Non-contrast cardiac computed tomography can accurately detect chronic myocardial infarction: Validation study

doi:10.1007/s12350-010-9314-3

Journal of Nuclear Cardiology

Volume 18, Issue 1, February 2011, Pages 96-103

https://doi.org/10.1007/s12350-010-9314-3 Get rights and content

Abstract

Background

This study evaluates whether non-contrast cardiac computed tomography (CCT) can detect chronic myocardial infarction (MI) in patients with irreversible perfusion defects on nuclear myocardial perfusion imaging (MPI).

Methods

One hundred twenty-two symptomatic patients with irreversible perfusion defect (N = 62) or normal MPI (N = 60) underwent coronary artery calcium (CAC) scanning. MI on these non-contrast CCTs was visually detected based on the hypo-attenuation areas (dark) in the myocardium and corresponding Hounsfield units (HU) were measured.

Results

Non-contrast CCT accurately detected MI in 57 patients with irreversible perfusion defect on MPI, yielding a sensitivity of 92%, specificity of 72%, negative predictive value (NPV) of 90%, and a positive predictive value (PPV) of 77%. On a per myocardial region analysis, non-contrast CT showed a sensitivity of 70%, specificity of 85%, NPV of 91%, and a PPV of 57%. The ROC curve showed that the optimal cutoff value of LV myocardium HU to predict MI on non-contrast CCT was 21.7 with a sensitivity of 97.4% and specificity of 99.7%.

Conclusion

Non-contrast CCT has an excellent agreement with MPI in detecting chronic MI. This study highlights a novel clinical utility of non-contrast CCT in addition to assessment of overall burden of atherosclerosis measured by CAC.

Introduction

The principal cause of morbidity and mortality in all industrialized nations is coronary artery disease (CAD). In approximately half of these patients, the initial presentation of CAD is either myocardial infarction (MI) or death.¹ Unrecognized MI leads to less effective management and increased major adverse cardiac events (MACE). Population-based studies have revealed that one-fourth of MIs demonstrated by Q waves on the ECG are clinically unrecognized and estimates of the frequency of unrecognized MI detected in the Framingham study may well underestimate the true prevalence of the condition.² The 10-year mortality from an unrecognized MI has been estimated to be 45% to 55%³^,⁴ comparable to or even higher than in patients with diagnosed MI. Given the implications of unrecognized MI, studies are needed to address screening strategies, risk stratification, and the role of post-infarction therapies in these patients.⁵

Nuclear myocardial perfusion imaging (MPI) has been widely used as a non-invasive method for the diagnosis of CAD. In comparative studies with autopsy findings, thallium (Tl)-201 myocardial single-photon emission computed tomography (SPECT) has been shown to accurately assess the extent of MI⁶ and myocardial viability for the selection of therapy and for predicting prognosis.7, 8, 9 Although rest Tc-99m-methoxyisobutyl isonitrile (MIBI) underestimates the extent of viable myocardium compared with Tl-201 imaging, however several studies show that sublingual administration of nitroglycerin before a rest Tc-99m-MIBI study improves the detection of defect reversibility in exercise-induced perfusion defects and thus improves the assessment of myocardial viability in comparison with the standard Tc-99m-MIBI exercise–rest protocol.¹⁰^,¹¹

Coronary artery calcium (CAC) score measured through non-contrast cardiac computed tomography (CCT) scanning has been shown to predict future coronary events in both asymptomatic and symptomatic patients.¹² Non-contrast CCT has also been used for assessing the pericardial fat,¹³ liver fat, and determining the field of view for CCT angiography (CCTA) to reduce radiation dose.¹⁴ The potential role of non-enhanced CCT to detect chronic MI, however, has not been well studied. Areas of chronic left ventricular (LV) infarction are readily apparent on non-contrast CCT as regions of hypo-attenuation either due to deposition of fibrous or adipose tissue¹⁵^,¹⁶ or probably reduced capillary density.¹⁷

We conducted this study to evaluate the accuracy and feasibility of using non-contrast CCT to detect chronic MI in patients with irreversible perfusion defect on MPI. We also define the optimal cutoff value for LV myocardium Hounsfield unit (HU) to detect chronic MI.

Section snippets

Study Population

Our study included 122 consecutive symptomatic patients (with exertional angina or dyspnea) who were referred for coronary CAC scanning at our institution after undergoing an MPI study. Patients with reversible perfusion defects on MPI were excluded. Subjects with arrhythmia, renal failure, or hemodynamic instability were excluded. The characteristics of the study population are summarized in Tables 1 and 2.

Demographic data and clinical history were retrieved from the clinical records for all

Results

A total of 122 patients were studied, including 62 patients (51%) with an irreversible perfusion defect on MPI and 60 patients with a normal MPI. The mean age for this patient cohort was 63.5 ± 12 years and 71(58%) were males.

Out of the 62 patients with irreversible perfusion defect on MPI, non-contrast CCT accurately detected infarct in 57 subjects. Thus, on a per patient level and using MPI as the reference standard, non-contrast CCT showed a sensitivity of 92% (95% CI, 82.2-97.3),

Discussion

Contrast-enhanced CCTA has been shown to be comparable to MPI and contrast-enhanced cardiac magnetic resonance (CMR) in detecting fixed perfusion defect or scar as areas of late contrast enhancement.20, 21, 22, 23 Hypo-enhanced regions on contrast-enhanced CCTA have been shown to closely relate to delayed enhancement of iodinated contrast.²⁴^,²⁵ The aim of this study was to evaluate the ability and feasibility of non-contrast CCT scans to detect chronic MI in patients with irreversible perfusion

Limitation

The primary limitation of this study is that we used irreversible perfusion defects on standard rest MIBI as the reference for detecting chronic MI on CAC scan. However, it should be noted that rest Tc-99m-MIBI underestimates the extent of viable myocardium compared with Tl-201 imaging, and thus some of the irreversible perfusion defects might represent hibernating viable myocardium. Thus, in this study some of the true positives on CAC scan could actually have been false positives. Sublingual

Conclusion

This study demonstrates that the non-contrast CCT has an excellent agreement with MPI in detecting chronic MI. Further prospective studies are warranted to evaluate the role of non-contrast CCT in infarct assessment for the management of at-risk patients.

Acknowledgments

None of the authors have received any funding for this study from any institution.

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: See related editorial, doi:10.1007/s12350-010-9325-0.

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Original ArticleNon-contrast cardiac computed tomography can accurately detect chronic myocardial infarction: Validation study

Abstract

Background

Methods

Results

Conclusion

Introduction

Section snippets

Study Population

Results

Discussion

Limitation

Conclusion

Acknowledgments

J Am Coll Cardiol

Semin Nucl Med

J Nucl Cardiol

Int J Cardiol

Clin Radiol

J Cardiovasc Comput Tomogr

J Nucl Cardiol

J Am Coll Cardiol

Cardiovasc Pathol

J Am Coll Cardiol

Lancet

Incidence, precursors and prognosis of unrecognized myocardial infarction

Adv Cardiol

The incidence and prognosis of unrecognized myocardial infarction in the Honolulu, Hawaii, Heart Program

Arch Intern Med

Incidence and prognosis of unrecognized myocardial infarction: an update on the Framingham study

N Engl J Med

Unrecognized myocardial infarction

Ann Intern Med

Quantification of the extent of myocardial infarction by thallium-201 single photon emission computed tomography: Comparisons with post-mortem findings

J Cardiol

Myocardial viability in cases with persistent perfusion defects on the dipyridamole thallium-201 scintigram. A comparative study with autopsy findings

Jpn Heart J

Original Article
Non-contrast cardiac computed tomography can accurately detect chronic myocardial infarction: Validation study