Left ventricular twist and untwist rate provide reliable measures of ventricular function in myocardial ischemia and a wide range of hemodynamic states

Left ventricular systolic motion pattern differs among patients with left bundle branch block patterns

The study aimed to investigate left ventricular (LV) motion pattern in patients with LBBB patterns including patients with pacemaker rhythm (PM), type B Wolff-Parkinson-White syndrome (B-WPW), premature ventricular complexes originating from the right ventricular outflow tract (RVOT-PVC), and complete left bundle branch block (CLBBB). Two-dimensional speckle tracking was used to evaluate peak value and time to peak value of the LV twist, LV apex rotation, and LV base rotation in patients with PM, B-WPW, RVOT-PVC, and CLBBB with normal LV ejection fraction, and in age-matched control subjects. The LV motion patterns were altered in all patients compared to the control groups. Patients with PM and CLBBB had a similar LV motion pattern with a reduced peak value of LV apex rotation and LV twist. Patients with B-WPW demonstrated the opposite trend in the reduction of LV rotation peak value, which was more dominant in the basal layer. The most impairment in the LV twist/rotation peak value was identified in patients with RVOT-PVC. Compared to the control group, the apical-basal rotation delay was prolonged in patients with CLBBB, followed by those with B-WPW, PM, and RVOT-PVC. The LV motion patterns were different among patients with different patterns of LBBB. CLBBB and PM demonstrated a reduction in LV twist/rotation that was pronounced in the apical layer, B-WPW showed a reduction in the basal layer, and RVOT-PVC in both layers. CLBBB had the most pronounced LV apical-basal rotation dyssynchrony.

Cardio-centric hemodynamic management improves spinal cord oxygenation and mitigates hemorrhage in acute spinal cord injury

Chronic high-thoracic and cervical spinal cord injury (SCI) results in a complex phenotype of cardiovascular consequences, including impaired left ventricular (LV) contractility. Here, we aim to determine whether such dysfunction manifests immediately post-injury, and if so, whether correcting impaired contractility can improve spinal cord oxygenation (SCO₂), blood flow (SCBF) and metabolism. Using a porcine model of T2 SCI, we assess LV end-systolic elastance (contractility) via invasive pressure-volume catheterization, monitor intraparenchymal SCO₂ and SCBF with fiberoptic oxygen sensors and laser-Doppler flowmetry, respectively, and quantify spinal cord metabolites with microdialysis. We demonstrate that high-thoracic SCI acutely impairs cardiac contractility and substantially reduces SCO₂ and SCBF within the first hours post-injury. Utilizing the same model, we next show that augmenting LV contractility with the β-agonist dobutamine increases SCO₂ and SCBF more effectively than vasopressor therapy, whilst also mitigating increased anaerobic metabolism and hemorrhage in the injured cord. Finally, in pigs with T2 SCI survived for 12 weeks post-injury, we confirm that acute hemodynamic management with dobutamine appears to preserve cardiac function and improve hemodynamic outcomes in the chronic setting. Our data support that cardio-centric hemodynamic management represents an advantageous alternative to the current clinical standard of vasopressor therapy for acute traumatic SCI.

Left Ventricular Twist Is Augmented in Hypoxia by β1-Adrenergic-Dependent and β1-Adrenergic-Independent Factors, Without Evidence of Endocardial Dysfunction

BACKGROUND

Left ventricular (LV) twist mechanics are augmented with both acute and chronic hypoxemia. Although the underlying mechanisms remain unknown, sympathetic activation and a direct effect of hypoxemia on the myocardium have been proposed, the latter of which may produce subendocardial dysfunction that is masked by larger subepicardial torque. This study therefore sought to (1) determine the individual and combined influences of β₁-AR (β₁-adrenergic receptor) stimulation and peripheral O₂ saturation (Spo₂) on LV twist in acute and chronic hypoxia and (2) elucidate whether endocardial versus epicardial mechanics respond differently to hypoxia.

METHODS

Twelve males (27±4 years) were tested near sea level in acute hypoxia (Spo₂=82±4%) and following 3 to 6 days at 5050 m (high altitude; Spo₂=83±3%). In both settings, participants received infusions of β₁-AR blocker esmolol and volume-matched saline (double-blind, randomized). LV mechanics were assessed with 2-dimensional speckle-tracking echocardiography, and region-specific analysis to compare subendocardial and subepicardial mechanics.

RESULTS

At sea level, compared with baseline (14.8±3.0°) LV twist was reduced with esmolol (11.2±3.3°; P=0.007) and augmented during hypoxia (19.6±4.9°; P<0.001), whereas esmolol+hypoxia augmented twist compared with esmolol alone (16.5±3.3°; P<0.001). At 5050 m, LV twist was increased compared with sea level (19.5±5.4°; P=0.004), and reduced with esmolol (13.0±3.8°; P<0.001) and Spo₂ normalization (12.8±3.4°; P<0.001). Moreover, esmolol+normalized Spo₂ lowered twist further than esmolol alone (10.5±3.1°; P=0.036). There was no mechanics-derived evidence of endocardial dysfunction with hypoxia at sea level or high altitude.

CONCLUSIONS

These findings suggest LV twist is augmented in hypoxia via β₁-AR-dependent and β₁-AR-independent mechanisms (eg, α₁-AR stimulation), but does not appear to reflect endocardial dysfunction.

Mechanisms, diagnosis, and treatment of heart failure with preserved ejection fraction and diastolic dysfunction

INTRODUCTION

Heart failure with preserved ejection fraction (HFpEF) continues to be a major challenge for clinicians. Many crucial aspects of the syndrome remain unclear, including the exact pathophysiology, early diagnosis, and treatment. Patients with HFpEF are often asymptomatic late into the disease process, and treatment with medications commonly used in heart failure with reduced ejection fraction (HFrEF) has not been proven to be beneficial. In addition, the confusion of similar terms with HFpEF, such as diastolic heart failure, and diastolic dysfunction (DD), has led to a misunderstanding of the true scope of HFpEF. Areas covered: In this review, authors highlight the differences in terminology and critically review the current knowledge on the underlying mechanisms, diagnosis, and latest treatment strategies of HFpEF. Expert commentary: While significant advances have been made in the understanding of HFpEF, the definitive diagnosis of HFpEF continues to be difficult. The development of improved and standardized methods for detecting DD has shown promise in identifying early HFpEF. However, even with early detection, there are few treatment options shown to provide mortality benefit warranting further investigation.

Left ventricular endocardial and epicardial strain changes with apical myocardial ischemia in an open-chest porcine model

Early detection of acute myocardial ischemia is critical to prevent permanent myocardial damage. The impact of apical ischemia on global left ventricular (LV) function can be difficult to characterize using traditional volume‐based echocardiography measures. Myocardial strain imaging is a sensitive, quantitative marker of myocardial deformation that can measure ventricular function. Recent advances allow layer‐specific measurement of endo‐ and epicardial strain, enhancing the ability to evaluate myocardial ischemia. This study investigates the effects of apical ischemia on LV function using epi‐ and endocardial strain. We hypothesize that myocardial strain will identify changes in regional and global myocardial function associated with focal apical ischemia as compared to ejection fraction (EF), and that longitudinal strain will be a better indicator of myocardial dysfunction compared to circumferential or radial strain. In a porcine model (n = 9), acute ischemia was induced by left anterior descending coronary artery occlusion. Echocardiograms were performed at baseline, during 15‐min ischemia, and after reperfusion. Global longitudinal strain decreased with acute focal ischemia of the left ventricular apical region (baseline: −16.4% vs. ischemia: −12.2%; P = 0.010), with no change observed in global circumferential and radial strain or EF. Both endocardial and epicardial longitudinal strain decreased by 68% (P < 0.001) in the ischemic and peri‐ischemic zone, while circumferential and radial strain only decreased in endocardium of the ischemic zone. Longitudinal strain was more sensitive to ischemia, being able to detect changes in global LV function and thus may confer clinical diagnostic advantage in the evaluation of acute LV apical ischemia.

Cardiac structure and function in adolescent Sherpa; effect of habitual altitude and developmental stage

The purpose of this study was to examine ventricular structure and function in Sherpa adolescents to determine whether age-specific differences in oxygen saturation (SpO2 ) and pulmonary artery systolic pressure (PASP) influence cardiac adaptation to chronic hypoxia early in life. Two-dimensional, Doppler, and speckle-tracking echocardiography were performed on adolescent (9-16 yr) highland Sherpa (HLS; 3,840 m; n = 26) and compared with age-matched lowland Sherpa (LLS; 1,400 m; n = 10) and lowland Caucasian controls (LLC; sea level; n = 30). The HLS were subdivided into pre- and postadolescence; SpO2 was also recorded. Only HLS exhibited a smaller relative left ventricular (LV) end-diastolic volume; however, both HLS and LLS demonstrated a lower peak LV untwisting velocity compared with LLC (92 ± 26 and 100 ± 45 vs. 130 ± 43°/s, P < 0.05). Although SpO2 was similar between groups, PASP was higher in post- vs. preadolescent HLS (30 ± 5 vs. 25 ± 5 mmHg, P < 0.05), which negatively correlated with right ventricular strain rate (r = 0.50, P < 0.01). Much like their adult counterparts, HLS and LLS adolescents exhibit slower LV diastolic relaxation, despite residing at different altitudes. These findings suggest fundamental differences exist in the diastolic function of Sherpa that are present at an early age and may be retained after migration to lower altitudes. The higher PASP in postadolescent Sherpa is in contrast to previous reports of lowland children at high altitude and, unlike that in lowlanders, was not explained by differences in SpO2 ; thus different regulatory mechanisms seem to exist between these two distinct populations.

Association of impaired left ventricular twisting-untwisting with vascular dysfunction, neurohumoral activation and impaired exercise capacity in hypertensive heart disease

AIMS

We investigated the association between left ventricular (LV) torsional deformation and vascular dysfunction, fibrosis, neurohumoral activation, and exercise capacity in patients with normal ejection fraction

METHODS AND RESULTS

In 320 newly-diagnosed untreated hypertensive patients and 160 controls, we measured: pulse wave velocity (PWV); coronary flow reserve (CFR) by Doppler echocardiography; global longitudinal strain and strain rate, peak twisting, the percentage changes between peak twisting, and untwisting at mitral valve opening (%dpTw - UtwMVO ), at peak (%dpTw - UtwPEF ), and the end of early LV diastolic filling (%dpTw - UtwEDF ) by speckle tracking imaging; transforming growth factor (TGFb-1), metalloproteinase-9 (MMP-9), tissue inhibitor of matrix metalloptoteinase-1(TIMP-1), markers of collagen synthesis, and N-terminal pro-brain natriuretic peptide (NT-proBNP). Oxygen consumption (VO2 ), measured by means of cardiopulmonary exercise test, was assessed in a subset of 80 patients. The PWV, CFR, longitudinal strain and strain rate, %dpTw-UtwMVO , %dpTw-UtwPEF , and %dpTw-UtwEDF were impaired in hypertensive patients compared with controls. In multivariable analysis, CFR, PWV, LV mass, and systolic blood pressure were independent determinants of longitudinal strain, strain rate, and untwisting markers (P < 0.05). Increased TGFb-1 was related with increased collagen synthesis markers, TIMP-1 and MMP-9 and these biomarkers were associated with impaired longitudinal systolic strain rate, untwisting markers, CFR and PWV (P < 0.05). Delayed untwisting as assessed by reduced %dpTw - UtwEDF was related with increased NT-proBNP and reduced VO2 (P < 0.05).

CONCLUSIONS

Impaired LV untwisting is associated with increased arterial stiffness and coronary microcirculatory dysfunction, and is linked to reduced exercise capacity and neurohumoral activation in hypertensive heart disease. A fibrotic process may be the common link between vascular dysfunction and abnormal myocardial deformation.

Diacerein improves left ventricular remodeling and cardiac function by reducing the inflammatory response after myocardial infarction

BACKGROUND

The inflammatory response has been implicated in the pathogenesis of left ventricular (LV) remodeling after myocardial infarction (MI). An anthraquinone compound with anti-inflammatory properties, diacerein inhibits the synthesis and activity of pro-inflammatory cytokines, such as tumor necrosis factor and interleukins 1 and 6. The purpose of this study was to investigate the effects of diacerein on ventricular remodeling in vivo.

METHODS AND RESULTS

Ligation of the left anterior descending artery was used to induce MI in an experimental rat model. Rats were divided into two groups: a control group that received saline solution (n = 16) and a group that received diacerein (80 mg/kg) daily (n = 10). After 4 weeks, the LV volume, cellular signaling, caspase 3 activity, and nuclear factor kappa B (NF-κB) transcription were compared between the two groups. After 4 weeks, end-diastolic and end-systolic LV volumes were reduced in the treatment group compared to the control group (p < .01 and p < .01, respectively). Compared to control rats, diacerein-treated rats exhibited less fibrosis in the LV (14.65%± 7.27% vs. 22.57%± 8.94%; p < .01), lower levels of caspase-3 activity, and lower levels of NF-κB p65 transcription.

CONCLUSIONS

Treatment with diacerein once a day for 4 weeks after MI improved ventricular remodeling by promoting lower end-systolic and end-diastolic LV volumes. Diacerein also reduced fibrosis in the LV. These effects might be associated with partial blockage of the NF-κB pathway.

Impaired myocardial function does not explain reduced left ventricular filling and stroke volume at rest or during exercise at high altitude

Impaired myocardial systolic contraction and diastolic relaxation have been suggested as possible mechanisms contributing to the decreased stroke volume (SV) observed at high altitude (HA). To determine whether intrinsic myocardial performance is a limiting factor in the generation of SV at HA, we assessed left ventricular (LV) systolic and diastolic mechanics and volumes in 10 healthy participants (aged 32 ± 7; mean ± SD) at rest and during exercise at sea level (SL; 344 m) and after 10 days at 5,050 m. In contrast to SL, LV end-diastolic volume was ∼19% lower at rest (P = 0.004) and did not increase during exercise despite a greater untwisting velocity. Furthermore, resting SV was lower at HA (∼17%; 60 ± 10 vs. 70 ± 8 ml) despite higher LV twist (43%), apical rotation (115%), and circumferential strain (17%). With exercise at HA, the increase in SV was limited (12 vs. 22 ml at SL), and LV apical rotation failed to augment. For the first time, we have demonstrated that EDV does not increase upon exercise at high altitude despite enhanced in vivo diastolic relaxation. The increase in LV mechanics at rest may represent a mechanism by which SV is defended in the presence of a reduced EDV. However, likely because of the higher LV mechanics at rest, no further increase was observed up to 50% peak power. Consequently, although hypoxia does not suppress systolic function per se, the capacity to increase SV through greater deformation during submaximal exercise at HA is restricted.

Acute Effects of Pacing at Different Ventricular Sites on Left Ventricular Rotational Mechanics in a Porcine Model

OBJECTIVE

The purpose of this study was to examine the acute effects of pacing at different ventricular sites on hemodynamics and left ventricular (LV) rotational mechanics using speckle-tracking echocardiography (STE) in a porcine model.

DESIGN

A prospective laboratory investigation.

SETTING

University research laboratory.

PARTICIPANTS

Yorkshire pigs.

INTERVENTIONS

In 9 pigs, after midline sternotomy, epicardial pacing was performed from the right ventricular outflow tract (RVOT), right ventricular apex (RVA), and LV free wall.

MEASUREMENTS AND MAIN RESULTS

Two-dimensional STE and conductance catheter-derived LV pressure-volume measurements were made to determine the impact of pacing from various sites on LV rotational parameters (twist/untwist) and hemodynamics. RVOT pacing caused the least decrease in end-systolic pressure from baseline (-9.5%), when compared with RVA (-19.1%) and LV (-23.4%). Systolic and diastolic parameters (Emax, Tau) also were different among RVOT (4.7±0.8 mmHg/mL, 32±4 ms), RVA (3.9±0.7 mmHg/mL, 37±6 ms), and LV sites (3.6±0.8 mmHg/mL, 42±7 ms). Similar to the effects of pacing on hemodynamics, RVOT pacing better preserved LV twist (11.1±1.8 v 8.6±1.7, 5.9±0.7 °) and untwisting rate (64.6±8.5 v 56.2±5.3, 48.2±8.5 °/s) when compared with RV apical pacing and LV pacing. Furthermore, prolongation of conduction from LV lateral to anteroseptal at LV base (26.5±3.8 v 13.8±3.3 ms, p<0.05) and LV midpapillary muscle level (35.6±5.6 v 14.1±2.4 ms, p<0.05) was observed with LV pacing compared with RVOT pacing.

CONCLUSIONS

The present data showed that the LV twist/untwist and cardiac systolic and diastolic function were least affected by RVOT pacing. This finding may be explained by the proximity of this location to the native ventricular conduction system.

Short-term adaptation and chronic cardiac remodelling to high altitude in lowlander natives and Himalayan Sherpa

NEW FINDINGS

What is the topic of this review? At high altitude, the cardiovascular system must adapt in order to meet the metabolic demand for oxygen. This review summarizes recent findings relating to short-term and life-long cardiac adaptation to high altitude in the context of exercise capacity. What advances does it highlight? Both Sherpa and lowlanders exhibit smaller left ventricular volumes at high altitude; however, myocardial relaxation, as evidenced by diastolic untwist, is reduced only in Sherpa, indicating that short-term hypoxia does not impair diastolic relaxation. Potential remodelling of systolic function, as evidenced by lower left ventricular systolic twist in Sherpa, may facilitate the requisite sea-level mechanical reserve required during exercise, although this remains to be confirmed. Both short-term and life-long high-altitude exposure challenge the cardiovascular system to meet the metabolic demand for O2 in a hypoxic environment. As the demand for O2 delivery increases during exercise, the circulatory component of oxygen transport is placed under additional stress. Acute adaptation and chronic remodelling of cardiac structure and function may occur to facilitate O2 delivery in lowlanders during sojourn to high altitude and in permanent highland residents. However, our understanding of cardiac structural and functional adaption in Sherpa remains confined to a higher maximal heart rate, lower pulmonary vascular resistance and no differences in resting cardiac output. Ventricular form and function are intrinsically linked through the left ventricular (LV) mechanics that facilitate efficient ejection, minimize myofibre stress during contraction and aid diastolic recoil. Recent examination of LV mechanics has allowed detailed insight into fundamental cardiac adaptation in high-altitude Sherpa. In this symposium report, we review recent advances in our understanding of LV function in both lowlanders and Sherpa at rest and discuss the potential consequences for exercise capacity. Collectively, data indicate chronic structural ventricular adaptation, with adult Sherpa having smaller absolute and relative LV size. Consistent with structural remodelling, cardiac mechanics also differ in Sherpa when compared with lowlanders at high altitude. These differences are characterized by a reduction in resting systolic deformation and slower diastolic untwisting, a surrogate of relaxation. These changes may reflect a functional cardiac adaptation that affords Sherpa the same mechanical reserve seen in lowlanders at sea level, which is absent when they ascend to high altitude.

Ventricular structure, function, and mechanics at high altitude: chronic remodeling in Sherpa vs. short-term lowlander adaptation

Short-term, high-altitude (HA) exposure raises pulmonary artery systolic pressure (PASP) and decreases left-ventricular (LV) volumes. However, relatively little is known of the long-term cardiac consequences of prolonged exposure in Sherpa, a highly adapted HA population. To investigate short-term adaptation and potential long-term cardiac remodeling, we studied ventricular structure and function in Sherpa at 5,050 m (n = 11; 31 ± 13 yr; mass 68 ± 10 kg; height 169 ± 6 cm) and lowlanders at sea level (SL) and following 10 ± 3 days at 5,050 m (n = 9; 34 ± 7 yr; mass 82 ± 10 kg; height 177 ± 6 cm) using conventional and speckle-tracking echocardiography. At HA, PASP was higher in Sherpa and lowlanders compared with lowlanders at SL (both P < 0.05). Sherpa had smaller right-ventricular (RV) and LV stroke volumes than lowlanders at SL with lower RV systolic strain (P < 0.05) but similar LV systolic mechanics. In contrast to LV systolic mechanics, LV diastolic, untwisting velocity was significantly lower in Sherpa compared with lowlanders at both SL and HA. After partial acclimatization, lowlanders demonstrated no change in the RV end-diastolic area; however, both RV strain and LV end-diastolic volume were reduced. In conclusion, short-term hypoxia induced a reduction in RV systolic function that was also evident in Sherpa following chronic exposure. We propose that this was consequent to a persistently higher PASP. In contrast to the RV, remodeling of LV volumes and normalization of systolic mechanics indicate structural and functional adaptation to HA. However, altered LV diastolic relaxation after chronic hypoxic exposure may reflect differential remodeling of systolic and diastolic LV function.