Thrombolysis and myocardial salvage. Results of clinical trials and the animal paradigm--paradoxic or predictable?

Impact of symptom-to-reperfusion-time on transmural infarct extent and left ventricular strain in patients with ST-segment elevation myocardial infarction: a 3D view on the wavefront phenomenon

AIMS

We examined the association between the symptom-to-reperfusion-time and cardiovascular magnetic resonance (CMR)-derived global strain parameters and transmural infarct extent in ST-segment elevation myocardial infarction (STEMI) patients.

METHODS AND RESULTS

The study included 108 STEMI patients who underwent successful primary percutaneous coronary intervention (PPCI). Patients were categorized according to the median symptom-to-reperfusion-time: shorter (<160 min, n = 54) and longer times (>160 min, n = 54). CMR was performed 2-7 days after PPCI and at 1 month. CMR cine imaging was performed for functional assessment and late gadolinium enhancement to evaluate transmural infarct extent. Myocardial feature-tracking was used for strain analysis. Groups were comparable in relation to incidence of LAD disease and pre- and post-PPCI thrombolysis in myocardial infarction (TIMI) flow grades. The mean transmural extent score at follow-up was lower in patients with shorter reperfusion time (P < 0.01). Both baseline and follow-up maximum transmural extent scores were smaller in patients with shorter reperfusion time (P = 0.03 for both). Patients with shorter reperfusion time had more favourable global left ventricular (LV) circumferential strain (baseline, P = 0.049; follow-up, P = 0.01) and radial strain (baseline, P = 0.047; follow-up, P < 0.01), whilst LV longitudinal strain appeared comparable for both baseline and follow-up (P > 0.05 for both). In multi-variable regression analysis including all three strain directions, baseline LV circumferential strain was independently associated with the mean transmural extent score at follow-up (β=1.89, P < 0.001).

CONCLUSION

In STEMI patients, time-to-reperfusion was significantly associated with smaller transmural extent of infarction and better LV circumferential and radial strain. Moreover, infarct transmurality and residual LV circumferential strain are closely linked.

Every minute counts: in-hospital changes of left ventricular regional and global function in patients with ST-segment elevation myocardial infarction

AIMS

The aim of our study was to assess the effects of an early percutaneous coronary intervention on changes of in-hospital left ventricular ejection fraction (LVEF) and wall motion score index (WMSI) in patients with ST-segment elevation myocardial infarction.

METHODS

The study population consisted of 324 consecutive patients with ST-segment elevation myocardial infarction undergoing percutaneous coronary intervention, divided into two groups, according to the first medical contact (FMC)-to-reperfusion time, respectively, 90 min or less (n = 173) and more than 90 min (n = 151). Moreover, we performed a sub-analysis in the group of patients who showed at discharge an improvement in the LVEF of at least 10%.

RESULTS

In both groups at baseline, patients suffered from a moderately reduced LVEF (40.88 ± 8.38% in ≤90 min group vs. 40.70 ± 8.98% in >90 min group; P = 0.858). A WMSI of more than 1 was recorded uniformly: 1.71 ± 0.37 in patients with FMC-to-reperfusion 90 min or less and 1.72 ± 0.38 in patients more than 90 min (P = 0.810). At the time of discharge, a significant improvement in LVEF (43.82 ± 8.38%, P = 0.001) and WMSI (1.60 ± 0.41, P = 0.009) exclusively emerged in the 90 min or less group. Furthermore, we identified 105 patients who experienced an improvement in the LVEF of at least 10% compared with baseline values. In these patients FMC-to-reperfusion and total ischemic time resulted as significantly shorter, when compared with patients with LVEF improvement of less than 10%.

CONCLUSION

Our study confirms and reinforces the concept that reducing the duration of the time between FMC and reperfusion, as well as the total ischemic time influences a positive recovery of left ventricular global and regional function during in-hospital stay.

International Comparison of Factors Associated with Delay in Presentation for AMI Treatment

BACKGROUND

Prehospital delay in response to acute myocardial infarction (AMI) symptoms is well documented in the US and Europe, but little is known about it in Asian countries where cardiovascular disease is increasing.

AIMS

We conducted an observational study of delay times and factors associated with hospital presentation times in 595 patients with AMI from the US, England, Japan and South Korea.

METHODS

Patients were interviewed about responses to symptoms within 72 h of hospital admission and the medical records were reviewed.

RESULTS

The proportions of patients with delay times of 1 h or less were: US--23%, Korea--18%, England--15% and Japan--8%. In the US and England when others present at symptom onset called an ambulance patients presented two to three times sooner. Independent predictors of presentation within an hour of symptom onset were attribution of symptoms to the heart and not waiting for symptoms to go away.

CONCLUSION

Similar education about the need to seek treatment early in response to AMI symptoms may be applicable in Western and Eastern industrialised populations.

Pharmacoinvasive and Primary Percutaneous Coronary Intervention Strategies in ST-Elevation Myocardial Infarction (from the Mayo Clinic STEMI Network)

The effectiveness of a pharmacoinvasive strategy consisting of fibrinolysis and transfer for percutaneous coronary intervention (PCI) compared to primary PCI (PPCI) in patients presenting to non-PCI-capable hospitals with ST-elevation myocardial infarction (STEMI) is not well defined. We analyzed data from the Mayo Clinic STEMI database of patients treated with a pharmacoinvasive strategy (favored in those presenting early after symptom onset) or PPCI in a regional STEMI network from 2004 to 2012. A total of 364 and 1,337 patients were included in the pharmacoinvasive and PPCI groups, respectively. Patients in the PPCI group were older and more frequently had cardiogenic shock at the time of presentation (12.1% vs 7.7%, p = 0.018). Death from any cause occurred in 58 (16%) and 314 (23%) patients in the pharmacoinvasive and PPCI groups, respectively (median follow-up 3.9 and 4.4 years, respectively). In multivariate analyses adjusting for age, gender, and other variables for which the 2 groups differed at baseline, there was no significant difference between the 2 strategies for 30-day (hazard ratio 0.66, 95% confidence interval 0.36 to 1.21) or overall mortality (hazard ratio 0.84, 95% confidence interval 0.63 to 1.12). Shorter door-to-balloon time was associated with increased effectiveness of PPCI (p for trend = 0.015), but there was no difference between the 2 strategies even when considering only the patients with door-to-balloon time in the lowest quartile. In conclusion, fibrinolysis followed by transfer for PCI represents a reasonable alternative when PPCI is not readily available especially in patients presenting early after symptom onset.

Lymphocyte subpopulations in myocardial infarction: a comparison between peripheral and intracoronary blood

The frequency and profile of lymphocyte subsets within the culprit coronary artery were investigated in 33 patients with myocardial infarction and compared to their systemic circulating counterparts. T cell subsets including CD4⁺CD28null, activated and regulatory T-cells, TH1/TH2/TH17 phenotypes, NK and B-cells were studied in intracoronary (IC) and arterial peripheral blood (PB) samples. CD4⁺CD28null T-lymphocytes were significantly increased in IC compared to PB (3.7 vs. 2.9 %, p < 0.0001). Moreover, patients with more than 6 h of evolution of STEMI exhibited higher levels of CD4⁺CD28null T-cells suggesting that this subset may be associated with more intense myocardial damage. The rare NK subpopulation CD3⁻CD16⁺CD56⁻ was also increased in IC samples (5.6 vs. 3.9 %, p = 0.006). CD4⁺CD28null T-cells and CD3⁻CD16⁺CD56⁻ NK subpopulations were also associated with higher CK levels. Additionally, IFN-γ and IL10 were significantly higher in IC CD4⁺ lymphocytes. Particular immune cell populations with a pro-inflammatory profile at the site of onset were increased relative to their circulating counterparts suggesting a pathophysiological role of these cells in plaque instability, thrombi and myocardial damage.

Quantitative evaluation of ischemic myocardial scar tissue by unenhanced T1 mapping using 3.0 Tesla MR scanner

PURPOSE

We aimed to use a noninvasive method for quantifying T1 values of chronic myocardial infarction scar by cardiac magnetic resonance imaging (MRI), and determine its diagnostic performance.

MATERIALS AND METHODS

We performed cardiac MRI on 29 consecutive patients with known coronary artery disease (CAD) on 3.0 Tesla MRI scanner. An unenhanced T1 mapping technique was used to calculate T1 relaxation time of myocardial scar tissue, and its diagnostic performance was evaluated. Chronic scar tissue was identified by delayed contrast-enhancement (DE) MRI and T2-weighted images. Sensitivity, specificity, and accuracy values were calculated for T1 mapping using DE images as the gold standard.

RESULTS

Four hundred and forty-two segments were analyzed in 26 patients. While myocardial chronic scar was demonstrated in 45 segments on DE images, T1 mapping MRI showed a chronic scar area in 54 segments. T1 relaxation time was higher in chronic scar tissue, compared with remote areas (1314±98 ms vs. 1099±90 ms, P < 0.001). Therefore, increased T1 values were shown in areas of myocardium colocalized with areas of DE and normal signal on T2-weighted images. There was a significant correlation between T1 mapping and DE images in evaluation of myocardial wall injury extent (P < 0.05). We calculated sensitivity, specificity, and accuracy as 95.5%, 97%, and 96%, respectively.

CONCLUSION

The results of the present study reveal that T1 mapping MRI combined with T2-weighted images might be a feasible imaging modality for detecting chronic myocardial infarction scar tissue.

Single-dose gadobutrol in comparison with single-dose gadobenate dimeglumine for magnetic resonance imaging of chronic myocardial infarction at 3 T

OBJECTIVES

The aim of this study was to compare the contrast-to-noise ratio (CNR) values of infarct and remote myocardium as well as infarct and blood after application of 0.1 mmol/kg gadobutrol and 0.1 mmol/kg gadobenate dimeglumine on late gadolinium enhancement magnetic resonance (MR) images.

MATERIAL AND METHODS

The study was a prospective randomized controlled clinical study. After informed consent was obtained, 20 patients (12 men, 8 women; mean age, 67 ± 11 years) with known chronic myocardial infarction were included for an intraindividual comparison of a single-dose gadobutrol and a single-dose gadobenate dimeglumine. Two MR imaging examinations were performed within a period of 28 days in a crossover design. Late gadolinium enhancement imaging was performed 10 minutes after gadolinium administration using a 2-dimensional phase-sensitive inversion recovery gradient echo sequence at 3 T. Infarct size, signal intensities (SIs), signal-to-noise ratio, and CNR were determined on phase-sensitive MR images. Values for CNR were calculated as CNRinfarct/myocardium = (SIinfarct - SImyocardium)/SDnoise and CNRinfarct/blood = (SIinfarct - SIblood)/SDnoise. In addition, the areas of myocardial infarction were determined on single slices. The entire infarct volumes were calculated by adding the areas with hyperenhancement multiplied by the slice thickness.

RESULTS

Late gadolinium enhancement was present in all patients. Median values of the infarct area, infarct volume, and transmurality for gadobutrol and gadobenate dimeglumine showed good to excellent concordance (rc = 0.85, rc = 0.95, and rc = 0.71, respectively). The mean signal-to-noise ratio values for infarct, remote myocardium, and ventricular blood were 18.6 ± 6.5, 4.1 ± 3.7, and 14.6 ± 7.5, respectively, for gadobutrol and 18.8 ± 8.9, 4.9 ± 4.5, and 17.8 ± 10.1, respectively, for gadobenate dimeglumine (P = 0.93, P = 0.48, and P = 0.149, respectively). The mean values of CNRinfarct/myocardium and CNRinfarct/blood were 14.5 ± 5.9 and 4.0 ± 4.6, respectively, for gadobutrol and 13.9 ± 6.1 and 0.9 ± 4.5, respectively, for gadobenate dimeglumine (P = 0.69 and P = 0.02, respectively).

CONCLUSION

Both gadobutrol and gadobenate dimeglumine allow for successful late gadolinium enhancement imaging of chronic myocardial infarction after a single-dose application (0.1 mmol/kg) at 3 T. Gadobutrol provides a higher CNR between infarct and blood. The CNRs between infarct and normal myocardium, infarct size, and transmural extent were similar for both contrast agents.

Magnetic resonance imaging (MRI) of inflamed myocardium using iron oxide nanoparticles in patients with acute myocardial infarction - preliminary results

OBJECTIVES

Superparamagnetic iron oxide nanoparticle (SPIO)-based molecular imaging agents targeting macrophages have been developed and successfully applied in animal models of myocardial infarction. The purpose of this clinical trial was to investigate whether magnetic resonance imaging (MRI) of macrophages using ferucarbotran (Resovist®) allows improved visualisation of the myocardial (peri-)infarct zone compared to conventional gadolinium-based necrosis/fibrosis imaging in patients with acute myocardial infarction.

MATERIAL AND METHODS

The clinical study NIMINI-1 was performed as a prospective, non-randomised, non-blinded, single agent phase III clinical trial (NCT0088644). Twenty patients who had experienced either an acute ST-elevation or non-ST-elevation myocardial infarction (STEMI/NSTEMI) were included to this study. Following coronary angiography, a first baseline cardiovascular magnetic resonance (CMR) study (pre-SPIO) was performed within seven days after onset of cardiac symptoms. A second CMR study (post-SPIO) was performed either 10 min, 4h, 24h or 48h after ferucarbotran administration. The CMR studies comprised cine-CMR, T2-weighted "edema" imaging, T2-weighted cardiac imaging and T1-weighted late-gadolinium-enhancement (LGE) imaging.

RESULTS

The median extent of short-axis in-plane LGE was 28% (IQR 19-31%). Following Resovist® administration the median extent of short-axis in-plane T2-weighted hypoenhancement (suggestive of intramyocardial haemorrhage and/or SPIO accumulation) was 0% (IQR 0-9%; p=0.68 compared to pre-SPIO). A significant in-slice increase (>3%) in the extent of T2-weighted "hypoenhancement" (post-SPIO compared to pre-SPIO) was seen in 6/16 patients (38%). However, no patient demonstrated "hypoenhancement" in T2-weighted images following Resovist® administration that exceeded the area of LGE.

CONCLUSIONS

T2/T2-weighted MRI aiming at non-invasive myocardial macrophage imaging using the approved dose of ferucarbotran does not allow improved visualisation of the myocardial (peri-) infarct zone compared to conventional gadolinium-based necrosis/fibrosis imaging.

How to reduce mortality in ST-elevation myocardial infarction patients treated with primary percutaneous coronary interventions: cut the bleeding

BACKGROUND

In-hospital mortality for ST-elevation myocardial infarction (STEMI) has declined thanks to a greater use of primary percutaneous coronary interventions (PCI) associated with more effective antiplatelet and anticoagulant drugs. In this regard, bivalirudin has been shown to decrease total and cardiac mortality as compared to unfractionated heparin (UFH).

OBJECTIVE

The primary purpose of this analysis is to evaluate the hypothesis that the reduction of in-hospital bleeding is the most plausible explanation for the improved survival of STEMI patients treated with bivalirudin during primary PCI. The secondary objective is to reconsider the prognostic significance of the radial access alone or in association with bivalirudin on the basis of the published data.

METHODS

We have done a comprehensive evaluation of the main and related publications of the HORIZONS-AMI trial in addition to an extensive research by Medline of randomized trials evaluating the prognostic impact of radial access as compared with the femoral one in primary PCI.

RESULTS

In the HORIZONS-AMI trial bivalirudin resulted in significantly lower rates of the 30 day primary endpoint (defined as major adverse ischemic outcomes plus major bleeding) over UFH plus GPI, largely due to the significantly lower rate of the protocol-defined major bleeding. All-cause and cardiac mortality were also reduced in the bivalirudin arm at 3 year follow-up. Recent studies have also shown that the use of the radial instead of the femoral approach for primary PCI is associated with reduced bleeding as well as reduced mortality.

CONCLUSIONS

Our research suggests that decreasing bleeding by either a pharmacologic strategy (use of bivalirudin) or a technical approach (the transradial access) improves survival in STEMI patients undergoing primary PCI. The validity of this hypothesis should be confirmed by specific randomized trials.

Imaging of myocardial infarction using ultrasmall superparamagnetic iron oxide nanoparticles: a human study using a multi-parametric cardiovascular magnetic resonance imaging approach

AIMS

The purpose of this clinical trial was to investigate whether cardiovascular magnetic resonance imaging (CMR) using ferumoxytol (Feraheme™, FH), an ultrasmall superparamagnetic iron oxide nanoparticle (USPIO), allows more detailed characterization of infarct pathology compared with conventional gadolinium-based necrosis/fibrosis imaging in patients with acute myocardial infarction.

METHODS AND RESULTS

Fourteen patients who had experienced an acute ST-elevation myocardial infarction were included in this study. Following coronary angiography, a first baseline study (pre-FH) was performed followed by subsequent CMR studies (post-FH) 48 h after intravenous ferumoxytol administration. The CMR studies comprised cine-CMR, T(2)-weighted short tau inversion recovery spin echo imaging, T(2)-mapping, and T(1)-weighted late gadolinium enhancement (LGE) imaging. The median extent of short-axis in-plane LGE was 30% [inter-quartile range (IQR) 26-40%]. The median in-plane extent of T(2)-weighted 'hypoenhancement' in the region of myocardial infarction, which was not present prior to ferumoxytol administration in any patient, was 19% (IQR 14-22%; P < 0.001 compared with the extent of LGE). The median in-plane extent of areas showing signal void in T(2)-mapping images post-FH in the region of myocardial infarction was 16% (IQR 12-18%; P < 0.001 compared with the extent of LGE; P = 0.34 compared with the extent of T(2)-weighted hypoenhancement). A substantial drop in absolute T(2)-values was observed not only in the infarct core and peri-infarct zone, but also in the remote 'healthy' myocardium, although there was only a minor change in the skeletal muscle. Substantial ferumoxytol uptake was detected only in cultured macrophages, but not in peripheral blood monocytes from study patients.

CONCLUSION

We could demonstrate in humans that USPIO-based contrast agents enable a more detailed characterization of myocardial infarct pathology mainly by detecting infiltrating macrophages. Considering the multi-functionality of USPIO-based particles and their superior safety profile compared with gadolinium-based compounds, these observations open up new vistas for the clinical application of USPIO.

Gender differences in contrast-enhanced magnetic resonance imaging after acute myocardial infarction

Besides different risk profiles for cardiovascular events in men and women, several studies reported gender differences in mortality after acute myocardial infarction (AMI). As infarct size has been shown to correlate with mortality, it is widely accepted as surrogate marker for clinical outcome. Currently, cardiovascular imaging studies covering the issue of gender differences are rare. As magnetic resonance scar characterization parameters are emerging as additional prognostic factors after acute myocardial infarction, we sought to evaluate gender differences in CMR infarct characteristics in patients after acute myocardial infarction. We prospectively analyzed patients (n = 448) with AMI and primary angioplasty, who underwent contrast-enhanced cardiac magnetic resonance (CMR) imaging on a 1.5 T scanner in median 5 [4, 6] days after the acute event. [corrected]. CMR scar size was measured 15 min after gadolinium injection. In addition presence and extent of microvascular obstruction (MVO) was assessed. A matched pair analysis was performed in order to exclude confounding by gender related co-morbidities and gender differences in established clinical risk factors. Matching process according to clinical risk defined by GRACE score resulted in 93 mixed gender couples. Women were significantly older than men (64.4 ± 11.9 vs. 60.5 ± 12.3, p = 0.03) and presented with a significantly better ejection fraction before angioplasty (48.9 ± 8.4 vs. 46.2 ± 8.9, p = 0.04). Infarct size did not differ significantly between women and men (13.5 ± 10.7 vs. 15.1 ± 11.8, p = 0.32). Size of MVO was significantly smaller in women than in men (0.48 ± 1.3 vs. 1.2 ± 3.0, p = 0.03). Comparing scar characterization between women and men with similar risk profiles revealed no gender differences in scar size. Size of MVO, however, was significantly smaller in women and might reflect better cardioprotective mechanisms in women. Whether these changes have prognostic implications has to be tested on a larger patient population.

Impact of system delay on infarct size, myocardial salvage index, and left ventricular function in patients with ST-segment elevation myocardial infarction

BACKGROUND

The association between reperfusion delay and myocardial damage has previously been assessed by evaluation of the duration from symptom onset to invasive treatment, but results have been conflicting. System delay defined as the duration from first medical contact to first balloon dilatation is less prone to bias and is also modifiable. The purpose was to evaluate the impact of system delay on myocardial salvage index (MSI) and infarct size in patients with ST-elevation myocardial infarction treated with primary percutaneous coronary intervention (PCI).

METHODS

In patients with ST-elevation myocardial infarction, MSI and final infarct size were assessed using cardiovascular magnetic resonance. Myocardial area at risk was measured within 1 to 7 days, and final infarct size was measured 90 ± 21 days after intervention. Patients were grouped according to system delay (0 to 120, 121 to 180, and >180 minutes).

RESULTS

In 219 patients, shorter system delay was associated with a smaller infarct size (8% [interquartile range 4-12%], 10% [6-16%], and 13% [8-17%]; P < .001) and larger MSI (0.77 [interquartile range 0.66-0.86], 0.72 [0.59-0.80], and 0.68 [0.64-0.72]; P = .005) for a system delay of up to 120, 121 to 180, and >180 minutes, respectively. A short system delay as a continuous variable independently predicted a smaller infarct size (r = 0.30, P < .001) and larger MSI (r = -0.25, P < .001) in multivariable linear regression analyses. Finally, shorter system delay (0-120 minutes) was associated with improved function (P = .019) and volumes of left ventricle (P = .022).

CONCLUSIONS

A shorter system delay resulted in smaller infarct size, larger MSI, and improved LV function in patients treated with primary PCI. Thus, this study confirms that minimizing system delay is crucial for primary PCI-related benefits.

Factors related to prehospital time delay in acute ST-segment elevation myocardial infarction

Despite recent successful efforts to shorten the door-to-balloon time in patients with acute ST-segment elevation myocardial infarction (STEMI), prehospital delay remains unaffected. Nonetheless, the factors associated with prehospital delay have not been clearly identified in Korea. We retrospectively evaluated 423 patients with STEMI. The mean symptom onset-to-door time was 255 ± 285 (median: 150) min. The patients were analyzed in two groups according to symptom onset-to-door time (short delay group: ≤ 180 min vs long delay group: > 180 min). Inhospital mortality was significantly higher in long delay group (6.9% vs 2.8%; P = 0.048). Among sociodemographic and clinical variables, diabetes, low educational level, triage via other hospital, use of private transport and night time onset were more prevalent in long delay group (21% vs 30%; P = 0.038, 47% vs 59%; P = 0.013, 72% vs 82%; P = 0.027, 25% vs 41%; P < 0.001 and 33% vs 48%; P = 0.002, respectively). In multivariate analysis, low educational level (1.66 [1.08-2.56]; P = 0.021), symptom onset during night time (1.97 [1.27-3.04]; P = 0.002), triage via other hospital (1.83 [1.58-5.10]; P = 0.001) and private transport were significantly associated with prehospital delay (3.02 [1.81-5.06]; P < 0.001). In conclusion, prehospital delay is more frequent in patients with low educational level, symptom onset during night time, triage via other hospitals, and private transport, and is associated with higher inhospital mortality.

Dual inversion-recovery mr imaging sequence for reduced blood signal on late gadolinium-enhanced images of myocardial scar

PURPOSE

To investigate whether a dual inversion-recovery (IR) prepulse improves scar-to-blood contrast and expert confidence and consistency at late gadolinium-enhanced magnetic resonance (MR) imaging of myocardial scar compared with the standard IR technique at 3.0 T.

MATERIALS AND METHODS

The study was approved by the local ethics committee, and all patients provided written informed consent. Twelve men (mean age±standard deviation, 63 years±8) with known myocardial scar underwent MR imaging 10, 20, and 30 minutes after administration of 0.2 mmol/kg gadobutrol with a standard and dual IR sequence. Contrast-to-noise ratios (CNRs) were measured by using region-of-interest analysis, and data were compared with the analysis of variance test. Two experts measured scar size and transmurality, and data were compared with the Student t test and Bland-Altman test. Experts assigned confidence scores for scar detection and transmurality, which were compared with a Wilcoxon matched-pairs signed rank test.

RESULTS

Patient data showed improved scar-to-blood CNR for the dual IR technique compared with the standard IR technique at all time points (P<.05). For images obtained 20 minutes after contrast material administration, the dual IR sequence provided higher confidence scores for scar detection and transmurality assessment (P<.05) and resulted in more consistent assessment of scar size and transmurality between readers compared with the IR sequence (P<.05).

CONCLUSION

In this preliminary patient study, the dual IR prepulse improved contrast, scar visualization, and expert confidence and reduced expert differences in transmurality and scar size assessment compared with the standard IR technique.

Computed tomography imaging in myocardial infarction

Over recent decades, noninvasive imaging has become well established in the diagnostic work-up of patients suffering from myocardial infarction. It provides insights into the individual patient's prognosis and guides therapeutic decisions. MRI has long been considered the standard of reference in the noninvasive imaging of myocardial infarction. Only recently have different multidetector-row spiral computed tomography (MDCT) techniques successfully been evaluated for the visualization of myocardial infarction. This article describes different concepts of cardiac MDCT imaging in acute and chronic myocardial infarction. MDCT assessment of myocardial edema, myocardial perfusion and delayed myocardial contrast enhancement are introduced, with the latter evolving as key concept of viability imaging by means of MDCT. The current status of MDCT in the diagnostic work-up of myocardial infarction is reviewed.

Improved detection of subendocardial hyperenhancement in myocardial infarction using dark blood-pool delayed enhancement MRI

OBJECTIVE

Delayed enhancement MRI using fast segmented k-space inversion recovery (IR) gradient-echo imaging is a well established "bright-blood" technique for identifying myocardial infarction and is used as the reference standard sequence in this study. The purpose of this study was to validate a recently developed dark blood-pool delayed enhancement technique in a porcine animal model, evaluate its performance in human patients, and quantify its performance compared with the reference standard in both.

SUBJECTS AND METHODS

In an animal study, the reference standard and dark blood-pool delayed enhancement were assessed in three pigs with induced myocardial infarction. In a human study, 26 patients, 31-81 years old (19 men and seven women), with a known history of myocardial infarction were imaged using the reference standard and dark blood-pool delayed enhancement. Contrast-to-noise ratio (CNR), signal intensity ratio, signal-to-noise ratio (SNR), and qualitative scores of hyperenhancement were recorded. Measurements were compared using paired samples t test and Wilcoxon's signed rank test.

RESULTS

In the animal study, the mean CNR of infarct to blood pool was 11 times higher for dark blood-pool delayed enhancement than for the reference standard. The mean SNR was 4.4 times higher for the reference standard. In the human study, the mean CNR and signal intensity ratio of hyperenhancing myocardium to the blood pool were 1.9 (p = 0.04) and 5.5 (p < 0.01) times higher, respectively, for dark blood-pool delayed enhancement compared with reference standard. The mean CNR and signal intensity ratio of hyperenhancing myocardium to normal myocardium and SNR were 2.8 (p < 0.01), 1.3 (p = 0.07), and 2.8 (p < 0.01) higher, respectively, for the reference standard. Qualitative analysis identified seven extra segments with grade 1 scars using dark blood-pool delayed enhancement (p < 0.01).

CONCLUSION

Dark blood-pool delayed enhancement is complementary to the reference standard. It can detect more subendocardial foci of hyperenhancement, thus potentially identifying more infarcts and changing patient management.

Upstream high-dose tirofiban does not reduce myocardial infarct size in patients undergoing primary percutaneous coronary intervention: a magnetic resonance imaging pilot study

BACKGROUND

Primary percutaneous coronary intervention (PCI) is more effective than fibrinolytic therapy for ST-segment elevation myocardial infarction (STEMI), but initial treatment delay to intervention is the main limitation of this strategy.

HYPOTHESIS

Upstream use of high-dose tirofiban could reduce myocardial infarct size, using analysis of contrast-enhanced magnetic resonance imaging (CE-MRI).

METHODS

Patients with STEMI within 12 hours after symptom onset were randomized to a facilitated PCI group (n = 19) or to a primary PCI group (n = 20). The primary endpoint was myocardial infarct size evaluated by the volume of delayed hyperenhancement on CE-MRI at 1 month after index procedure.

RESULTS

The baseline clinical characteristics were not significantly different between the 2 groups. Although the incidence of pre-PCI thrombolysis in myocardial infarction (TIMI) flow grade 2 to 3 was significantly higher in the facilitated PCI group than in the primary PCI group (47.4% vs 15.0%, P = 0.03), the achievement of myocardial blush grade 2 to 3 or ST-segment resolution at 30 minutes after procedure was not significantly different between the facilitated PCI and the primary PCI group (36.8% vs 40%, P = 0.84 and 31.6% vs 20%, P = 0.41, respectively). Infarct size on CE-MRI was similar in the facilitated PCI group and the conventional primary PCI group (22.1% +/- 11.7% vs 25.2% +/- 13.2%, P = 0.44). At 6 months, the left ventricular ejection fraction (LVEF) on echocardiography was 52.6% +/- 10.4% in the facilitated PCI group and 50.9% +/- 9.8% in the primary PCI group (P = 0.68).

CONCLUSION

Despite the improvement of initial TIMI flow grade, the upstream use of high-dose tirofiban did not reduce myocardial infarct size measured by CE-MRI.

Acute myocardial infarction: serial cardiac MR imaging shows a decrease in delayed enhancement of the myocardium during the 1st week after reperfusion

PURPOSE

To evaluate the time course of delayed gadolinium enhancement of infarcted myocardium by using serial contrast agent-enhanced (CE) cardiac magnetic resonance (MR) images obtained during the acute, subacute, and chronic stages of infarction.

MATERIALS AND METHODS

The study protocol was reviewed and approved by the local ethics committee, and written informed consent was obtained. Seventeen patients with reperfused acute myocardial infarction (AMI) underwent cine and CE cardiac MR a median of 1, 7, 35, and 180 days after reperfusion. Infarct size determined on the basis of delayed enhancement MR imaging at different times was compared by using nonparametric tests and Bland-Altman analysis. Extent of myocardial enhancement was compared with single photon emission computed tomographic (SPECT) measures of infarct size with Spearman correlation. Regional myocardial enhancement extent and contractility were analyzed with nonparametric tests.

RESULTS

Infarct size was 18.3% of total myocardial LV volume on day 1 after AMI and decreased to 12.9% on day 7, 11.3% on day 35, and 11.6% on day 180 (all P < .001). Estimated infarct size on day 7, as compared with day 1 enhancement size, declined by 57.1% within the epicardium and by 6.3% within the endocardium (both P < .001). Infarct size on day 7 showed only minor changes at subsequent imaging and yielded a high correlation with SPECT measurements of infarct size (r = 0.84). Infarct size on day 7 inversely correlated with long-term wall thickening (P < .0001) and allowed prediction of contractile function.

CONCLUSION

In patients with AMI and successful coronary reperfusion, the size of delayed gadolinium enhancement at CE cardiac MR imaging significantly diminished during the 1st week after infarction. Thus, timing of CE cardiac MR imaging is crucial for accurate measurement of myocardial infarct size early after AMI.

Acceptable reperfusion delay to prefer primary angioplasty over fibrin-specific thrombolytic therapy is affected (mainly) by the patient's mortality risk: 1 h does not fit all

AIMS

The mortality benefit of primary percutaneous coronary angioplasty (PPCI) is time-dependent. We explored the relationship between risk and PPCI delay, adjusted for the delay at presentation, which leads to equivalent 30-day mortality between PPCI and fibrin-specific thrombolytic therapy (TT).

METHODS AND RESULTS

Sixteen randomized trials were analysed. The mortality rate in the TT arm was interpreted as a proxy for mortality risk. We calculated the PPCI-related delay as the difference between 'door-to-balloon minus door-to-needle' time and PPCI survival benefit as 30-day mortality after TT minus 30-day mortality after PPCI. Baseline mortality risk (P = 0.004), PPCI delay (P = 0.006), and presentation delay (P = 0.03) were correlated with 30-day survival benefit of PPCI. By the regression analysis, the following equation: Z = 0.59X - 0.033Y - 0.0003W - 1.3 (where Z is the absolute reduction in mortality of PPCI over TT, X the mortality risk, Y the PPCI-delay, and W the presentation delay), can be calculated. According to this equation, acceptable angioplasty-related delay shows a wide range based mainly on the different risk profiles.

CONCLUSION

Baseline mortality risk of ST elevation myocardial infarction patients is a major determinant of the acceptable time delay to choose the most appropriate therapy. Although a longer delay lowers the survival advantage of PPCI, a longer PPCI-related delay could be acceptable in high-risk STEMI patients.

Systematic review of fibrinolytic-facilitated percutaneous coronary intervention: potential benefits and future challenges

BACKGROUND

Facilitated percutaneous coronary intervention (PCI) is defined as the administration of fibrinolytic therapy and/or glycoprotein (GP) IIb/IIIa inhibitors to minimize myocardial ischemia time while waiting for PCI. A pooled meta-analysis suggested that facilitated PCI was associated with higher rates of mortality and morbidity compared with nonfacilitated PCI.

OBJECTIVE

The heterogeneous and complex trials of facilitated PCI were systematically reviewed to identify where this strategy may be beneficial and deserving of further research.

METHODS

MEDLINE, EMBASE, the Cochrane database, the Internet and conference proceedings were searched to obtain relevant trials. Human studies that randomly assigned patients to fibrinolytic-facilitated PCI (administration of fibrinolytic therapy alone or in combination with GP IIb/IIIa inhibitors before angiography) versus nonfacilitated PCI were included.

RESULTS

Nine trials encompassing 3836 patients were reviewed. The facilitated PCI strategy was fibrinolytic therapy alone in seven trials and half-dose fibrinolytic therapy plus GP IIb/IIIa inhibitors in two trials. In patients who had fibrinolysis less than 2 h after symptom onset (mainly in the prehospital setting) and/or slightly delayed PCI 3 h to 24 h after fibrinolysis, facilitated PCI was associated with the greatest Thrombolysis In Myocardial Infarction (TIMI) grade 3 flow and a trend toward reduced mortality. Overall, facilitated PCI was associated with increased intracranial hemorrhage and reinfarction. Combining half-dose fibrinolytic therapy and GP IIb/IIIa inhibitors reduced reinfarction but increased major bleeding.

CONCLUSIONS

Facilitated PCI cannot be recommended outside of experimental protocols at this time. Further research should focus on selecting patients with higher benefit-to-risk ratios and performing prehospital fibrinolysis with optimal antiplatelet or antithrombin therapy, as well as slightly delayed PCI in patients who are stable or geographically removed from PCI facilities.

Simultaneous transdermal extraction of glucose and lactate from human subjects by reverse iontophoresis

This study investigated the possibility of simultaneously extracting glucose and lactate from human subjects, at the same skin location, using transdermal reverse iontophoresis. Transdermal monitoring using iontophoresis is made possible by the skin’s permeability to small molecules and the nanoporous and microporous nature of the structure of skin. The study was intended to provide information which could be used to develop a full, biosensor-based, monitoring system for multiple parameters from transdermal extraction. As a precursor to the human study, in vitro reverse iontophoresis experiments were performed in an artificial skin system to establish the optimum current waveforms to be applied during iontophoresis. In the human study, a bipolar DC current waveform (with reversal of the electrode current direction every 15 minutes) was applied to ten healthy volunteers via skin electrodes and utilized for simultaneous glucose and lactate transdermal extraction at an applied current density of 300 μA/cm². Glucose and lactate were successfully extracted through each subject’s skin into the conducting gel that formed part of each iontophoresis electrode. The results suggest that it will be possible to noninvasively and simultaneously monitor glucose and lactate levels in patients using this approach and this could have future applications in diagnostic monitoring for a variety of medical conditions.

Contrast-enhanced magnetic resonance imaging in the assessment of myocardial infarction and viability

Contrast-enhanced magnetic resonance imaging (MRI) can be used to visualize the transmural extent of myocardial infarction with high spatial resolution. The aim of this review is to provide an overview of the use of contrast-enhanced MRI for characterization of ischemic myocardial injury in comparison to other imaging methods and its relevance in clinical syndromes related to coronary artery disease. Infarcted myocardium appears hyperenhanced compared with normal myocardium when imaged by a delayed-enhancement MRI technique with the use of an inversion-prepared T(1)-weighted sequence after injection of gadolinium chelates, such as gadolinium-diethylenetriamine pentaacetic acid. Experimental and clinical studies indicate that the extent of delayed enhancement is reproducible and closely correlates with the size of myocardial necrosis or infarct scar as determined by established in vitro and in vivo methods. Furthermore, MRI appears to be more sensitive than other imaging methods in detecting small subendocardial infarctions. The transmural extent of delayed enhancement potentially predicts functional outcome after revascularization in acute myocardial infarction and chronic ischemic heart disease, indicating that it can accurately discriminate between infarction and dysfunctional but viable myocardium. Further experience from clinical trials is needed to understand the association of delayed enhancement with clinical outcomes.

Thrombolysis in acute myocardial infarction: current status

ST-segment elevation myocardial infarction (STEMI) is still a major public health problem in the modern world. Therapeutic options have changed much over the last 20 years, with a shift in favor of mechanical reperfusion over pharmacologic reperfusion. Thrombolytic therapy still has much to offer in the management of STEMI, however, because many patients do not have timely access to a facility with the required expertise for establishing mechanical reperfusion. This review highlights the history of thrombolytic therapy, adjunctive therapies, the relationship with mechanical reperfusion, and potential roles for thrombolysis in the future.

Quantitation of infarct size in patients with chronic coronary artery disease using rest-redistribution Tl-201 myocardial perfusion SPECT: correlation with contrast-enhanced cardiac magnetic resonance

BACKGROUND

Rest and rest-redistribution thallium 201 myocardial perfusion single photon emission computed tomography (SPECT) (MPS) has been incompletely validated in patients for determination of the total amount of scarred myocardium. We sought to determine whether rest or redistribution Tl-201 MPS provides an accurate determination of infarct size as defined by delayed contrast-enhanced cardiac magnetic resonance (CMR).

METHODS AND RESULTS

We studied patients (n = 44) with chronic coronary artery disease referred for rest-redistribution Tl-201 MPS, who were also studied by contrast-enhanced CMR within 3 +/- 4 days. Patients were considered retrospectively based on a series of patients referred for clinically indicated MPS. Defect size, as a percent of left ventricular mass (% LV), was determined by quantitative perfusion SPECT (QPS) and compared with the volume of delayed hyperenhancement on contrast-enhanced CMR, normalized to LV mass. Infarct size varied from 0% to 43% LV. Rest QPS defect size correlated with the amount of nonviable myocardium assessed by contrast-enhanced CMR (r = 0.76; mean difference, 4.3% +/- 8.0% LV). When delayed thallium data were considered, redistribution QPS was superior to rest QPS for determination of infarct size (redistribution r = 0.90; mean difference, 2.4% +/- 5.2% LV; P = .03 vs rest).

CONCLUSION

Rest-redistribution Tl-201 MPS provides a more accurate measurement of total infarct size than rest-only Tl-201 MPS and correlates with contrast-enhanced CMR.

Low Tube Voltage Improves Computed Tomography Imaging of Delayed Myocardial Contrast Enhancement in an Experimental Acute Myocardial Infarction Model

OBJECTIVE

We sought to evaluate the influence of tube voltage on the visualization of acute myocardial infarction (MI) in cardiac multislice spiral computed tomography (MSCT).

MATERIALS AND METHODS

Acute MI was induced in 12 domestic pigs by a 45-minute balloon occlusion of the left anterior descending artery. Delayed enhancement magnetic resonance imaging was performed 15 minutes after the injection of 0.2 mmol/kg Gd-DTPA. On the same day, retrospectively ECG-gated MSCT was performed at 120, 100, and 80 kV (16x0.75mm, 550mAseff.) 15 minutes after the injection of 140 mL of iopromide (1 g/iodine/kg). The pigs were killed and the hearts were excised and stained with 2,3,5-triphenyltetrazolium chloride. The area of acute MI, contrast-to-noise ratio (CNR), and percent signal difference were compared among the different imaging techniques by applying Bland-Altman plots and 2-way analysis of variance.

RESULTS

On MSCT at 120, 100, and 80 kV, the respective mean acute MI sizes were 18.4+/-11.4%, 19.3+/-11.5%, and 20.5+/-11.6%. The mean MI sizes were 20.8+/-12.2% and 20.1+/-12.4% on magnetic resonance imaging and 2,3,5-triphenyltetrazolium chloride staining. Analysis of variance did not show any statistically significant differences between the different techniques with respect to the size of acute MI (P=0.9880). Comparing the different kV settings on MSCT, the highest percent signal difference (74.7+/-12.1%) and the highest CNR (6.7+/-1.8) between infarcted and healthy remote myocardium were achieved at 80 kV.

CONCLUSIONS

When compared with routine scan protocols, low tube voltage MSCT allows for the assessment of the MI size with an improved CNR and contrast resolution. This technique appears to be advantageous for assessing myocardial viability from contrast enhanced late-phase MSCT.

Late-phase MSCT in the different stages of myocardial infarction: animal experiments

The purpose of this study was to intraindividually evaluate myocardial late enhancement on multislice spiral computed tomography (MSCT) for the assessment of the different stages of myocardial infarction (MI) in comparison with magnetic resonance (MR) imaging. Reperfused MI was successfully induced in seven pigs. Delayed enhancement MR imaging and late-phase MSCT were performed on day 0 as well as 7, 28 and 90 days after the procedure. The pigs were sacrificed, and 2,3,5-triphenyltetrazolin-chloride (TTC) staining was acquired. MI size was compared between the different imaging techniques and over time applying Bland-Altman plots and multivariate analysis with repeated measures. On day 0 the mean MI size was 23.7 +/- 11.8% of the left ventricular area on MSCT and 24.5 +/- 10.6% on MR imaging. On day 90 infarct sizes decreased significantly to 16.9 +/- 8.4% and 18.9 +/- 8.0%, respectively (P = 0.0019). On TTC staining the size of MI was 16.8 +/- 8.2%. Bland-Altman plots showed a good agreement between MSCT and MR imaging with mean deviations ranging from -3.4% to -1.9%. No significant difference between MSCT and MR imaging was found. Myocardial late enhancement on MSCT correlates well with delayed enhancement MR imaging during the different stages of MI and allows for reliable assessment of reperfused MI during acute, subacute and chronic stages.

Characterization of myocardial viability using MR and CT imaging

Cardiovascular magnetic resonance (MR) imaging is of proven clinical value for the noninvasive characterization of myocardial viability. Computed tomography (CT) is also being exploited for this indication. Examples of each of these imaging strategies for the assessment of myocardial viability will be provided in this review. Key MRI concepts and practical considerations such as customized MR imaging techniques and tailored imaging protocols dedicated to viability assessment are outlined with the primary focus on recent developments. Clinical applications of MR-based viability assessment are reviewed, ranging from rapid functional cine imaging to tissue characterization using T2-weighted imaging and T1-weighted late-contrast-enhanced imaging. Next, the merits and limitations of state-of-the-art CT imaging are surveyed, and their implications for viability assessment are considered. The final emphasis is on current trends and future directions in noninvasive viability assessment using MRI and CT.

Diagnostic Value of Contrast-Enhanced Magnetic Resonance Imaging and Single-Photon Emission Computed Tomography for Detection of Myocardial Necrosis Early After Acute Myocardial Infarction

OBJECTIVES

This study sought to evaluate the diagnostic value of contrast-enhanced magnetic resonance imaging (CMR) and single-photon emission computed tomography (SPECT) for detection of myocardial necrosis after acute myocardial infarction (AMI).

BACKGROUND

Single-photon emission computed tomography is widely accepted in the clinical setting for detection and estimation of myocardial infarction. Contrast-enhanced magnetic resonance imaging offers technical advantages and is therefore a promising new method for identification of infarcted tissue.

METHODS

Seventy-eight patients with AMI were examined by CMR and SPECT 7 days after percutaneous coronary intervention. Contrast-enhanced magnetic resonance imaging and SPECT images were scored for presence and location of infarction using a 17-segment model. Results were compared with the peak troponin T level, electrocardiographic, and angiographic findings.

RESULTS

Acute myocardial infarction was detected significantly more often by CMR than SPECT (overall sensitivity: 97% vs. 87%; p = 0.008). Sensitivity of CMR was superior to SPECT in detecting small infarction as assessed by the peak troponin T level <3.0 ng/ml (92 vs. 69%; p = 0.03), and infarction in non-anterior location (98% vs. 84%; p = 0.03). Non-Q-wave infarctions were more likely to be detected by CMR (sensitivity 85% vs. 46%; p = 0.06). While CMR offered high sensitivity for detection of AMI irrespective of the infarct-related artery, SPECT was less sensitive, particularly within the left circumflex artery territory.

CONCLUSIONS

Contrast-enhanced magnetic resonance imaging is superior to SPECT in detecting myocardial necrosis after reperfused AMI because CMR detects small infarcts that were missed by SPECT independent of the infarct location. Thus, CMR is attractive for accurate detection and assessment of the myocardial infarct region in patients early after AMI.

Volumetric assessment of myocardial viability in rats using 3D double contrast enhanced T1 and T2-weighted MRI

OBJECTIVE

Volumetric evaluation of the myocardial viability post-infarction in rats using 3D in vivo MR imaging at 7 T using injection of an extracellular paramagnetic contrast agent and intravascular superparamagnetic iron oxide nanoparticles in the same imaging session.

MATERIALS AND METHODS

Five hours after induction of permanent myocardial infarction in rats (n=6), 3D in vivo T1- and T2-weighted MR Imaging was performed prior to and after Gd-DOTA injection (0.2 mmol/kg) and prior to and after nanoparticle injection (5 mg Fe/kg) to assess infarct size and myocardial viability.

RESULTS

3D MR Imaging using a successive contrast agent injection showed a difference of infarct size after Gd-DOTA injection on T1-weighted images compared to the one measured on T2-weighted images after Gd-DOTA and nanoparticle injection.

CONCLUSION

The use of 3D T1- and T2-weighted MR Imaging using a double contrast agents protocol made possible the accurate characterization of myocardial infarction volume and allowed the detection of myocardial viability post-infarction in rats.

Myocardial infarct: depiction with contrast-enhanced MR imaging--comparison of gadopentetate and gadobenate

Institutional review board approval and patient written informed consent were obtained. On two separate occasions, 24 hours apart, contrast-enhanced cardiac magnetic resonance (MR) imaging was performed prospectively at 1, 3, 5, 10, and 20 minutes after injection of gadopentetate dimeglumine and gadobenate dimeglumine in 15 patients (11 men, four women) with history of myocardial infarction. Both agents allowed detection of infarcted myocardium. T1 values at all times were significantly (P < .05) lower for gadobenate, compared with values for gadopentetate, in both infarcted and noninfarcted myocardium. At 1 minute after administration of both agents, T1 values in left ventricular cavity (LVC) were not different; at 3-20 minutes after injection, values were significantly (P < .05) lower for gadobenate. Differences between contrast-to-noise ratio (CNR) values of infarcted and noninfarcted myocardium were significantly higher on gadobenate-enhanced images (P < .05). CNR values between infarcted myocardium and LVC were significantly higher on gadopentetate-enhanced images (P < .05). Gadopentetate might permit better delineation of infarcts, especially subendocardial infarcts.

Management of acute coronary syndromes, a questionnaire survey of the clinical practice of cardiologists and other medical physicians belonging to west midland hospitals

OBJECTIVE

To assess the management of acute coronary syndromes by cardiologists and other medical physicians in a clinical setting.

DESIGN

Questionnaire survey consisting of 10 hypothetical clinical scenarios and four possible therapeutic options for each scenario.

SETTING

Consultants and specialist registrars in Cardiology (with or without access to interventional facilities) and consultant physicians belonging to various hospitals in the west midland region of United Kingdom.

MAIN OUTCOME MEASURES

Respondents' ability to recognise high risk patients and their management of the hypothetical clinical cases. To establish any differences in management strategy between cardiologists and general physicians, and whether these differences, if any, relate to access to interventional cardiac facilities.

RESULTS

Overall no significant differences were found in the responses between cardiologists and general physicians with or without access to cardiac interventional facilities. However, cardiologists were more inclined to use percutaneous transluminal coronary angioplasty (PTCA) compared to other physicians (scenario 8, 18.4% vs. 6.7%, p = 0.05 and scenario 9, 44.9% vs. 26.7%, p = 0.01). In two other situations, physicians from institutions with access to interventional facilities were more inclined to use 'other' treatment strategies (intravenous nitrates, antiplatelet treatment, inotropes, Intra-aortic balloon pump) compared to their colleagues from non-tertiary hospitals with no interventional facility on site (scenario 3, 21.7% vs. 2.4%, p = 0.04) and more use of PTCA ( scenario 6, 52.2% vs. 26.8%, p = 0.04).

CONCLUSIONS

The management of acute coronary syndromes in this questionnaire survey was satisfactory and evidence based. No real differences were found between the management strategies adopted by cardiologists or non-cardiologists. Physicians working in centres with interventional facilities were no more inclined towards using primary PTCA or rescue angioplasty than those working in centres without such facilities.

Late gadolinium-enhanced magnetic resonance imaging in acute and chronic myocardial infarction

OBJECTIVES

We sought to determine serial changes of enhanced and nonenhanced tissue on late gadolinium-enhanced cardiac magnetic resonance (CMR) imaging in patients with a myocardial infarction (MI) and to assess whether thickness of nonenhanced myocardium can improve the detection of preserved contractile function in the chronic state.

BACKGROUND

Previous studies demonstrated that enhancement on late gadolinium-enhanced CMR images indicates myocardial necrosis, and nonenhancement shows the presence of viable myocardium.

METHODS

The CMR studies were performed within one week (scan 1) and more than five months (scan 2) after the onset of MI in 18 patients. The area and mean thickness of enhanced tissue and nonenhanced myocardium were measured by using a 30-segment model. Systolic wall thickening on cine CMR at scan 2 was assessed for evaluating regional contractile function.

RESULTS

The amount of enhanced tissue significantly decreased from scan 1 to 2 (22.1 +/- 14.0 ml vs. 15.0 +/- 9.3 ml, p < 0.001). The averaged thickness of nonenhanced myocardium in the infarct segments significantly increased from scan 1 to 2 (5.2 +/- 3.0 mm vs. 6.6 +/- 3.2 mm, p < 0.001). Receiver operating characteristic analysis demonstrated that the measurement of thickness of nonenhanced myocardium, compared with measurement of percent transmural enhancement, had better diagnostic accuracy for predicting improved systolic wall thickening form scan 1 to 2 in dysfunctional segments (Az 0.650 vs. 0.594, p < 0.05).

CONCLUSIONS

The amounts of enhanced tissue and nonenhanced myocardium significantly altered from the acute to chronic state in MI patients. The diagnostic performance of CMR imaging for detection of preserved contractile function can be significantly improved by measuring thickness of nonenhanced myocardium in MI patients.

Quantitative measurement of infarct size by contrast-enhanced magnetic resonance imaging early after acute myocardial infarction

OBJECTIVES

The aim of this research was to evaluate kinetics and extent of myocardial contrast enhancement (CE) in comparison with single-photon emission computed tomography (SPECT) early after acute myocardial infarction (AMI).

BACKGROUND

Quantification of infarct size serves as a surrogate end point in evaluating new therapies of AMI. Contrast-enhanced magnetic resonance imaging (CeMRI) of the myocardium is a promising new method for identification of irreversible tissue injury.

METHODS

A total of 33 patients were examined by CeMRI and SPECT 7 +/- 2 days after AMI and successful coronary intervention. After gadolinium-diethylenetraimine pentaacetic acid injection (0.2 mmol/kg), continuous short-axis slices of the left ventricle (LV) were acquired every 7 min up to 42 min using different inversion times (TI). Myocardial CE at each imaging time point was quantified and compared with corresponding SPECT perfusion defect.

RESULTS

All patients showed myocardial CE in the infarct region. A constant TI for CeMRI resulted in a decrease of signal intensity and extent of CE on late acquisitions. With TI adjustment, infarct image intensity peaked at 21 min with a contrast of 478% of remote myocardium and remained at this level up to 42 min after contrast injection (437%); CE extent was stable over time and agreed well with SPECT within an average difference of 3% of the LV myocardium, yielding the best correlation at 28 min (r = 0.86).

CONCLUSIONS

In patients after AMI and successful reperfusion, CE is stable over time and matches well with SPECT perfusion defect; CeMRI under standardized conditions can accurately assess myocardial infarct size in vivo and may be attractive for serving as a surrogate end point early after AMI.

Early assessment of myocardial contractility by contrast-enhanced magnetic resonance (ceMRI) imaging after revascularization in acute myocardial infarction (AMI)

BACKGROUND

Recent studies have demonstrated that the size and shape of the hyperenhanced areas on contrast-enhanced magnetic resonance imaging (ceMRI) were nearly identical to areas of irreversible injury, as defined by histochemical staining. We compared the transmural extent of infarct (TEI), as defined by ceMRI, to the initial ECG findings for acute myocardial infarction (AMI), and we also assessed functional contractility according to TEI.

METHODS

12 patients who presented with their first myocardial infarction underwent cine and ceMRI 4 weeks later after their successful revascularization. TEI and wall thickening were determined by using a 30-segment model.

RESULTS

Infarction was observed in 81 (23.9%) segments, of which 46 segments (56.8%) had abnormal wall motion and 35 segments (43.2%) had normal wall motion. Of the 35 segments, 33 (94.3%) had subendocardial infarction. 17 segments had infarct of less than 25% of the wall thickness, and all of them had normal wall motion. On the other hand, 11 segments had infarct of more than 75% of wall thickness, of which 11 (100%) had abnormal wall motion. None of segments with nearly transmural infarction were observed in non ST-elevation AMI. The majority of the segments with infarct had non-transmural infarction (87.5%), even if the segments were in ST-elevation AMI (76.1%). Infarct size, as defined by ceMRI, was strongly correlated with peak CK-MB and Troponin-T (r = 0.96, p < 0.001, r = 0.91, p < 0.001, respectively).

CONCLUSION

TEI defined by ceMRI is inversely related to the contractility after revascularization in AMI. We were able to predict the future contractile function of segments with infarction using ceMRI before revascularization.

MRI in coronary artery disease

Diagnosis of coronary artery disease (CAD) is a major challenge for medical imaging, because CAD is the leading cause of death in developed nations. Several non-invasive tests are used in clinical routine for the detection of CAD. However, due to limited sensitivity and specificity, the reliable diagnosis as well as the exclusion of CAD can only be established by catheter angiography. In patients with known CAD, therapeutic decisions require accurate information on myocardial function, ischemia and viability. Recently, magnetic resonance (MR) imaging has emerged as a non-invasive cardiac imaging technique that provides information on cardiac morphology, cardiac function, myocardial viability, and coronary morphology. This review discusses technical aspects and the clinical impact of different MR techniques.

Clinical perspectives and therapeutics of thrombolysis

Reperfusion therapy with thrombolytic agents has been a significant advancement in the management of patients with acute ST elevation myocardial infarction. The outcome of acute myocardial infarction has significantly improved by early application of thrombolytic therapy. Intracoronary streptokinase has been used for >30 years, but reawakening interest occurred in the early 1980s in the use of thrombolytic therapy to establish rapid reperfusion during an acute myocardial infarction. Initial studies aimed at direct intracoronary thrombolysis, but owing to its cumbersome process and requirement of an active round the clock cardiac catheterization laboratory, it has been replaced by regimens of intravenous thrombolytic therapy which is as efficacious as intracoronary administration. Consideration of thrombolytic therapy has become a standard treatment for patients presenting with acute ST elevation myocardial infarction and various well-controlled trials have demonstrated the importance of both early and full reperfusion in improving clinical outcome in the setting of acute myocardial infarction. The subject of intravenous thrombolysis is perhaps the most rapidly evolving area in the management of acute myocardial infarction patients in the past decade. The current review focuses on the thrombolysis in the treatment of myocardial infarction and other conditions.

The effect of ST resolution on QT dispersion after interventional treatment in acute myocardial infarction

BACKGROUND

It has been reported that reperfusion treatment reduces QT dispersion (QTD) in cases of acute myocardial infarction (AMI). Successful myocardial perfusion is not synonymous with Thrombolysis in Myocardial Infarction (TIMI) III flow. It has been demonstrated that in AMI, the grade of ST-resolution correlates strongly with left ventricular (LV) function, enzyme elevation, and mortality after primary angioplasty.

HYPOTHESIS

This study investigated the relation between ST-resolution grade and QTD and the feasibility of using QTD as a determinant of successful myocardial tissue perfusion in patients in whom TIMI III flow in the infarct-related artery (IRA) is restored by interventional treatment for AMI.

METHODS

The study included 57 patients (38 men, 19 women, average age 54.4 +/- 11.6 years), whose IRA was perfused by primary angioplasty after the diagnosis of anterior AMI with ST elevation. Electrocardiograms of patients were taken 45 +/- 12 min post procedure, and patients were divided into three groups depending on the grade of ST resolution: Group 1, full ST resolution; Group 2, partial ST resolution; and Group 3, unsuccessful ST resolution.

RESULTS

Full ST resolution was seen in 19 cases (33%), partial resolution in 26 cases (47%), and unsuccessful resolution in 12 cases (20%). There were no differences among groups in terms of risk factors, stent diameters, symptom onset-balloon time, LV function, and preprocedure corrected QTD (QTcD) (p = 0.274). After the procedure, a significant reduction in QTcD was found within the groups (p = 0.0001 in Group 1, p = 0.004 in Group 2, and p = 0.011 in Group 3). Reductions in QTcD post procedure were 24.21 +/- 14.27, 11.85 +/- 16.18, and 12.50 +/- 11.58 ms in Groups 1, 2, and 3, respectively. There was a statistically significant difference of p = 0.015 between Groups 1 and 2 and a difference of p = 0.028 between Groups 1 and 3. There was no statistically significant difference between Groups 2 and 3 (p = 0.916).

CONCLUSION

In acute MI, TIMI III flow led to a reduction in QTcD, and full myocardial perfusion made an additional contribution to the electrical stability of the myocardium.