Summary
Aims
Myocardial infarction with unobstructed coronary artery disease represents a serious diagnostic challenge. The role of cardiac magnetic resonance in the management of cardiomyopathies is increasing. We examined the diagnostic contributions of cardiac magnetic resonance in patients presenting with acute chest pain syndrome, elevated serum cardiac troponin concentrations and no significant coronary artery stenoses.
Methods
Over a 3-year period, 107 consecutive patients (mean age 43.5 years; 62% men) presented to our institution with acute onset of chest pain, elevated serum troponin concentration and unobstructed coronary arteries, and underwent 3-tesla cardiac magnetic resonance at a mean delay of 6.9 days. A diagnosis was made based on: wall motion abnormalities and pericardial effusion on cine mode; myocardial oedema on T2-weighted imaging; abnormalities on first-pass perfusion imaging; and late gadolinium enhancement on T1-weighted imaging.
Results
Cardiac magnetic resonance was normal in 10.3% of patients and contributed a diagnosis in 89.7%, including myocarditis in 59.9%, stress cardiomyopathy (takotsubo syndrome) in 14% and myocardial infarction in 15.8%. Patients with normal cardiac magnetic resonance had a significantly lower mean peak troponin concentration (2.6 ng/mL) than patients with diagnostic cardiac magnetic resonance (9.7 ng/mL; P = 0.01).
Conclusion
Cardiac magnetic resonance contributed a diagnosis in nearly 90% of patients presenting with acute chest pain, elevated serum troponin and unobstructed coronary arteries.
Résumé
Objectif
Les infarctus du myocarde sans lésion coronaire significative constituent une difficulté diagnostique importante. Le rôle de l’IRM cardiaque dans la prise en charge des cardiopathies est croissante. Nous avons étudié l’apport diagnostique de l’IRM cardiaque chez les patients présentant un syndrome douloureux thoracique avec élévations des troponines et absence de lésion coronaire significative.
Méthode et résultats
Sur une période de trois ans, 107 patients consécutifs (âge moyen : 43,5 ; hommes : 62 %) ont été hospitalisés dans notre service pour syndrome douloureux thoracique, troponine sérique élevée, absence de lésion coronaire significative et ont bénéficié d’une IRM cardiaque 3 tesla dans un délai moyen de 6,9 jours. Le diagnostic était basé sur : (a) la présence d’anomalies de la cinétique segmentaire ou d’un épanchement péricardique sur les séquences « ciné » ; (b) d’un œdème myocardique sur les séquences pondérées T2 ; (c) les anomalies de la perfusion de premier passage ; (d) le rehaussement tardif sur les séquences pondérées T1. L’IRM était normal chez 10,3 % et a apporté un diagnostic chez 89,7 % des patients, dont 59,9 % de myocardite, 14 % de cardiopathie de stress (syndrome de takotsubo) et 15,8 % d’infarctus du myocarde. Les patients avec une IRM normale avaient un pic de troponine significativement plus bas (2,6 ng/ml) que les patients avec une IRM contributive (9,7 ng/ml ; p = 0,01).
Conclusion
L’IRM cardiaque apporte un diagnostic étiologique chez près de 90 % des patients présentant un syndrome douloureux thoracique avec élévations des troponines et absence de lésion coronaire significative.
Introduction
Cardiac magnetic resonance (CMR) is a safe, non-invasive and reliable diagnostic test . Chest pain syndrome with elevated troponin concentration (cTn) occurring in the absence of significant coronary artery stenosis represents a serious diagnostic challenge . Studies have recently been published describing the usefulness of CMR in the diagnosis of myocardial infarction , myocarditis and apical ballooning or “takotsubo syndrome” . Consequently, its role is increasing in the initial diagnosis and management of various heart diseases . In this study, we sought to define the prevalence of the different aetiological diagnoses in patients presenting with acute chest pain syndrome, elevated serum cTn and unobstructed coronary arteries, because few studies have been published regarding the systematic use of CMR in this situation.
Methods
This single-centre, prospective study enrolled consecutive patients between November 2006 and November 2009 who presented with: acute onset of chest pain; serum cTn >0.1 ng/mL in two separate assays; and unobstructed coronary arteries (stenosis <50% of the diameter of the vessel) on angiography, computed tomography or both. Initial management, including left ventriculography or transthoracic echocardiography (TTE), was carried out according to the usual local practice. Patients with a history of myocardial infarction, significant valvular disease or hypertrophic cardiomyopathy were excluded.
Cardiac magnetic resonance study
All CMR examinations were performed with a 3-tesla Achieva ® clinical imager (Philips Medical Systems, Best, The Netherlands). A six-element, phased-array, cardiac synergy coil was used for signal detection. Cardiac synchronization was performed using a four-electrode vectorcardiogram. CMR imaging associated cine and morphological sequences for each patient, as described below.
The typical protocol (see details below) involved three stages, after surveys (scout views) to determine cardiac axis locations. First, cine-mode sequences were acquired in the short-axis view (left ventricular function) and T2-weighted black-blood spin echo was carried out in the three typical planes before gadolinium-chelate injection. Second, first-pass perfusion images were acquired in the short-axis view during a first infusion of gadolinium-chelate; immediately after a second gadolinium injection, cine sequences in four chambers and left ventricular long-axis views were acquired. Third, about 8 to 10 minutes after the second injection, inversion-time scouting was carried out and then late gadolinium enhancement sequences were done in the three cardiac planes.
Cine mode
Steady-state, free precession sequences (balanced fast field echo) were acquired in three cardiac conventional planes with these typical settings: 30 phases/R-R; breath-hold acquisition/each slice; slice thickness, 7 mm without or with minimal (≤1 mm) gap; shortest TR/TE, typically 3.7/1.9 ms; flip angle, 45°; field of view (FOV), 320–400 mm; temporal resolution, 30–50 ms; in-plane resolution, 2 × 1.6 mm; matrix, 200 × 256. In the short-axis view, 10–12 slices were acquired with complete coverage of the left ventricle from base to apex, before injection of gadolinium-chelate (Dotarem ® ; Guerbet, Roissy, France). Left ventricular long-axis (three slices) and four-chamber (four to five slices) views were acquired after the injection of gadolinium-chelate. In some difficult cases, these views enabled complementary study of myocardial enhancement.
T2-weighted black-blood spin echo
Multislice, monophase, single-shot, turbo, spin-echo sequences with inversion recovery and fat suppression (T2 BB SPAIR-SSH–T2 Black Blood spectral presaturation attenuated inversion-recovery single shot) were acquired. The following settings were used in three planes covering the entire left ventricle: 10 slices in short-axis view, seven slices in left ventricular long-axis view, eight slices in four-chamber view; breath-hold acquisition in mid-diastole; slice thickness/gap, 7/0.7 mm; TR, 2 × R-R intervals; TE, 45 ms; inversion time, 100 ms; FOV, 370; matrix, 216 × 86; flip angle, 90°.
First-pass perfusion imaging
A single-shot, spoiled, gradient-echo sequence with saturation prepulse (dynamics turbo field gradient-echo) was used with these typical settings: five to six non-contiguous slices in short-axis view placed to cover the left ventricular basal to apical planes and recorded continuously for each cardiac cycle; slice thickness/gap, 8/8 mm; shortest TR/TE, typically 3.8/1/9 ms; flip angle, 20°; matrix, 128 × 77; in-plane resolution, 3 × 5 mm; FOV, 390; total duration, 1 minute with partial breath-hold during initial myocardial enhancement. The acquisition was synchronized to the intravenous injection of 0.1 mmol/kg of gadolinium-chelate at a rate of 4 mL/second, followed by a flush infusion at the same rate.
Late gadolinium enhancement imaging
Two-dimensional, multislice, T1-weighted, inversion-recovery, spoiled, turbo-field, gradient-echo sequences (Spoiled inversion recuperation turbo field echo 3D [SIRTFE 3D]) were acquired 10 minutes after a second injection of 0.1 mmol/kg gadolinium-chelate in three planes, with breath-holding for each stack. The inversion time was chosen to null healthy myocardium, with a previous inversion-time scouting scan sequence. These settings were typically used: stack of 14–18 contiguous slices in the short-axis view; mean duration of apnoea, 18–20 seconds; 10–12 slices in left ventricular long-axis and four-chamber views; mean duration of apnoea, 12 seconds. Typical variables were: slice thickness, 10 mm; TR/TE, 4/1.25 ms; flip angle, 15°; FOV, 350–400; in-plane resolution, 1.5 × 2.4 mm; matrix, 224 × 142.
Cardiac magnetic resonance analysis
The CRM scans were analysed by an experienced cardiologist and an experienced radiologist. Left ventricular ejection fraction (LVEF) and volumes were measured on short-axis stack cine imaging, using the dedicated software of a separate ViewForum™ workstation (Philips). LVEF and volumes, and the presence of myocardial abnormalities and pericardial effusion, were ascertained using standard techniques on cine mode . T2-weighted sequences were visually reviewed for high-signal-intensity areas, consistent with myocardial oedema. The presence of microvascular obstruction was visually ascertained on first-pass perfusion images. Finally, the late gadolinium enhancement images were also visually reviewed for the presence, anatomical distribution and extent of subendocardial, subepicardial, mid-wall, and transmural contrast enhancement. A final CMR diagnosis was made according to the criteria listed in Table 1 . CMR imaging was repeated if the images were interpreted as equivocal by the experienced observers.
| Diagnosis | Wall-motion abnormalities | Pericardial effusion | Oedema | Microvascular obstruction on first-pass perfusion imaging | Late gadolinium enhancement | ||
|---|---|---|---|---|---|---|---|
| Present | Distribution | Extent | |||||
| Myocarditis | 1/0 | 1/0 | 1/0 | 0 | 1 | No coronary artery distribution | Subepicardial; mid-wall |
| Myocardial infarction | 1/0 | 1/0 | 1/0 | 1/0 | 1 | Coronary artery distribution | Subendocardial; transmural |
| Stress cardiomyopathy | 1/0 a | 1/0 | 1/0 | 0 | 0 | – | – |
| No specific diagnosis | 0 | 0 | 0 | 0 | 0 | – | – |
a Wall-motion abnormalities could be absent if cardiac magnetic resonance was delayed.
Statistical analysis
The clinical, biological, electrocardiographic, TTE and CMR characteristics of patients with diagnostic versus normal CMR were compared. Quantitative data are expressed as means ± standard deviations. Between-group comparisons were made using Wilcoxon’s test. Qualitative data are expressed as percentages and were compared using the Chi 2 or Fisher’s test, as appropriate. All analyses were performed using SAS ® statistical package version 9.1 (SAS Institute Inc., Cary, NC, USA). A P value <0.05 was considered statistically significant.
Results
Study population
The flow of patients between screening and entry into the study is shown in Fig. 1 . Among 854 patients referred to our institution for acute chest pain with cTn elevation, 114 (13.3%) presented with an unobstructed coronary angiogram and 107 (12.5%) ultimately underwent CMR during the period of study enrolment. The baseline characteristics of the study population are presented in Table 2 . No patient had a history of cardiomyopathy before enrolment. Coronary computed angiotomography was performed in eight patients (7.4%). LVEF at admission was 48.2 ± 13%. An LVEF ≤40% was found in 32 patients (29.9%) during the initial hospitalization and two patients (1.8%) required extracorporeal life support for 5 and 22 days, before undergoing CMR.
| Characteristics | |
|---|---|
| Clinical | |
| Age (years) | 43.5 ± 19 |
| Men | 67 (62.6) |
| Recent infection/inflammation | 46 (42.9) |
| Recent stress | 13 (12.1) |
| Biological | |
| Peak serum concentration of | |
| Troponin (ng/mL) | 9.0 ± 11 |
| C-reactive protein (mg/L) | 49.2 ± 77 |
| Electrocardiographic | |
| Repolarization abnormalities | 76 (71.0) |
| ST-segment elevation | 14 (13.1) |
| Others | 62 (57.9) |
| Transthoracic echocardiogram | |
| LVEF at admission (%) | 48.2 ± 13 |
| LVEF ≤40% | 32 (29.9) |
| Pericardial effusion | 15 (14.0) |
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