Gerald G. Blackwell

Interstudy reproducibility of biplane cine nuclear magnetic resonance measurements of left ventricular function

Cine nuclear magnetic resonance (NMR) imaging, as a noninvasive and high-resolution imaging modality, has been shown to be reliable for determining absolute left ventricular (LV) volumes and ejection fraction. A relatively new gradient echo cine NMR approach using 2 orthogonal long-axis planes (2- and 4-chamber) aligned with the true axes of the left ventricle has been previously developed and validated against radiographic biplane LV cineangiography. The aim of the present investigation was to determine the reproducibility of this more rapid cine NMR approach for the measurement of LV volumes and ejection fraction. Eighteen normal subjects underwent 2 cine NMR studies, on different days, using a 1.5-tesla clinical imaging system. Studies were analyzed on-line and blindly by 2 independent observers. Intraobserver error was also determined in a blinded manner. Mean values of measurements determined by this method in this group of normal subjects were end-diastolic volume (120 +/- 20 ml), end-systolic volume (39 +/- 9 ml) and ejection fraction (67 +/- 4%). Paired analysis of data revealed no significant bias between interstudy, interobserver or intraobserver measurements, except for interobserver end-diastolic volume, where the first observer measurements were slightly elevated (5.6 +/- 7.8 ml) compared with the second. This resulted in a small difference in ejection fraction (1.7 +/- 2.3%) between observers. The absolute variation between measurements (square root of variance components) was low for all interstudy, interobserver and intraobserver comparisons: end-diastolic volume was less than +/- 6.7 ml, end-systolic volume less than +/- 3.5 ml and ejection fraction less than +/- 2.4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of biplane long-axis left ventricular volume determined by cine magnetic resonance imaging in patients with regional and global dysfunction

Left ventricular (LV) volumes and ejection fraction can be obtained by applying Simpsons rule to multiple short-axis tomographic planes. A simpler method for determining LV volumes using the area-length equation is widely accepted and requires less time to acquire and analyze. Its accuracy, however, is questionable in deformed or asymmetrically contracting ventricles. This study compares biplane long-axis to serial short-axis computed LV volumes obtained by cine gradient-echo magnetic resonance imaging (MRI) in 2 distinct patient populations: (1) patients with global LV dysfunction, and (2) patients with regional LV dysfunction. A total of 114 patients were studied using both methods. Among 37 patients with global LV dysfunction, there was no statistically significant difference between methods (long axis vs short axis) for determining LV end-diastolic volume (203 +/- 91 vs 201 +/- 90 ml), end-systolic volume (142 +/- 81 vs 141 +/- 82 ml), and ejection fraction (33 +/- 12 vs 33 +/- 13%). However, in the 77 patients with regional dysfunction, LV end-diastolic volume was statistically slightly higher when obtained using the long-axis approach (157 +/- 53 vs 152 +/- 51 ml; p=0.004). Otherwise, end-systolic volume (97 +/- 49 vs 95 +/- 49 ml) and ejection fraction (40 +/- 13 vs 40 +/- 13%) were similar (p=NS). The correlation between LV volumes and ejection fractions for both groups was excellent (r >0.91). Thus, in this study group, biplane long-axis and serial short-axis computed LV volumes and ejection fractions were similar in patients with global or regional LV dysfunction. In critically ill patients unable to complete a comprehensive MRI examination, the biplane long-axis-derived volumes provide adequate data.

Angiotensin-converting enzyme inhibitor therapy affects left ventricular mass in patients with ejection fraction > 40% after acute myocardial infarction.

OBJECTIVES We tested the hypothesis that angiotensin-converting enzyme (ACE) inhibitor therapy decreases left ventricular (LV) mass in patients with a left ventricular ejection fraction (LVEF) > 40% and no evidence of heart failure after their first acute Q wave myocardial infarction (MI). BACKGROUND Recently, ACE inhibitor therapy has been shown to have an early mortality benefit in unselected patients with acute MI, including patients without heart failure and a LVEF > 35%. However, the effects on LV mass and volume in this patient population have not been studied. METHODS Thirty-five patients with a LVEF > 40% after their first acute Q wave MI were randomized to titrated oral ramipril (n = 20) or conventional therapy (control, n = 15). Magnetic resonance imaging (MRI) performed an average of 7 days and 3 months after MI provided LV volumes and mass from summated serial short-axis slices. RESULTS Left ventricular end-diastolic volume index did not change in ramipril-treated patients (62 +/- 16 [SD] to 66 +/- 17 ml/m2) or in control patients (62 +/- 16 to 68 +/- 17 ml/m2), and stroke volume index increased significantly in both groups. However, LV mass index decreased in ramipril-treated patients (82 +/- 18 to 73 +/- 19 g/m2, p = 0.0002) but not in the control patients (77 +/- 15 to 79 +/- 23 g/m2). Systolic arterial pressure did not change in either group at 3-month follow-up. CONCLUSIONS In patients with a LVEF > 40% after acute MI, ramipril decreased LV mass, and blood pressure and LV function were unchanged after 3 months of therapy. Whether the decrease in mass represents a sustained effect that is associated with a decrease in morbid events requires further investigation.

ASSESSMENT OF VENTRICULAR VOLUMES USING CINE MAGNETIC RESONANCE IN THE INTACT DOG : A COMPARISON OF MEASUREMENT METHODS

RATIONALE, OBJECTIVE AND METHODSThe authors recently combined magnetic resonance imaging with high-fidelity left ventricular (LV) pressure measurement in a closed-chested, intact animal model. However, LV volumes derived from summated serial short axis slices require long imaging times and make it difficult to record LV volumes in response to acute alterations in load. In this study, geometry-based LV end-systolic volume estimates calculated from a single long-axis image (Area-Length formula) and from a long-axis and short-axis image (Bullet formula) were compared to those derived from summated short-axis images of the left ventricle (Simpsons rule) during altered loading conditions in six anesthetized, intact dogs. RESULTSAngiotensin infusion produced three different LV systolic pressures (89 ± 8 vs. 123 ± 12 vs. 151 ± 10 mmHg, P < .001). Area-Length and Bullet formula end-systolic volumes correlated with Simpsons rule volumes (r = .95 and .97; respectively). However, Bullet formula end-systolic volumes provided a significantly better agreement with Simpsons rule end-systolic volumes. CONCLUSIONSThe Bullet formula can be substituted for Simpsons rule to record magnetic resonance LV volumes during steady-state alterations in load in our intact animal model.

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

BackgroundThe 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 ResultsTo 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 equeilibrium 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 idendity (p<0.01).ConclusionsCine-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.

The usefulness of cardiovascular magnetic resonance imaging

Cardiovascular applications of magnetic resonance methods are now available clinically, and cost-effective strategies are being devised to bring this technology further into the clinical mainstream. Incorporation of magnetic resonance methods into the core curriculum of cardiovascular training programs is needed to provide practitioners with the necessary background to apply this exciting technology.

796-2 Application of Lessons Learned from Cardiac Interventional Techniques to Carotid Angioplasty (PTA)

PTA of the carotid and vertebral arteries remains a challenging area of vascular intervention and optimal techniques have yet to be determined. We describe our initial experience with a novel approach to carotid PTA utilizing: 1) “active” perfusion, as is done during coronary angioplasty, which allows prolonged balloon inflations without cerebral ischemia; 2) transcranial doppler (TCD) monitoring, when anatomically feasible, during PTA to assess antegrade flow and detect cerebral emboli; 3) temporary pacing for bradycardia during intra-Carotid balloon inflation; and 4) magnetic resonance angiography (MRA) for screening and follow-up. We have also used the previously described “protected” carotid PTA technique using an additional occluding balloon to prevent cerebral emboli. Six symptomatic patients had 7 PTAs (6 carotids, 1 vertebral). Pt. # Angioplasty Technique Transcrania Doppler StenosisPre→Post Complications Stenosis 3m. F/U 1 Protected 73 emboli 90%→20% none 10% 2 Protected 40 emboli 90%→0% none 0% 3 Active Perf. no window 95%→0% none 0% 4 Active Perf. 10 emboli 99%→0% none 0% 5 Active Perf. no window 99%→0% hemorrh→death 6 Standard no window 100%→30%→ none pending (vertebral) stent→0% Active Perf. 70%→dissec, none pending (carotid) 20%→stent→0% Maintenance of cerebral perfusion during PTA by “active” perfusion and cardiac pacing allows prolonged balloon inflations which minimize residual stenosis; when feasible, TCD monitoring is a valuable adjunct. Ongoing studies with more patients will elucidate the value of this approach for carotid angioplasty.

When can magnetic resonance angiography replace contrast angiograms for vascular disease

Summary On the basis of the rapid proliferation of magnetic resonance methods, it seems likely that magnetic resonance angiography will obviate the need for invasive x-ray angiography in the initial screening of many patients with known or suspected vascular disease. As it relates to the stable patient with thoracic aortic disease, MRA has already replaced invasive contrast angiography and is now widely accepted as the gold standard. For abdominal aortic disease, MRA can best be considered a viable alternative, but developments need to be made before this can be considered a first-line approach. For the peripheral vasculature MRA has already assumed an important role but technical developments need to occur before this is more widely disseminated. Finally, in the extracranial cerebral vasculature, several centers are already performing therapeutic interventions based on noninvasive testing, most notably the combination of MRA and data from ultrasound-based techniques. The ultimate goal is to move as many diagnostic studies as possible into the noninvasive arena to reduce morbidity associated with straightforward diagnoses. In parallel, the invasive angiography suite will be used primarily for therapeutic work and for the occasional diagnostic study in which noninvasive testing fails to reveal a clear-cut diagnosis. Cardiovascular specialists need to assume a leadership role in developing and applying this technology to help improve the care of the large number of patients with vascular diseases.

Cardiovascular magnetic resonance imaging: A review of principles and utilities

Magnetic resonance imaging (MRI) is used to image the human body with excellent temporal and spatial resolution and is ideally suited for visualizing the cardiovascular system. The chief advantages of MRI are its ability to acquire images noninvasively in the absence of ionizing radiation, in any tomographic plane, without interference from surrounding bone or soft tissues.

Transesophageal Echocardiographic Findings in Complete Unilateral Anomalous Pulmonary Venous Connection of Right Lung to Right Atrium

Transesophageal echocardiographic findings in a patient with anomalous drainage of both right‐ sided pulmonary veins into the right atrium are described. The atrial septum was intact and the left‐ sided veins connected normally with the left atrium.