Changes In Left Ventricular Volume Research Articles

Effect of Cardiac Resynchronization Therapy in Patients With New York Heart Association Functional Class IV Heart Failure

Cardiac resynchronization therapy (CRT) is considered a class I indication in treatment of patients with New York Heart Association (NYHA) functional class III and IV heart failure. However, only small numbers of patients in large clinical trials have been in NYHA functional class IV. Therefore, little is known about the effects of CRT in this group. Therefore, we evaluated the effects of CRT in patients with NYHA functional class IV heart failure. Of all patients referred for CRT implantation, 61 patients with symptoms according to NYHA functional class IV were included. All patients were evaluated before implantation and at 6-month follow-up for clinical changes according to the clinical composite score and changes in left ventricular (LV) volumes and function. In addition, survival was evaluated during long-term follow-up. At 6-month follow-up, 9 patients (15%) had died and 2 patients (3%) were admitted for worsening heart failure. The remaining 39 patients (64%) showed improvement according to the clinical composite score. Decreases in LV end-systolic volume (from 167 ± 88 to 147 ± 93 ml, p = 0.009) and LV end-diastolic volume (from 211 ± 100 to 199 ± 113 ml, p = 0.135) were observed, as was a significant increase in LV ejection fraction (from 22 ± 8% to 28 ± 9%, p <0.001). During a mean follow-up of 30 ± 26 months, 36 patients (59%) died, 27 (75%) from worsening heart failure. Respective 1- and 2-year mortality rates were 25% and 38%. In conclusion, CRT decreases LV volumes and improves cardiac function in patients with NYHA functional class IV heart failure. Nevertheless, (heart failure) mortality remains high in these patients.

Comments on Point:Counterpoint: Left ventricular volume during diastasis is/is not the physiological in vivo equilibrium volume and is/is not related to diastolic suction

Comments on Point:Counterpoint: Left ventricular volume during diastasis is/is not the physiological in vivo equilibrium volume and is/is not related to diastolic suction

Counterpoint: Left ventricular volume during diastasis is not the physiological in vivo equilibrium volume and is not related to diastolic suction

Counterpoint: Left ventricular volume during diastasis is not the physiological in vivo equilibrium volume and is not related to diastolic suction

Beneficial effects of catheter ablation on left ventricular and right ventricular function in patients with frequent premature ventricular contractions and preserved ejection fraction

BackgroundImprovement of left ventricular ejection fraction (LVEF) after radiofrequency catheter ablation (RFCA) of frequent premature ventricular contractions (PVCs) has been reported. However, most patients with frequent PVCs have a normal...

Quantitative Evaluation of Drug or Device Effects on Ventricular Remodeling as Predictors of Therapeutic Effects on Mortality in Patients With Heart Failure and Reduced Ejection Fraction: A Meta-Analytic Approach

The purpose of this study was to quantitatively assess the relationship between therapy-induced changes in left ventricular (LV) remodeling and longer-term outcomes in patients with left ventricular dysfunction (LVD). Whether therapy-induced changes in left ventricular ejection fraction (LVEF), end-diastolic volume (EDV), and end-systolic volume (ESV) are predictors of mortality in patients with LVD is not established. Searches for randomized controlled trials (RCTs) were conducted to identify drug or device therapies for which an effect on mortality in patients with LVD was studied in at least 1 RCT of > or = 500 patients (mortality trials). Then, all RCTs involving those therapies were identified in patients with LVD that described changes in LVEF and/or volumes over time (remodeling trials). We examined whether the magnitude of remodeling effects is associated with the odds ratios for death across all therapies or associated with whether the odds ratio for mortality was favorable, neutral, or adverse (i.e., statistically significantly decreased, nonsignificant, or statistically significantly increased odds for mortality, respectively). Included were 30 mortality trials of 25 drug/device therapies (n = 69,766 patients; median follow-up 17 months) and 88 remodeling trials of the same therapies (n = 19,921 patients; median follow-up 6 months). The odds ratio for death in the mortality trials was correlated with drug/device effects on LVEF (r = -0.51, p < 0.001), EDV (r = 0.44, p = 0.002), and ESV (r = 0.48, p = 0.002). In (ordinal) logistic regressions, the odds for neutral or favorable effects in the mortality RCTs increased with mean increases in LVEF and with mean decreases in EDV and ESV in the remodeling trials. In patients with LVD, short-term trial-level therapeutic effects of a drug or device on LV remodeling are associated with longer-term trial-level effects on mortality.

Assessment of regional myocardial wall stress before and after surgical correction of functional ischaemic mitral regurgitation using multidetector computed tomography and novel software system☆☆☆

The objective of this study was to assess changes in left ventricular (LV) volume, function and regional myocardial wall stress in non-infarcted segments following restrictive mitral annuloplasty (RMA) in patients with ischaemic cardiomyopathy (ICM) and severe functional mitral regurgitation (MR). Twenty-two patients with ICM (ejection fraction <35%) and severe MR were investigated before and 3 months after RMA using cine-angiographic multidetector row computed tomography (cine-MDCT). For comparative purposes, 38 normal subjects were also studied. Cine-MDCT LV images were reconstructed in a cardiac cycle and regional circumferential wall stress (end-systolic stress (ESS)) was evaluated from the LV end-systolic image using Janz's method. The ESS was determined in six basal and six mid-LV segments of the ventricle based on AHA/ASE criteria. Five apical infarcted segments were not analysed. Mean circumferential fibre shortening (CFS) in both basal and mid-LV regions was determined as a parameter of regional systolic performance. Left ventricular end-diastolic volume (index) (LVEDVI) and left ventricular end-systolic volume (index) (LVESVI) decreased significantly and left ventricular ejection fraction (LVEF) increased after surgery. Neither end-systolic nor end-diastolic sphericity index changed significantly after surgery. Regional ESS significantly decreased in both basal and mid-LV regions after surgery. There was a significant inverse correlation between the change in average value of regional ESS and magnitude of increase in mean CFS of the mid-LV region (r=-0.67, p=0.0018). Postoperative reduction in ESS in the mid-LV region was also correlated with improvement in global EF (r=-0.72, p<0.01). The present cine-MDCT may be useful for assessing regional myocardial stress in patients with ICM. We found that RMA could reduce both end-diastolic and end-systolic volume leading to reduction in regional systolic wall stress, which resulted in improved ejection performance of non-infarcted myocardium in patients with functional MR and ICM.

Oblique 3D MRI tags for the estimation of true 3D cardiac motion parameters

Aim of this study is to demonstrate the advantages of oblique 3D tags in cardiac magnetic resonance imaging (MRI) and the potential to accurately describe the complex motion of the myocardial wall. 3D cardiac Cine data were densely tagged with 3D oblique tags. The latter were tracked using Gabor analysis and active geometries. From the tag intersections, common 2D parameters such as long axis shortening, radial shortening and rotation were evaluated on a global as well as detailed local level. Finally, the same data were used to estimate left ventricular volume change and myocardial stress/strain. We have successfully tracked dense 3D tags and evaluated common parameters on a detailed local level. In addition, inherently 3D parameters could be estimated. Global motion data are in accordance with previously published data. Oblique tags allow for unambiguous localization of the tag plane in all MRI slices and in any time frame. In contrast to HARP, our tag tracking methodology allows for tracking of the tags even when they are dense. Motion parameters can be extracted in greater detail. Moreover, the intersections of dense oblique 3D tags provide a natural basis for a finite element model of the heart. Straight forward access to the 3D characteristics of the cardiac motion is provided.

Long-term β-blocker therapy improves diastolic function even without the therapeutic effect on systolic function in patients with reduced ejection fraction

The beneficial effects of beta-blocker therapy on the clinical outcomes of heart failure with reduced ejection fraction (HFREF) are attributed to the improvement in ejection fraction (EF) and left ventricular (LV) reverse remodeling. Previous studies only reported the beta-blocker therapy-induced improvement of diastolic function accompanied by the increase in EF in HFREF patients. This retrospective study aimed to elucidate whether beta-blocker therapy improves diastolic function even without an increase in EF. Out of the consecutive 11,830 echocardiographic reports, HFREF patients without an increase in EF following long-term beta-blocker therapy comprised the study subjects (n=19). During the mean follow-up of 17 months, beta-blocker therapy significantly decreased peak mitral E-wave velocity (70±25-50±18 cm/s, p<0.01) and ratio of peak mitral E- to A-wave velocities (E/A ratio) (1.4±0.8-0.9±0.4, p<0.05), prolonged deceleration time of the mitral E-wave velocity (DcT) (167±54-206±61 ms, p<0.05), and improved New York Heart Association functional class (2.3±0.7-1.8±0.4, p<0.01) without changes in LV volume. Because DcT and E/A ratio are well known to correlate with LV filling pressures in patients with reduced EF, our results indicate a reduction in LV filling pressures without changes in LV volume, suggesting a reduction in LV stiffness. Thus, long-term beta-blocker therapy is likely to improve diastolic function even without a concomitant increase in EF in HFREF patients, which may be also responsible for the beta-blocker-induced improvement of their symptoms of heart failure.

Intracardiac impedance as a method for ventricular volume monitoring – Investigation by a finite-element model and clinical data

A method for monitoring left ventricular (LV) volume changes of the human heart by intracardiac impedance measurement was developed. In order to model this method, we simulated the ventricular contraction using a finite-element model (FEM). The myocardium comprised three layers with anatomical fiber orientation. During excitation propagation contraction forces were applied, taking into account the myocardial elastic properties and the blood pressure time course. For a set of 21 contraction stages we calculated the intracardiac impedance Z between the right ventricular (RV) and LV leads for a set of common LV lead positions. The FEM results were compared to clinical data. Impedance and stroke volume were determined during overdrive pacing and end diastolic volume (EDV) at rest in 14 patients. All clinical EDV values were in the range of 147-394ml. Both the clinical data and the FEM in this volume range showed a linear correlation between admittance Y=1/Z and ventricular volume. For a quantitative comparison end diastolic impedance EDZ and the slope dY/dV were calculated. The model results across all LV lead positions were EDZ=0.16-1.2Ω, and dY/dV=3.3-21mS/ml, corresponding to clinical values of EDZ=0.14-1.46Ω and dY/dV=1-64mS/ml. In conclusion, the FEM resembled the clinical measurement data and serves as theoretical basis for ventricular volume monitoring via intracardiac impedance.

Measurements of changes in left ventricular volume, strain, and twist during isovolumic relaxation using MRI

Left ventricular (LV) active relaxation begins before aortic valve closure and is largely completed during isovolumic relaxation (IVR), before mitral valve opening. During IVR, despite closed mitral and aortic valves, indirect assessments of LV volume have suggested volume increases during this period. The aim of this study is to measure LV volume throughout IVR and to determine the sources of any volume changes. For 10 healthy individuals (26.0 + or - 3.8 yr), magnetic resonance imaging was used to measure time courses of LV volume, principal myocardial strains (circumferential, longitudinal, radial), and LV twist. Mitral leaflet motion was observed using echocardiography. During IVR, LV volume measurements showed an apparent increase of 4.6 + or - 1.5 ml (5.0 + or - 2.0% of the early filling volume change), the LV untwisted by 4.5 + or - 1.9 degrees (36.6 + or - 18.0% of peak systolic twist), and changes in circumferential, longitudinal, and radial strains were +0.87 + or - 0.64%, +0.93 + or - 0.57%, and -1.46 + or - 1.66% (4.2 + or - 3.3%, 5.9 + or - 3.3%, and 5.3 + or - 7.5% of peak systolic strains), respectively. The apparent changes in volume correlated (P < 0.01) with changes in circumferential, longitudinal, and radial strains (r = 0.86, 0.69, and -0.37, respectively) and untwisting (r = 0.83). The closed mitral valve leaflets were observed to descend into the LV throughout IVR in all subjects in apical four- and three-chamber and parasternal long-axis views by 6.0 + or - 3.3, 5.1 + or - 2.4, and 2.1 + or - 5.0 mm, respectively. In conclusion, LV relaxation during IVR is associated with changes in principal strains and untwisting, which are all correlated with an apparent increase in LV volume. Since closed mitral and aortic valves ensure true isovolumic conditions, the apparent volume change likely reflects expansion of the LV myocardium and the inward bowing of the closed mitral leaflets toward the LV interior.

MECHANISM OF IMPROVEMENT IN MITRAL REGURGITATION IN THE ACUTE PHASE AFTER CARDIAC RESYNCHRONIZATION THERAPY

Abstract Category: General Echocardiography: TTEPresentation Number: 1145-212Authors: Michio Imai, Katsuomi Iwakura, Atsunori Okamura, Yasushi Koyama, Motoo Date, Yoshiharu Higuchi, Koichi Inoue, Ryusuke Kimura, Hiroyuki Nagai, Yuko Toyoshima, Makito Ozawa, Norihisa Ito, Yukinori Okazaki, Masahiko Shibuya, Shigemiki Omiya, Takashi Takagi, Daisuke Morisawa, Kenshi Fujii, Cardiovascular Center,Sakurabashi-Watanabe Hospital, Osaka, JapanBackground: Cardiac resynchronization therapy (CRT) could improve mitral regurgitation (MR) in patients with severe heart failure. We investigated the mechanism of improvement of functional MR early after CRT implantation. Method. The study population consisted of consecutive 31 patients with severe heart failure who showed moderate to severe MR (> grade 2). Echocardiography was performed at baseline and 7days after CRT implantation to measure LV end-diastolic/end-systolic volumes (EDV/ESV) and ejection fraction (EF). We assessed severity of MR as %Jet/Left atrium (LA) area. We also measured tenting height (TH) and tenting area (TA) of mitral valve at the mid-systole to assess tethering effect. Patients were classiied into 2 groups by improvement of MR (%Jet/LA area>12% n=13, <12% n=18). Results: LVEDV/LVESV were not signiicantly different between two groups before CRT (improvement group EDV:152.617.8 vs. non-improvement group, p=.**,ESV:108.314.9 vs. 159.822.5 p=.**), and one week after CRT (EDV: 145.619.6 vs. 187.519.6 mL, p=.**,ESV: 94.716.2 vs. 136.319.5 mL, p=.**). LVEF increased signiicantly after CRT only in the improvement group(improvement group; 3111 to 3913%, p<.05% non-improvement group 2811 to 319%, p=**). TH/TA were not signiicantly different before CRT, but reduced signiicantly only in improvement group after CRT (improvement group TH: 6.21.8 to 4.51.7 , p<.05 vs. non-improvement group 5.81.8 to 5.61.6 mm, TA: 1.30.5 to 0.80.2, p<.05 vs. 1.10.3 to 1.10.3 mm2).Conclusion: Improvement of MR in acute phase after CRT could be associated with correction of tethering of mitral valves more than with changes in LV volumes.

Intracardiac impedance monitors stroke volume in resynchronization therapy patients

Monitoring of haemodynamic parameters or surrogate parameters of the left ventricle is especially important for patients under cardiac resynchronization therapy (CRT). Intracardiac impedance reflects left ventricular (LV) volume changes well in animal models. Since it is unknown whether this also holds in humans with heart failure (HF), we examined the correlation of LV intracardiac impedance with haemodynamic parameters in CRT patients for different positions of the LV lead. In 14 HF patients with non-ischaemic cardiomyopathy (four female, age 70 +/- 6 years, NYHA 2.9 +/- 0.3, EF 26 +/- 6%), one or two suitable implantation sites for the LV lead were selected. Following atrial, right ventricular, and LV catheter positioning, a micro-manometer catheter was placed in the ascending aorta. Surface ECG, impedance, and aortic pressure were recorded during graded overdrive bi-ventricular pacing in DDD mode. The correlation between impedance and stroke volume (SV) or pulse pressure (PP) changes was compared for different LV lead positions. In total, 20 overdrive pacing tests were performed at six different LV lead positions. Strong correlations were found between stroke impedance (SZ) and SV (R = 0.82 +/- 0.16) as well as between SZ and PP (R = 0.81 +/- 0.16) without significant influence of LV lead position. In HF patients, a strong correlation between changes in intracardiac impedance and LV SV was found. Typical LV lead implant positions have been tested and all appear to be suitable for this method of LV volume monitoring.

Changes in Left Ventricular Volume and Geometry During Normal Ageing from Early Adulthood to Middle-Age

Changes in Left Ventricular Volume and Geometry During Normal Ageing from Early Adulthood to Middle-Age

La anestesia subaracnoidea (espinal) podría disminuir la función ventricular izquierda: Estudio con ecocardiografía transtorácica intraoperatoria

Spinal anesthesia reduces arterial blood pressure mainly because of vasodilation secondary to blocking preganglionic fibers in the sympathetic nervous system. It is hypothesized, however, that spinal anesthesia may also be a direct cause of some degree of myocardial depression. These factors may be studied by means of transthoracic echocardiography to detect changes in left ventricular function following start of spinal anesthesia. Left ventricular function was assessed in ASA 1 patients before spinal anesthesia, by means of measurements of left ventricular systolic and diastolic volumes, ejection fraction, the Doppler transmitral (E and A) and tissue (E', A', and Sm) inflow velocities, and the left ventricular outflow tract velocity. The measurements were repeated after the start of spinal anesthesia. Fifty-five patients (58% men; mean [SD] age, 46.9 [15.7] years) were studied. The spinal block caused a significant reduction in systolic and diastolic arterial blood pressures (P < .0009). Diastolic function also decreased (the E wave from 69.52 [11.24] to 61.59 [10.82] cm x s(-1) and the A wave from 50.18 [10.69] to 43.67 [13.75] cm x s(-1); P < .0001). Also reduced was the left ventricular outflow tract velocity, from 18.77 (4.89) to 15.64 (4.75) cm x s(-1) (P < .00001). There were no significant changes in systolic and diastolic volumes or ejection fraction. There was no correlation between the level of spinal block and the magnitude of changes. Left ventricular function was compromised after spinal anesthesia without significant changes in left ventricular volumes. We can infer that the reduction in arterial blood pressure after a spinal block might be due to some degree of direct ventricular depression.

Feasibility of regional left ventricular endocardial curvature analysis from cardiac magnetic resonance images

Introduction Left ventricular (LV) remodeling is usually assessed using changes in LV volume. Because this methodology describes only global effects of remodeling while disregarding changes in ventricular shape that may occur independently of volume, the importance of shape analysis is increasingly recognized. While most previous studies focused on global LV shape, we hypothesized that 3D analysis of regional endocardial curvature could provide clinically useful information on localized remodeling.

Roles of ghrelin in left-ventricular remodelling after acute myocardial infarction

ObjectiveThe purpose of this study was to elucidate the role of ghrelin after acute myocardial infarction (AMI) in left ventricular (LV) remodelling.DesignProspective observational study.SettingJichi Medical University Hospital.PatientsFifty consecutive patients experiencing...

Reperfusion injury components and manifestations determined by cardiovascular MR and MDCT imaging

Advances in magnetic resonance (MR) and computed tomography (CT) imaging have improved visualization of acute and scar infarct. Over the past decade, there have been and continues to be many significant technical advancements in cardiac MR and multi-detector computed tomography (MDCT) technologies. The strength of MR imaging relies on a variety of pulse sequences and the ability to noninvasively provide information on myocardial structure, function and perfusion in a single imaging session. The recent technical developments may also allow CT technologies to rise to the forefront for evaluating clinical ischemic heart disease. Components of reperfusion injury including myocardial edema, hemorrhage, calcium deposition and microvascular obstruction (MO) have been demonstrated using MR and CT technologies. MR imaging can be used serially and noninvasively in assessing acute and chronic consequences of reperfusion injury because there is no radiation exposure or administration of radioactive materials. MDCT is better suited for assessing coronary artery stenosis and as an alternative technique for assessing viability in patients where MR imaging is contraindicated. Changes in left ventricular (LV) volumes and function measured on cine MR are directly related to infarct size measured on delayed contrast enhanced images. Recent MR studies found that transmural infarct, MO and peri-infarct zone are excellent predictors of poor post-infarct recovery and mortality. Recent MR studies provided ample evidence that growth factor genes and stem cells delivered locally have beneficial effects on myocardial viability, perfusion and function. The significance of deposited calcium in acute infarct detected on MDCT requires further studies. Cardiac MR and MDCT imaging have the potential for assessing reperfusion injury components and manifestations.

Assessment of Resynchronization Therapy on Functional Status and Quality of Life in Patients Requiring an Implantable Defibrillator

The effect of cardiac resynchronization therapy (CRT) on physical function and Quality of Life (QoL) in patients who require an implantable defibrillator but do not meet guideline criteria for CRT has not been studied in detail. This was a randomized study of 72 patients with high risk of sudden cardiac death, ejection fraction (EF) < or =35%, mild-to-moderate heart failure symptoms, and QRS > 120 ms. Patients received a CRT defibrillator and were randomized to CRT turned ON or OFF. Objective and subjective measures were performed at baseline and after 6 months. There was no difference in change in left ventricular end-systolic volume (ESV) by radionuclid angiogram scan, the primary endpoint, between the CRT ON group (DeltaESV =-7 +/- 52 mL), and CRT OFF group (DeltaESV =-30 +/- 47 mL). Similarly, echocardiogram measures of ESV and EF showed no difference between the two groups. In the CRT ON group, selected measures of QoL and subjective exercise tolerance but not heart failure symptoms improved significantly. Six-minute walk distance prolonged in the CRT ON group (baseline 313.6 +/- 114.4 m, 6-month 365.0 +/- 122.5 m, P = 0.01), but the difference in change in walk distance between the two groups was not significant. Further studies with larger sample size and longer follow-up will be required to allow definite conclusions regarding the potential benefit of CRT in this patient population.

Left Ventricular Mass and Volume With Telmisartan, Ramipril, or Combination in Patients With Previous Atherosclerotic Events or With Diabetes Mellitus (from the ONgoing Telmisartan Alone and in Combination With Ramipril Global Endpoint Trial [ONTARGET

The ONgoing Telmisartan Alone and in combination with Ramipril Global Endpoint Trial (ONTARGET) showed that the angiotensin receptor blocker telmisartan 80 mg was not inferior to the angiotensin-converting enzyme inhibitor ramipril 10 mg, and the combination no more effective than ramipril alone, in decreasing morbidity and mortality in patients with cardiovascular disease or high-risk diabetes. Although therapy targeting angiotensin II is known to decrease left ventricular (LV) mass and volume, the relative influence of angiotensin-converting enzyme inhibitor inhibitors and angiotensin receptor blocker, and their combination, on the heart remains unclear in this population. Magnetic resonance imaging was performed in 287 patients enrolled in ONTARGET, across 8 centers in 6 countries, at randomization and after 2-year treatment (90, 100, and 97 patients in the ramipril, telmisartan, and combination therapy groups, respectively). Baseline patient characteristics showed higher frequencies of coronary artery disease, Asian ethnicity, and use of statins and beta blockers than the main ONTARGET trial. LV mass decreased in all groups (p <0.0001 for each), but there were no significant differences in change in LV mass or volume among groups, except that LV mass index decreased more on combination versus telmisartan (p = 0.04). Key determinants of LV mass decrease were a history of hypertension (p = 0.03), baseline mass (p <0.0001), and decrease in systolic blood pressure (p <0.0001). The best magnetic resonance imaging predictor of composite events was end-systolic volume (p <0.0001). In conclusion, telmisartan and ramipril had similar effects on LV mass and volume, and combination therapy was not more effective, in high-risk patients with cardiovascular disease. These results are consistent with the major outcome findings of the main ONTARGET study.

Intrathoracic and Ventricular Impedances are Associated with Changes in Ventricular Volume in Patients Receiving Defibrillators for CRT

Some implantable cardioverter defibrillators (ICD) are able to monitor intrathoracic impedance to detect pulmonary fluid overload. This is achieved by measuring impedance between the ICD case and the right ventricular (RV) lead. We hypothesized that the measured impedance would rise with improvement in left ventricular (LV) volumes during cardiac resynchronization therapy (CRT), and that such impedance changes would be more apparent when measured with an alternative pacing vector. We analyzed echocardiographic and impedance data from heart failure patients implanted with a CRT-ICD capable of intrathoracic impedance measurement for fluid accumulation diagnosis, and LV pacing impedance recording for lead integrity monitoring. In 127 out of 170 patients that received de novo CRT implantation, the LV end-systolic volume (LVESV) decreased at 6-month follow-up (LVESV at 6 month-LVESV at baseline <0: group A). For the remaining 43 patients (group B) the change was > or = 0. Despite comparable values at baseline (P = 0.262), the impedances of groups A and B gradually diverged soon after the implant, resulting in significant difference between the two groups at the 6-month visit (P = 0.001). The changes in LV dimensions produced larger differences between groups in the impedance measured between the LV and the RV leads (P < 0.001). The regression analysis demonstrated an inverse correlation between paired changes of volume and intrathoracic impedance. Higher correlation coefficient was obtained using the LV-to-RV measurement vector (r =-0.635, P < 0.001). The changes in ICD-measured impedance seem associated with the LV volume changes induced by CRT. Specifically, the LV-to-RV impedance estimations seem to better correlate with paired changes of ventricular volumes.