Guidelines for training in cardiovascular magnetic resonance (CMR)

These "Guidelines for training in Cardiovascular Magnetic Resonance" were developed by the Certification Committee of the Society for Cardiovascular Magnetic Resonance (SCMR) and approved by the SCMR Board of Trustees.

Prevalence and clinical relevance of the morphological substrate of ventricular arrhythmias in patients without known cardiac conditions detected by cardiovascular MR

OBJECTIVE

Cardiac MR (CMR) identifies the substrate of ventricular arrhythmia (VA) in cardiomyopathies and coronary heart disease. However, little is known about the value of CMR in patients with VA without previously known cardiac disorders.

METHODS

76 patients with VA (Lown ≥2) without known cardiac disease after regular diagnostic work-up were studied with CMR, and findings were correlated with electrocardiogram (ECG) and electrophysiological stimulation (EPS). Structural abnormalities matching the VA origin as defined by ECG and/or EPS, or a CMR-detected cardiac condition known to cause arrhythmia were defined as VA substrate. CMR findings were defined as clinically relevant, if resulting in a new diagnosis, change of treatment or additional diagnostic procedure.

RESULTS

44/76 patients demonstrated pathological CMR findings. In 24/76 patients, the pathology was detected by CMR and not by echocardiography. CMR-based diagnoses of cardiac disease were established in 20/76 patients, and all were morphological substrates for VA. In seven patients, the location of the CMR finding (scar) directly matched the VA origin. CMR findings resulted in a change of treatment in 21 patients and/or additional diagnostics in 8 patients.

CONCLUSION

Undetected cardiac conditions are frequent causes of VA. This is the first study demonstrating the value of CMR for detection of morphological substrate and/or underlying cardiac disorders in VA patients without known cardiac disease.

ADVANCES IN KNOWLEDGE

The high incidence of clinically relevant CMR findings which were not detected during initial diagnostic work-up strongly supports the use of CMR to screen VA patients for underlying heart disease.

T1-weighted cine FLASH is superior to IR imaging of post-infarction myocardial viability at 4.7T

PURPOSE

Data are unavailable for rational selection of pulse sequences to assess postinfarction myocardial viability in rodents at high field strength. We implemented a widely used clinical inversion recovery (IR) sequence at 4.7T and compared the results to a heavily T1-weighted cine FLASH sequence (T1-CF) for assessment of infarction size.

MATERIALS AND METHODS

Eleven infarcted rats were examined within 24 h of infarction after injection of Gadophrin-3 contrast agent. Images were acquired using both pulse sequences and a standard cine (SC) sequence. Estimates of infarct size were compared to TTC. Global LV function was compared between the T1-CF and SC sequences.

RESULTS

SNR, relative SNR, and CNR for the infarcted and normal myocardium were significantly greater for the IR sequence. Infarction size was overestimated by both sequences, but correlated highly and showed very close agreement with TTC. Global function revealed no significant differences between T1-CF and SC.

CONCLUSION

Both IR and T1-CF produced reliable results for assessment of infarction size at 4.7T. While the IR sequence delivers better overall SNR and CNR, the T1-CF allows concomitant assessment of global cardiac function with a much shorter acquisition time.

Homogene Strain-Analyse im Vergleich zur Wanddickenzunahme für die MR-tomographische Beurteilung der regionalen Myokardfunktion

PURPOSE

To compare strain analysis and wall thickening (WT) analysis in differentiating the infarcted, adjacent, and remote zones in a rat model of myocardial infarction (MI).

MATERIAL AND METHODS

Three normal (NL) and ten rats subjected to myocardial infarction were imaged on a 4.7T scanner. Gradient-echo and SPAMM-tagged cine images were acquired at three short axis levels of the left ventricle (LV). A homogenous strain analysis (principal strains lambda1 and lambda2, displacement D, angle beta) and a WT-analysis (mm- and %-thickening) were performed in all slices demonstrating MI. Regional function was compared between infarcted rats (infarcted, adjacent and remote zone) and corresponding regions in the NL rats. Additional segmental analysis was performed in the NL rats for the anterior, lateral, inferior and septal wall.

RESULTS

In the NL rats, lambda (1) (greatest radial thickening) was greatest in the lateral and anterior wall. WT-analysis showed a pattern of function similar to lambda1, however, regional differences using WT-analysis were not significant. lambda (2) (greatest circumferential shortening) was most negative in the anterior wall. D was greatest in the lateral and inferior wall. The angle beta was radially directed in all segments. In the infarcted rats, both strain and WT-analyses revealed significant impairment in function in the infarcted and adjacent zones as compared to NL (p < 0.001). However, only the strain analysis (lambda1, lambda2, p < 0.001) detected significant remote myocardial dysfunction. Myocardial function differed significantly between the infarcted and adjacent and between the infarcted and remote regions. Strain analysis (lambda2, D, beta, p < 0.001) also identified significant functional differences between the adjacent and remote zones, however, no statistically significant differences were found using WT-analysis.

CONCLUSION

Strain analysis is superior to WT-analysis in detecting regional functional variations in NL rats and in discriminating function in the infarcted, adjacent and remote zones post MI.

Quantitative assessment of regional myocardial function in a rat model of myocardial infarction using tagged MRI

We characterized global and regional left ventricular (LV) function during post myocardium infarction (MI) remodeling in rats, which has been incompletely described by previous MRI studies. To assess regional wall motion, four groups of infarcted animals corresponding to 1-2, 3-4, 6-8 and 9-12 weeks post-MI respectively were imaged using a fast gradient echo sequence with a 2D spatial modulation of magnetization (SPAMM) tagging preparation. An additional group was serially imaged (1-2 and 6-7 weeks post-MI) to assess the global function. Regional and global functional parameters of infarcted rats were compared to non-infarcted normal rats. Compared to normal rats, a decrease in ejection fraction (70 +/-7 vs. 40 +/- 8%, p<0.05) was observed in rats with MI. Maximal and minimal principal stretches (lambda1, lambda2) and strains (E1, E2), principal angle (beta) and displacement varied regionally in normal rats but deviated significantly from the normal values in rats with MI particularly in the infarcted and adjacent zones. Not only was strain magnitude reduced segmentally post-MI, but strain direction became more circumferentially oriented, particularly in rats with larger infarctions. We report the first regional myocardial strain values in normal and infarcted rats. These results parallel findings in humans, and provide a unique tool to examine regional mechanical influences on the remodeling process.

Pulmonary MR angiography with contrast agent at 4 Tesla: a preliminary result

In this study, pulmonary MR angiography (MRA) using a tailored coil at 4 Tesla in conjunction with an intravenous injection of contrast agent is described. Three-dimensional gradient-echo images were obtained during the intravenous injection of 0.05, 0.1, and 0.2 mmol/kg body weight of gadodiamide to investigate the signal enhancement effect of the contrast agent in pulmonary arteries qualitatively and quantitatively. In the qualitative analysis, the subsegmental branches were visualized on every dose. In the quantitative analysis, the average contrast-to-noise ratios (CNRs) of the main pulmonary arteries increased in a dose-dependent manner. However, the CNRs of segmental arteries did not increase as the dose of contrast agent increased, as observed at 1.5 Tesla MRI. These observations demonstrate the feasibility of delineating the pulmonary vasculature using a contrast agent; however, our results also suggest possible high-field-related disabilities that need to be overcome before high-field (> or =4 Tesla) MRI can be used to full advantage.

Right ventricular dysplasia in an asymptomatic young man: an uncommon case with biventricular involvement and no known family history

A 33-year-old man had cardiomegaly on a routine x-ray examination. He was asymptomatic with no history of infarction, syncope, or palpitations. There was no family history of congenital heart disease or sudden death. Two-dimensional transthoracic echocardiography demonstrated marked enlargement of the right atrium and ventricle with severely depressed right and left ventricular function that was consistent with right ventricular dysplasia. The patient was treated with an angiotensin-converting enzyme inhibitor and did well for 6 months, but then developed symptomatic left-sided congestive heart failure. Short-term improvement was obtained with intravenous inotropic therapy, but he continued to have progressive symptoms of heart failure. Approximately 7 months after his initial presentation, the patient underwent orthotopic heart transplantation for intractable congestive heart failure. Pathologic examination of the explanted heart established the diagnosis of right ventricular dysplasia with left ventricular involvement. This is an uncommon presentation of right ventricular dysplasia with biventricular involvement and no known family history.

Ultrafast three-dimensional contrast-enhanced magnetic resonance angiography and imaging in the diagnosis of partial anomalous pulmonary venous drainage

OBJECTIVES

The purpose of our study was to evaluate patients with suspected anomalous pulmonary veins (APVs) and atrial septal defects (ASDs) using fast cine magnetic resonance imaging (MRI) and ultrafast three-dimensional magnetic resonance angiography (MRA).

BACKGROUND

Precise anatomic definition of anomalous pulmonary and systemic veins, and the atrial septum are prerequisites for surgical correction of ASDs. Cardiac catheterization and transesophageal echocardiography (TEE) are currently used to diagnose APVs, but did not provide complete information in our patients.

METHODS

Twenty consecutive patients with suspected APVs were studied by MRA after inconclusive assessment by catheterization, TEE or both. The MRI images were acquired with a fast cine sequence and a novel ultrafast three-dimensional sequence before and after contrast injection.

RESULTS

Partial anomalous pulmonary venous drainage was demonstrated in 16 of 20 patients and was excluded in four patients. Magnetic resonance imaging correctly diagnosed APVs and ASDs in all patients (100%) who underwent surgery. For the diagnosis of APVs, the MRI and catheterization results agreed in 74% of patients and the MRI and TEE agreed in 75% of patients. For ASDs, MRI agreed with catheterization and TEE in 53% and 83% of patients, respectively.

CONCLUSIONS

Fast cine MRI with three-dimensional contrast-enhanced MRA provides rapid and comprehensive anatomic definition of APVs and ASDs in patients with adult congenital heart disease in a single examination.

Assessment of synchronized direct mechanical ventricular actuation in a canine model of left ventricular dysfunction

Direct mechanical ventricular actuation (DMVA) is an experimental procedure that provides biventricular cardiac assistance by intracorporeal pneumatic compression of the heart. The advantages this technique has over other assist devices are biventricular assistance, no direct blood contact, pulsatile blood flow, and rapid, less complicated application. Prior studies of nonsynchronized DMVA support have demonstrated that a subject can be maintained for up to 7 days. The purpose of this study was to determine the acute hemodynamic effects of cardiac synchronized, partial DMVA support in a canine model (RVP) of left ventricular (LV) dysfunction. The study consisted of rapidly pacing seven dogs for 4 weeks to create LV dysfunction. At the conclusion of the pacing period, the DMVA device was positioned around the heart by means of a median sternotomy. The animals were then imaged in a 1.5 T whole body high speed clinical MR system, with simultaneous LV pressure recording. Left ventricular pressure-volume (PV) loops of the nonassisted and DMVA assisted heart were generated and demonstrated that DMVA assist shifted the loops leftward. In addition, assist significantly improved pressure dependent LV systolic parameters (left ventricular peak pressure and dp/dt max, p < 0.05), with no diastolic impairment. This study demonstrates that DMVA can provide synchronized partial assist, resulting in a decrease in the workload of the native heart, thus having a potential application for heart failure patients.

Dynamic cardiomyoplasty decreases myocardial workload as assessed by tissue tagged MRI

The effects of dynamic cardiomyoplasty (CMP) on global and regional left ventricular (LV) function in end-stage heart failure still remain unclear. MRI with tissue-tagging is a novel tool for studying intramyocardial motion and mechanics. To date, no studies have attempted to use MRI to simultaneously study global and regional cardiac function in a model of CMP. In this study, we used MRI with tissue-tagging and a custom designed MR compatible muscle stimulating/pressure monitoring system to assess long axis regional strain and displacement variations, as well as changes in global LV function in a model of dynamic cardiomyoplasty. Three dogs underwent rapid ventricular pacing (RVP; 215 BPM) for 10 weeks; after 4 weeks of RVP, a left posterior CMP was performed. After 1 year of dynamic muscle stimulation, the dogs were imaged in a 1.5 T clinical MR scanner. Unstimulated and muscle stimulated tagged long axis images were acquired. Quantitative 2-D regional image analysis was performed by dividing the hearts into three regions: apical, septal, and lateral. Maximum and minimum principal strains (lambda, and lambda2) and displacement (D) were determined and pooled for each region. MR LV pressure-volume (PV) loops were also generated. Muscle stimulation produced a leftward shift of the PV loops in two of the three dogs, and an increase in the peak LV pressure, while stroke volume remained unchanged. With stimulation, lambda1 decreased significantly (p<0.05) in the lateral region, whereas lambda2 increased significantly (p<0.05) in both the lateral and apical regions, indicating a decrease in strain resulting from stimulation. D only increased significantly (p<0.05) in the apical region. The decrease in strain between unassisted and assisted states indicates the heart is performing less work, while maintaining stroke volume and increasing peak LV pressure. These findings demonstrate that the muscle wrap functions as an active assist, decreasing the workload of the heart, while preserving total pump performance.

Structural determinants of aortic regurgitation in type A dissection and the role of valvular resuspension as determined by intraoperative transesophageal echocardiography

Disruption of the aortic root by dissection often produces significant aortic regurgitation (AR). Resuspension of the native valve usually reestablishes competence. The mechanisms of this complex process are poorly understood. We used intraoperative transesophageal echocardiography to characterize the in vivo aortic root structure of type A aortic dissection and the changes brought about by native valve resuspension. Intraoperative transesophageal echocardiograms were obtained from 34 patients with type A dissection and aortic resuspension between January 1990 and April 1997. The severity of AR, aortic root diameter, circumference of the aortic annulus, percentage of the annulus dissected, and presence of leaflet prolapse were assessed in multiple planes. Preoperatively, AR of varying degree was present in 25 patients (73%). Multivariate analysis revealed that preoperative AR was most related to percentage of the annulus dissected (p<0.0001) and less related to root diameter (p<0.01). Leaflet prolapse was predicted by percent aortic annulus dissected (p <0.0001). After resuspension, annular dissection and leaflet prolapse were no longer present. Postoperative AR was significantly decreased from preoperative AR (p<0.0001) and was considered trace to mild. Although postoperative root diameter and annular circumference decreased (p<0.001), individual reductions in AR did not correlate with individual changes in root diameter or annular circumference. The degree of dissection of the valve annulus is the most significant determinant of leaflet prolapse and AR severity. Overall size of the aortic root also contributes to AR. Surgical resuspension significantly decreases root size, but its primary benefit is restoration of the structural integrity of the aortic annulus.

Cardiac-respiratory gating method for magnetic resonance imaging of the heart

In studies of transmural myocardial function, acquisitions of high spatial and temporal resolution tagged cardiac images often exceed the practical time limit for breath-hold fast imaging techniques. Therefore, a dual cardiac-respiratory gating device has been constructed to acquire SPAMM-tagged cardiac MR images at or near end-expiration during spontaneous breathing, by providing an external trigger to a conventional MRI system. Combined cardiac and respiratory gating essentially eliminates the respiratory motion artifacts in tagged cardiac MR images. Compared to cardiac-gated images obtained during intermittent breath-holds, cardiac-respiratory gated images show improved tag-myocardium contrast due to magnetization recovery during inspiration.

Extrinsic compression of the left main coronary artery by the pulmonary artery in patients with long-standing pulmonary hypertension

Left main coronary artery compression by the pulmonary artery may be seen in patients with pulmonary hypertension who are undergoing cardiac catheterization. Cardiac magnetic resonance imaging is useful in these patients to document extrinsic compression, which might otherwise be mistaken for intrinsic atherosclerotic disease.

Effect of dobutamine on regional left ventricular function measured by tagged magnetic resonance imaging in normal subjects

The effect of inotropic stimulation on the pattern and magnitude of regional left ventricular contraction was studied using tagged magnetic resonance imaging to assess whether dobutamine exacerbates variation in regional contraction at rest. Dobutamine stress testing defines a normal response as a homogeneous increase in regional wall motion. In 8 normal subjects, 4 equally spaced left ventricular short-axis levels were imaged through systole using tagged magnetic resonance imaging. The baseline imaging sequence was repeated with 5-, 10-, 15-, and 20-microg/kg/min dobutamine infusion. Regional myocardial displacement, radial thickening, and circumferential shortening were measured. The left ventricle was analyzed by level (base to apex) and wall (septum, inferior, lateral, anterior). Dobutamine did not alter baseline regional functional heterogeneity. Dobutamine infusion resulted in a uniform increase in displacement, radial thickening, and circumferential shortening from baseline to 10-microg/kg/min infusion without additional increases at higher doses.

Determination of global function and regional mechanics of dynamic cardiomyoplasty using magnetic resonance imaging

This study used tissue tagged magnetic resonance (MR) to assess regional strain and generate pressure-volume (PV) loops in a canine model of cardiomyoplasty (CMP). Three dogs with rapid ventricular pacing induced heart failure underwent dynamic CMP chronic cardiac assistance for 1 year. At the end of the study period, we performed a MR study with the myostimulator "on" and "off" and recording of left ventricular (LV) pressure. We determined the short axis displacement (D) and maximal and minimal principal strains (lambda1 and lambda2) by quantitative two-dimensional regional spatial modulation of magnetization visualization utility image analysis. LV PV loops were generated by combining the LV volume data from the MR images with the LV pressure recorded during imaging. Muscle stimulation produced a leftward shift of the LV PV loops in two of the three dogs, and an increase in LV peak pressure and dp/dt max. In contrast, short axis lambda1 and lambda2 did not change significantly (p = NS). D increased significantly in the anterolateral, posterolateral, and posteroseptal regions (p < 0.05) but did not change for the septal region (p = NS). Flap stimulation augments LV function in the absence of short axis strain change; this suggests that dynamic CMP exerts its main action along the long axis of the heart.

Integrated MRI assessment of regional function and perfusion in canine myocardial infarction

A single integrated examination using regional measurements of perfusion from contrast-enhanced MRI and three-dimensional (3D) strain from tissue-tagged MRI was developed to differentiate infarcted myocardium from adjacent tissue with functional abnormalities. Ten dogs were studied at baseline and 10 days after a 2-hour occlusion of the left anterior descending coronary artery (LAD). Strain was determined using a 3D finite element model. Two-dimensional measurements of hypoenhancing regions were highly correlated with myocardial viability (r = 0.96). Signal intensity versus time curves obtained from contrast-enhanced MRI were used for quantitative perfusion analysis. The remote and adjacent noninfarcted tissue of the dogs with LAD occlusion, as well as the infarcted tissue, exhibited abnormal deformation patterns as compared to normal dogs (positive predictive value (PPV) of strain determination of infarction = 66%). Integration of contrast-enhanced MRI results with 3D strain analysis enabled the delineation of the myocardial infarction (PPV = 100%) from functionally compromised myocardium. This integrated cardiac examination shows promise for noninvasive serial assessment of potentially jeopardized noninfarcted myocardium to study the process of infarct remodeling and expansion.

Right ventricular regional function using MR tagging: normals versus chronic pulmonary hypertension

Right ventricular (RV) regional function, in both normal and diseased states, is not well characterized. Using 1D MR myocardial tagging, RV and septal intramyocardial segmental shortening was noninvasively measured in ten healthy subjects and in seven patients with chronic pulmonary hypertension. The normal RV free wall regional shortening was not uniform. A pattern of increasing RV free wall short-axis shortening was found from the RV outflow tract to the RV apex, and a more complex pattern of RV free wall long-axis shortening was observed. Both regional short- and long-axis shortening were globally reduced in pulmonary hypertension patients, with the greatest decreases in the RV outflow tract and in the basal septal wall region. Regional RV function can be quantitatively evaluated using MR tagging to determine the impact of chronic pulmonary hypertension on RV performance.

Diagnosis of a persistent coronary fistula after ventricular septal defect patch closure

Penetrating chest trauma can result in multiple clinical syndromes depending on the structures involved. Tamponade, valvular regurgitation, ventricular septal defect (VSD), conduction system abnormalities, and coronary lacerations have been reported. We report a case of right ventricular free wall laceration, VSD, and coronary artery fistula involving a septal perforator.

Right and left ventricular volume and ejection fraction by tomographic gated blood-pool scintigraphy

Tomographic techniques separate overlying structures, permitting measurements of absolute ventricular volumes. The purpose of this study was to determine absolute right and left ventricular volume and ejection fraction measurements with tomographic gated equilibrium blood-pool scintigraphy (TMUGA) compared to MRI and conventional planar scintigraphy.

METHODS

Eighteen patients were studied. Ventricular volumes for TMUGA and MRI were calculated by modified Simpson's rule. TMUGA regions were defined by constraints including phase analysis, intensity threshold and visual inspection. MRI studies were acquired with a fast gradient-echo, ECG-gated, breath-hold technique and boundaries were defined by a semiautomated contour method. Conventional gated first-pass radionuclide angiography (FP) and planar gated equilibrium blood-pool scintigraphy (PMUGA) were performed for RV EF and LV EF, respectively.

RESULTS

TMUGA absolute right ventricular volumes showed excellent-correlation with MRI for both right ventricular volumes (r = 0.91, slope = 0.90, s.e.e. = 15.7) and left ventricular volumes (r = 0.96, slope = 0.88, s.e.e. = 18.2). For left ventricular ejection fraction, TMUGA also showed excellent correlation with MRI (r = 0.94, slope = 1.10, s.e.e. = 9.0) and planar MUGA (r = 0.97, slope = 1.23, s.e.e. = 6.2). For right ventricular ejection fraction, TMUGA showed good correlation with both MRI (r = 0.88, slope = 0.79, s.e.e. = 6.0) and first-pass planar scintigraphy (r = 0.86, slope = 1.2, s.e.e. = 7.9).

CONCLUSION

Tomographic gated blood-pool scintigraphy absolute right and left ventricular volumes and ejection fractions show good correlation with accepted techniques. Further studies are necessary to define the reproducibility of this method.

Global cardiac function using fast breath-hold MRI: validation of new acquisition and analysis techniques

Calculation of global cardiac function parameters has been validated using fast, segmented k-space, breath-hold, gradient-echo, magnetic resonance images. Images of phantoms, experimental animals, normal volunteers, and patients were acquired with a 1.5 T clinical scanner. Humans were imaged using two phased-array surface coils in multicoil mode. Myocardial contours were extracted using a new interactive, semi-automated method based on the active contour model method. Images were acquired in the short-axis orientation, and, using a new imaging and analysis strategy, in rotating plane long-axis orientations, to provide better definition of the valve planes and the apex, and also to reduce the number of slices (compared with the short-axis method) required to sample the whole heart. Validation was accomplished through calculation of the volumes of phantoms and left and right ventricular masses of animal hearts. Functional parameters from MRI were compared with those from echocardiograms and radionuclide angiograms in normal volunteers and patients, respectively.

Single coronary artery: an angiographic and MRI case report

A single coronary artery is a rare cause of cardiac ischemia, congestive heart failure, and sudden death. We report the second known antemortem diagnosis of a single right coronary artery supplying the entire myocardium.

Angiotensin-converting enzyme inhibition limits dysfunction in adjacent noninfarcted regions during left ventricular remodeling

OBJECTIVES

We hypothesized that angiotensin-converting enzyme inhibitors would limit dysfunction in the first 8 weeks after transmural infarction in adjacent noninfarcted regions, as well as attenuate left ventricular remodeling.

BACKGROUND

Angiotensin-converting enzyme inhibition limits ventricular dilation and hypertrophy and improves survival after anterior infarction, but its effect on regional function during remodeling is not well characterized.

METHODS

Thirteen sheep underwent coronary ligation to create an anteroapical infarction. At postinfarction day 2, eight sheep were randomized to therapy with the angiotensin-converting enzyme inhibitor ramipril, and five sheep received no therapy. Animals were studied with magnetic resonance myocardial tagging before and 8 weeks after infarction. Left ventricular volume, mass and ejection fraction were measured, as were changes in percent circumferential shortening within the subendocardium and subepicardium of infarcted and noninfarcted myocardium, both adjacent to and remote from the infarction.

RESULTS

Angiotensin-converting enzyme inhibition limited the increase in end-diastolic volume from a mean (+/- SD) of +1.5 +/- 0.7 ml/kg in control animals to +0.5 +/- 0.8 ml/kg in the treated group (p < 0.04). Segmental function within infarcted and remote noninfarcted tissue did not differ between groups. However, angiotensin-converting enzyme inhibition limited the decline in function in the adjacent noninfarcted region 8 weeks after infarction. Percent circumferential shortening in the subendocardium decreased by -13 +/- 5% in the control group compared with -5 +/- 5% in the treated group (p < 0.03).

CONCLUSIONS

In concert with a reduction in left ventricular remodeling after anterior infarction, angiotensin-converting enzyme inhibition limits the decline in function in the adjacent noninfarcted region. Dysfunction in adjacent noninfarcted regions may be an important determinant of left ventricular remodeling after infarction.

Acute systolic and diastolic indices of left ventricular function after cardiomyoplasty in a chronic model of heart failure

Recent experimental studies have suggested that the initial nonstimulated stage of dynamic cardiomyoplasty acutely impairs ventricular function. Those investigations were performed on normal hearts and primarily examined diastolic alterations as a result of the passive muscle wrap. The purpose of this study was to assess the acute systolic and diastolic effects of a nonstimulated muscle wrap in chronic heart failure induced by rapid ventricular pacing in canines. Pressure-volume analysis of ventricular function based on conductance catheter volume and micromanometer pressure data was used. Each animal was studied before rapid pacing, before cardiomyoplasty, and immediately after wrap. By the end of the pacing period and before wrap, left ventricular dysfunction developed in all dogs, manifested by significant deterioration of both systolic and diastolic indices of ventricular function, as well as progressive increases in left ventricular volumes. However, no further deterioration with load insensitive indices of systolic or diastolic indicators of ventricular function was found as a result of the passive muscle wrap. These results suggest that the cardiomyoplasty procedure can be safely performed on failing hearts without prohibitive acute impairment of ventricular function.

Pathogenesis of acute ischemic mitral regurgitation in three dimensions

Changes in the geometric and intravalvular relationships between subunits of the ovine mitral valve were measured before and after acute posterior wall myocardial infarction in three dimensions by means of sonomicrometry array localization. In 13 sheep, nine sonomicrometer transducers were attached around the mitral anulus and to the tip and base of each papillary muscle. Five additional transducers were placed on the epicardium. Snares were placed around three branches of the circumflex coronary artery. One to 2 weeks later, echocardiograms, dimension measurements, and left ventricular pressures were obtained before and after the coronary arteries were occluded. Data were obtained from seven sheep. Coronary occlusion infarcted 32% of the posterior left ventricle and produced 2 to 3+ mitral regurgitation by Doppler color flow mapping. Multidimensional scaling of dimension measurements obtained from sonomicrometry transducers produced three-dimensional spatial coordinates of each transducer location throughout the cardiac cycle before and after infarction and onset of mitral regurgitation. After posterior infarction, the mitral anulus enlarges asymmetrically along the posterior anulus, and the tip of the posterior papillary muscle moves 1.5 +/- 0.3 mm closer to the posterior commissure at end-systole. The posterior papillary muscle also elongates 1.9 +/- 0.3 mm at end-systole. The left ventricle enlarges asymmetrically and ventricular torsion along the long axis changes. The development of postinfarction mitral regurgitation appears to be the consequence of multiple small changes in ventricular shape and contractile deformation and in the spatial relationship of mitral valvular subunits.

Segmental motion and deformation of transmurally infarcted myocardium in acute postinfarct period

Mechanical behavior of infarcted myocardium in the first week following coronary occlusion has not been well characterized. Prior unidimensional studies failed to account for perpendicular deformation or shearing. This study characterizes three-dimensional motion and deformation of transmural infarcts 1 wk after coronary ligation in seven sheep. Principal strains and systolic in-plane translation and rotation were calculated for triangular elements defined by tissue tagging in short- and long-axis magnetic resonance images. The magnitudes of the first and second principal strains were reduced in both the short- and long-axis planes 1 wk after infarction. In addition, the absolute angular difference between the direction of the first principal strain and the radial direction increased from 14.7 +/- 1.9 to 43.5 +/- 2.7 degrees in the short-axis plane and from 19.6 +/- 7.3 to 43.9 +/- 10.0 degrees (P < 0.05) in the long-axis plane. In-plane rigid-body translation and rotation were also reduced in both planes. In conclusion, marked reduction and reorientation of principal strains and reduction in segmental rigid-body motion characterize nonreperfused transmural myocardial infarctions 1 wk after coronary occlusion.

Three-dimensional left ventricular deformation in hypertrophic cardiomyopathy

BACKGROUND

In hypertrophic cardiomyopathy, ejection fraction is normal or increased, and force-length relations are reduced. However, three-dimensional (3D) motion and deformation in vivo have not been assessed in this condition. We have reconstructed the 3D motion of the left ventricle (LV) during systole in 7 patients with hypertrophic cardiomyopathy (HCM) and 12 normal volunteers by use of magnetic resonance tagging.

METHODS AND RESULTS

Transmural tagging stripes were automatically tracked to subpixel resolution with an active contour model. A 3D finite-element model was used to interpolate displacement information between short- and long-axis slices and register data on a regional basis. Displacement and strain data were averaged into septal, posterior, lateral, and anterior regions at basal, midventricular, and apical levels. Radial motion (toward the central long axis) decreased slightly in patients with HCM, whereas longitudinal displacement (parallel to the long axis) of the base toward the apex was markedly reduced: 7.5 +/- 2.5mm (SD) versus 12.5 +/- 2.0 mm, P < .001. Circumferential and longitudinal shortening were both reduced in the septum (P < .01 at all levels). The principal strain associated with 3D maximal contraction was slightly depressed in many regions, significantly in the basal septum (-0.18 +/- 0.05 versus -0.22 +/- 0.02, P < .05) and anterior (-0.20 +/- 0.05 versus -0.23 +/- 0.02, P < .05) walls. In contrast, LV torsion (twist of the apex about the long axis relative to the base) was greater in HCM patients (19.9 +/- 2.4 degrees versus 14.6 +/- 2.7 degrees, P < .01).

CONCLUSIONS

HCM patients had reduced 3D myocardial shortening on a regional basis; however, LV torsion was increased.

Regional heterogeneity of function in hypertrophic cardiomyopathy

BACKGROUND

In patients with hypertrophic cardiomyopathy (HCM), left ventricular ejection performance may be normal while segmental myocardial function is distinctly abnormal. The advent of magnetic resonance tissue tagging has allowed the noninvasive evaluation of intramyocardial segmental shortening in vivo in a topographic and temporal manner.

METHODS AND RESULTS

Ten patients with HCM documented by echocardiography and 10 healthy volunteers were studied with magnetic resonance tissue tagging by spatial modulation of magnetization. Percent circumferential myocardial shortening (%S) was compared at endocardium, midwall, and epicardial levels at four regions around the left ventricular short axis and from four short axis slices from apex to base at four or five time intervals during systole. In 8 patients and 8 control subjects, longitudinal shortening was evaluated within the septum and the lateral free wall at three levels from apex to base. Circumferential %S was less in HCM patients than in control subjects in the septal (13 +/- 5% versus 24 +/- 6%, P = .0002), inferior (13 +/- 5% versus 21 +/- 4%, P = .001), and anterior (17 +/- 5% versus 21 +/- 3%, P < .03) regions but not in the lateral region. Circumferential end-systolic %S was reduced in patients with HCM compared with control subjects at all levels from apex to base. The normal transmural gradient in circumferential end-systolic shortening was preserved with greatest %S at the endocardium. Most of the total cumulative circumferential shortening occurred earlier in systole in patients compared with control subjects, especially within the septum. Longitudinal end-systolic %S was depressed throughout the septum in patients compared with control subjects, most markedly at the base, but was normal in the lateral free wall.

CONCLUSIONS

Circumferential myocardial segment shortening is depressed in HCM in the septum, inferior, and anterior regions and at all levels from apex to base, and much of the total cumulative shortening occurs early in systole. Longitudinal shortening is reduced in the basal septum in HCM. The heterogeneity of regional function in these patients may reflect the regional variation in the myocardial disarray and fibrosis that is characteristic of this disorder.

Regional differences in function within noninfarcted myocardium during left ventricular remodeling

BACKGROUND

The mechanisms of ventricular enlargement and dysfunction during postinfarct remodeling remain largely unknown. Although global left ventricular architectural changes after myocardial infarction are well documented, differences in function between adjacent and remote noninfarcted myocardium during left ventricular remodeling have not been investigated. These functional differences may relate to regional differences in wall stress during contraction and may contribute to chamber enlargement and global dysfunction after infarction.

METHODS AND RESULTS

Anteroapical infarcts were produced in seven sheep by ligation of the mid left anterior descending coronary artery and second diagonal branch at thoracotomy. Magnetic resonance short-axis and long-axis images tagged by spatial modulation of magnetization were obtained before and 1 week, 8 weeks, and 6 months after infarction. Left ventricular volumes, mass, ejection fraction, and lengths of infarcted and noninfarcted segments were measured. Circumferential and longitudinal shortening in the subendocardium and subepicardium, wall thickness, and histopathology were assessed in infarcted segments and regions adjacent to and remote from the infarct border. We found that a difference in circumferential and longitudinal segmental shortening between adjacent and remote noninfarcted myocardium present at 1 week persisted up to 6 months after myocardial infarction. However, partial improvement of function in adjacent regions occurred during infarct healing between 1 and 8 weeks after infarction. Left ventricular volume increased up to 6 months after infarction, out of proportion to the concomitant eccentric hypertrophy, whereas the ejection fraction fell. Left ventricular dilatation late in the remodeling process was secondary to lengthening of noninfarcted segments, which were free of significant fibrosis.

CONCLUSIONS

Left ventricular dilatation and eccentric hypertrophy during remodeling are associated with persistent differences in segmental function between adjacent and remote noninfarcted regions. These functional differences may reflect increased wall stress in adjacent noninfarcted regions and contribute to the global dilatation and dysfunction characteristic of left ventricular remodeling after infarction.

Pulmonary artery hemodynamics in primary pulmonary hypertension

OBJECTIVES

The present investigation compared and contrasted steady and pulsatile pulmonary hemodynamics at rest and during exercise in patients with primary pulmonary hypertension and normal control subjects.

BACKGROUND

A complete description of the relation between pressure and flow in the pulmonary circulation includes both steady and pulsatile hemodynamic behavior. Patients with primary pulmonary hypertension provide a unique opportunity to study the effects of primary alterations in pulmonary vasculature on pulmonary artery vascular hydraulic load.

METHODS

Catheter tip pressure and velocity recordings from the main pulmonary artery in 8 patients with primary pulmonary hypertension and 10 control subjects were used to derive the pulmonary artery input impedance spectrum and the extent of pulse wave reflection at rest and during exercise.

RESULTS

As expected, in patients with primary pulmonary hypertension, mean pulmonary artery pressure (50 +/- 10 mm Hg) and pulmonary vascular resistance (880 +/- 446 dynes.s.cm-5) were markedly elevated at rest and remained so during exercise (mean pressure 71 +/- 15 mm Hg, mean resistance 750 +/- 530 dynes.s.cm-5). Pulmonary artery characteristic impedance was elevated at rest and did not change with exercise (rest 55 +/- 25 dynes.s.cm-5; exercise 66 +/- 33 dynes.s.cm-5). Measures of arterial wave reflection indicated that the extent of wave reflection in the pulmonary bed in those with primary pulmonary hypertension is large at rest (reflection coefficient 0.89 +/- 0.09) and that the composite reflected wave arrived during the midportion of right ventricular ejection. Although the extent of wave reflection decreased with exercise (reflection coefficient 0.81 +/- 0.10, p < 0.05), the magnitude and timing of these reflections remained adverse. Furthermore, in patients with primary pulmonary hypertension, the stroke volume response to exercise was strongly related to rest levels of pulmonary artery diastolic pressure, pulmonary vascular resistance and the reflection factor, whereas no such relation was found in the control subjects.

CONCLUSIONS

In addition to the expected abnormalities in steady measures of pulmonary artery hemodynamics at rest in patients with primary pulmonary hypertension, rest and exercise measures of oscillatory behavior (characteristic impedance and pulse wave reflection) are perturbed. Measures of steady and pulsatile behavior, particularly wave reflection, appear to have an important role in the exercise response of these patients.

Estimation of total systemic arterial compliance in humans

Systemic arterial compliance, a major component of aortic input impedance, was determined in 10 patients with congestive heart failure secondary to idiopathic dilated cardiomyopathy and 11 age-matched control subjects found free of detectable cardiovascular disease. Total arterial compliance was determined from high-fidelity ascending aortic pressure and velocity recordings using 1) the traditional monoexponential aortic diastolic pressure decay and 2) the direct solution of the equation, which describes the three-element windkessel model of the arterial system. Resting values for total arterial compliance (x10(-3) cm5/dyn) derived from method 1 were significantly correlated with compliance derived from method 2 (r = 0.89, P less than 0.01). However, method 1 values (control mean 1.15 +/- 0.27, heart failure mean 1.18 +/- 0.54) were consistently and significantly lower (P less than 0.001) than method 2 values (control mean 1.59 +/- 0.50, heart failure mean 1.38 +/- 0.60). Resting total arterial compliance in heart-failure patients was not significantly different from control subjects. Total arterial compliance did not significantly change with exercise in either group despite increases in arterial pressure. However, nitroprusside administration in the heart-failure group increased total arterial compliance both at rest and on exercise compared with the unmedicated state. These different methodological approaches to the estimation of total arterial compliance in humans resulted in significantly different absolute values for compliance, although both methods provided concordant results with respect to the response of arterial compliance to physiological and pharmacological interventions.(ABSTRACT TRUNCATED AT 250 WORDS)