Erik Hedström

Myocardium at risk after acute infarction in humans on cardiac magnetic resonance: quantitative assessment during follow-up and validation with single-photon emission computed tomography.

OBJECTIVES Our goal was to validate myocardium at risk on T2-weighted short tau inversion recovery (T2-STIR) cardiac magnetic resonance (CMR) over time, compared with that seen with perfusion single-photon emission computed tomography (SPECT) in patients with ST-segment elevation myocardial infarction, and to assess the amount of salvaged myocardium after 1 week. BACKGROUND To assess reperfusion therapy, it is necessary to determine how much myocardium is salvaged by measuring the final infarct size in relation to the initial myocardium at risk of the left ventricle (LV). METHODS Sixteen patients with first-time ST-segment elevation myocardial infarction received (99m)Tc tetrofosmin before primary percutaneous coronary intervention. SPECT was performed within 4 h and T2-STIR CMR within 1 day, 1 week, 6 weeks, and 6 months. At 1 week, patients were injected with a gadolinium-based contrast agent for quantification of infarct size. RESULTS Myocardium at risk at occlusion on SPECT was 33 +/- 10% of the LV. Myocardium at risk on T2-STIR did not differ from SPECT, at day 1 (29 +/- 7%, p = 0.49) or week 1 (31 +/- 6%, p = 0.16) but declined at week 6 (10 +/- 12%, p = 0.0096 vs. 1 week) and month 6 (4 +/- 11%, p = 0.0013 vs. 1 week). There was a correlation between myocardium at risk demonstrated by T2-STIR at week 1 and myocardium at risk by SPECT (r(2) = 0.70, p < 0.001), and the difference between the methods on Bland-Altman analysis was not significant (-2.3 +/- 5.7%, p = 0.16). Both modalities identified myocardium at risk in the same perfusion territory and in concordance with angiography. Final infarct size was 8 +/- 7%, and salvage was 75 +/- 19% of myocardium at risk. CONCLUSIONS This study demonstrates that T2-STIR performed up to 1 week after reperfusion can accurately determine myocardium at risk as it was before opening of the occluded artery. CMR can also quantify salvaged myocardium as myocardium at risk minus final infarct size.

Quantification of absolute myocardial perfusion in patients with coronary artery disease: comparison between cardiovascular magnetic resonance and positron emission tomography

OBJECTIVES The aim of this study was to compare fully quantitative cardiovascular magnetic resonance (CMR) and positron emission tomography (PET) myocardial perfusion and myocardial perfusion reserve (MPR) measurements in patients with coronary artery disease (CAD). BACKGROUND Absolute quantification of myocardial perfusion and MPR with PET have proven diagnostic and prognostic roles in patients with CAD. Quantitative CMR perfusion imaging has been established more recently and has been validated against PET in normal hearts. However, there are no studies comparing fully quantitative CMR against PET perfusion imaging in patients with CAD. METHODS Forty-one patients with known or suspected CAD prospectively underwent quantitative (13)N-ammonia PET and CMR perfusion imaging before coronary angiography. RESULTS The CMR-derived MPR (MPR(CMR)) correlated well with PET-derived measurements (MPR(PET)) (r = 0.75, p < 0.0001). MPR(CMR) and MPR(PET) for the 2 lowest scoring segments in each coronary territory also correlated strongly (r = 0.79, p < 0.0001). Absolute CMR perfusion values correlated significantly, but weakly, with PET values both at rest (r = 0.32; p = 0.002) and during stress (r = 0.37; p < 0.0001). Area under the receiver-operating characteristic curve for MPR(PET) to detect significant CAD was 0.83 (95% confidence interval: 0.73 to 0.94) and for MPR(CMR) was 0.83 (95% confidence interval: 0.74 to 0.92). An MPR(PET) ≤1.44 predicted significant CAD with 82% sensitivity and 87% specificity, and MPR(CMR) ≤1.45 predicted significant CAD with 82% sensitivity and 81% specificity. CONCLUSIONS There is good correlation between MPR(CMR) and MPR(PET.) For the detection of significant CAD, MPR(PET) and MPR(CMR) seem comparable and very accurate. However, absolute perfusion values from PET and CMR are only weakly correlated; therefore, although quantitative CMR is clinically useful, further refinements are still required.

Rapid Initial Reduction of Hyperenhanced Myocardium After Reperfused First Myocardial Infarction Suggests Recovery of the Peri-Infarction Zone One-Year Follow-Up by MRI

Background—The time course and magnitude of infarct involution, functional recovery, and normalization of infarct-related electrocardiographic (ECG) changes after acute myocardial infarction (MI) are not completely known in humans. We sought to explore these processes early after MI and during infarct-healing using cardiac MRI. Methods and Results—Twenty-two patients with reperfused first-time MI were examined by MRI and ECG at 1, 7, 42, 182, and 365 days after infarction. Global left ventricular function and regional wall thickening were assessed by cine MRI, and injured myocardium was depicted by delayed contrast-enhanced MRI. Infarct size by ECG was estimated by QRS scoring. The reduction of hyperenhanced myocardium occurred predominantly during the first week after infarction (64% of the 1-year reduction). Furthermore, during the first week the amount of nonhyperenhanced myocardium increased significantly (P<0.001), although the left ventricular mass remained unchanged. Left ventricular ejection fraction increased gradually, whereas the greater the regional transmural extent of hyperenhancement at day 1, the later the recovery of regional wall thickening. Regional wall thickening decreased progressively with increasing initial transmural extent of hyperenhancement (Ptrend<0.0001). The time course and magnitude of decrease in QRS score corresponded with the reduction of hyperenhanced myocardium. Conclusions—The early reduction of hyperenhanced myocardium may reflect recovery of hyperenhanced, reversibly injured myocardium, which must be considered when predicting functional recovery from delayed contrast-enhanced MRI findings early after infarction. Also, the time course and magnitude for reduction of hyperenhanced myocardium were associated with normalization of infarct-related ECG changes.

Age and gender specific normal values of left ventricular mass, volume and function for gradient echo magnetic resonance imaging: a cross sectional study

BackgroundKnowledge about age-specific normal values for left ventricular mass (LVM), end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and ejection fraction (EF) by cardiac magnetic resonance imaging (CMR) is of importance to differentiate between health and disease and to assess the severity of disease. The aims of the study were to determine age and gender specific normal reference values and to explore the normal physiological variation of these parameters from adolescence to late adulthood, in a cross sectional study.MethodsGradient echo CMR was performed at 1.5 T in 96 healthy volunteers (11–81 years, 50 male). Gender-specific analysis of parameters was undertaken in both absolute values and adjusted for body surface area (BSA).ResultsAge and gender specific normal ranges for LV volumes, mass and function are presented from the second through the eighth decade of life. LVM, ESV and EDV rose during adolescence and declined in adulthood. SV and EF decreased with age. Compared to adult females, adult males had higher BSA-adjusted values of EDV (p = 0.006) and ESV (p < 0.001), similar SV (p = 0.51) and lower EF (p = 0.014). No gender differences were seen in the youngest, 11–15 year, age range.ConclusionLV volumes, mass and function vary over a broad age range in healthy individuals. LV volumes and mass both rise in adolescence and decline with age. EF showed a rapid decline in adolescence compared to changes throughout adulthood. These findings demonstrate the need for age and gender specific normal ranges for clinical use.

Semi-automatic quantification of myocardial infarction from delayed contrast enhanced magnetic resonance imaging.

Objective. Accurate and reproducible assessment of myocardial infarction is important for treatment planning in patients with ischemic heart disease. This study describes a novel method to quantify myocardial infarction by semi-automatic delineation of hyperenhanced myocardium in delayed contrast enhanced (DE) magnetic resonance (MR) images. Design. The proposed method automatically detects the hyperenhanced tissue by first determining the signal intensity of non-enhanced myocardium. A fast level set algorithm was used to limit the heterogeneity of the hyperenhanced regions, and to exclude small regions that constitute noise rather than infarction. The method was evaluated in 40 patients; 20 with acute infarction and 20 with chronic healed infarction using scanners from two different manufacturers. Infarct size measured by the proposed semi-automatic method was compared with manual measurements from three experienced observers. The software used is freely available for research purposes at http://segment.heiberg.se. Results. The difference in infarct size between semi-automatic quantification and the mean of the three observers was 6.1±6.6 ml (mean±SD), and the interobserver variability (SD) was 4.2 ml. Conclusions. The method presented is a highly automated method for analyzing myocardial viability from DE-MR images. The bias of the method is acceptable and the variability is in the same order of magnitude as the interobserver variability for manual delineations.

Cardiovascular magnetic resonance of the myocardium at risk in acute reperfused myocardial infarction: comparison of T2-weighted imaging versus the circumferential endocardial extent of late gadolinium enhancement with transmural projection

BackgroundIn the situation of acute coronary occlusion, the myocardium supplied by the occluded vessel is subject to ischemia and is referred to as the myocardium at risk (MaR). Single photon emission computed tomography has previously been used for quantitative assessment of the MaR. It is, however, associated with considerable logistic challenges for employment in clinical routine. Recently, T2-weighted cardiovascular magnetic resonance (CMR) has been introduced as a new method for assessing MaR several days after the acute event. Furthermore, it has been suggested that the endocardial extent of infarction as assessed by late gadolinium enhanced (LGE) CMR can also be used to quantify the MaR. Hence, we sought to assess the ability of endocardial extent of infarction by LGE CMR to predict MaR as compared to T2-weighted imaging.MethodsThirty-seven patients with early reperfused first-time ST-segment elevation myocardial infarction underwent CMR imaging within the first week after percutaneous coronary intervention. The ability of endocardial extent of infarction by LGE CMR to assess MaR was evaluated using T2-weighted imaging as the reference method.ResultsMaR determined with T2-weighted imaging (34 ± 10%) was significantly higher (p < 0.001) compared to the MaR determined with endocardial extent of infarction (23 ± 12%). There was a weak correlation between the two methods (r2 = 0.17, p = 0.002) with a bias of -11 ± 12%. Myocardial salvage determined with T2-weighted imaging (58 ± 22%) was significantly higher (p < 0.001) compared to myocardial salvage determined with endocardial extent of infarction (45 ± 23%). No MaR could be determined by endocardial extent of infarction in two patients with aborted myocardial infarction.ConclusionsThis study demonstrated that the endocardial extent of infarction as assessed by LGE CMR underestimates MaR in comparison to T2-weighted imaging, especially in patients with early reperfusion and aborted myocardial infarction.

Measurements of wound edge microvascular blood flow during negative pressure wound therapy using thermodiffusion and transcutaneous and invasive laser Doppler velocimetry

The effects of negative pressure wound therapy (NPWT) on wound edge microvascular blood flow are not clear. The aim of the present study was therefore to further elucidate the effects of NPWT on periwound blood flow in a porcine peripheral wound model using different blood flow measurement techniques. NPWT at –20, –40, –80, and –125 mmHg was applied to a peripheral porcine wound (n = 8). Thermodiffusion, transcutaneous, and invasive laser Doppler velocimetry were used to measure the blood perfusion 0.5, 1.0, and 2.5 cm from the wound edge. Thermodiffusion (an invasive measurement technique) generally showed a decrease in perfusion close to the wound edge (0.5 cm), and an increase further from the edge (2.5 cm). Invasive laser Doppler velocimetry showed a similar response pattern, with a decrease in blood flow 0.5 cm from the wound edge and an increase further away. However, 1.0 cm from the wound edge blood flow decreased with high pressure levels and increased with low pressure levels. A different response pattern was seen with transcutaneous laser Doppler velocimetry, showing an increase in blood flow regardless of the distance from the wound edge (0.5, 1.0, and 2.5 cm). During NPWT, both increases and decreases in blood flow can be seen in the periwound tissue depending on the distance from the wound edge and the pressure level. The pattern of response depends partly on the measurement technique used. The combination of hypoperfusion and hyperperfusion caused by NPWT may accelerate wound healing.

Peak CKMB and cTnT accurately estimates myocardial infarct size after reperfusion

Objectives. To find the time-to-peak for creatine kinase MBmass (CKMB) and cardiac troponin T (cTnT) after acute reperfusion, to compare peak and cumulative values to estimate infarct size (IS), and to evaluate clinical routine sampling for assessment of IS. Design. Acute primary percutaneous coronary intervention (PCI) was performed in 38 patients with first-time myocardial infarction. In 21 patients, CKMB and cTnT were acquired before PCI and at 1.5, 3, 6, 12, 18, 24, and 48 hours thereafter. In 17 patients, clinical routine samples were acquired at arrival, and at 10 and 20 h. IS was assessed by delayed contrast-enhanced MRI (DE-MRI). Results. Time-to-peak was 7.6±3.6 h for CKMB and 8.1±3.4 h for cTnT. Peak values correlated strongly to cumulative values (rs=0.97–0.98) as well as to DE-MRI (rs=0.8–0.82). Clinical routine sampling showed lower rs values (0.47–0.60). Conclusions. Peak values are likely captured if CKMB and cTnT are acquired at 3, 6, and 12 h after acute PCI. These peak values can be used to estimate myocardial infarct size after acute PCI.

Determination of the left ventricular long-axis orientation from a single short-axis MR image: relation to BMI and age.

Accurate determination of imaging planes in relation to the left ventricular (LV) long‐axis orientation is important for anatomical and functional evaluation as well as for serial comparisons with cardiac magnetic resonance (CMR) imaging. Therefore, a fast and reliable method to test the accuracy of CMR imaging for measuring the orientation of the LV long‐axis was developed and validated. In addition, the relationship between LV long‐axis orientation and body mass index (BMI), gender and age was assessed. Two approaches were used, a long‐axis approach (based on a manually defined vector) and a short‐axis approach (based on a calculated vector). The concordance between the two approaches was assessed in 72 healthy volunteers. The accuracy and precision of MR imaging for measuring three‐dimensional orientations were tested using a LV phantom. The mean difference between the long‐ and short‐axis approaches for measuring the LV long‐axis orientation in the study population was 0 ± 3°, 0 ± 2°, and −1 ± 3° in the frontal, transverse and sagittal plane, respectively. BMI and age were shown to influence LV long‐axis orientation, especially in the frontal and sagittal planes. A significant difference in LV long‐axis orientation in the frontal and sagittal planes was found between genders. The correlation coefficient between MR‐measured phantom orientation and true phantom orientation was >0·98 in all three orthogonal planes. These observations suggest that a single LV short‐axis MR image can be used for measuring LV long‐axis orientation in patients with no cardiac disease.

The Dipolar ElectroCARdioTOpographic (DECARTO)-like method for graphic presentation of location and extent of area at risk estimated from ST-segment deviations in patients with acute myocardial infarction

A graphic method was developed for presentation of the location and extent of the myocardium at risk in patients with acute myocardial infarction (AMI). This method is based on a mathematical processing of ST-segment deviations of standard 12-lead electrocardiogram following the concept of Titomir and Ruttkay-Nedecky in their dipolar electrocardiotopographic method. The center of the location of the area at risk is given by the spatial orientation of the resultant spatial ST vector, and the extent of the area at risk is derived from the Aldrich score. The areas at risk are projected on a spherical image surface, on which a texture of the anatomical quadrants of the ventricular surface and its coronary artery supply are projected. The method was tested in 10 patients with AMI with single-vessel disease, including 6 patients with an occlusion in the proximal left anterior descending coronary artery (LAD), 3 patients with an occlusion in the right coronary artery, and one patient with occlusion in the left circumflex coronary artery. The estimated areas at risk were compared with myocardial perfusion single photon emission computed tomography. Eight (80%) patients of 10 were correctly localized according to the Aldrich decision rules for the location of AMI. The areas at risk in patients with LAD occlusion correctly localized by the Aldrich score were situated in the anteroseptal and anterosuperior quadrants. In the inferior AMI group, the area at risk was localized in the posterolateral and inferior quadrants. The visual comparison with myocardial perfusion single photon emission computed tomography (SPECT) showed best agreement in patients with LAD involvement. The initial testing showed that this method allows a graphic presentation of estimated area at risk using clinically defined diagnostic rules. The area at risk can be displayed in images that are familiar for clinicians and can be compared with or superimposed on results of other imaging methods used in cardiology.