Correlation of thallium uptake with left ventricular wall thickness by cine magnetic resonance imaging in patients with acute and healed myocardial infarcts.

Myocardial infarction (MI) is characterized by cellular necrosis which undergoes fibrotic transformation over time. Cine magnetic resonance imaging (MRI) offers high-resolution 3-dimensional images of the left ventricular myocardium, allowing sampling of the myocardial wall thickness over the entire left ventricle. Tomographic (single-photon emission computed tomography [SPECT]) thallium images also provide 3-dimensional information on the location and level of thallium uptake, which has been shown to correlate with myocardial viability. The purposes of this study were: (1) to examine the relation between both end-diastolic and end-systolic wall thickness and normalized thallium-201 uptake over the left ventricle in a group of patients with MI, (2) to examine the relation between regional wall thickening and normalized thallium uptake, and (3) to examine the relation between thallium uptake and wall thickness both early and late after infarction. Twenty-four patients with MI underwent stress, redistribution, and reinjection thallium SPECT imaging and cine MRI within several days. Seventeen patients underwent imaging late after infarction and 7 underwent imaging early after infarction. Normalized thallium activity was correlated with MRI wall thicknesses at both end-diastole and end-systole for 18 segments for each ventricle. In addition, end-diastolic and end-systolic wall thicknesses were grouped by their corresponding thallium activity levels into percentiles. End-systolic wall thickness correlated significantly with normalized thallium uptake in 14 of 18 segments, end-diastolic wall thickness in only 4 of 18 segments, and wall thickening in only 3 of 18 segments. Mean values for end-diastolic and end-systolic wall thicknesses corresponding to severely reduced (<50%) normalized thallium activity were 9.9 +/- 1.1 and 8.5 +/- 0.6, respectively. Using receiver-operating curve analysis, end-systolic wall performed as a better diagnostic parameter than end-diastolic wall for identifying severely reduced thallium activity levels. For all levels of thallium activity, end-diastolic wall thicknesses were all thinner late versus early after MI, whereas end-systolic wall thickness was thinner only in the segments corresponding to severely reduced thallium activity. Based on these results, end-systolic wall thickness is the best noninvasive anatomic parameter of myocardial scar.

Optimizing the method to calculate right ventricular ejection fraction from first-pass data acquired with a multicrystal camera.

BACKGROUND: The advantage of radionuclide angiographic techniques used to measure right ventricular ejection fraction (RVEF) is geometry independence, but the weakness is right atrial (RA) overlap. To minimize the effect of RA counts on right ventricular time activity curve (TAC), two regions of interest (ROI), one drawn for the end-diastolic image and one for the end-systolic image, are used for the calculation of RVEF from equilibrium gated blood pool scans (GBPS) and from gated first-pass studies with an Anger camera. A multicrystal camera offers both temporal separation of the bolus to the right side of the heart and good count statistics; therefore first-pass studies performed on a multicrystal camera theoretically should yield the most accurate measurements of RVEF, but few studies have been performed to validate RVEF against a reliable gold standard. METHODS AND RESULTS: To develop and validate an accurate method to measure RVEF from multicrystal first-pass data, 25 patients underwent sequential cine-MRI, first-pass radionuclide angiography, and gated equilibrium imaging. Five additional healthy volunteers underwent cine-MRI alone. Right and left ventricular volumes were measured from serial short axis cine-MRI views according to Simpson's rule. Three methods were used to calculate RVEF from first-pass data: a single ROI method, a dual ROI method, and a method in which a single ROI is applied to RA subtracted first-pass dynamic data. Five additional healthy volunteers underwent cine-MRI alone. When right ventricular stroke volume was plotted versus left ventricular stroke volume for the 5 volunteers and the 15 patients without valvular regurgitation, the regression line was not significantly different from the line of identity, supporting the accuracy of cine-MRI to measure RVEF. The RVEF by cine-MRI ranged from 34% to 59%; first-pass RVEF with a single ROI from 26% to 48%; first-pass RVEF with two ROIs from 31% to 59%; first-pass RVEF with RA subtracted single ROI from 29% to 60%; and RVEF from GBPS with multiple ROIs from 28% to 55%. The regressions for all three of the first-pass methods versus cine-MRI were significant (p < 0.01) as was the regression for the equilibrium GBPS versus cine-MRI but the correlation was weaker. The regressions for the 2-ROI method and for the RA subtracted single ROI method were not significantly different from the line of identity, whereas the regressions for both the single ROI method and for equilibrium GBPS were significantly different from the line of identity (p < 0.01). CONCLUSIONS: Cine-MRI can be used to validate radionuclide algorithms. Of the four radionuclide methods for measuring RVEF that were assessed, the first-pass 2-ROI method and the first-pass RA subtracted single ROI are the most accurate, the first-pass single ROI method underestimates RVEF, and the RVEF values measured from GBPS are less accurate.

Long-term effect of thrombolytic therapy on left ventricular ejection fraction after acute myocardial infarction.

To assess the long-term effect of thrombolytic therapy on left ventricular (LV) systolic function, 222 patients with acute myocardial infarction treated with intravenous tissue plasminogen activator within 4 hours of symptom onset underwent assessment of LV ejection fraction (EF) by radionuclide equilibrium angiography at hospital discharge and 1 year later. Mean EF at hospital discharge (46 +/- 12) was similar to that at 1 year (45 +/- 13). Stepwise multivariate linear regression analysis identified EF at discharge and patency of the infarct-related artery before discharge as independent predictors of EF change at 1 year (p = 0.0002 and 0.003, respectively). Random assignments to invasive versus conservative treatment strategies or to early versus delayed beta-blocker therapy did not affect EF change during follow-up. No significant deterioration of EF was observed in patients with larger infarcts. However, EF decreased from 45 +/- 10 at hospital discharge to 39 +/- 12 (p = 0.005) at 1-year follow-up in a subgroup of patients with history of prior infarction. Thus, patients with acute myocardial infarction, treated with intravenous tissue plasminogen activator early after onset of symptoms, appear to have stable LV function between hospital discharge and 1 year follow-up. The change in EF between hospital discharge and 1 year can be predicted from the EF value at discharge, patency of the infarct-related artery before discharge and history of previous myocardial infarction.