imaging were compared between diabetic and nondiabetic patients. Of the 341 patients with diabetes, 153 (45%) were randomized to the imaging strategy. Patients with DM had higher rates of hospitalization (66% vs 49.6%, P = .0001) and ACI (21.1% vs 12.0%, P < .001) than patients without DM. Among diabetic patients without ACI, the admission rate was 63% in the usual strategy group versus 54% in the imaging strategy group (relative risk [RR] = 0.91 [95% CI, 0.76-1.06]; P = .24). There was no difference in the magnitude of this reduced risk of admission compared with patients without DM (RR = 0.84 [95% CI, 0.77-0.92]; P = .0002 for patients without DM and P = .35 for interaction of diabetes and RR reduction).

CONCLUSIONS

Acute resting MPI with Tc-99m sestamibi is associated with improved triage decision making in symptomatic ED patients with diabetes.

Imaging in the evaluation of the patient with suspected acute coronary syndrome

Patients presenting to the emergency department with chest pain have a common problem. Definitive diagnosis at presentation is difficult due to limitations of the initial evaluation, and, thus, the majority of patients are admitted. Recognition of these limitations has driven the investigation of alternative evaluation techniques and protocols to attempt to improve diagnostic sensitivity without increasing overall costs. Acute myocardial perfusion imaging has been a highly valuable technique for risk stratification of intermediate to low-risk patients with chest pain. However, for a variety of reasons, it has not been widely embraced. In the past few years, alternative techniques have been investigated for use in the diagnosis of acute coronary syndromes in the acute setting. Coronary calcium scoring and cardiac magnetic resonance imaging show promise as new tools in the armamentarium for acute coronary syndromes. The challenge now lays in developing a strategy that uses these and future techniques most appropriately to support optimal medical decision making.