Correcting bias in cardiac geometries derived from multimodal images using spatiotemporal mapping.

Cardiovascular imaging studies provide a multitude of structural and functional data to better understand disease mechanisms. While pooling data across studies enables more powerful and broader applications, performing quantitative comparisons across datasets with varying acquisition or analysis methods is problematic due to inherent measurement biases specific to each protocol. We show how dynamic time warping and partial least squares regression can be applied to effectively map between left ventricular geometries derived from different imaging modalities and analysis protocols to account for such differences. To demonstrate this method, paired real-time 3D echocardiography (3DE) and cardiac magnetic resonance (CMR) sequences from 138 subjects were used to construct a mapping function between the two modalities to correct for biases in left ventricular clinical cardiac indices, as well as regional shape. Leave-one-out cross-validation revealed a significant reduction in mean bias, narrower limits of agreement, and higher intraclass correlation coefficients for all functional indices between CMR and 3DE geometries after spatiotemporal mapping. Meanwhile, average root mean squared errors between surface coordinates of 3DE and CMR geometries across the cardiac cycle decreased from 7 ± 1 to 4 ± 1 mm for the total study population. Our generalised method for mapping between time-varying cardiac geometries obtained using different acquisition and analysis protocols enables the pooling of data between modalities and the potential for smaller studies to leverage large population databases for quantitative comparisons.

Atrial fibrillation cardiac radioablation target visibility on magnetic resonance imaging.

Magnetic resonance imaging (MRI) guided cardiac radioablation (CR) for atrial fibrillation (AF) is a promising treatment concept. However, the visibility of AF CR targets on MRI acquisitions requires further exploration and MRI sequence and parameter optimization has not yet been performed for this application. This pilot study explores the feasibility of MRI-guided tracking of AF CR targets by evaluating AF CR target visualization on human participants using a selection of 3D and 2D MRI sequences.MRI datasets were acquired in healthy and AF participants using a range of MRI sequences and parameters. MRI acquisition categories included 3D free-breathing acquisitions (3Dacq), 2D breath-hold ECG-gated acquisitions (2DECG-gated), stacks of 2D breath-hold ECG-gated acquisitions which were retrospectively interpolated to 3D datasets (3Dinterp), and 2D breath-hold ungated acquisitions (2Dreal-time). The ease of target delineation and the presence of artifacts were qualitatively analyzed. Image quality was quantitatively analyzed using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and non-uniformity. Confident 3D target delineation was achievable on all 3Dinterp datasets but was not possible on any of the 3Dacq datasets. Fewer artifacts and significantly better SNR, CNR and non-uniformity metrics were observed with 3Dinterp compared to 3Dacq. 2Dreal-time datasets had slightly lower SNR and CNR than 2DECG-gated and 3Dinterp n datasets. AF CR target visualization on MRI was qualitatively and quantitatively evaluated. The study findings indicate that AF CR target visualization is achievable despite the imaging challenges associated with these targets, warranting further investigation into MRI-guided AF CR treatments.

MITEA: A dataset for machine learning segmentation of the left ventricle in 3D echocardiography using subject-specific labels from cardiac magnetic resonance imaging.

Segmentation of the left ventricle (LV) in echocardiography is an important task for the quantification of volume and mass in heart disease. Continuing advances in echocardiography have extended imaging capabilities into the 3D domain, subsequently overcoming the geometric assumptions associated with conventional 2D acquisitions. Nevertheless, the analysis of 3D echocardiography (3DE) poses several challenges associated with limited spatial resolution, poor contrast-to-noise ratio, complex noise characteristics, and image anisotropy. To develop automated methods for 3DE analysis, a sufficiently large, labeled dataset is typically required. However, ground truth segmentations have historically been difficult to obtain due to the high inter-observer variability associated with manual analysis. We address this lack of expert consensus by registering labels derived from higher-resolution subject-specific cardiac magnetic resonance (CMR) images, producing 536 annotated 3DE images from 143 human subjects (10 of which were excluded). This heterogeneous population consists of healthy controls and patients with cardiac disease, across a range of demographics. To demonstrate the utility of such a dataset, a state-of-the-art, self-configuring deep learning network for semantic segmentation was employed for automated 3DE analysis. Using the proposed dataset for training, the network produced measurement biases of -9 ± 16 ml, -1 ± 10 ml, -2 ± 5 %, and 5 ± 23 g, for end-diastolic volume, end-systolic volume, ejection fraction, and mass, respectively, outperforming an expert human observer in terms of accuracy as well as scan-rescan reproducibility. As part of the Cardiac Atlas Project, we present here a large, publicly available 3DE dataset with ground truth labels that leverage the higher resolution and contrast of CMR, to provide a new benchmark for automated 3DE analysis. Such an approach not only reduces the effect of observer-specific bias present in manual 3DE annotations, but also enables the development of analysis techniques which exhibit better agreement with CMR compared to conventional methods. This represents an important step for enabling more efficient and accurate diagnostic and prognostic information to be obtained from echocardiography.

MRI-guided cardiac-induced target motion tracking for atrial fibrillation cardiac radioablation.

BACKGROUND AND PURPOSE: Atrial fibrillation (AF) cardiac radioablation (CR) challenges radiotherapy tracking: multiple small targets close to organs-at-risk undergo rapid differential cardiac contraction and respiratory motion. MR-guidance offers a real-time target tracking solution. This work develops and investigates MRI-guided tracking of AF CR targets with cardiac-induced motion. MATERIALS AND METHODS: A direct tracking method (Trackingdirect) and two indirect tracking methods leveraging population-based surrogacy relationships with the left atria (Trackingindirect_LA) or other target (Trackingindirect_target) were developed. Tracking performance was evaluated using transverse ECG-gated breathhold MRI images from 15 healthy and 10 AF participants. Geometric and volumetric tracking errors were calculated, defined as the difference between the ground-truth and tracked target centroids and volumes respectively. Transverse, breath-hold, noncardiac-gated cine images were acquired at 4 Hz in 5 healthy and 5 AF participants to qualitatively characterize tracking performance on images more comparable to MRILinac acquisitions. RESULTS: The average 3D geometric tracking errors for Trackingdirect, Trackingindirect_LA and Trackingindirect_target respectively were 1.7 ± 1.2 mm, 1.6 ± 1.1 mm and 1.9 ± 1.3 mm in healthy participants and 1.7 ± 1.3 mm, 1.5 ± 1.0 mm and 1.7 ± 1.2 mm in AF participants. For Trackingdirect, 88% of analyzed images had 3D geometric tracking errors <3 mm and the average volume tracking error was 1.7 ± 1.3 cc. For Trackingdirect on non-cardiac-gated cine images, tracked targets overlapped organsat-risk or completely missed the target area on 2.2% and 0.08% of the images respectively. CONCLUSION: The feasibility of non-invasive MRI-guided tracking of cardiac-induced AF CR target motion was demonstrated for the first time, showing potential for improving AF CR treatment efficacy.

Right Ventricular Flow Vorticity Relationships With Biventricular Shape in Adult Tetralogy of Fallot.

Remodeling in adults with repaired tetralogy of Fallot (rToF) may occur due to chronic pulmonary regurgitation, but may also be related to altered flow patterns, including vortices. We aimed to correlate and quantify relationships between vorticity and ventricular shape derived from atlas-based analysis of biventricular shape. Adult rToF (n = 12) patients underwent 4D flow and cine MRI imaging. Vorticity in the RV was computed after noise reduction using a neural network. A biventricular shape atlas built from 95 rToF patients was used to derive principal component modes, which were associated with vorticity and pulmonary regurgitant volume (PRV) using univariate and multivariate linear regression. Univariate analysis showed that indexed PRV correlated with 3 modes (r = -0.55,-0.50, and 0.6, all p < 0.05) associated with RV dilatation and an increase in basal bulging, apical bulging and tricuspid annulus tilting with more severe regurgitation, as well as a smaller LV and paradoxical movement of the septum. RV outflow and inflow vorticity were also correlated with these modes. However, total vorticity over the whole RV was correlated with two different modes (r = -0.62,-0.69, both p < 0.05). Higher vorticity was associated with both RV and LV shape changes including longer ventricular length, a larger bulge beside the tricuspid valve, and distinct tricuspid tilting. RV flow vorticity was associated with changes in biventricular geometry, distinct from associations with PRV. Flow vorticity may provide additional mechanistic information in rToF remodeling. Both LV and RV shapes are important in rToF RV flow patterns.

Cardiac radioablation for atrial fibrillation: Target motion characterization and treatment delivery considerations.

PURPOSE: The safe delivery of cardiac radioablation (CR) for atrial fibrillation (AF) is challenged by multi-direction target motion, cardiac rate variability, target proximity to critical structures, and the importance of complete target dose coverage for therapeutic benefit. Careful selection of appropriate treatment procedures is therefore essential. This work characterizes AF cardiac radioablation target motion and target proximity to surrounding structures in both healthy and AF participants to guide optimal treatment technique and technology choice. METHODS: Ten healthy participants and five participants with AF underwent MRI acquisition. Multi-slice, cardiac-gated, breath-hold cines were acquired and interpolated to create three-dimensional images for 18-30 cardiac phases. Treatment targets at the left and right pulmonary vein ostia (CTVLeft and CTVRight respectively) and adjacent cardiac structures were contoured and their displacements throughout the cardiac cycle were assessed. Target proximity to surrounding structures were measured. Free-breathing real-time two-dimensional cine images were also acquired at 4 Hz frequency for between 1- and 2-min duration. The motion of easily identifiable points within the target, diaphragm and sternum was measured to assess respiratory motion. RESULTS: Target motion due to cardiac contraction was most prominent in the medial-lateral direction and of 4-5 mm magnitude. CTVRight displacements were smaller in participants with AF than healthy participants in normal sinus rhythm. Nearby cardiac structures often moved with different magnitudes and motion trajectories. CTVLeft and/or CTVRight were in direct contact with the esophagus in 73% of participants. Target motion due to respiration was most prominent in the superior-inferior direction and of 13-14 mm magnitude in both healthy and AF participants. CONCLUSION: AF CR target motion and relative displacement was characterized. The combination of target motion magnitude and relative displacement to critical structures highlights the importance of personalizing motion compensation techniques for effective AF CR treatments.

Cardiac output as a predictor in congenital heart disease: Are we stating the obvious?

BACKGROUND: Significant pulmonary regurgitation, declining right-sided ejection fraction, increased right ventricular (RV) volumes as well as left ventricular (LV) dysfunction have all been identified as predictors of poor outcomes in patients with congenital heart disease (CHD). The prognostic value of the cardiac output (CO) in these patients however has never been studied. METHODS: All consecutive ambulatory adult patients with CHD referred for magnetic resonance imaging (MRI) at the Montreal Children's Hospital between June 2007 and May 2009 were included. Right ventricular (RV) and left ventricular (LV) variables including end diastolic and end systolic volumes (EDV, ESV respectively), ejection fractions (EF) and regurgitant volumes were obtained. Cardiac index (CI) was calculated. Patients were followed for cardiac-related hospitalizations and cardiac interventions. RESULTS: Ninety-six patients were included. Median follow up was 3.9 ± 1.4 years. Nineteen percent of patients had a systemic CI<2.4 l/min/m(2). LVEDV, LVEF and RVEF were significantly diminished in the low CI group with a significant increase in RVESV and total regurgitant volume. Best predictors of low CI were LVEF (AUC=0.74), RVEF (AUC=0.71), total RV regurgitant volume (AUC=0.64) and RVESV (AUC=0.563). Low systemic CI was the best predictor of cardiac-related hospitalizations (hazard ratio 3.5, 95% confidence interval 1.5-8.5) and cardiac interventions (hazard ratio 2.2, 95% confidence interval 1.3-4.0), superior to LVEF, RVEF, total regurgitant volume and RVESV parameters. CONCLUSIONS: In patients with congenital heart disease, cardiac index is the best predictor of cardiac hospitalizations and cardiac interventions.

The role of echocardiography in Staphylococcus aureus bacteraemia at Auckland City Hospital.

AIMS: Current guidelines recommend echocardiography in all episodes of Staphylococcus aureus bacteraemia (SAB). This study aimed to determine whether a very low-risk group of patients with SAB could be found in whom echocardiography was of no incremental diagnostic value for the diagnosis of infective endocarditis. METHODS: Using the ANZCOSS dataset, we identified 574 eligible episodes of adult SAB at Auckland District Health Board (ADHB) between 2007 and 2012, and retrospectively obtained additional microbiological and clinical data. Prevalence of IE was determined using the modified Duke's criteria for diagnosis of IE. Multivariate logistic regression analysis was used to determine whether risk factors were independently associated with IE, and we also assessed their negative predictive value (NPV). RESULTS: Transthoracic and/or transoesophageal echocardiography was performed in 370 (65%) episodes of SAB. The prevalence of clinically definite and clinically possible IE was 5.6% and 8.5%, respectively. Thirty day all-cause mortality was 11.7%. The factors with the highest NPV when absent in hospital-acquired SAB were non central venous line-associated bacteraemia (100%), persistent bacteraemia (96%), and presence of a prosthetic valve or cardiac rhythm management (CRM) device (95%). When none of these three criteria were present the NPV was 100% (99-100%). CONCLUSIONS: A group of very low risk patients was found in our study: central line-associated SAB without prosthetic valves / CRM devices and without persistent bacteraemia. These patients had no episodes of IE and echocardiography is of no incremental diagnostic benefit.

Prognostic significance of left atrial appendage "sludge" in patients with atrial fibrillation: a new transesophageal echocardiographic thromboembolic risk factor.

BACKGROUND: When stratifying thromboembolic risk to patients with atrial fibrillation (AF), left atrial appendage (LAA) thrombus is currently the only echocardiographic index that absolutely contraindicates cardioversion. The aim of this study was to identify the predictors of LAA "sludge" and its impact on subsequent thromboembolism and survival in patients with AF. METHODS: A total of 340 patients (mean age, 66 ± 12 years; 75% men) who underwent transesophageal echocardiography to exclude LAA thrombus before electrical cardioversion or radiofrequency pulmonary vein isolation) for AF were retrospectively studied. LAA sludge was defined as a dynamic, viscid, layered echodensity without a discrete mass, visualized throughout the cardiac cycle. Follow-up was obtained after a mean of 6.7 ± 3.7 years, and patients were analyzed according to LAA thrombus (n = 62 [18%]), sludge (n = 47 [14%]), or spontaneous echocardiographic contrast (n = 84 [25%]). Patients without these transesophageal echocardiographic characteristics served as controls (n = 147 [43%]). RESULTS: LAA sludge was independently predicted by enlarged left atrial area (odds ratio, 4.54; 95% confidence interval [CI], 2.38-8.67; P < .001), reduced LAA emptying velocity (odds ratio, 12.7; 95% CI, 6.11-26.44; P < .001), and reduced left ventricular ejection fraction (odds ratio, 2.11; 95% CI, 1.03-4.32; P < .001). Thromboembolic event and all-cause mortality rates in patients with sludge were 23% and 57%, respectively. Multiple logistic regression analyses identified the presence of LAA sludge to be independently associated with thromboembolic complications (adjusted hazard ratio, 3.43; 95% CI, 1.42-8.28; P = .006) and all-cause mortality (adjusted hazard ratio, 2.02; 95% CI, 1.22-3.36; P = .007). CONCLUSION: Sludge within the LAA is independently associated with subsequent thromboembolic events and all-cause mortality in patients with AF.

Role of Transesophageal Echocardiography Compared to Computed Tomography in Evaluation of Pulmonary Vein Ablation for Atrial Fibrillation (ROTEA study).

BACKGROUND: Computed tomography (CT) is the gold standard for assessing pulmonary vein (PV) anatomy and stenosis after ablation for atrial fibrillation (AF), but radiation exposure can be a concern. Transesophageal echocardiography (TEE) provides anatomic and functional assessment of the PVs, although no study has prospectively compared findings on TEE with those on CT. METHODS: The Role of Transesophageal Echocardiography Compared to Computed Tomography in Evaluation of Pulmonary Vein Ablation for Atrial Fibrillation (ROTEA) study was a prospective, single-blinded observational study of patients with paroxysmal or persistent AF undergoing ablation. TEE and CT were performed immediately before and 3 months after AF ablation. The study included 43 patients (84% men; mean age, 56 ± 11 years). RESULTS: In the preprocedural study, TEE identified 98% of PVs with adequate Doppler measurements obtained. After ablation, no moderate or severe PV stenosis was detected on CT, and a 30% to 50% reduction in luminal diameter was seen in 5% of studied veins. Functional PV stenosis by pulsed-wave Doppler was seen in two veins on TEE. PV diameters decreased after ablation by 0.20 ± 0.03 and 0.22 ± 0.03 cm as measured by CT and TEE, respectively (P < .001). However, TEE underestimated PV ostial dimensions compared with CT, especially for the inferior PVs. Severe spontaneous echo contrast and low left atrial appendage emptying velocities, were identified in 10% of patients in sinus rhythm after ablation. CONCLUSIONS: In the ROTEA study, TEE was feasible in assessing PVs before and after ablation, providing both anatomic and functional information that complemented CT. PV ostial dimensions after ablation can be monitored using either modality, although TEE underestimates PV dimensions, especially for the inferior veins.

Diagnosis of pulmonary hypertension in the congenital heart disease adult population impact on outcomes.

OBJECTIVES: The aim of this study was to assess the impact of the diagnosis of pulmonary hypertension (PH) on mortality, morbidity, and health services utilization (HSU) in an adult congenital heart disease (CHD) population. BACKGROUND: Although PH is a well-recognized complication of CHD, population-based studies of its significance on the survival and functional capacity of patients are uncommon. METHODS: A retrospective longitudinal cohort study was conducted in an adult CHD population with 23 years of follow-up, from 1983 to 2005. The prevalence of PH was measured in 2005. Mortality, morbidity, and HSU outcomes were compared between patients with and without diagnoses of PH using multivariate Cox (mortality and morbidity) and Poisson (HSU) regression models within a subcohort matched for age and CHD lesion type. RESULTS: Of 38,430 adults alive with CHD in 2005, 2,212 (5.8%) had diagnoses of PH (median age 67 years, 59% women). The diagnosis of PH increased the all-cause mortality rate of adults with CHD more than 2-fold compared with patients without PH (hazard ratio [HR]: 2.69; 95% confidence interval [CI]: 2.41 to 2.99). Morbid complications including heart failure and arrhythmia occurred with a 3-fold higher risk compared with patients without PH (HR: 3.01; 95% CI: 2.80 to 3.22). The utilization of inpatient and outpatient services was increased, especially cardiac catheterization, excluding the index diagnostic study (rate ratio: 5.04; 95% CI: 4.27 to 5.93) and coronary and intensive care hospitalizations (rate ratio: 5.03; 95% CI: 4.86 to 5.20). CONCLUSIONS: A diagnosis of PH in adults with CHD is associated with a more than 2-fold higher risk for all-cause mortality and 3-fold higher rates of HSU, reflecting high morbidity.

Influence of concentric left ventricular remodeling on early mortality after aortic valve replacement.

BACKGROUND: Severe left ventricular (LV) hypertrophy increases risk for adverse outcome after aortic valve replacement. Whether LV geometry influences mortality risk after aortic valve replacement is unclear. And, whether LV mass or relative wall thickness (RWT) better predicts risk for adverse postoperative outcomes is unknown. The purpose of this investigation was to examine the influence of LV geometry and LV hypertrophy on morbidity and in-hospital mortality after aortic valve replacement, and to determine whether LV mass or RWT had better prognostic ability. METHODS: Between January 1996 and June 2004, 5,083 patients underwent aortic valve replacement. Preoperative echocardiographic data was used to calculate LV mass and RWT. Left ventricular geometry was classified into one of four categories on the basis of LV mass indexed to body height and RWT: (1) concentric hypertrophy, (2) eccentric hypertrophy, (3) concentric remodeling, and (4) normal. Postoperative mortality and multisystem morbidities of patients with concentric geometries were compared to patients with nonconcentric geometries by propensity and logistic regression modeling. Also, prognostic ability of RWT and LV mass was compared. RESULTS: Nine hundred sixty-four patients with concentric geometry were propensity-matched to 964 patients with nonconcentric geometry. In-hospital mortality (38 [3.9%] versus 18 [1.9%]; p = 0.007), cardiac morbidity (33 [3.4%] versus 17 [1.8%]; p = 0.022), and prolonged intubation (85 [8.8%] versus 58 [6.0%]; p = 0.019) were higher in patients with concentric versus nonconcentric geometry. Increasing RWT, not LV mass, was associated with adverse outcomes. CONCLUSIONS: Concentric geometries are associated with increased risk for in-hospital mortality after aortic valve replacement. Increased RWT is associated with adverse outcomes. Preoperative risk stratification should include assessments of LV hypertrophy and LV geometry.