Imaging cardiac structure and pump function

Novel approach to early detection of doxorubicin cardiotoxicity by gadolinium-enhanced cardiovascular magnetic resonance imaging in an experimental model

BACKGROUND

We sought to determine whether cardiovascular magnetic resonance measures of gadolinium (Gd) signal intensity (SI) within the left ventricular myocardium are associated with future changes in left ventricular ejection fraction (LVEF) after receipt of doxorubicin (DOX).

METHODS AND RESULTS

Forty Sprague-Dawley rats were divided into 3 groups scheduled to receive weekly intravenous doses of normal saline (n = 7), 1.5 mg/kg DOX (n = 19), or 2.5 mg/kg DOX (n = 14). Magnetic resonance determinations of LVEF and myocardial Gd-SI were performed before and at 2, 4, 7, and 10 weeks after DOX initiation. During treatment, animals were euthanized at different time points so that histopathologic assessments of the left ventricular myocardium could be obtained. Within-group analyses were performed to examine time-dependent relations between Gd-SI and primary events (deterioration in LVEF or an unanticipated death). Six of 19 animals receiving 1.5 mg/kg DOX and 10 of 14 animals receiving 2.5 mg/kg DOX experienced a primary event; no normal saline animals experienced a primary event. In animals with a primary event, histopathologic evidence of myocellular vacuolization occurred (P = 0.04), and the Gd-SI was elevated relative to baseline at the time of the event (P < 0.0001) and during the measurement period before the event (P = 0.0001). In all animals (including normal saline) without an event, measures of Gd-SI did not differ from baseline.

CONCLUSIONS

After DOX, low serial measures of Gd-SI predict an absence of an LVEF drop or unanticipated death. An increase in Gd-SI after DOX forecasts a subsequent drop in LVEF as well as histopathologic evidence of intracellular vacuolization consistent with DOX cardiotoxicity.

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.

Relation of left ventricular infarct transmurality and infarct size after primary percutaneous coronary angioplasty to time from symptom onset to balloon inflation

This study was performed to evaluate the impact of time to reperfusion on infarct size and transmurality after primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI). In 73 patients undergoing primary PCI for STEMI, contrast-enhanced magnetic resonance imaging was performed. Infarct size and transmurality on delayed-enhancement imaging were measured. Infarct size was not associated with symptom onset-to-balloon time (23 +/- 9% for <180 minutes, 22 +/- 9% for 180 to 360 minutes, and 24 +/- 11% for >360 minutes, p = 0.62) or door-to-balloon time (23 +/- 8% for <90 minutes, 23 +/- 10% for 90 to 120 minutes, and 22 +/- 11% for >120 minutes, p = 0.88). Infarct transmurality increased significantly with a delay of symptom onset-to-balloon time (73 +/- 22% for <180 minutes, 78 +/- 14% for 180 to 360 minutes, and 86 +/- 14% for >360 minutes, p = 0.04), but not for door-to-balloon time (79 +/- 15% for <90 minutes, 76 +/- 19% for 90 to 120 minutes, and 81 +/- 18% for >120 minutes, p = 0.62). In multivariate analysis, anterior infarction (odds ratio 4.15, 95% confidence interval 1.31 to 13.18, p = 0.02) and myocardial blush grade 0/1 (odds ratio [OR] 3.89, 95% confidence interval [CI] 1.13 to 13.51, p = 0.03) independently predicted a large infarct (infarct size > or =25%). Symptom onset-to-balloon time (OR per 30 minutes 1.26, 95% CI 1.04 to 1.53, p = 0.02) was an independent predictor of transmural infarct (average transmural extent > or =75%) and use of glycoprotein IIb/IIIa inhibitors showed a protective effect (OR 0.09, 95% CI 0.02 to 0.53, p = 0.007). In conclusion, symptom onset-to-balloon time was significantly associated with infarct transmurality but not infarct size in patients undergoing primary PCI for STEMI.

Assessment of ventricular function with cardiovascular magnetic resonance

The high spatial and temporal resolution of cardiovascular magnetic resonance (CMR) images makes it well-suited for use in the assessment of right ventricular and left ventricular function in patients who have cardiovascular disorders. This article reviews CMR methods used to assess regional and global ventricular function.

Effects of balloon-based distal protection during primary percutaneous coronary intervention on early and late infarct size and left ventricular remodeling: a pilot study using serial contrast-enhanced magnetic resonance imaging

BACKGROUND

Distal protection devices are effective in preventing distal embolization during primary percutaneous coronary intervention (PCI). We investigated whether balloon-based distal protection could reduce early and late infarct size and left ventricular (LV) remodeling using serial analysis of contrast-enhanced magnetic resonance imaging (CE-MRI).

METHODS

Patients undergoing primary PCI for ST-segment elevation myocardial infarction within 12 hours after symptom onset were randomized to a distal protection group (n = 19) or to a control group (n = 20). The primary end point was infarct size evaluated by the volume of delayed hyperenhancement on CE-MRI at 3 days. The secondary end point included infarct size on CE-MRI at 6 months and LV remodeling assessed by the change between LV end-diastolic volume on CE-MRI at 3 days (baseline) and 6 months (follow-up).

RESULTS

Percutaneous coronary intervention procedures were fully protected with balloon-based distal protection in all patients of the protection group. Infarct size was similar in the distal protection group and the control group at baseline (25.9 +/- 7.8% vs 26.1 +/- 8.2%; P = .93) and at follow-up (21.4 +/- 9.1% vs 18.5 +/- 9.1%; P = .51). The change in LV end-diastolic volume was 10.5 +/- 32.2 mL in the distal protection group and 8.9 +/- 40.7 mL in the control group (P = .86). There was no significant difference in the 6-month rate of major adverse cardiac events between groups (none in the distal protection group and 4 patients in the control group; P = .11).

CONCLUSIONS

Serial CE-MRI showed that the balloon-based distal protection during primary PCI did not reduce early and late infarct size or prevent LV remodeling.

Magnetic resonance imaging in the assessment of coronary artery disease

Magnetic resonance imaging (MRI) is gaining importance in cardiology as the noninvasive test of choice for patients with a multitude of cardiovascular problems. Recently, cardiovascular MRI has emerged as an important noninvasive diagnostic modality in the assessment of coronary artery disease. Because of its superior spatial resolution, integration of qualitative and quantitative methodology, and excellent reproducibility, MRI has advantages over conventional noninvasive modalities currently used in the evaluation of coronary artery disease. This article reviews the rapidly expanding recent literature that has now established cardiovascular MRI as an ideal choice in the evaluation of myocardial ischemia (including dobutamine cine MRI and vasodilator perfusion MRI techniques). We further discuss the role of delayed contrast-enhanced MRI and low-dose dobutamine cine MRI for evaluation of myocardial viability. Comparisons with more established techniques, such as dobutamine stress echocardiography, single-photon emission computed tomography perfusion imaging, and positron emission tomography, are reviewed.

MRI for the diagnosis of myocardial ischemia and viability

Assessment of myocardial ischemia and viability plays a crucial role in the clinical management of patients with coronary artery disease. Recently, cardiovascular MRI has emerged as an important noninvasive diagnostic modality in the assessment of coronary artery disease. MRI is able to evaluate both myocardial perfusion as well as myocardial contractile reserve. Because of its superior spatial resolution, integration of qualitative and quantitative methodology, and excellent reproducibility, MRI has advantages over conventional noninvasive modalities currently used in the evaluation of myocardial ischemia and viability, and may well emerge as the premier noninvasive technique in the assessment of patients with coronary artery disease. The authors review the rapidly expanding recent literature that has now established cardiovascular MRI (including dobutamine cine MRI and vasodilator perfusion MRI techniques) as an ideal choice in the evaluation of myocardial ischemia and delayed contrast-enhanced MRI and low-dose dobutamine cine MRI for evaluation of viability. Comparisons with more established techniques such as dobutamine stress echocardiography, single photon emission computed tomography perfusion imaging, and positron emission tomography are reviewed.

Assessment of cardiac function with MR imaging

A variety of black or white blood imaging techniques are available for assessing global and regional LV and RV function during cardiovascular MR imaging examinations. In addition to providing information about LV function at rest, these techniques provide diagnostic and prognostic information regarding myocardial ischemia and viability during MR imaging stress tests.

Magnetic resonance perfusion imaging in patients with coronary artery disease: a qualitative approach

Although contrast-enhanced first pass magnetic resonance imaging (MRI) has potential to quantify blood flow through extensive image post-processing, clinical utility is likely to depend on rapid qualitative analysis.

AIMS

To investigate use of an on-line analytical approach for detection of coronary artery disease (CAD).

METHODS AND RESULTS

Thirty subjects with CAD underwent contrast-enhanced rest/adenosine stress MRI with basal, mid-papillary and apical short-axis image acquisition. Each short axis was divided into eight regions of interest (ROI). Regional perfusion was visually classified as normal or impaired according to transmural distribution and defect reversibility. MRI and angiographic data were compared. Qualitative MRI reporting was possible for 98% ROI. Eighty-six coronary artery (CA) territories were assessed of which 71 (83%) had stenoses. Sensitivity and specificity for detection of stenoses were 93 and 60%, respectively. The proportion of hypoperfused ROI rose from 31% with < 50% stenosis to 65% with occlusion. More transmural defects were seen in infarction-related territories (75 vs. 54%, p < 0.05). More ROI demonstrated defect reversibility in occluded rather than in stenosed infarction-related vessels (89 vs. 58%, p < 0.05). Occluded vessels with grade 2-3 collaterals contained a higher proportion of normal ROI (44 vs. 25%, p < 0.05).

CONCLUSIONS

Qualitative MRI analysis had high sensitivity and moderate specificity for detecting CA stenoses. Additional information was obtained relating to lesion severity, previous infarction, myocardial viability and impact of collateral circulation. The technique has potential for de novo diagnosis of CAD and as a complementary modality to angiography to assess the significance of given angiographic lesions.

Real-time 3-dimensional echocardiographic evaluation of left ventricular volume: correlation with magnetic resonance imaging--a validation study

BACKGROUND

The purpose of our study was to validate the ability of real-time 3-dimensional echocardiography (RT3D) to measure cardiac volume.

METHODS

We studied 25 patients with various cardiac disorders who had a regular heart rhythm and a good precordial echocardiographic window. Each patient underwent complete transthoracic echocardiography (TTE), RT3D, and magnetic resonance imaging (MRI) studies. Left ventricular dimension was calculated from slices of the whole left ventricle obtained by 7 different equidistant azimuth tilts. Planimetry of the endocardial (for volume data) and epicardium (for mass data) surface was performed for each azimuth tilt. The left ventricular end-diastolic volume (LVEDV) and the left ventricular end-systolic volume (LVESV) were calculated. The cardiac mass data were derived with the formula (Epicardial volume - LVEDV) x 1.055. The parameters of LVEDV, LVESV, stroke volume, ejection fraction, and cardiac mass were compared with those derived from MRI.

RESULTS

No statistically significant differences were found between the data from RT3D and MRI (P > or =.05). Good correlations were found between these two methods for left ventricle volume and mass measurements (r from 0.92 to 0.99). However, a weaker correlation was found with larger chamber sizes because extrapolation was necessary for the volume of myocardial segments that were not covered by the small sector angle.

CONCLUSIONS

For data acquisition, RT3D is faster than either TTE or MRI. It is also better than MRI for measuring cardiac volume and mass. To improve results with larger cardiac chamber sizes, enlargement of the sector angle will be necessary.