Hemodynamic improvement in cardiac resynchronization does not require improvement in left ventricular rotation mechanics: three-dimensional tagged MRI analysis

Acute Modifications of Left Ventricular Torsional Mechanics Induced by Cardiac Resynchronization Therapy Affect Short-Term Reverse Remodeling

BACKGROUND

Left ventricular (LV) torsion is an important aspect of cardiac mechanics and is altered in heart failure patients. Cardiac resynchronization therapy (CRT) has a positive effect on LV function, but the exact mechanisms through which it works are not completely depicted. Our aim was to investigate (1) the acute CRT effect on LV torsional mechanics in heart failure patients using 3D speckle tracking echocardiography (3DSTE) and (2) its effect on short-term LV remodeling.

METHODS AND RESULTS

We considered 48 patients (age 72±11 years, 35 men) who received CRT. They underwent 3DSTE during CRT-on (biventricular stimulation) vs. CRT-off (intrinsic conduction/right atrial/ventricular stimulation alone), in a random fashion. Patients were classified as CRT responders based on LV systolic volume reduction ≥15% at 6 months (final population: 31 responders, 17 non-responders). Acute CRT positively affected responders in terms of LV torsion (from 0.32±0.06°/cm CRT-off to 0.41±0.06°/cm CRT-on), but adversely affected non-responders (from 0.54±0.08°/cm CRT-off to 0.28±0.08°/cm CRT-on, interaction P=0.02). A similar trend was confirmed for apical (interaction P<0.04), but not for basal torsion (interaction P=0.351).

CONCLUSIONS

CRT has a positive role in acute recovery of LV torsion (particularly in its apical component) in responders, likely modulating the improvement in LV remodeling at early follow-up.

Proteomic analysis of cardiac ventricles: baso-apical differences

The heart is characterized by a remarkable degree of heterogeneity. Since different cardiac pathologies affect different cardiac regions, it is important to understand molecular mechanisms by which these parts respond to pathological stimuli. In addition to already described left ventricular (LV)/right ventricular (RV) and transmural differences, possible baso-apical heterogeneity has to be taken into consideration. The aim of our study has been, therefore, to compare proteomes in the apical and basal parts of the rat RV and LV. Two-dimensional electrophoresis was used for the proteomic analysis. The major result of this study has revealed for the first time significant baso-apical differences in concentration of several proteins, both in the LV and RV. As far as the LV is concerned, five proteins had higher concentration in the apical compared to basal part of the ventricle. Three of them are mitochondrial and belong to the "metabolism and energy pathways" (myofibrillar creatine kinase M-type, L-lactate dehydrogenase, dihydrolipoamide dehydrogenase). Myosin light chain 3 is a contractile protein and HSP60 belongs to heat shock proteins. In the RV, higher concentration in the apical part was observed in two mitochondrial proteins (creatine kinase S-type and proton pumping NADH:ubiquinone oxidoreductase). The described changes were more pronounced in the LV, which is subjected to higher workload. However, in both chambers was the concentration of proteins markedly higher in the apical than that in basal part, which corresponds to the higher energetic demand and contractile activity of these segments of both ventricles.

Magnetic Resonance Imaging of Cardiac Strain Pattern Following Transplantation of Human Tissue Engineered Heart Muscles

BACKGROUND

The use of tissue engineering approaches in combination with exogenously produced cardiomyocytes offers the potential to restore contractile function after myocardial injury. However, current techniques assessing changes in global cardiac performance after such treatments are plagued by relatively low detection ability. Since the treatment is locally performed, this detection could be improved by myocardial strain imaging that measures regional contractility.

METHODS AND RESULTS

Tissue engineered heart muscles (EHMs) were generated by casting human embryonic stem cell-derived cardiomyocytes with collagen in preformed molds. EHMs were transplanted (n=12) to cover infarct and border zones of recipient rat hearts 1 month after ischemia reperfusion injury. A control group (n=10) received only sham placement of sutures without EHMs. To assess the efficacy of EHMs, magnetic resonance imaging and ultrasound-based strain imaging were performed before and 4 weeks after transplantation. In addition to strain imaging, global cardiac performance was estimated from cardiac magnetic resonance imaging. Although no significant differences were found for global changes in left ventricular ejection fraction (control -9.6±1.3% versus EHM -6.2±1.9%; P=0.17), regional myocardial strain from tagged magnetic resonance imaging was able to detect preserved systolic function in EHM-treated animals compared with control (control 4.4±1.0% versus EHM 1.0±0.6%; P=0.04). However, ultrasound-based strain failed to detect any significant change (control 2.1±3.0% versus EHM 6.3±2.9%; P=0.46).

CONCLUSIONS

This study highlights the feasibility of using cardiac strain from tagged magnetic resonance imaging to assess functional changes in rat models following localized regenerative therapies, which may not be detected by conventional measures of global systolic performance.

Pre-Operative Left Ventricular Torsion, QRS Width/CRT, and Post-Mitral Surgery Outcomes in Patients With Nonischemic, Chronic, Severe Secondary Mitral Regurgitation

The selection of appropriate candidates for mitral surgery among symptomatic patients with nonischemic, chronic, secondary severe mitral regurgitation (NICSMR) remains a clinical challenge. We studied 50 consecutive symptomatic NICSMR patients for a median follow-up of 2.5 years after mitral surgery and concluded that the pre-operative 2-dimensional speckle tracking echocardiography-derived left ventricular torsional profile and QRS width/cardiac resynchronization therapy are potentially important prognostic indicators for post-surgery survival and reverse remodeling.

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Determining which patients with NICSMR will benefit from MS is a clinical dilemma.

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LV torsion (which is a shear strain, not volume strain such as ejection fraction and originates in LV myocardial architectures) may reveal the myopathic conditions and reflect intra-LV electrical conduction.

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The LV torsional profile predicted post-MS outcomes in NICSMR patients with a narrow QRS but not in those with a wide QRS.

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The findings may help to resolve the clinical dilemma and identify appropriate candidates for mitral surgery (and other resources) in patients with NICSMR.

QRS duration in left bundle branch block does not affect left ventricular twisting in chronic systolic heart failure

PURPOSE

Left ventricular (LV) torsion is an important parameter of LV performance and can be influenced by several factors. Aim of this investigation was to evaluate whether QRS prolongation in left bundle branch block (LBBB) may influence global LV twist and twisting/untwisting rate in chronic systolic heart failure (HF) patients.

METHODS

We prospectively evaluated 30 healthy subjects (control group) and 100 chronic HF patients with severely impaired LV systolic function (ejection fraction ≤ 35%). Patients were divided into three groups according to QRS duration: A: QRS < 120 ms (n 49), B: 120 ≤ QRS ≤ 150 ms (n 28) and C: QRS > 150 ms (n 23). Patients in groups B and C presented LBBB. All subjects underwent standard trans-thoracic echocardiography and two-dimensional speckle-tracking echocardiography evaluation. Categorical variables were compared by the chi-square or the Fisher's exact test. Continuous variables were compared using the ANOVA test. Correlations between variables were analysed with linear regression.

RESULTS

Control subjects presented higher torsion parameters, when compared with patients in any HF group. Among the three HF groups, no differences were detected in global twist (4.79 ± 3.54, 3.8 ± 3.0 and 4.15 ± 3.14 degrees, respectively), twist rate max (44.81 ± 25.03, 37.94 ± 19.09 and 37.61 ± 24.49 degrees s(-1), respectively) and untwist rate max (-36.31 ± 30.89, -27.68 ± 34.67 and -39.62 ± 26.27 degrees s(-1), respectively) (P>0.05 for all). At linear regression analysis, there was no relation between QRS duration and any torsion parameter (P>0.05 for all).

CONCLUSIONS

In patients with chronic severe systolic heart failure, QRS duration and LBBB morphology do not affect LV twisting and untwisting.

Ventricular structure-function relations in health and disease: part II. Clinical considerations

Normal cardiac function of the left and right ventricles, together with the septum, is related to form/function interactions within the helical ventricular myocardial band. This knowledge is a prerequisite to understanding form/function interactions in diseases and for planning new treatments. Topics discussed include congestive heart failure in dilated hearts of ischaemic, valvar or nonischaemic origin as well as diastolic dysfunction. Similar thinking underlies novel treatments for dyssynchrony in pacing, together with focusing upon varying global left or right ventricular anatomy to correct mitral and tricuspid insufficiency caused by tethering of the leaflets. The septum is the lion of the right ventricle and insight is provided into offsetting septal damage during cardiac surgery, rebuilding its anatomical structure in post-tetralogy pulmonary insufficiency, as well as rectifying its dysfunction by decompression in patients with a left ventricular assist device.

Effects of biventricular pacing on left heart twist and strain in a porcine model of right heart failure

BACKGROUND

Biventricular pacing (BiVP) improves cardiac output (CO) in selected cardiac surgery patients, but response remains variable, necessitating a better understanding of the mechanism. Accordingly, we used speckle tracking echocardiography (STE) to analyze BiVP during acute right ventricular pressure overload (RVPO).

MATERIALS AND METHODS

In nine pigs, the inferior vena cava (IVC) was snared to decrease CO and establish a control model. Heart block was induced, the pulmonary artery snared, and BiVP initiated. Echocardiograms of the left ventricular midpapillary level were taken at varying atrioventricular delay (AVD) and interventricular delay (VVD) for STE analysis of regional circumferential strain (CS) and radial strain (RS). Echocardiograms were taken of the left ventricular base, midpapillary, and apex during baseline, IVC occlusion, and each BiVP setting for STE analysis of twist, apical and basal rotations, CS, RS, and synchrony. Indices were correlated against CO with mixed linear models.

RESULTS

During IVC occlusion, CO correlated with twist, apical rotation, RS, RS synchrony, and CS (P < 0.05). During RVPO with BiVP, CO only correlated with RS synchrony and CS (P < 0.05). During AVD and VVD variations, CO was associated with free wall RS (P < 0.008). CO correlated with septal wall CS during AVD variation and free wall CS during VVD variation (P < 0.008).

CONCLUSIONS

In an open chest model, twist, RS, RS synchrony, and CS analyzed by STE may be noninvasive surrogates for changes in CO. During RVPO, changes in RS synchrony and CS with varying regional strain contributions may be the primary mechanism in which BiVP improves CO. Lack of correlation of remaining indices may reflect postsystolic function.

New insights in LV torsion for the selection of cardiac resynchronisation therapy candidates

Recent literature indicates that torsion of the left ventricle (LV) is a promising predictor for response to cardiac resynchronisation therapy (CRT). Among patients with severe heart failure, 45 to 75% of patients show rigid body rotation, where the base and apex rotate in the same direction, instead of normal, opposite rotation. The occurrence of this phenomenon seems to be a good indicator for response to CRT. From this review, it can be concluded that LV torsion might be a welcome addition to current selection criteria.

Circulation: Cardiovascular Imaging Editors’ Picks

The following articles are being highlighted as part of Circulation: Cardiovascular Imaging ’s Topic Review. This series summarize the most important articles, as selected by the editors, that have been published in the Circulation portfolio. The studies included in this article represent the most significant research in clinical translation of novel imaging technologies.

Protective effects of hyperbaric oxygen and iloprost on ischemia/reperfusion-induced lung injury in a rabbit model

Background

The role of multiorgan damage in the mortality caused by ischemic limb injury is still not clarified. The objective of this study was to examine the potential protective effects of hyperbaric oxygen (HBO) and iloprost (IL) therapy on lung damage induced by limb ischemia/reperfusion injury in a rabbit model, using both biochemical and histopathological aspects.

Methods

Forty New Zealand white rabbits were randomly allocated into one of five study groups: HBO group (single session of HBO treatment); IL group (25 ng/kg/min infusion of IL); HBO + IL group (both HBO and IL); Control group (0.9% saline only); and a sham group. Acute hind limb ischemia-reperfusion was established by clamping the abdominal aorta for 1 h. HBO treatment and IL infusion were administrated during 60 min of ischemia and 60 min of reperfusion period. Blood pH, partial pressure of oxygen, partial pressure of carbon dioxide and levels of bicarbonate, sodium, potassium, creatine kinase, lactate dehydrogenase, and tumor necrosis factor alpha were determined at the end of the reperfusion period. Malondialdehyde was measured in the plasma and lung as an indicator of free radicals. After sacrifice, left lungs were removed and histopathological examination determined the degree of lung injury.

Results

In the control group, blood partial pressure of oxygen and bicarbonate levels were significantly lower and creatine kinase, lactate dehydrogenase, malondialdehyde and tumor necrosis factor-α levels were significantly higher than those of the HBO group, IL group, HBO + IL group and sham group. Similarly, the malondialdehyde levels in the lung tissue and plasma levels were significantly lower in the treatment groups compared with the control group. The extent of lung injury according to the histological findings was significantly higher in the control group.

Conclusions

These results suggest that both HBO and IL therapies and their combination might be effectively used in the prevention of lung injury after ischemia/reperfusion injury of the lower extremities.

Circulation: Heart Failure Editors' Picks

The following are highlights from Circulation: Heart Failure Topic Review. This series will summarize the most important articles, as selected by the editors, that have published in the Circulation portfolio. The objective of this series is to provide our readership with a timely comprehensive selection of important papers that are relevant to the heart failure audience. The studies included in this article represent the most noteworthy research in the areas of heart failure and electrophysiology.

Circulation: Heart Failure Editors' Picks: Most Important Papers in Heart Failure and Imaging

The following are highlights from Circulation: Heart Failure Topic Review. This series will summarize the most important manuscripts, as selected by the editors, that have been published in the Circulation portfolio. The objective of this series is to provide our readership with a timely comprehensive selection of important papers that are relevant to the heart failure audience. The studies included in this article represent the most noteworthy research in the areas of heart failure and imaging.