Stephanie Clement-Guinaudeau

Automated left ventricular diastolic function evaluation from phase-contrast cardiovascular magnetic resonance and comparison with Doppler echocardiography

BackgroundEarly detection of diastolic dysfunction is crucial for patients with incipient heart failure. Although this evaluation could be performed from phase-contrast (PC) cardiovascular magnetic resonance (CMR) data, its usefulness in clinical routine is not yet established, mainly because the interpretation of such data remains mostly based on manual post-processing. Accordingly, our goal was to develop a robust process to automatically estimate velocity and flow rate-related diastolic parameters from PC-CMR data and to test the consistency of these parameters against echocardiography as well as their ability to characterize left ventricular (LV) diastolic dysfunction.ResultsWe studied 35 controls and 18 patients with severe aortic valve stenosis and preserved LV ejection fraction who had PC-CMR and Doppler echocardiography exams on the same day. PC-CMR mitral flow and myocardial velocity data were analyzed using custom software for semi-automated extraction of diastolic parameters. Inter-operator reproducibility of flow pattern segmentation and functional parameters was assessed on a sub-group of 30 subjects. The mean percentage of overlap between the transmitral flow segmentations performed by two independent operators was 99.7 ± 1.6%, resulting in a small variability (<1.96 ± 2.95%) in functional parameter measurement. For maximal myocardial longitudinal velocities, the inter-operator variability was 4.25 ± 5.89%. The MR diastolic parameters varied significantly in patients as opposed to controls (p < 0.0002). Both velocity and flow rate diastolic parameters were consistent with echocardiographic values (r > 0.71) and receiver operating characteristic (ROC) analysis revealed their ability to separate patients from controls, with sensitivity > 0.80, specificity > 0.80 and accuracy > 0.85. Slight superiority in terms of correlation with echocardiography (r = 0.81) and accuracy to detect LV abnormalities (sensitivity > 0.83, specificity > 0.91 and accuracy > 0.89) was found for the PC-CMR flow-rate related parameters.ConclusionsA fast and reproducible technique for flow and myocardial PC-CMR data analysis was successfully used on controls and patients to extract consistent velocity-related diastolic parameters, as well as flow rate-related parameters. This technique provides a valuable addition to established CMR tools in the evaluation and the management of patients with diastolic dysfunction.

MR-based calf muscle perfusion index correlates with treadmill exercise test parameters in patients with peripheral arterial disease

Background The functional impairment caused by peripheral arterial disease (PAD) is difficult to evaluate objectively and quantitatively. Current methods used to assess the efficacy of therapeutic interventions in patients with PAD are limited by variability and changes representing the placebo effect. Recently, Gadolinium-enhanced first-pass (FP) MRI has emerged as a new method to assess perfusion in peripheral muscles at peak exercise. We seek to demonstrate that calf muscle perfusion index measured with FP MRI at peak exercise correlates with treadmill exercise measures of ischemia in patients with PAD.

Atrial late gadolinium enhancement on MRI relates to the electrophysiological substrate of persistent atrial fibrillation

Background The mechanisms responsible for atrial fibrillation (AF) maintenance are poorly understood. We studied the relationship between focal atrial fibrosis as assessed with late gadolinium enhanced (LGE) cardiac magnetic resonance (CMR), and the electrophysiological substrate of persistent AF as assessed with body surface potential mapping (BSM). Methods We studied 41 patients with persistent AF (6 women, age 56+/-12 years). Patients underwent LGE CMR using an respiratory navigated and inversion recovery prepared 3D turbo FLASH sequence with fat saturation (pixel size 1.25×1.25×2.5mm), as well as non-invasive BSM during atrial fibrillation using a 256-electrode vest, enabling real-time panoramic mapping of atrial electrical activation. On CMR images, the bi-atrial wall was manually segmented and LGE was quantified using an adaptive histogram thresholding algorithm. The result was both a global quantification of LGE on the left atrial wall expressed in % of the wall and categorized according to Utah classification (I: 40%), and a patient-specific 3D map displaying LGE distribution on both atria. On BSM data, phase mapping was applied to visualize electrical activation, and atrial fibrillation drivers were defined as rotors (phase singularities) lasting more than 200ms. The sites exhibiting high rotor activity were defined as driving regions and targeted by catheter ablation, with the acute endpoint of AF termination. We assessed the relationship between global LGE burden and patients’ clinical characteristics, electrophysiological characteristics, and acute procedural success. In a subset of 12 patients, CMR and BSM data were registered to assess the spatial relationship between LGE and AF drivers.

U-SHAPED CONTRACTION PATTERN DERIVED BY CARDIOVASCULAR MAGNETIC RESONANCE PREDICTS CARDIAC RESYNCHRONIZATION THERAPY RESPONSE IN PATIENTS WITH NON-CLASSIC ELECTROCARDIOGRAM PATTERNS

Patients undergoing cardiac resynchronization therapy (CRT) have higher response rates if they have typical left bundle branch block (LBBB) with QRS durations of >150ms. However, the benefits of CRT are less certain in those with wide QRS without classic LBBB or in those with QRS duration <150ms.

Postsurgical hemodynamics of the aortic valve bypass operation evaluated with phase contrast magnetic resonance

To characterize the postsurgical hemodynamics in aortic valve bypass (AVB) patients, and to determine the relationship between presurgical native aortic valve pressure gradient and postsurgical hemodynamics.

New Research PaperRelationship Between Fibrosis Detected on Late Gadolinium-Enhanced CMR and Re-Entrant Activity Assessed With ECGI in Human Persistent Atrial Fibrillation

OBJECTIVES This study sought to assess the relationship between fibrosis and re-entrant activity in persistent atrial fibrillation (AF). BACKGROUND The mechanisms involved in sustaining re-entrant activity during AF are poorly understood. METHODS Forty-one patients with persistent AF (age 56 ± 12 years; 6 women) were evaluated. High-resolution electrocardiographic imaging (ECGI) was performed during AF by using a 252-chest electrode array, and phase mapping was applied to locate re-entrant activity. Sites of high re-entrant activity were defined as re-entrant regions. Late gadolinium-enhanced (LGE) cardiac magnetic resonance (CMR) was performed at 1.25 × 1.25 × 2.5 mm resolution to characterize atrial fibrosis and measure atrial volumes. The relationship between LGE burden and the number of re-entrant regions was analyzed. Local LGE density was computed and characterized at re-entrant sites. All patients underwent catheter ablation targeting re-entrant regions, the procedural endpoint being AF termination. Clinical, CMR, and ECGI predictors of acute procedural success were then analyzed. RESULTS Left atrial (LA) LGE burden was 22.1 ± 5.9% of the wall, and LA volume was 74 ± 21 ml/m2. The number of re-entrant regions was 4.3 ± 1.7 per patient. LA LGE imaging was significantly associated with the number of re-entrant regions (R = 0.52, p = 0.001), LA volume (R = 0.62, p < 0.0001), and AF duration (R = 0.54, p = 0.0007). Regional analysis demonstrated a clustering of re-entrant activity at LGE borders. Areas with high re-entrant activity showed higher local LGE density as compared with the remaining atrial areas (p < 0.0001). Failure to achieve AF termination during ablation was associated with higher LA LGE burden (p < 0.001), higher number of re-entrant regions (p < 0.001), and longer AF duration (p = 0.008). CONCLUSIONS The number of re-entrant regions during AF relates to the extent of LGE on CMR, with the location of these regions clustering to LGE areas. These characteristics affect procedural outcomes of ablation.Objectives This study sought to assess the relationship between fibrosis and re-entrant activity in persistent atrial fibrillation (AF).

Characterization of ARVC substrate on MRI and electrophysiological mapping

Methods We studied consecutive patients with definite ARVC diagnosis according to Task Force criteria (TFC), undergoing electrophysiological study for ventricular tachycardia. CMR imaging was performed on a 1.5T system (Avanto, Siemens, Erlangen, Germany). SSFP cine imaging was performed in 2 stacks of contiguous 6 mm-thick slices encompassing the whole ventricles in short axis and 4-chamber orientations. BH-LGE imaging was performed 10 min after the injection of 0.2 mmol/Kg gadoterate meglumine using a 3D turbo FLASH sequence in 3 stacks of contiguous 6 mm-thick slices encompassing the whole ventricles in short axis, 2-chamber and 4-chamber orientations (pixel size 1.6 × 1.6 × 6 mm). FB-LGE acquisition was initiated 15 min after contrast using an inversion recovery-prepared and respiratory navigated 3D Turbo FLASH sequence with fat saturation, in order to acquire a whole heart volume at higher spatial resolution (pixel size 1.25 × 1.25 × 2.5mm). Wall motion abnormalities (WMA) and LGE were assessed by 2 observers analyzing the images in consensus. This substrate was distributed over a biventricular 16-segment model: the RV and LV free walls comprised 7 segments each (3 basal, 3 midventricular and 1 apical), and the septum comprised 2 segments (basal and midventricular). All patients underwent electrophysiological contact mapping during sinus rhythm on RV endocardium and RV and LV epicardium. Low bipolar voltage and local abnormal ventricular activity (LAVA) were distributed over the same segmentation.

A new method for accurate localization of the LV pacing lead from fluoroscopy images to MRI images: application to studies involving lead placement and CRT

Background In Cardiac Resynchronization Therapy (CRT), studies examining the importance of placing the LV pacing lead in the latest contracting segment have produced conflicting results. Some studies have shown higher response rates when the lead is placed in the latest contracting segment, while others show no relationship between lead placement and response. All of these studies relied on subjective manual methods to retrospectively transfer the LV lead position from the fluoroscopy images to the wall motion data .W e have developed an ew, objective method to map LV lead location onto the pre-implant MRI data using standard intra-procedural fluoroscopic imaging. The method was validated on a cardiac phantom and compared to manual methods. Methods MRI: 3D MR coronary vein (MRCV) scans were performed using slow infusion of Gadolinium contrast agent. The coronary veins were identified manually throughout the imaging volume. Fluoroscopy: During CRT device implantation, dual-plane venograms were acquired (30° LAO and RAO). After LV lead implantation, dual-plane lead location images were acquired with the same orientations as the venograms, and the LV lead tip location was mapped onto the corresponding dualplane venograms. Registration: The 3D MR coronary vein locations were back-projected onto the venograms, and corresponding branch points were used to determine the spatial relationship between each of the venograms and the MR imaging system. Using this relationship, the two lead localizers were used to project the lead position into the MR coordinate system, and subsequently displayed on the AHA 17-segment model. Phantom: The accuracy of the lead mapping was determined using a coronary vein phantom with six potential lead location sites marked with fiducials visible in both MR and fluoroscopy imaging (to determine true position). The accuracy of the lead registration technique was compared to the true lead position and to Mortensen’ so ’clock, a commonly employed manual technique for estimating LV lead position in CRT. Results The true lead position and the lead position determined by our method were within the same AHA segment in all six sites within the phantom. The average circumferential error was 7 ± 4% of an AHA segment (Range: 2-11%) and the average longitudinal error was 13 ± 17% of an AHA segment (Range: 4-27%). Using Mortensen’ so ’clock method, the correct AHA segment was selected in only two of six sites (33%). The average circumferential error was 38 ± 17% of an AHA segment (Range: 7-54%) and the average longitudinal error was 58 ± 30% of an AHA segment (Range: 6-83%). Conclusions LV lead registration using the 3D projection of lead location from dual-plane fluoroscopic images onto 3D coronary vein anatomy allows for more accurate localization of the LV pacing lead compared to manual methods. This method can be used to accurately register LV lead position to MR wall motion data, and enable assessment of the

Presence of a CMR-based U-shaped contraction pattern and optimal LV pacing lead position determines best response to CRT.

Background Cardiac resynchronization therapy (CRT) improves outcomes in many heart failure patients, yet 1 in 3 patients do not positively respond. A “U-shaped” left ventricular (LV) activation pattern (type II), suggestive of electrical conduction block, can be characterized by cardiovascular magnetic resonance (CMR) and has been associated with improved CRT response compared to a more homogenous (type I) activation pattern. In other studies, targeting the LV pacing lead to the latest site of LV activation has been associated with improved response. We hypothesized that patients with CMR derived type II ventricular activation pattern and a concordant LV lead placement would have superior CRT response.

TRAUMATIC LOWER EXTREMITY AMPUTATIONS CAUSE DISTURBED BLOOD FLOW IN THE INFRARENAL AORTA LEADING TO ABDOMINAL AORTIC ANEURISMS

Abdominal aortic aneurysms (AAA) are a major cause of morbidity and mortality in the US. The most common place of AAA is infrarenal abdominal aorta where oscillatory shear stress (OSS) is present. OSS is known to initiate inflammatory endothelial response. Patients with lower extremity traumatic