Regional circumferential strain is a biomarker for disease severity in duchenne muscular dystrophy heart disease: a cross-sectional study.

The aim of this study is to determine the contribution of strain ε cc in mid left ventricular (LV) segments to the reduction of composite LV circumferential ε cc in assess severity of duchenne muscular dystrophy (DMD) heart disease as assessed by cardiac magnetic resonance imaging (CMR). DMD patients and control subjects were stratified by age, LV ejection fraction, and late gadolinium enhancement (LGE) status. Tagged CMR images were analyzed for global ventricular function, LGE imaging, and composite and segmental ε cc. The relationship between changes in segmental ε cc changes and LGE across patient groups was assessed by a statistical step-down model. LV ε cc exhibited segmental heterogeneity; in control subjects and young DMD patients, ε cc was greatest in LV lateral free wall segments. However, with increasing age and cardiac disease severity as demonstrated by decreased EF and development of myocardial strain the segmental differences diminished. In subjects with advanced heart disease as evidenced by reduced LV ejection fraction and presence of LGE, very little segmental heterogeneity was present. In control subjects and young DMD patients, ε cc was greatest in LV lateral free wall segments. Increased DMD heart disease severity was associated with reduced composite; ε cc diminished regional ε cc heterogeneity and positive LGE imaging. Taken together, these findings suggest that perturbation of segmental, heterogeneous ε cc is an early biomarker of disease severity in this cross-section of DMD patients.

Comparison of stroke work between repaired tetralogy of Fallot and normal right ventricular physiologies.

Adult patients who underwent tetralogy of Fallot repair surgery (rTOF) confront life-threatening ailments due to right ventricular (RV) myocardial dysfunction. Pulmonary valve replacement (PVR) needs to be performed to restore the deteriorating RV function. Determination of correct timing to perform PVR in an rTOF patient remains subjective, due to the unavailability of quantifiable clinical diagnostic parameters. The objective of this study is to evaluate the possibility of using RV body surface area (BSA)-indexed stroke work (SW(I)) to quantify RV inefficiency in TOF patients. We hypothesized that RV SW(I) required to push blood to the lungs in rTOF patients is significantly higher than that of normal subjects. Seven patients with rTOF pathophysiology and eight controls with normal RV physiology were registered for this study. Right ventricular volume and pressure were measured using cardiac magnetic resonance imaging and catheterization, respectively. Statistical analysis was performed to quantify the difference in SW(I) between the RV of the rTOF and control groups. Right ventricular SW(I) in rTOF patients (0.176 ± 0.055 J/m(2)) was significantly higher by 93.4% (P = 0.0026) than that of controls (0.091 ± 0.030 J/m(2)). Further, rTOF patients were found to have significantly higher (P < 0.05) BSA normalized RV end-systolic volume, end-systolic pressure, and regurgitation fraction than control subjects. Ejection fraction and peak ejection rate of rTOF patients were significantly lower (P < 0.05) than those of controls. Patients with rTOF pathophysiology had significantly higher RV SW(I) compared with subjects with normal RV physiology. Therefore, RV SW(I) may be useful to quantify RV inefficiency in rTOF patients along with currently used clinical end points such as RV volume, pressure, regurgitation fraction, and ejection fraction.

Partial anomalous pulmonary venous return is common in Turner syndrome.

BACKGROUND: Cardiovascular disease affects >50% of Turner syndrome (TS) patients. With newer imaging modalities, this prevalence increases and the spectrum of recognized anomalies broadens. OBJECTIVE: To determine the prevalence and hemodynamic significance of partial anomalous pulmonary venous return (PAPVR) in adolescents and young adults with TS using transthoracic echocardiogram (TTE) and cardiac magnetic resonance (CMR), and to study the association with phenotype. METHODS: The records of 39 young TS patients who had received TTE and CMR were reviewed. RESULTS: PAPVR was diagnosed in seven (18%) patients; six were newly diagnosed by CMR after normal TTE. In one subject, PAPVR was associated with right ventricular enlargement and a pulmonic blood flow (Qp) to systemic blood flow (Qs) ratio of 1.9:1.0, necessitating surgical repair. In other subjects with and without PAPVR, Qp:Qs and the right ventricle to left ventricle end-diastolic volume ratio were statistically different. Other clinical features were not predictive of PAPVR. CONCLUSIONS: The prevalence of PAPVR is high in TS, and it may be hemodynamically significant. Diagnosis by TTE can be difficult. Appropriate screening and management are indicated.

Presence of mechanical dyssynchrony in Duchenne muscular dystrophy.

BACKGROUND: Cardiac dysfunction in boys with Duchenne muscular dystrophy (DMD) is a leading cause of death. Cardiac resynchronization therapy (CRT) has been shown to dramatically decrease mortality in eligible adult population with congestive heart failure. We hypothesized that mechanical dyssynchrony is present in DMD patients and that cardiovascular magnetic resonance (CMR) may predict CRT efficacy. METHODS: DMD patients (n = 236) were stratified into 4 groups based on age, diagnosis of DMD, left ventricular (LV) ejection fraction (EF), and presence of myocardial fibrosis defined as positive late gadolinum enhancement (LGE) compared to normal controls (n = 77). Dyssynchrony indices were calculated based on timing of CMR derived circumferential strain (ecc). The calculated indices included cross-correlation delay (XCD), uniformity of strain (US), regional vector of variance (RVV), time to maximum strain (TTMS) and standard deviation (SD) of TTMS. Abnormal XCD value was defined as > normal + 2SD. US, RVV, TTMS and SD were calculated for patients with abnormal XCD. RESULTS: There was overall low prevalence of circumferential dyssynchrony in the entire DMD population; it increased to 17.1% for patients with abnormal EF and to 31.2% in the most advanced stage (abnormal EF with fibrosis). All but one DMD patient with mechanical dyssynchrony exhibited normal QRS duration suggesting absence of electrical dyssynchrony. The calculated US and RVV values (0.91 ± 0.09, 1.34 ± 0.48) indicate disperse rather than clustered dyssynchrony. CONCLUSION: Mechanical dyssynchrony is frequent in boys with end stage DMD-associated cardiac dysfunction. It is associated with normal QRS complex as well as extensive lateral fibrosis. Based on these findings, it is unlikely that this patient population will benefit from CRT.

Effects of steroids and angiotensin converting enzyme inhibition on circumferential strain in boys with Duchenne muscular dystrophy: a cross-sectional and longitudinal study utilizing cardiovascular magnetic resonance.

BACKGROUND: Steroid use has prolonged ambulation in Duchenne muscular dystrophy (DMD) and combined with advances in respiratory care overall management has improved such that cardiac manifestations have become the major cause of death. Unfortunately, there is no consensus for DMD-associated cardiac disease management. Our purpose was to assess effects of steroid use alone or in combination with angiotensin converting enzyme inhibitors (ACEI) or angiotension receptor blocker (ARB) on cardiovascular magnetic resonance (CMR) derived circumferential strain (εcc). METHODS: We used CMR to assess effects of corticosteroids alone (Group A) or in combination with ACEI or ARB (Group B) on heart rate (HR), left ventricular ejection fraction (LVEF), mass (LVM), end diastolic volume (LVEDV) and circumferential strain (εcc) in a cohort of 171 DMD patients >5 years of age. Treatment decisions were made independently by physicians at both our institution and referral centers and not based on CMR results. RESULTS: Patients in Group A (114 studies) were younger than those in Group B (92 studies)(10 ± 2.4 vs. 12.4 ± 3.2 years, p < 0.0001), but HR, LVEF, LVEDV and LVM were not different. Although εcc magnitude was lower in Group B than Group A (-13.8 ± 1.9 vs. -12.8 ± 2.0, p = 0.0004), age correction using covariance analysis eliminated this effect. In a subset of patients who underwent serial CMR exams with an inter-study time of ~15 months, εcc worsened regardless of treatment group. CONCLUSIONS: These results support the need for prospective clinical trials to identify more effective treatment regimens for DMD associated cardiac disease.

Left ventricular T2 distribution in Duchenne muscular dystrophy.

BACKGROUND: Although previous studies have helped define the natural history of Duchenne muscular dystrophy (DMD)-associated cardiomyopathy, the myocardial pathobiology associated with functional impairment in DMD is not yet known.The objective of this study was to assess the distribution of transverse relaxation time (T2) in the left ventricle (LV) of DMD patients, and to determine the association of myocardial T2 heterogeneity to the severity of cardiac dysfunction. DMD patients (n = 26) and normal control subjects (n = 13) were studied by cardiovascular magnetic resonance (CMR). DMD subject data was stratified based on subject age and LV ejection fraction (EF) into the following groups: A (<12 years old, n = 12); B (>or=12 years old, EF or=12 years old, EF = 55%, n = 6). Controls were also stratified by age into Groups N1 (<12 years, n = 6) and N2 (>12 years, n = 5). LV mid-slice circumferential myocardial strain (epsilon cc) was calculated using tagged CMR imaging. T2 maps of the LV were generated for all subjects using a black blood dual spin echo method at two echo times. The full width at half maximum (FWHM) was calculated from a histogram of LV T2 distribution constructed for each subject. RESULTS: In DMD subject groups, FWHM of the T2 histogram rose progressively with age and decreasing EF (Group A FWHM= 25.3 +/- 3.8 ms; Group B FWHM= 30.9 +/- 5.3 ms; Group C FWHM= 33.0 +/- 6.4 ms). Further, FWHM was significantly higher in those with reduced circumferential strain (|epsilon cc| 12% (Group A). Group A FWHM was not different from the two normal groups (N1 FWHM = 25.3 +/- 3.5 ms; N2 FWHM= 24.0 +/- 7.3 ms). CONCLUSION: Reduced EF and epsilon cc correlates well with increased T2 heterogeneity quantified by FWHM, indicating that subclinical functional impairments could be associated with pre-existing abnormalities in tissue structure in young DMD patients.

Methodology for implementing patient-specific spatial boundary condition during a cardiac cycle from phase-contrast MRI for hemodynamic assessment.

Pulmonary insufficiency (PI) can render the right ventricle dysfunctional due to volume overloading and hypertrophy. The treatment requires a pulmonary valve replacement surgery. However, determining the right time for the valve replacement surgery has been difficult with currently employed clinical techniques such as, echocardiography and cardiac MRI. Therefore, there is a clinical need to improve the diagnosis of PI by using patient-specific (PS) hemodynamic endpoints. While there are many reported studies on the use of PS geometry with time varying boundary conditions (BC) for hemodynamic computation, few use spatially varying PS velocity measurement at each time point of the cardiac cycle. In other words, the gap is that, there are limited number of studies which implement both spatially- and time-varying physiologic BC directly with patient specific geometry. The uniqueness of this research is in the incorporation of spatially varying PS velocity data obtained from phase-contrast MRI (PC-MRI) at each time point of the cardiac cycle with PS geometry obtained from angiographic MRI. This methodology was applied to model the complex developing flow in human pulmonary artery (PA) distal to pulmonary valve, in a normal and a subject with PI. To validate the methodology, the flow rates from the proposed method were compared with those obtained using QFlow software, which is a standard of care clinical technique. For the normal subject, the computed time average flow rates from this study differed from those obtained using the standard of care technique (QFlow) by 0.8 ml/s (0.9%) at the main PA, by 2 ml/s (3.4%) at the left PA and by 1.4 ml/s (3.8%) at the right PA. For the subject with PI, the difference was 7 ml/s (12.4%) at the main PA, 5.5 ml/s (22.6%) at the left PA and 4.9 ml/s (18.0%) at the right PA. The higher percentage differences for the subject with PI, was the result of overall lower values of the forward mean flow rate caused by excessive flow regurgitation. This methodology is expected to provide improved computational results when PS geometry from angiographic MRI is used in conjunction with PS PC-MRI data for solving the flow field.

Patterns of left ventricular remodeling in patients with Duchenne Muscular Dystrophy: a cardiac MRI study of ventricular geometry, global function, and strain.

The cardiac disease ubiquitously associated in Duchenne Muscular Dystrophy (DMD) has traditionally been considered a progressive dilated cardiomyopathy (DCM). However, left ventricular (LV) dilatation as measured with cardiac MRI has not been a consistent finding in this population, even as circumferential strain (ε(cc)) declines with advancing disease. We hypothesized that a distinct pattern of changes in LV geometry, during the course of ε(cc) decline, distinguishes DMD associated heart disease from DCM. Using CMR, LV end-diastolic volume (EDV), mass (LVM), ejection fraction, ε(cc) and myocardial delayed enhancement (MDE) were determined in DMD patients and normal control subjects. The LV Remodeling Index (LVRI) was calculated as the ratio of LV Mass to Volume (LVM/EDV). Statistical comparisons between all LV parameters and genotype were also performed. Median LVRI in DMD (n = 127) and control subjects (n = 41) were different (0.75 vs. 0.65, P = 0.0150) but within normal range. Furthermore, the median LVRI in DMD boys with reduced LV systolic function was significantly reduced compared to those with normal LV systolic function (0.64 vs. 0.75, P = 0.0974). However, the presence of MDE was associated with a lower median LVRI (0.57 vs. 0.76, P = 0.0471). Regression analysis showed no significant correlation between ε(cc) and LVRI (r = -0.03). The LVRI of DMD patients is unexpectedly normal and not correlated with ε(cc.) Based on these findings, DMD-associated heart disease exhibits a unique remodeling pattern distinct from DCM.

Comparison of hemodynamic endpoints between normal subject and tetralogy patient using Womersley velocity profile and MR based flow measurements.

Right ventricular (RV) enlargement and pulmonary valve insufficiency (PI) are well-known, unavoidable long term sequelae encountered by patients who undergo tetralogy of Fallot (TOF) surgery. Despite their lifelong need for cardiac surveillance and occasional re-intervention, there is a paucity of numerical data characterizing blood flows in their pulmonary arteries (PA). Specifically, although PA regurgitation is well-known to be ubiquitously present in adult repaired TOF (rTOF) patients yet, there have been only limited numerical studies to fully characterize this process. The few studies available have utilized idealized, simplistic geometric models or overly simplistic boundary conditions that fail to account for flow reversals near the arterial walls as observed in in-vitro and MRI based in-vivo studies. The objective of this study was to establish and validate a numerical methodology of PA blood flow using actual patient specific geometry and flow measurements obtained using phase-contrast MRI, employing Womersley type velocity profiles that model flow reversals near walls. The results from computation were validated with measurements. For the normal subject, the time averaged right PA pressure from computation (13.8 mmHg) and experiment (14.6 mmHg) differed by 6%. The time-averaged main PA pressure from computation (16.5 mmHg) and experiment (16.3 mmHg) differed by 1%. The numerically computed left PA regurgitant fraction was 89% compared to measured 77.5%, while the same for the rTOF was 43% (computation), compared to 39.6% (measured). We conclude that the use of numerical computations using the Womersley boundary condition allows reliable modeling of the pathophysiology of PA flow in rTOF.

Magnetic resonance derived myocardial strain assessment using feature tracking.

PURPOSE: An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that strain is a more sensitive and earlier marker for contractile dysfunction than the frequently used parameter EF. Current technologies for CMR are time consuming and difficult to implement in clinical practice. Feature tracking is a technology that can lead to more automatization and robustness of quantitative analysis of medical images with less time consumption than comparable methods. METHODS: An automatic or manual input in a single phase serves as an initialization from which the system starts to track the displacement of individual patterns representing anatomical structures over time. The specialty of this method is that the images do not need to be manipulated in any way beforehand like e.g. tagging of CMR images. RESULTS: The method is very well suited for tracking muscular tissue and with this allowing quantitative elaboration of myocardium and also blood flow. CONCLUSIONS: This new method offers a robust and time saving procedure to quantify myocardial tissue and blood with displacement, velocity and deformation parameters on regular sequences of CMR imaging. It therefore can be implemented in clinical practice.

Right ventricular inefficiency in repaired tetralogy of Fallot: proof of concept for energy calculations from cardiac MRI data.

Repaired tetralogy of Fallot (rTOF) patients develop right ventricular (RV) dilatation and dysfunction. To prevent their demise, pulmonary valve replacement is necessary, though appropriate timing for it is challenged by a paucity of reliable diagnostic parameters. In this pilot study, we hypothesized that stroke work (SW) and energy calculations would delineate the inefficiency of RV performance in rTOF. RV SW was calculated for both an rTOF and a normal subject by utilizing RV pressure and volume measurements obtained during cardiac catheterization and MRI studies. Energy transfer rate and ratio were computed at the main pulmonary artery (PA). Compared to the normal RV, the rTOF RV had higher operating pressure, lower computed SW (0.078 J vs. 0.115 J for normal), and higher negative energy transfer at the PA (0.044 J vs. 0.002 J for normal). Furthermore, the energy transfer ratio was nearly twice as high for the normal RV (1.06) as for the rTOF RV (0.56). RV SW and energy transfer ratio delineate important operational efficiency differences in blood flow from the RV to the PA between rTOF and normal subjects. Our pilot data suggest that the rTOF RV is significantly less efficient than normal.

Detection of progressive cardiac dysfunction by serial evaluation of circumferential strain in patients with Duchenne muscular dystrophy.

The present study evaluated progressive cardiac dysfunction using serial circumferential strain (epsilon(cc)) measurements in patients with Duchenne muscular dystrophy (DMD). DMD is characterized by progressive cardiac dysfunction and myocardial fibrosis late in the disease process. We hypothesized that serial epsilon(cc) changes could be detected in individual patients with DMD during a time when the left ventricular ejection fraction (EF) changes are insignificant. Cardiac magnetic resonance imaging data from patients with DMD were evaluated. The left ventricular EF was calculated from steady-state free precession cine images and the composite epsilon(cc) measurement from tagged cine images. The serial epsilon(cc) and EF values for each patient were analyzed using the Wilcoxon sign rank test. Data from 51 patients with DMD (2 studies per patient, mean age at the initial study 11.8 +/- 3.5 years, range 7.4 to 25.4) were analyzed, with a mean interval between cardiac magnetic resonance studies of 15.6 +/- 6.0 months (range 6.2 to 28.1). In the interval between studies, the epsilon(cc) had decreased in all patients with DMD. The average decrease was 1.8 +/- 1.3 (p <0.001). However, the EF had decreased in 33 of the 51 patients and had increased in 18 of the 51 patients. On average, the EF decreased by 2.9 +/- 8.57% (p = NS). In conclusion, in patients with DMD, epsilon(cc) abnormalities indicate progression within a relatively short period when the EF changes were not significant. Serial epsilon(cc) measurements might provide reliable monitoring of the progression of DMD-associated cardiac dysfunction before overt heart failure develops, because it is more sensitive than the EF.

Comparison of magnetic resonance feature tracking for strain calculation with harmonic phase imaging analysis.

OBJECTIVES: To compare a steady-state free precession cine sequence-based technique (feature tracking [FT]) to tagged harmonic phase (HARP) analysis for peak average circumferential myocardial strain (epsilon(cc)) analysis in a large and heterogeneous population of boys with Duchenne muscular dystrophy (DMD). BACKGROUND: Current epsilon(cc) assessment techniques require cardiac magnetic resonance-tagged imaging sequences, and their analysis is complex. The FT method can readily be performed on standard cine (steady-state free precession) sequences. METHODS: We compared mid-left ventricular whole-slice epsilon(cc) by the 2 techniques in 191 DMD patients grouped according to age and severity of cardiac dysfunction: group B: DMD patients 10 years and younger with normal ejection fraction (EF); group C: DMD patients older than 10 years with normal EF; group D: DMD patients older than 10 years with reduced EF but negative myocardial delayed enhancement (MDE); group E: DMD patients older than 10 years with reduced EF and positive MDE; and group A: 42 control subjects. Retrospective, offline analysis was performed on matched tagged and steady-state free precession slices. RESULTS: For the entire study population (N = 233), mean FT epsilon(cc) values (-13.3 +/- 3.8%) were highly correlated with HARP epsilon(cc) values (-13.6 +/- 3.4%), with a Pearson correlation coefficient of 0.899. The mean epsilon(cc) of DMD patients determined by HARP (-12.52 +/- 2.69%) and FT (-12.16 +/- 3.12%) was not significantly different (p = NS). Similarly, the mean epsilon(cc) of the control subjects by determined HARP (-18.85 +/- 1.86) and FT (-18.81 +/- 1.83) was not significantly different (p = NS). Excellent correlation between the 2 methods was found among subgroups A through E, except there was no significant difference in strain between groups B and C with FT analysis. CONCLUSIONS: FT-based assessment of epsilon(cc) correlates highly with epsilon(cc) derived from tagged images in a large DMD patient population with a wide range of cardiac dysfunction and can be performed without additional imaging.

Late gadolinium enhancement: precursor to cardiomyopathy in Duchenne muscular dystrophy?

BACKGROUND: Progressive cardiomyopathy is a common cause of death in Duchenne muscular dystrophy (DMD), presumably secondary to fibrosis of the myocardium. The posterobasal and left lateral free wall of the left ventricle (LV) are initial sites of myocardial fibrosis pathologically. The purposes of this study were to assess whether cardiac magnetic resonance imaging (CMRI), utilizing late gadolinium enhancement (LGE), could identify fibrosis in selective areas of the myocardium, and to assess the relationship of the presence and extent of fibrosis to LV function. METHODS: The cardiology databases at Primary Children's Medical Center and Cincinnati Children's Hospital Medical Center were reviewed to identify patients with DMD who had undergone a CMRI within the last 2 years. Age, LV ejection fraction, LV mass, presence and location of LGE were documented. Volumes were measured using MASS (Medis, Inc.) to calculate ejection fraction and mass. LGE images were acquired and when positive, customized computer assisted sizing of the areas of late gadolinium enhancement were performed on all slices. Normal function was defined as LV ejection fraction >54%. RESULTS: A total of 74 patients with DMD had complete data sets (median age 13.7 years, range 7.7-26.4). Twenty-four patients (32%) had LGE involving the posterobasal region of the LV in a sub-epicardial distribution. Those patients with more involvement had spread to the inferior and left lateral free wall with progressive transmural fibrous replacement. There was relative sparing of the interventricular septum and right ventricle. Patients with LGE were significantly older than those without (mean age 16.4 vs 12.9 years, P < 0.001). LGE was positively associated with BSA-adjusted LV mass, LV end-diastolic volume, LV end-systolic volume, and RV end-systolic volume but inversely correlated with ejection fraction of the LV (P < 0.001) and RV (P = 0.004). CONCLUSIONS: LGE by CMRI is able to detect fibrosis in selective regions of myocardium in patients with DMD. Unfavorable LV remodeling, with a corresponding decreased ejection fraction, is associated with the presence of LGE. Serial studies are warranted to determine if LGE precedes a decrease in function, and if early medical management is useful in preventing progression once LGE is documented.

Circumferential strain analysis identifies strata of cardiomyopathy in Duchenne muscular dystrophy: a cardiac magnetic resonance tagging study.

OBJECTIVES: This study sought to evaluate the natural history of occult cardiac dysfunction in Duchenne muscular dystrophy (DMD). BACKGROUND: Duchenne muscular dystrophy is characterized by progressive cardiac dysfunction and myocardial fibrosis late in the disease process. We hypothesized that left ventricular myocardial peak circumferential strain (epsilon(cc)) would decrease in DMD before global systolic functional abnormalities regardless of age or ventricular ejection fraction (EF). METHODS: We evaluated cardiac magnetic resonance image (MRI) data from 70 DMD patients and 16 aged-matched control subjects. Standard imaging data included steady-state free precession short-axis cine stack images, cine myocardial tagged images, and myocardial delayed enhancement (MDE) (an indicator of myocardial fibrosis) sequences. Analysis was performed with QMASS (Medis Medical Imaging Systems, Leiden, the Netherlands) and HARP (Diagnosoft, Palo Alto, California) software. The DMD patient data were subdivided by age (<10 or >10 years), EF (>55% or <55%), and the presence or absence of MDE. RESULTS: The DMD patients with normal EF had reduced epsilon(cc) at an early age (<10 years) compared with control subjects (p < 0.01). The DMD patients age >10 years with normal EF had further decline in epsilon(cc) compared with younger DMD patients (p < 0.01). There was further decline in epsilon(cc) with age in patients with reduced EF (p < 0.01) without MDE. The oldest patients, with both reduced EF and positive MDE, exhibited the lowest epsilon(cc). None of the patients had ventricular hypertrophy. CONCLUSIONS: Myocardial strain abnormalities are prevalent in young DMD patients despite normal EF, and these strain values continue to decline with advancing age. Strain analysis in combination with standard MRI and MDE imaging provides a means to stratify DMD cardiomyopathy.

Concurrent assessment of epicardial coronary artery stenosis and microvascular dysfunction using diagnostic endpoints derived from fundamental fluid dynamics principles.

BACKGROUND: Simultaneously measured pressure and flow distal to coronary stenoses can be combined, in conjunction with anatomical measurements, to assess the status of both the epicardial and microvascular circulations. METHODS AND RESULTS: Assessments of coronary hemodynamics were performed using fundamental fluid dynamics principles. We hypothesized that the pressure-drop coefficient (CDPe; trans-stenotic pressure drop divided by the dynamic pressure in the distal vessel) correlates linearly with epicardial and microcirculatory resistances concurrently. In 14 pigs, simultaneous measurements of distal coronary arterial pressure and flow were performed using a dual sensor-tipped guidewire in the setting of both normal and disrupted microcirculation, with the presence of epicardial coronary lesions of lt; 50% area stenosis (AS) and > 50% AS. The CDPe progressively increased from lesions of < 50% AS to > 50% AS and had a higher resolving power (45 +/- 22 to 193 +/- 140 in normal microcirculation; 248 +/- 137 to 351 +/- 140 in disrupted microcirculation) as compared to fractional flow reserve (FFR) and coronary flow reserve (CFR). Strong multiple linear correlation was observed for CDPe with combined FFR and CFR (r = 0.72; p < 0.0001). Further, the ratio of maximum pressure drop coefficient evaluated at the site of stenosis and its theoretical limiting value of minimum cross-sectional area was also able to distinguish different combinations of coronary artery diseases. CONCLUSIONS: The CDPe can be readily obtained during routine pressure and flow measurements during cardiac catheterization. It is a promising clinical diagnostic parameter that can independently assess the severity of epicardial stenosis and microvascular impairment.

Morphological studies of pulmonary arteriovenous shunting in a lamb model of superior cavopulmonary anastomosis.

We sought to identify and characterize the abnormal vascular structures responsible for pulmonary arteriovenous shunting following the Glenn cavopulmonary shunt. Superior cavopulmonary shunt is commonly performed as part of the staged pathway to total cavopulmonary shunt to treat univentricular forms of congenital heart disease, however, clinically significant pulmonary arteriovenous malformations develop in some patients after the procedure. The causes of pulmonary arteriovenous malformations and other pulmonary vascular changes that occur after cavopulmonary shunt are not known. Using a juvenile lamb model of superior cavopulmonary anastomosis that reliably produces pulmonary arteriovenous malformations, we performed echocardiography and morphological analyses to determine the anatomic site of shunting and to identify the vascular structures involved. Pulmonary arteriovenous shunting was identified by contrast echocardiography in all surviving animals (n = 40) following superior cavopulmonary anastomosis. Pulmonary vascular corrosion casts revealed abnormal tortuous vessels joining pulmonary arteries and veins in cavopulmonary shunt animals but not control animals. In conclusion, unusual channels that bridged pulmonary arteries and veins were identified. These may represent the vascular structures responsible for arteriovenous shunting following the classic Glenn cavopulmonary shunt. Detailed analysis of these structures may elucidate factors responsible for their development.

Implementation of an objective testing system in noninvasive cardiac imaging for evaluation of pediatric cardiology fellows.

INTRODUCTION: Current evaluation of pediatric cardiology fellow performance is subjective and qualitative. More objective tools are recommended by credentialing boards and may provide more effective evaluation and education. OBJECTIVE: A series of training level-specific multiple-choice tests were developed and evaluated for their effectiveness as evaluation and educational tools for pediatric cardiology fellows. METHODS: Imaging tests were created by 3 attending physicians and one sonographer with combined expertise in echocardiography, cardiac magnetic resonance imaging, and cardiac computed tomography. Test content was derived from educational materials, textbooks, journal articles, and lectures previously given to the fellows. The tests were computerized and installed on the hospital intranet. After completion of each test, a posttest session was conducted between the fellow and the director of echocardiography to review concepts surrounding incorrect answers. A survey of the test use was then completed by each fellow. RESULTS: Four progressively more difficult tests corresponding to each 1-month image rotation and an advanced fifth test for fellows intending to subspecialize in noninvasive cardiac imaging were created. Fifteen fellows took 39 tests (test 1, 15 fellows; test 2, 9 fellows; test 3, 9 fellows; test 4, 4 fellows; and test 5, 2 fellows). The difficulty level of the tests was similar relative to fellow academic level. The majority of fellows welcomed more objective data provided by the tests and 93% of the fellows stated the posttest session was educational. CONCLUSION: Implementation of a fellow testing system using training level-specific computerized questions and images provides objective data for fellow performance evaluations and is a unique and beneficial educational tool.

A rapid hemodynamic monitor of acute ischemia during cardiac procedures: changes in relaxation via a continuous left ventricular pressure-derivative loop.

BACKGROUND: Procedures that induce ischemic pre-conditioning during cardiac surgery will require a rapidly visualized hemodynamic monitor of acute ischemia. This study investigated the utility of a continuous loop tracing of left ventricular pressure (LVP) plotted against its derivative (dP/dt) as a visual beat-to-beat monitor of acute changes in myocardial relaxation due to global ischemia. MATERIALS AND METHODS: In 11 dogs, LVP, recorded via a micromanometer-tip catheter, was plotted against dP/dt as a continuous loop. The angle of the loop during relaxation is inversely related to tau, the time constant of isovolumic relaxation. The angle was measured before and during: infusion of dextran to increase pre-load, infusion of nitroprusside to reduce after-load, and a 30-s occlusion of the left main coronary artery to induce temporary global ischemia. RESULTS: The relaxation angle of the loop did not change with dextran or nitroprusside infusion. During left main occlusion, the angle increased from 57 +/- 7 degrees to 92 +/- 3 degrees (P < 0.001), reflecting markedly impaired relaxation. In five of nine cases, the angle became greater than 90 degrees, rendering the monoexponential model of pressure decay inapplicable. However, the beat-to-beat progression of the angle could easily be followed visually. CONCLUSIONS: The LVP-dP/dt loop is a readily visualized, continuous display of beat-to-beat changes in myocardial relaxation. It provides a dynamic and specific display of immediate changes in relaxation during global ischemia, even when the exponential model of pressure decay is not applicable. The loop may be useful for guiding procedures that induce ischemic pre-conditioning or post-conditioning during cardiac surgery.