Late Gadolinium Enhancement Signal Intensity Research Articles

The relationship between the quantitative extent of late gadolinium enhancement and burden of nonsustained ventricular tachycardia in hypertrophic cardiomyopathy: A delayed contrast-enhanced magnetic resonance study.

To examine the relationship between late gadolinium enhancement (LGE) extent and nonsustained ventricular tachycardia (NSVT) characteristics in patients with hypertrophic cardiomyopathy (HCM). NSVT has been shown to be independently associated with sudden cardiac death (SCD) in HCM. Previous studies have found LGE on cardiac magnetic resonance (CMR) to be independently associated with NSVT. Seventy-three patients who had 14-day Holter monitoring for either risk stratification for SCD (n = 62) or evaluation of atrial fibrillation (n = 11) on a CMR study were included. Areas of LGE in left ventricle (LV) were visually identified and analyzed quantitatively for both high (≥6 SD above the mean signal intensity of normal myocardium) and intermediate (≥4 but <6 SD) LGE signal intensity. Patients with more extensive LGE had longer (P = 0.0028) and more frequent (P = 0.02) episodes of NSVT. In univariate analyses, frequency of NSVT was associated with LGE extent (rs = 0.43, P = 0.001), LV ejection fraction (rs = -0.38, P < 0.001), LV mass (rs = 0.32, P = 0.005), LV maximal wall thickness (rs = 0.28, P = 0.016), and left atrium diameter (rs = 0.29, P = 0.001); maximal length of NSVT was associated with LGE extent (rs = 0.52, P < 0.001), LV ejection fraction (rs = -0.44, P < 0.001), LV mass (rs = 0.37, P = 0.001), and left atrium diameter (rs = 0.3, P < 0.001). In multivariable analyses, LGE extent remained the sole variable independently associated with frequency (P = 0.001) and maximal length of episodes of NSVT (P = 0.001). No significant association was found between the rate of NSVT and LGE extent. LGE extent is independently associated with a greater burden and longer episodes of NSVT in HCM. These findings support the association between myocardial fibrosis as represented by LGE and ventricular tachyarrhythmias in HCM.

First-in-Man Analysis of the Relationship Between Electrical Rotors From Noninvasive Panoramic Mapping and Atrial Fibrosis From Magnetic Resonance Imaging in Patients With Persistent Atrial Fibrillation.

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging can be used to evaluate characteristics of atrial fibrosis. The novel noninvasive epicardial and endocardial electrophysiology system (NEEES) allows for the identification of sources with rotor activity. This study describes a new technique to examine the relationship between rotors and LGE signal intensity in patients with persistent atrial fibrillation (PERS) scheduled for ablation. Ten consecutive patients underwent pulmonary vein isolation for persistent atrial fibrillation. LGE CMR of both atria was performed, and NEEES-based analysis was conducted to identify rotors. For each mapping point, the intracardiac locations were transferred onto an individual CMR-derived 3-dimensional shell. This allowed the LGE signal intensity to be projected onto the anatomy from the NEEES analysis. NEEES analysis identified a total number of 410 electric rotors, 47.8% were located in the left atrium and 52.2% in the right atrium. Magnetic resonance imaging analysis was performed from 10 right atria and 10 left atria data sets, including 86 axial LGE CMR planes per atrium. The mean LGE burden for left atrium and right atrium was 23.9±1.6% and 15.9±1.8%, respectively. Statistical analysis demonstrated a lack of regional association between the extent of LGE signal intensity and the presence of rotors. This is the first study demonstrating that the presence of rotors based on NEEES analysis is not directly associated with the extent and anatomic location of LGE signal intensity from CMR. Further studies evaluating the relationship between rotors and fibrosis in patients with persistent atrial fibrillation are mandatory and may inform strategies to improve ablation outcome.

16-26: Electrical Remodeling Does not Reproducibly Mirror Structural Change on Atrial MRI

Purpose of the Study: Left atrial (LA) late gadolinium enhancement (LGE) CMR has been proposed to guide ablation therapy and predict procedure outcome. AF electrical and structural remodeling are known to occur to varying extents in patients with AF. The extent to which pre-procedural LGE CMR reflects LA electrophysiological remodeling is unknown. Methods Used: Intracardiac contact mapping during programmed stimulation was used to characterize conduction delay, activation dispersion, electrogram morphology and AF vulnerability in 8 patients undergoing first-time pulmonary vein isolation. Pre-procedural LGE CMR imaging was performed and quantified by LGE signal intensity (SI; image intensity ratio, IIR), % LGE area and LA sphericity indices. Summary of Results: Although electrogram voltage was significantly reduced at areas of high SI (IIR > 0.97 - 0.9mV vs 1.3mV P = 0.049), IIR showed no relationship with electrogram duration (17.7ms vs 18.3ms, P = 0.673), conduction delay (322ms vs 316ms, P = 0.3939) or conduction block (262ms vs. 262ms, P = 0.8667). There was no relationship between % LGE area or sphericity and any of the LA remodeling parameters (all P > 0.05). LA extrastimulus conduction curves showed significant variation between patients with similar LGE CMR findings (Figure).

The Effect of Contact Force in Atrial Radiofrequency Ablation: Electroanatomical, Cardiovascular Magnetic Resonance, and Histological Assessment in a Chronic Porcine Model

ObjectivesThis study sought to determine the effect of contact force (CF) on atrial lesion size, quality, and transmurality by using a chronic porcine model of radiofrequency ablation. BackgroundCF is a major determinant of ventricular lesion formation, but uncertainty exists regarding the most appropriate CF parameters to safely achieve permanent, transmural lesions in the atria. MethodsIntercaval linear ablation (30 W, 42°C, 17 ml/min irrigation) was performed in 8 Göttingen minipigs by using a force-sensing catheter with CF >20 g (high force) or <10 g (low force) at alternate ends of the line, separated by an intentional gap. Voltage mapping and cardiovascular magnetic resonance (CMR) imaging were performed pre-ablation, immediately after ablation, and at 2 months’ post-procedure. Lesions were sectioned orthogonal to the axis of ablation to assess transmurality. ResultsMean CF was 22.6 ± 11.4 g and 7.8 ± 4.0 g in the high and low CF regions. Acute tissue edema was greater with high CF, both caudally (7.0 mm vs. 4.6 mm; p = 0.016) and cranially (6.9 mm vs. 4.6 mm; p = 0.038). There was no difference in chronic lesion size (voltage mapping) or volume (late gadolinium enhancement CMR) between high and low CF regions. There was no difference in scar density (assessed by low-voltage criteria and late gadolinium enhancement signal intensity) or histological transmurality between high and low CF regions. ConclusionsAlthough high CF (>20 g) resulted in more acute tissue edema than low CF (<10 g), chronically there was no difference in lesion size, quality, or transmurality. Appropriate CF targets for atrial ablation may be lower than previously thought.

Repeat left atrial catheter ablation: cardiac magnetic resonance prediction of endocardial voltage and gaps in ablation lesion sets.

Studies have reported an inverse relationship between late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) signal intensity and left atrial (LA) endocardial voltage after LA ablation. However, there is controversy regarding the reproducibility of atrial LGE CMR and its ability to identify gaps in ablation lesions. Using systematic and objective techniques, this study examines the correlation between atrial CMR and endocardial voltage. Twenty patients who had previous ablation for atrial fibrillation and represented with paroxysmal atrial fibrillation or atrial tachycardia underwent preablation LGE CMR. During the ablation procedure, high-density point-by-point Carto voltage maps were acquired. Three-dimensional CMR reconstructions were registered with the Carto anatomies to allow comparison of voltage and LGE signal intensity. Signal intensities around the left and right pulmonary vein antra and along the LA roof and mitral lines on the CMR-segmented LA shells were extracted to examine differences between electrically isolated and reconnected lesions. There were a total of 6767 data points across the 20 patients. Only 119 (1.8%) of the points were ≤ 0.05 mV. There was only a weak inverse correlation between either unipolar (r = -0.18) or bipolar (r = -0.17) voltage and LGE CMR signal intensities with low voltage occurring across a large range of signal intensities. Signal intensities were not statistically different for electrically isolated and reconnected lesions. This study demonstrates that there is only a weak point-by-point relationship between LGE CMR and endocardial voltage in patients undergoing repeat LA ablation. Using an objective method of assessing gaps in ablation lesions, LGE CMR is unable to reliably predict sites of electrical conduction.

28Does a greater contact force create more scar? A quantification of the relationship between late gadolinium enhancement on cardiac MR imaging and catheter contact on af ablation

Introduction: Catheter-myocardium contact force (CF) is an important determinant of radiofrequency (RF) lesion generation. Novel RF-catheters enable real-time monitoring of CF, but evidence that CF is the primary determinant of lesion quality is lacking in humans. We used late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) to assess the relationship between applied contact force and chronic scar formation. Method: Twelve patients underwent pulmonary vein isolation using a CF-sensing catheter (SmartTouch Thermocool, Biosense-Webster, CA, USA). Ablation position was recorded using the CARTO-3 electroanatomical mapping system. LGE CMR was performed at a median of 7.2 (range 3-11) months post- ablation using an Achieva 3.0T MRI scanner (Philips, Amsterdam, The Netherlands) with a 3D ECG triggered, free-breathing inversion recovery turbo field echo scan sequence. The LGE-CMR images were segmented using Seg3D by an experienced observer. Signal intensities (SI) were projected onto the segmented shell, using a maximum intensity projection and fused to the CARTO-3 shell using an Iterative Closest Point (ICP) algorithm. The two shells (Contact Force and LGE signal) were then compared using custom built software. The shells were thresholded to blind the observer to local variations in LGE SI and CF before paired paths along the ablation lines were manually drawn on the surface of each shell. Results: For 1710 ablation points across 12 patients, there is a small but significant relationship between applied CF and chronic scar formation as indicated by CMR LGE SI (p<0.0001, R2=0.02) and between grouped CF and mean LGE SI (one- ANOVA, p=0.02). For every ablation line, regions are identifiable in which there is a relationship between CF and SI (see figure). Conversely, other regions of the same ablation lines do not show a close correlation between applied CF and resulting scar formation. Conclusions: Post-ablation scar, as assessed by MRI LGE signal intensity, is qualitatively related to CF, and quantitative analysis shows a weak but significant correlation. However, the majority of variation in scar formation is not explained purely by contact force, and may be related to other ablation parameters such as local cardiac anatomy, regional cooling effects and catheter stability. ![Graphic][1] [1]: /embed/inline-graphic-1.gif

Quantitative Magnetic Resonance Imaging Analysis of the Relationship Between Contact Force and Left Atrial Scar Formation After Catheter Ablation of Atrial Fibrillation

Catheter contact force (CF) is an important determinant of radiofrequency (RF) lesion quality during pulmonary vein isolation (PVI). Late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) allows good visualization of ablation lesions. This study describes a new technique to examine the relationship between CF during RF delivery and LGE signal intensity (SI) following PVI. Six patients underwent PVI for paroxysmal AF using a CF-sensing catheter and following preprocedural MRI. During ablation, CF-time integral (FTI) and position was documented for each RF application. All patients underwent repeat LGE MRI 3 months later. The LGE SIs were projected onto a MRI-derived 3-dimensional left atrial (LA) shell and a CF map was generated on the same shell. The entire LA surface was divided into 5 mm(2) segments. Force and LGE maps were fused and compared for each 5 mm(2) zone. An effective lesion was defined when MRI-defined scar occupied >90% of a 5 mm(2) analysis zone. Acute PVI was achieved in 100%. Two hundred sixty-eight RF lesions were tagged on the LA shells and given a lesion-specific FTI. Increasing FTI correlated with increased LGE SI, which was greater when the FTI was > 1,200 gs. Below an FTI of 1,200 gs, an increment in the FTI resulted in only a small increment in scar, whereas above 1,200 gs an increment in the FTI resulted in a large change of scar. There is a correlation between FTI and LGE SI in MRI following AF ablation. Real-time FTI maps are feasible and may prevent inadequate lesion formation.

Comparison of the amount of affected myocardium quantified by late gadolinium enhancement and the degree of myocardial necrosis measured by cardiac troponin T in patients with myocarditis

Background The diagnosis of myocarditis is challenging due to its often subclinical or unspecific course. Yet, myocardial focal late gadolinium enhancement (LGE) patterns, which represent focal myocardial necrosis and imply negative clinical outcomes, can be assessed by cardiovascular magnetic resonance (CMR). Serologically, not only focal but also diffuse myocardial cell necrosis can be highly accurately detected by the cardiac-specific release of cardiac troponin T (cTnT) which has shown to have also prognostic value in these patients. However, data regarding the relationship between the focal necrosis size visualized by LGE-CMR and the serum marker of myocardial cell damage measured by cTnT are scarce. Therefore, we sought to investigate the relationship between focal LGE-CMR patterns, applying different standard deviations (std) of the LGE signal intensity, and serum levels of cTnT. Methods We retrospectively included 44 myocarditis patients (39 male, 5 female). CMR images were acquired on a 1.5 T whole-body MRI (Achieva, Philips Healthcare) and LGE imaging was performed (Gadolinium-DTPA (Magnevist, Bayer Schering Pharma), 0.2 mmol/kg body weight) using an inversion-recovery SSFP sequence. Short-axis LGE images were analyzed with a dedicated scar software (cmr42, Circle Cardiovascular Imaging) which allowed the measurement of the myocardial mass affected by focal LGE applying different std of contrast enhancement (2, 3, 4, 5, 6, 8, 10 std). Values for cTnT or high-sensitive cardiac troponin T (hscTnT) where applicable were retrieved from the patients’ records. Correlation analysis was performed using Pearson’s r or Spearman’s rho where applicable (p-value<0.05 was regarded significant).

Understanding why edema in salvaged myocardium is difficult to detect by late gadolinium enhancement

T2-weighted cardiac magnetic resonance (CMR) can visualize myocardial edema in salvaged myocardium which appears non-infarcted by late gadolinium enhancement (LGE) CMR. However, the mechanisms governing why LGE does not visualize edema in noninfarcted myocardium remain unclear. The objective of the study was to evaluate the extracellular volume fraction (ECV) of edematous salvaged myocardium using quantitative T1-mapping techniques in order to better understand why this tissue may be difficult to detect by LGE imaging. Methods Dogs (n=10) underwent coronary occlusion and reperfusion, followed by 1.5T CMR. Salvaged myocardium was defined as having bright signal intensity on T2-prepared steady-state free precession (T2-prep) images and the absence of infarction by LGE, and signal intensities were quantified SD units brighter than remote myocardium. Myocardial extracellular volume fraction (ECV) was measured by T1 quantification before and after GdDTPA contrast administration and calibration by blood hematocrit. Results LGE signal intensity of salvaged and infarcted myocardium were 1.7±0.4 and 8.1±1.5 SD from remote, respectively. T2-prep signal intensity of salvaged and infarcted myocardium were 2.8±0.2 and 4.9±1.0 SD from remote, respectively. Compared to remote myocardium, T1 of salvaged myocardium was 14% higher before contrast (1050±114ms vs 919±66ms, p<0.001) and 10% lower 30 minutes after contrast (461±57ms vs 512±67ms, p<0.001). The ECV of salvaged myocardium was 34 +/-7% which was significantly different than ECV of normal myocardium 24+/-3% (p=0.04). Conclusions Salvaged myocardium has a post-contrast T1 which is approximately 50 ms less than remote myocardium and has an LGE image intensity less than 2 SD from remote, making it difficult to appreciate in LGE images. However, contrast concentration, and thus extracellular space, is determined by the change in 1/T1 (R1) which occurs from pre- to post-contrast. The combined and directionally opposed differences in pre- and post-contrast T1 explain why the extracellular volume fraction of salvaged myocardium is increased compared to remote. LGE image intensity does not incorporate information on pre-contrast T1, thus giving the impression of no change in the size of the extracellular space of salvaged myocardium despite the presence of extracellular edema.

Intermediate-Signal-Intensity Late Gadolinium Enhancement Predicts Ventricular Tachyarrhythmias in Patients With Hypertrophic Cardiomyopathy

In hypertrophic cardiomyopathy (HCM), the arrhythmic potential associated with a variety of left ventricular myocardial signal intensities evident on contrast-enhanced cardiovascular magnetic resonance with late gadolinium enhancement (LGE) is unresolved. In 145 HCM patients (43±15 years old), visually identified areas of LGE in left ventricle were analyzed quantitatively for intermediate (≥4 but <6 SD) and high (≥6 SD above the mean signal intensity of normal myocardium) LGE signal intensity (LGE-SI). Ambulatory Holter ECGs were obtained within 7.8±8.3 weeks of cardiovascular magnetic resonance. HCM patients with nonsustained ventricular tachycardia, ventricular couplets, and premature ventricular contractions showed greater amounts of intermediate LGE-SI (17±7 versus 10±10 g, 16±10 versus 10±11 g, and 13±8 versus 10±13 g, respectively; P=0.003 to <0.001) and greater amounts of high LGE-SI (15±6 versus 10±8 g, 14±9 versus 10±12 g, and 12±7 versus 10±8 g, respectively; P=0.02-0.003) than patients without these arrhythmias. In HCM patients with either nonsustained ventricular tachycardia, couplets, or premature ventricular contractions, the extent of intermediate LGE-SI exceeded that of high LGE-SI (17±7 versus 15±6 g, 16±10 versus 14±9 g, and 13±8 versus 12±7 g, respectively; P=0.01-0.04). In addition, the receiver operating characteristic area under the curve established intermediate LGE-SI as a better discriminator of patients with nonsustained ventricular tachycardia than was high LGE-SI, with 7 additional patients with this arrhythmia identified. In patients with HCM, intermediate LGE-SI is a better predictor of ventricular tachyarrhythmias (including nonsustained ventricular tachycardia, a risk factor for sudden death) than is high LGE-SI. Longitudinal studies in larger HCM cohorts are justified to define the independent prognostic impact of intermediate LGE-SI.

Quantification of acute myocardial injury by ShMOLLI T1-Mapping, T2-weighted and late gadolinium imaging in patients presenting with chest pain, positive troponins and non-obstructive coronary arteries

Methods 16 patients (8 men, mean age 51±16 years) with acute chest pain, Troponin I >1.0 ug/L and non-obstructive coronary arteries underwent 1.5T CMR imaging within 7 days of presentation (median 3 days). CMR protocol included Shortened Modified Look-Locker inversion recovery (ShMOLLI) for T1-mapping, T2-STIR and late gadolinium enhancement (LGE) imaging. Regional wall motion was assessed with SSFP cines. Volumetric fractions of injured myocardium were quantified by (1) T2 signal intensity (SI) of myocardium:skeletal muscle >1.9:1; (2) T1>110% of normal myocardial T1; and (3) LGE SI>2SD of remote myocardium SI. Results 8 cases of myocarditis, 4 cases of Takotsubo cardiomyopathy and 4 cases of myocardial infarction were diagnosed based on CMR findings. All demonstrated abnormalities by at least 2 out of the 3 sequences (Table1). All but one (focal myocarditis) demonstrated global/focal increase in T2 SI. All demonstrated global/ focal increase in T1 values. Except for patients with Takotsubo cardiomyopathy, all demonstrated LGE. Volumetric fractions of injury by T2-STIR and T1mapping overlapped but did not necessarily co-localize topographically; there was moderate correlation between the two methods (R=0.45) (Fig.1). Patients with Takotsubo cardiomyopathy (mean EF=54 ±7%) had the highest average T1 values (1028±34ms vs. 968±76ms in normal controls; p<0.025*). Except for one with global myocarditis, patients with myocarditis and MI were without significant LVEF impairment with focal injury. Accordingly, average T1 values in these subgroups were not statistically different from normal. On a regional level, compared to segments with normal wall motion, segments with abnormal wall motion had significantly increased T1 values (958±60 ms vs.1068±76 ms, respectively; p<0.001*) (Fig.2), larger fractions of injury by T1-mapping (median 12% vs. 62%; p<0.001*), T2-STIR (15% vs. 62%; p<0.001*) and LGE (8% vs 10%; p<0.04*). LVEF correlated best with T1-mapping derived fractions of injured myocardium (R=0.59; T2-STIR R=0.18, LGE R=0.1). University of Oxford, Oxford, UK Full list of author information is available at the end of the article Ferreira et al. Journal of Cardiovascular Magnetic Resonance 2011, 13(Suppl 1):P16 http://jcmr-online.com/content/13/S1/P16