The pulmonary venous systolic flow pulse--its origin and relationship to left atrial pressure

Left atrium as key player and essential biomarker in heart failure

This article reviews roles of the left atrium as regulator of left ventricular filling, as compensatory reserve in left ventricular dysfunction and as diagnostic marker in patients with cardiovascular disorders. Application of novel imaging tools to assess left atrial function and their integration with conventional clinical methods are discussed. This includes a review of clinical applications of left atrial strain as a method to quantify the reservoir and booster pump components of left atrial function. Emerging methods for assessing left atrial wall stiffness and active work by pressure-strain loop analysis are discussed. Recommendations for how to apply left atrial strain in clinical routine to diagnose elevated left ventricular filling pressure are provided. Furthermore, a role for left atrial strain in the diagnostic work-up in patients suspected of pre-capillary pulmonary hypertension is proposed. The article also reviews how to implement parameters of atrial structure and function in clinical routine as recommended by recent international guidelines for imaging of heart failure.

Left ventricular dysfunction in pulmonary arterial hypertension is attributed to underfilling rather than intrinsic myocardial disease: a CMR 2D phase contrast study

The pathophysiology underlying impaired LV function in PAH remains unclear, with some studies implicating intrinsic myocardial dysfunction and others pointing to LV underfilling. Evaluation of pulmonary vein area (PVA) and flow may offer novel, mechanistic insight by distinguishing elevated LV filling pressure common in myocardial dysfunction from LV underfilling. This study aimed to elucidate LV filling physiology in PAH by assessing PVA and flow using cardiac magnetic resonance (CMR) and compare pulmonary vein flow in PAH with HFrEF as a model representing elevated filling pressures, in addition to healthy controls. Patients with PAH or heart failure with reduced ejection fraction (HFrEF) referred for CMR were retrospectively reviewed, and healthy controls were included as reference. Pulmonary vein S, D and A-wave were compared between groups. Associations between pulmonary vein area (PVA) by CMR and echocardiographic indices of LV filling pressure were evaluated. Nineteen patients with PAH, 25 with HFrEF and 24 controls were included. Both PAH and HFrEF had lower ejection fraction and S-wave velocity than controls. PAH displayed smaller LV end-diastolic volumes than controls, while HFrEF demonstrated larger PVA and higher A-wave reversal. PVA was associated with mitral E/e' ratio (r2 = 0.10; p = 0.03), e' velocity (r2 = 0.23; p = 0.001) and left atrial volume (r2 = 0.07; p = 0.005). Among PAH, PVA was not associated with LV-GLS. A PVA cut-off of 2.3cm2 displayed 87% sensitivity and 72% specificity to differentiate HFrEF and PAH (AUC = 0.82). PAH displayed lower pulmonary vein S-wave velocity, smaller LV volume and reduced function compared with controls. Reduced LV function in PAH may be owing to underfilling rather than intrinsic myocardial disease. PVA demonstrates promise as a novel, non-invasive imaging marker to assess LV filling status.

Left atrial reservoir pressure-volume relations during exercise in healthy older adults

The left atrium (LA) mediates cardiopulmonary interactions. During ventricular systole, the LA functions as a compliant reservoir that is coupled to the left ventricle (LV) and offloads volume from the pulmonary vasculature. We aimed to describe LA reservoir function using phasic relationships between pulmonary artery wedge pressure (PAWP) and LA volume events. We included healthy adults (7 M/6 F, 56 ± 8 yr) who were studied at rest and during semirecumbent cycle ergometry at a target of 100 beats/min heart rate. Right heart catheterization was performed to record the PAWP and two-dimensional (2-D) echocardiography was used to measure LA and LV volumes. We manually measured A-wave, x-trough, V-wave, and y-trough PAWP beat-by-beat, as well as minimal, maximal, and precontraction biplane LA volumes. Heart rate increased by 40 ± 7 beats/min with exercise; stroke volume and cardiac output also rose. Although all phasic PAWP measurements increased with exercise, the x-V pressure pulse during LA filling doubled from 4 ± 2 to 8 ± 4 mmHg (P = 0.001). LA minimal volume was unchanged but maximal volume increased from 39 ± 9 to 48 ± 9 mL (P < 0.001) with exercise, and so reservoir volume increased from 24 ± 5 to 32 ± 8 mL (P < 0.001). As such, calculated LA compliance decreased from 6.8 ± 3.4 to 4.8 ± 2.6 mL/mmHg (P = 0.029). The product of V-wave PAWP and LA maximal volume, a surrogate for LA wall stress, increased from 486 ± 193 to 953 ± 457 mmHg·mL (P < 0.001). In healthy older adults during submaximal exercise, the PAWP waveform shifts upward and its amplitude widens, LA filling increases, LA compliance decreases modestly, and LA wall stress may augment substantially.NEW & NOTEWORTHY We combined invasive estimates of left atrial pressure with noninvasive left atrial volume measurements made at rest and during exercise in healthy humans. Left atrial pressure and volume both increased with exercise, though the pressure increase was relatively greater, and calculated compliance decreased modestly while estimated peak wall stress nearly doubled. Our results demonstrate left atrial loading during exercise in healthy older adults and provide insight into how the left atrium mediates cardiopulmonary interactions.

Blood flow analysis with computational fluid dynamics in the left atrium after left atrial plication: a prospective study

OBJECTIVE

This study aimed to evaluate blood flow stagnation in an enlarged left atrium (LA) and prove that left atrial plication (LAP) could alleviate the stagnation.

METHODS

Five patients with chronic atrial fibrillation who underwent mitral valve surgery followed by LAP for an enlarged LA with a ≥ 60-mm diameter were included. We performed computational fluid dynamics (CFD) analysis using preoperative and postoperative computed tomography and four-dimensional flow magnetic resonance imaging. Additionally, computer graphics were used to create virtual left atrial appendage resection (LAAR) images. We performed CFD analysis to assess blood flow stagnation in the LA for three groups: preoperative, LAAR, and LAP.

RESULTS

When the average and constant stagnation volumes were both set to 100 preoperatively, the average stagnation volumes of the LAAR and LAP groups were 67.42 ± 18.64 and 35.88 ± 8.20, respectively. The constant stagnation volumes of these groups reduced to 45.01 ± 7.43 and 21.14 ± 7.70, respectively. The LAP group also had significantly lower average and constant stagnation volumes than those in the LAAR group (p = 0.006 and p = 0.033, respectively).

CONCLUSIONS

Blood flow stagnation was noted in the LAA and enlarged LA. CFD analysis revealed that LAP for the enlarged LA improved blood flow stagnation more than the virtual LAAR alone.

CLINICAL TRIAL REGISTRY NUMBER

UMIN000049923.

On the importance of fundamental computational fluid dynamics toward a robust and reliable model of left atrial flows

Computational fluid dynamics (CFD) studies of left atrial flows have reached a sophisticated level, for example, revealing plausible relationships between hemodynamics and stresses with atrial fibrillation. However, little focus has been on fundamental fluid modeling of LA flows. The purpose of this study was to investigate the spatiotemporal convergence, along with the differences between high- (HR) versus normal-resolution/accuracy (NR) solution strategies, respectively. Rigid wall CFD simulations were conducted on 12 patient-specific left atrial geometries obtained from computed tomography scans, utilizing a second-order accurate and space/time-centered solver. The convergence studies showed an average variability of around 30% and 55% for time averaged wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT), and endothelial cell activation potential (ECAP), even between intermediate spatial and temporal resolutions, in the left atrium (LA) and left atrial appendage (LAA), respectively. The comparison between HR and NR simulations showed good correlation in the LA for WSS, RRT, and ECAP (R 2 > .9 ), but not for OSI (R 2 = .63 ). However, there were poor correlations in the LAA especially for OSI, RRT, and ECAP (R 2 = .55, .63, and .61, respectively), except for WSS (R 2 = .81 ). The errors are comparable to differences previously reported with disease correlations. To robustly predict atrial hemodynamics and stresses, numerical resolutions of 10 M elements (i.e., Δ x = ∼ .5 mm) and 10 k time-steps per cycle seem necessary (i.e., one order of magnitude higher than normally used in both space and time). In conclusion, attention to fundamental numerical aspects is essential toward establishing a plausible, robust, and reliable model of LA flows.

Investigating the importance of left atrial compliance on fluid dynamics in a novel mock circulatory loop

The left atrium (LA) hemodynamic indices hold prognostic value in various cardiac diseases and disorders. To understand the mechanisms of these conditions and to assess the performance of cardiac devices and interventions, in vitro models can be used to replicate the complex physiological interplay between the pulmonary veins, LA, and left ventricle. In this study, a comprehensive and adaptable in vitro model was created. The model includes a flexible LA made from silicone and allows distinct control over the systolic and diastolic functions of both the LA and left ventricle. The LA was mechanically matched with porcine LAs through expansion tests. Fluid dynamic measures were validated against the literature and pulmonary venous flows recorded on five healthy individuals using magnetic resonance flow imaging. Furthermore, the fluid dynamic measures were also used to construct LA pressure-volume loops. The in vitro pressure and flow recordings expressed a high resemblance to physiological waveforms. By decreasing the compliance of the LA, the model behaved realistically, elevating the a- and v-wave peaks of the LA pressure from 12 to 19 mmHg and 22 to 26 mmHg, respectively, while reducing the S/D ratio of the pulmonary venous flowrate from 1.5 to 0.3. This model provides a realistic platform and framework for developing and evaluating left heart procedures and interventions.

Difference in tissue temperature change between two cryoballoons

BACKGROUND

Cryoballoon ablation, especially Arctic Front Advance Pro (AFA-Pro) (Medtronic, Minneapolis, Minnesota, USA), has been widely recognised as a standard approach to atrial fibrillation (AF). Recently, Boston Scientific has released a novel cryoballoon system (POLARx). Despite comparable acute clinical outcomes of these two cryoballoons, the recent study reported a higher complication rate, especially for phrenic nerve palsy, with POLARx. However, their impact on biological tissue remains unclear.

OBJECTIVE

The purpose of our study is to evaluate temperature change of biological tissue during cryoablation of each cryoballoon using a porcine experimental model.

METHOD

A tissue-based pulmonary vein model was constructed from porcine myocardial tissue and placed on a stage designed to simulate pulmonary vein anatomy and venous flow. Controlled cryoablations of AFA-Pro and POLARx were performed in this model to evaluate the tissue temperature. A temperature sensor was set behind the muscle and cryoballoon ablation was performed after confirming the occlusion of pulmonary vein with cryoballoon.

RESULTS

The mean tissue nadir temperature during cryoablation with AFA-Pro was -41.5°C±4.9°C, while the mean tissue nadir temperature during cryoablation with POLARx was -58.4°C±5.9°C (p<0.001). The mean balloon nadir temperature during cryoablation with AFA-Pro was -54.6°C±2.6°C and the mean balloon nadir temperature during cryoablation with POLARx was -64.7°C±3.8°C (p<0.001).

CONCLUSION

POLARx could freeze the biological tissue more strongly than AFA-Pro.

Cerebral microcirculatory pulse wave propagation and pulse wave amplitude mapping in retrospectively gated MRI

To analyze cerebral arteriovenous pulse propagation and to generate phase-resolved pulse amplitude maps from a fast gradient-echo sequence offering flow-related enhancement (FREE). Brain MRI was performed using a balanced steady-state free precession sequence at 3T followed by retrospective k-space gating. The time interval of the pulse wave between anterior-, middle- and posterior cerebral artery territories and the superior sagittal sinus were calculated and compared between and older and younger groups within 24 healthy volunteers. Pulse amplitude maps were generated and compared to pseudo-Continuous Arterial Spin Labeling (pCASL) MRI maps by voxel-wise Pearson correlation, Sørensen-Dice maps and in regards to signal contrast. The arteriovenous delays between all vascular territories and the superior sagittal sinus were significantly shorter in the older age group (11 individuals, ≥ 31 years) ranging between 169 ± 112 and 246 ± 299 ms versus 286 ± 244 to 419 ± 299 ms in the younger age group (13 individuals) (P ≤ 0.04). The voxel-wise pulse wave amplitude values and perfusion-weighted pCASL values correlated significantly (Pearson-r = 0.33, P < 0.01). Mean Dice overlaps of high (gray) and low (white matter) regions were 73 ± 3% and 59 ± 5%. No differences in image contrast were seen in the whole brain and the white matter, but significantly higher mean contrast of 0.73 ± 0.23% in cortical gray matter in FREE-MRI compared to 0.52 ± 0.12% in pCASL-MRI (P = 0.01). The dynamic information of flow-related enhancement allows analysis of the cerebral pulse wave propagation potentially providing information about the (micro)circulation on a regional level. However, the pulse wave amplitude reveals weaknesses in comparison to true perfusion-weighting and could rather be used to calculate a pulsatility index.

Stagnating blood flow related to thrombus formation in pulmonary vein stump after left upper lobectomy

OBJECTIVES

A thrombus can occur in the stump of the pulmonary vein after left upper lobectomy, potentially causing postoperative cerebral infarction. This study aimed to verify the hypothesis that stagnation of blood flow inside the pulmonary vein stump causes thrombus formation.

METHODS

The three-dimensional geometry of the pulmonary vein stump after left upper lobectomy was recreated using contrast-enhanced computed tomography. Blood flow velocity and wall shear stress (WSS) inside the pulmonary vein stump were analysed using the computational fluid dynamics (CFD) method and compared between the two groups (those with or without thrombus).

RESULTS

The volumes of average flow velocity per heartbeat < 10 mm/s, 3 mm/s, 1 mm/s (p-values 0.0096, 0.0016, 0.0014, respectively) and the volumes where flow velocity was always below the three cut-off values (p-values 0.019, 0.015, 0.017, respectively) were significantly larger in patients with a thrombus than in those without thrombus. The areas of average WSS per heartbeat < 0.1 Pa, 0.03 Pa, 0.01 Pa (p-values 0.0002, < 0.0001, 0.0002, respectively), and the areas where WSS was always below the three cut-off values (p-values 0.0088, 0.0041, 0.0014, respectively) were significantly larger in patients with thrombus than in those without thrombus.

CONCLUSIONS

The area of blood flow stagnation in the stump calculated by CFD method was significantly larger in patients with than in those without thrombus. This result elucidates that stagnation of blood flow promotes thrombus formation in the pulmonary vein stump in patients who undergo left upper lobectomy.

Impact of left atrial appendage occlusion device position on potential determinants of device-related thrombus: a patient-specific in silico study

BACKGROUND

Device-related thrombus (DRT) after left atrial appendage occlusion (LAAO) is potentially linked to adverse events. Although clinical reports suggest an effect of the device type and position on the DRT risk, in-depth studies of its mechanistic basis are needed. This in silico study aimed to assess the impact of the position of non-pacifier (Watchman) and pacifier (Amulet) LAAO devices on surrogate markers of DRT risk.

METHODS

The LAAO devices were modeled with precise geometry and virtually implanted in different positions into a patient-specific left atrium. Using computational fluid dynamics, the following values were quantified: residual blood, wall shear stress (WSS) and endothelial cell activation potential (ECAP).

RESULTS

In comparison to an ostium-fitted device position, deep implantation led to more residual blood, lower average WSS and higher ECAP surrounding the device, especially on the device's atrial surface and the surrounding tissue, suggesting increased risk for potential thrombus. For the non-pacifier device, an off-axis device orientation resulted in even more residual blood, higher ECAP and similar average WSS as compared to an ostium-fitted device position. Overall, the pacifier device showed less residual blood, higher average WSS and lower ECAP, compared to the non-pacifier device.

CONCLUSIONS

In this in silico study, both LAAO device type and implant position showed an impact on potential markers of DRT in terms of blood stasis, platelet adhesion and endothelial dysfunction. Our results present a mechanistic basis for clinically observed risk factors of DRT and the proposed in silico model may aid in the optimization of device development and procedural aspects.

Coupled thermal-hemodynamics computational modeling of cryoballoon ablation for pulmonary vein isolation

Cryoballoon ablation (CBA) is a cryo-energy based minimally invasive treatment procedure for patients suffering from left atrial (LA) fibrillation. Although this technique has proved to be effective, it is prone to reoccurrences and some serious thermal complications. Also, the factors affecting thermal distribution at the pulmonary vein-antrum junction that are critical to the treatment success is poorly understood. Computer modeling of CBA can resolve this issue and help understand the factors affecting this treatment. To do so, however, numerical challenges associated with the simulation of advection-dominant transport process must be resolved. Here, we describe the development of a thermal-hemodynamics computational framework to simulate incomplete occlusion in a patient-specific LA geometry during CBA. The modeling framework uses the finite element method to predict hemodynamics, thermal distribution, and lesion formation during CBA. An incremental pressure correction scheme is used to decouple velocity and pressure in the Navier-Stokes equation, whereas several stabilization techniques are also applied to overcome numerical instabilities. The framework was implemented using an open-source FE library (FEniCS). We show that model predictions of the hemodynamics in a realistic human LA geometry match well with measurements. The effects of cryoballoon position, pulmonary vein blood velocity and mitral regurgitation on lesion formation during CBA was investigated. For a -70⁰C cryoballoon temperature, the model predicts lesion formation for gaps less than 2.5 mm and increasing efficiency of CBA for higher balloon tissue contact areas. The simulations also predict that lesion formation is not sensitive to variation in pulmonary vein blood velocity and mitral regurgitation. The framework can be applied to optimize CBA in patients for future clinical studies.

The relationship between pesi score and pulmonary venous flow parameters in patients with acute pulmonary embolism

BACKGROUND

Acute pulmonary embolism (APE) is an important cause of cardiovascular morbidity and mortality. PESI scoring is used in risk classification. This study was designed to determine the relationship between echocardiographic pulmonary vein measurements and PESI score, which is an important tool in diagnosis and treatment.

METHODS

A total of 210 patients were evaluated. Pulmonary vein measurements and PESI scores of the patients at the time of diagnosis were calculated. Correlation analysis was performed to determine the relationship between the two parameters.

RESULTS

Total PESI scores were 112.9 ± 33.9. The pulmonary vein S wave .39 ± .14, the D wave .48 ± .18, and the S/D ratio was found to be .86 ± .35. It was determined that there was a significant correlation between pulmonary S/D ratio and PESI score. (Pearson correlation coefficient = -.693, R2 Linear:.484; p < .001) The AUC of S/D for mortality prediction was .729 (95% CI = .653-.804; p < .001), the cutoff value was .63, the sensitivity and specificity were 55.6% and 55.7%, respectively.

CONCLUSION

Pulmonary vein measurements were found to be correlated with the PESI score and were found to be a parameter that could predict mortality.

Bedside assessment of left atrial pressure in critical care: a multifaceted gem

Evaluating left atrial pressure (LAP) solely from the left ventricular preload perspective is a restrained approach. Accurate assessment of LAP is particularly relevant when pulmonary congestion and/or right heart dysfunction are present since it is the pressure most closely related to pulmonary venous pressure and thus pulmonary haemodynamic load. Amalgamation of LAP measurement into assessment of the ‘transpulmonary circuit’ may have a particular role in differentiating cardiac failure phenotypes in critical care. Most of the literature in this area involves cardiology patients, and gaps of knowledge in application to the bedside of the critically ill patient remain significant. Explored in this review is an overview of left atrial physiology, invasive and non-invasive methods of LAP measurement and their potential clinical application.

Prevalence, distribution, and determinants of pulmonary venous systolic flow reversal in severe mitral regurgitation

AIMS

This study aimed to evaluate the prevalence and distribution of pulmonary venous systolic flow reversal (PVSFR) in patients with severe mitral regurgitation (MR), and to examine the relationship between PVSFR profile and cardiac parameters.

METHODS AND RESULTS

A total of 125 patients with severe MR who had transoesophageal echocardiography (TOE) performed were reviewed. Of these, 121 (96.8%) patients showed all four pulmonary venous (PV) flows by TOE. They were categorized into three groups by the MR aetiology: degenerative MR (DMR) (n = 72), ventricular functional MR (V-FMR) (n = 20), and atrial functional MR (A-FMR) (n = 16). Eighteen (16.7%) patients had PVSFR in all four PVs. Twenty-nine (26.9%) had PVSFR in three PVs, 23 (21.3%) in two PVs, and 23 (21.3%) in one PV. PVSFR appeared at right PVs more frequently compared with left PVs. A high number of PVSFR was significantly correlated with higher pulmonary capillary wedge pressure (PCWP) and 3D vena contracta area (3D-VCA). With regard to MR aetiology, the number of PVSFRs was correlated with high 3D-VCA in patients with DMR and A-FMR, while it was correlated with high PCWP in patients with V-FMR. Laminar-type PVSFR appeared more frequently in FMR compared with DMR, and it had a relationship with higher PCWP and lower right ventricular fractional area change (RVFAC).

CONCLUSION

All four PV were detected in 96.8%, and 16.8% patients had PVSFR in all four PVs. PCWP and 3D-VCA were correlated with the number of PVSFRs in severe MR patients. Laminar-type PVSFR was related to higher PCWP and lower RVFAC.

Subject-Specific Calculation of Left Atrial Appendage Blood-Borne Particle Residence Time Distribution in Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia that leads to thrombus formation, mostly in the left atrial appendage (LAA). The current standard of stratifying stroke risk, based on the CHA2DS2-VASc score, does not consider LAA morphology, and the clinically accepted LAA morphology-based classification is highly subjective. The aim of this study was to determine whether LAA blood-borne particle residence time distribution and the proposed quantitative index of LAA 3D geometry can add independent information to the CHA2DS2-VASc score. Data were collected from 16 AF subjects. Subject-specific measurements included left atrial (LA) and LAA 3D geometry obtained by cardiac computed tomography, cardiac output, and heart rate. We quantified 3D LAA appearance in terms of a novel LAA appearance complexity index (LAA-ACI). We employed computational fluid dynamics analysis and a systems-based approach to quantify residence time distribution and associated calculated variable (LAA mean residence time, t m) in each subject. The LAA-ACI captured the subject-specific LAA 3D geometry in terms of a single number. LAA t m varied significantly within a given LAA morphology as defined by the current subjective method and it was not simply a reflection of LAA geometry/appearance. In addition, LAA-ACI and LAA t m varied significantly for a given CHA2DS2-VASc score, indicating that these two indices of stasis are not simply a reflection of the subjects' clinical status. We conclude that LAA-ACI and LAA t m add independent information to the CHA2DS2-VASc score about stasis risk and thereby can potentially enhance its ability to stratify stroke risk in AF patients.

Mitral prolapsing volume is associated with increased cardiac dimensions in patients with mitral annular disjunction

Introduction

In patients with mitral annular disjunction (MAD), it can be difficult to assess the severity of mitral regurgitation (MR), as they present with a prolapsing volume (i.e. volume resulting from mitral valve prolapse, blood volume shift) rather than a regurgitant jet. The influence of the mitral prolapsing volume (MPV) on cardiac dimensions is unknown. We hypothesised that the severity of MR is underestimated in these patients. Our aim was to measure MPV and to investigate its influence on cardiac dimensions in patients with MAD.

Methods

We retrospectively included 131 consecutive patients with MAD from our institution’s echocardiographic database. Transthoracic echocardiography was used to assess MPV. Additionally, we established a control group of 617 consecutive patients with degenerative mitral valve disease and performed propensity score matching.

Results

Median MPV in the MAD group was 12 ml. MPV was an independent predictor for left ventricular end-diastolic (LVEDD) and end-systolic diameter (LVESD) and left atrial volume (all p < 0.001). In patients with large prolapsing volumes (> 15 ml), LVEDD (56 ± 6 mm vs 51 ± 6 mm, p < 0.001), LVESD [38 mm (34–41) vs 34 mm (31–39), p < 0.01] and left atrial volume [105 ml (86–159) vs 101 ml (66–123), p = 0.04] were significantly increased compared to matched patients with degenerative mitral valve disease and similarly assessed severity of MR.

Conclusion

Due to a volume shift based on the MPV rather than an actual regurgitant jet, MR severity cannot be assessed adequately in MAD patients. Increased MPV induces ventricular and atrial enlargement. These findings warrant future studies to focus on MPV as an additional parameter for assessment of the severity of MR in MAD patients.

Supplementary Information

The online version of this article (10.1007/s12471-021-01575-6) contains supplementary material, which is available to authorized users.

Fluid-structure interaction in a fully coupled three-dimensional mitral-atrium-pulmonary model

This paper aims to investigate detailed mechanical interactions between the pulmonary haemodynamics and left heart function in pathophysiological situations (e.g. atrial fibrillation and acute mitral regurgitation). This is achieved by developing a complex computational framework for a coupled pulmonary circulation, left atrium and mitral valve model. The left atrium and mitral valve are modelled with physiologically realistic three-dimensional geometries, fibre-reinforced hyperelastic materials and fluid–structure interaction, and the pulmonary vessels are modelled as one-dimensional network ended with structured trees, with specified vessel geometries and wall material properties. This new coupled model reveals some interesting results which could be of diagnostic values. For example, the wave propagation through the pulmonary vasculature can lead to different arrival times for the second systolic flow wave (S2 wave) among the pulmonary veins, forming vortex rings inside the left atrium. In the case of acute mitral regurgitation, the left atrium experiences an increased energy dissipation and pressure elevation. The pulmonary veins can experience increased wave intensities, reversal flow during systole and increased early-diastolic flow wave (D wave), which in turn causes an additional flow wave across the mitral valve (L wave), as well as a reversal flow at the left atrial appendage orifice. In the case of atrial fibrillation, we show that the loss of active contraction is associated with a slower flow inside the left atrial appendage and disappearances of the late-diastole atrial reversal wave (AR wave) and the first systolic wave (S1 wave) in pulmonary veins. The haemodynamic changes along the pulmonary vessel trees on different scales from microscopic vessels to the main pulmonary artery can all be captured in this model. The work promises a potential in quantifying disease progression and medical treatments of various pulmonary diseases such as the pulmonary hypertension due to a left heart dysfunction.

The Prognostic Value of Left Atrial Global Longitudinal Strain and Left Atrial Phasic Volumes in Patients Undergoing Transcatheter Valve Implantation for Severe Aortic Stenosis

INTRODUCTION

The changes and the prognostic implications of left atrial (LA) volumes (LAV), LA function, and vascular load in patients undergoing transcatheter aortic valve implantation (TAVI) for severe aortic stenosis (AS) are less known.

METHODS

We enrolled 150 symptomatic patients (mean age 82 ± 8 years, 58% female, and pre-TAVI aortic valve area 0.40 ± 0.19 cm/m2) with severe AS who underwent 2D transthoracic echocardiography and 2D speckle tracking echocardiography at average 21 ± 35 days before and 171 ± 217 days after TAVI. The end point was a composite of new onset of atrial fibrillation, hospitalization for heart failure and all-cause death (major adverse cardiac events [MACE]).

RESULTS

After TAVI, indexed maximal LA volume and minimum volume of the LA decreased by 2.1 ± 10 mL/m2 and 1.6 ± 7 mL/m2 (p = 0.032 and p = 0.011, respectively), LA function index increased by 6.8 ± 11 units (p < 0.001), and LA stiffness decreased by 0.38 ± 2.0 (p = 0.05). No other changes in the LA phasic volumes, emptying fractions, and vascular load were noted. Post-TAVI, both left atrial and ventricular global peak longitudinal strain improved by about 6% (p = 0.01 and 0.02, respectively). MACE was reached by 37 (25%) patients after a median follow-up period of 172 days (interquartile range, 20-727). In multivariable models, MACE was associated with both pre- and post-TAVI LA global peak longitudinal strain (hazard ratio [HR] 0.75, CI 0.59-0.97; and HR 0.77, CI 0.60-1.00, per 5 percentage point units, respectively), pre-TAVI LV global endocardial longitudinal strain (HR 1.37, CI 1.02-1.83 per 5 percentage point units), and with most of the LA phasic volumes.

CONCLUSION

Within 6 months after TAVI, there is reverse LA remodeling and an improvement in LA reservoir function. Pre- and post-TAVI indices of LA function and volume remain independently associated with MACE. Larger studies enrolling a greater diversity of patients may provide sufficient evidence for the utilization of these imaging biomarkers in clinical practice.

Hemodynamic function of the right ventricular-pulmonary vascular-left atrial unit: normal responses to exercise in healthy adults

With each heartbeat, the right ventricle (RV) inputs blood into the pulmonary vascular (PV) compartment, which conducts blood through the lungs at low pressure and concurrently fills the left atrium (LA) for output to the systemic circulation. This overall hemodynamic function of the integrated RV-PV-LA unit is determined by complex interactions between the components that vary over the cardiac cycle but are often assessed in terms of mean pressure and flow. Exercise challenges these hemodynamic interactions as cardiac filling increases, stroke volume augments, and cycle length decreases, with PV pressures ultimately increasing in association with cardiac output. Recent cardiopulmonary exercise hemodynamic studies have enriched the available data from healthy adults, yielded insight into the underlying mechanisms that modify the PV pressure-flow relationship, and better delineated the normal limits of healthy responses to exercise. This review will examine hemodynamic function of the RV-PV-LA unit using the two-element Windkessel model for the pulmonary circulation. It will focus on acute PV and LA responses that accommodate increased RV output during exercise, including PV recruitment and distension and LA reservoir expansion, and the integrated mean pressure-flow response to exercise in healthy adults. Finally, it will consider how these responses may be impacted by age-related remodeling and modified by sex-related cardiopulmonary differences. Studying the determinants and recognizing the normal limits of PV pressure-flow relations during exercise will improve our understanding of cardiopulmonary mechanisms that facilitate or limit exercise.

Prevalence of pulmonary hypertension in adults after atrial switch and role of ventricular filling pressures

OBJECTIVE

To assess the prevalence of elevated systemic right ventricular (sRV) end-diastolic pressure and pulmonary arterial hypertension in adults with transposition of the great arteries (TGA) who have undergone atrial switch operation.

METHODS

Forty-two adults (aged ≥18 years) with complete TGA and atrial switch palliation undergoing cardiac catheterisation between 2004 and 2018 at Mayo Clinic, MN, were identified. Clinical, echocardiographic and invasive haemodynamic data were abstracted from the medical charts and procedure logs.

RESULTS

Mean age was 37.6±7.9 years; 28 were male (67%). The Mustard operation was performed in 91% of individuals. Mean estimated sRV ejection fraction by echocardiography was 33.3%±10.9% and ≥moderate tricuspid (systemic atrioventricular valve) regurgitation was present in 15 patients (36%). Mean sRV end-diastolic pressure was 13.2±5.4 mm Hg. An sRV end-diastolic pressure >15 mm Hg was present in 35% of individuals whereas a pulmonary artery wedge pressure (PAWP) >15 mm Hg was seen in 59%. Mean pulmonary artery pressure ≥25 mm Hg was seen in 47.5% of patients with PAWP being >15 mm Hg in all but one patient.

CONCLUSION

In adults after atrial switch, elevated sRV end-diastolic pressure was present in only one-third of patients whereas increased PAWP was seen in almost 60%. These findings are most likely related to a combination of decreased pulmonary atrial (functional left atrium) compliance and, in a subset of patients, pulmonary venous baffle obstruction. Elevation in pulmonary pressures was highly prevalent with concomitant elevation in PAWP being present in essentially all patients.

Measurement, Analysis and Interpretation of Pressure/Flow Waves in Blood Vessels

The optimal performance of the cardiovascular system, as well as the break-down of this performance with disease, both involve complex biomechanical interactions between the heart, conduit vascular networks and microvascular beds. ‘Wave analysis’ refers to a group of techniques that provide valuable insight into these interactions by scrutinizing the shape of blood pressure and flow/velocity waveforms. The aim of this review paper is to provide a comprehensive introduction to wave analysis, with a focus on key concepts and practical application rather than mathematical derivations. We begin with an overview of invasive and non-invasive measurement techniques that can be used to obtain the signals required for wave analysis. We then review the most widely used wave analysis techniques—pulse wave analysis, wave separation and wave intensity analysis—and associated methods for estimating local wave speed or characteristic impedance that are required for decomposing waveforms into forward and backward wave components. This is followed by a discussion of the biomechanical phenomena that generate waves and the processes that modulate wave amplitude, both of which are critical for interpreting measured wave patterns. Finally, we provide a brief update on several emerging techniques/concepts in the wave analysis field, namely wave potential and the reservoir-excess pressure approach.

Contemporary usefulness of pulmonary venous flow parameters to estimate left ventricular end-diastolic pressure on transthoracic echocardiography

Measurement of pulmonary venous flow (PVF) parameters can be used to estimate left ventricular end-diastolic pressure (LVEDP) on transthoracic echocardiography. Despite that, 2016 American Society of Echocardiography (ASE)/European Association of Cardiovascular Imaging (EACVI) algorithm gave a secondary role to PVF to assess left ventricular filling pressure. We aimed to test correlations between several PVF parameters, including novel measurements, with LVEDP and to analyze whether PVF parameters have an incremental usefulness over ASE/EACVI algorithm to estimate LVEDP. Seventy-two patients that underwent left and right cardiac catheterization for assessment of heart failure or pulmonary hypertension were enrolled. All patients had a detailed echocardiographic study immediately before catheterization. Patients were categorized into those with an LVEDP < 15 mmHg vs. LVEDP ≥ 15 mmHg to analyze data. Patients with an elevated LVEDP had significantly lower peak S/D velocity ratio, S wave deceleration time, D wave acceleration time and D wave deceleration time (DWDT), as well as higher D wave acceleration rate (DWAR), but only peak S/D velocity ratio (β = - 0.28, p = 0.01), DWDT (β = - 0.33, p = 0.001) and DWAR (β = 0.23, p = 0.03) were independent predictors for an elevated LVEDP. ASE/EACVI algorithm had a sensitivity of 71% and specificity of 74% to predict an elevated LVEDP. When PVF parameters were adjusted for ASE/EACVI algorithm; DWDT and DWAR remained as independent predictors. Sensitivity and specificity of ASE/EACVI algorithm increased to 79% and 96%, respectively, if either DWDT or DWAR was also suggestive of an elevated LVEDP. DWDT and DWAR have incremental usefulness over existing algorithm to determine LVEDP.

Increased pulmonary blood volume variation in patients with heart failure compared to healthy controls: a noninvasive, quantitative measure of heart failure

Variation of the blood content of the pulmonary vascular bed during a heartbeat can be quantified by pulmonary blood volume variation (PBVV) using magnetic resonance imaging (MRI). The aim was to evaluate whether PBVV differs in patients with heart failure compared with healthy controls and investigate the mechanisms behind the PBVV. Forty-six patients and 10 controls underwent MRI. PBVV was calculated from blood flow measurements in the main pulmonary artery and a pulmonary vein, defined as the maximum difference in cumulative PBV over one heartbeat. PBVV was indexed to stroke volume (SV) in the main pulmonary artery (PBVV_SV). Patients displayed higher PBVV_SV than controls (58 ± 14 vs. 43 ± 7%, P < 0.001). The change in PBVV_SV could be explained by left ventricular (LV) longitudinal contribution to SV (R² = 0.15, P = 0.02) and the phase shift between in- and outflow (R² = 0.31, P < 0.001) in patients. Both variables contributed to the multiple regression analysis model and predicted PBVV_SV (R² = 0.38); however, the phase shift alone explained ~30% of the variation in PBVV_SV. No correlation was found between PBVV_SV and large vessel area. In conclusion, PBVV_SV was higher in patients compared with controls. Approximately 40% of the variation of PBVV_SV in patients can be explained by the LV longitudinal contribution to SV and the phase shift between pulmonary in- and outflow, where the phase shift alone accounts for ~30%. The remaining variation (60-70%) most likely occurs on a small vessel level. Future studies are needed to show the clinical added value of PBVV_SV compared with right-heart catheterization.NEW & NOTEWORTHY This study shows that the pulmonary blood volume variation indexed to the stroke volume is higher in patients with heart failure compared with controls. The mechanisms behind this are lack of systolic suction from the left ventricular atrioventricular plane descent and increased phase shift between the in- and outflow to the pulmonary circulation (~40%), where the phase shift alone accounts for ~30%. The remaining variation (60-70%) is suggested to occur on a small vessel level.

The natural matching of harmonic responses in the pulmonary circulation

Key points

The right ventricle of the mammal heart is highly sensitive to the afterload imposed by a combination of the pulmonary circulation and the retrograde contribution of the left heart.

Right ventricular afterload can be analysed in terms of pulmonary artery input impedance, which we were able to decompose as the result of the harmonic frequency responses of the pulmonary vessels and the left heart attached in series.

Using spectral methods, we found a natural matching between the pulmonary vasculature and the left chambers of the heart. This coupling implies that the upstream transmission of the left heart frequency‐response has favourable effects on the pulmonary tree.

This physiological mechanism protects the right ventricle against acute changes in preload, and its impairment may be a relevant contribution to right ventricle dysfunction in pulmonary hypertension.

Abstract

The right ventricle (RV) of the mammal heart is highly sensitive to the afterload imposed by the pulmonary circulation, and the left heart (LH) retrogradely contributes significantly to this vascular load. Transmission‐line theory anticipates that the degree of matching between the frequency responses of the pulmonary vasculature and the LH should modulate the global right haemodynamic burden. We measured simultaneous high‐fidelity flow (pulmonary artery) and pressure (pulmonary artery and left atrium) in 18 healthy minipigs under acute haemodynamic interventions. From these data, we decomposed the impedance spectra of the total right‐circulation system into the impedance of the pulmonary vessels and the harmonic response of the LH. For frequencies above the first harmonic, total impedance was below the pulmonary impedance during all phases (P < 0.001; pooled phases), demonstrating a favourable effect of the LH harmonic response on RV pulsatile load: the LH harmonic response was responsible for a 20% reduction of pulse pulmonary artery pressure (P < 0.001 vs. a theoretical purely‐resistive response) and a 15% increase of pulmonary compliance (P = 0.009). This effect on compliance was highest during acute volume overload. In the normal right circulation, the longitudinal impedance of the pulmonary vasculature is matched to the harmonic response of the LH in a way that efficiently reduces the pulmonary pulsatile vascular load. This source of interaction between the right and left circulations of mammals protects the RV against excessive afterload during acute volume transients and its disruption may be an important contributor to pulmonary hypertension.

The right ventricle of the mammal heart is highly sensitive to the afterload imposed by a combination of the pulmonary circulation and the retrograde contribution of the left heart.

Right ventricular afterload can be analysed in terms of pulmonary artery input impedance, which we were able to decompose as the result of the harmonic frequency responses of the pulmonary vessels and the left heart attached in series.

Using spectral methods, we found a natural matching between the pulmonary vasculature and the left chambers of the heart. This coupling implies that the upstream transmission of the left heart frequency‐response has favourable effects on the pulmonary tree.

This physiological mechanism protects the right ventricle against acute changes in preload, and its impairment may be a relevant contribution to right ventricle dysfunction in pulmonary hypertension.

Heart filling exceeds emptying during late ventricular systole in patients with systolic heart failure and healthy subjects - a cardiac MRI study

Background

Total heart volume (THV) within the pericardium is not constant throughout the cardiac cycle and THV would intuitively be lowest at end systole. We have, however, observed a phase shift between ventricular outflow and atrial inflow which causes the minimum THV to occur before end systole. The aims were to explain the mechanism of the late‐systolic net inflow to the heart and determine whether this net inflow is affected by increased cardiac output or systolic heart failure.

Methods and Results

Healthy controls (n = 21) and patients with EF<35% (n = 14) underwent magnetic resonance imaging with flow measurements in vessels to and from the heart, and this was repeated in nine controls during 140 μgram kg⁻¹ min⁻¹ adenosine infusion. Minimum THV occurred 78 ± 6 ms before end of systolic ejection (8 ± 1% of the cardiac cycle) in controls. The late‐systolic net inflow was 12·3 ± 1·1 ml or 6·0 ± 0·5% of total stroke volume (TSV). Cardiac output increased 66 ± 8% during adenosine but late‐systolic net inflow to the heart did not change (P = 0·73). In patients with heart failure, late‐systolic net inflow of the heart′s left side was lower (3·4 ± 0·5%) compared to healthy subjects (5·3 ± 0·6%, P = 0·03).

Conclusions

Heart size increases before end systole due to a late‐systolic net inflow which is unaffected by increased cardiac output. This may be explained by inertia of blood that flows into the atria generated by ventricular systole. The lower late‐systolic net inflow in patients with systolic heart failure may be a measure of decreased ventricular filling due to decreased systolic function, thus linking systolic to diastolic dysfunction.

Relation Between Pulmonary Venous Flow and Left Atrial Pressure During Percutaneous Mitral Valve Repair With the MitraClip

Pulmonary venous (PV) flow may provide valuable information in terms of the severity of mitral regurgitation and left atrial (LA) pressure. We sought to find PV flow determinants of LA pressure during MitraClip procedure. We analyzed 575 PV flows in 290 patients using transesophageal echocardiography before and after MitraClip procedure. We measured peak systolic velocity (Sv), diastolic velocity (Dv), systolic velocity time integral (Svti), diastolic velocity time integral (Dvti), and those systolic to diastolic ratio as PV flow parameters. Systolic PV flow velocity was lower than diastolic PV flow velocity before the procedure, but systolic PV flow velocity markedly increased after the procedure. Peak Sv/Dv ratio and Svti/Dvti ratio after the procedure were significantly higher than those before the procedure (peak Sv/Dv; 1.06 [inter-quartile range (IQR) 0.73 to 1.34] vs 0.32 [IQR 0.03 to 0.55], p <0.001, Svti/Dvti; 1.06 [IQR 0.76 to 1.61] vs 0.26 [IQR 0.02 to 0.51], p <0.001). Peak Sv/Dv ratio and Svti/Dvti ratio were negatively correlated with mean LA pressure and LA pressure V wave, respectively (peak Sv/Dv ratio; r = -0.50 and r = -0.59, Svti/Dvti ratio; r = -0.47 and r = -0.58, p <0.001). In receiver operating characteristics curve assessing the ability of PV flow to predict mean LA pressure ≥20 mm Hg after the successful procedure, the area under the curve of peak Sv/Dv ratio was 0.76 (p <0.001). Peak Sv/Dv ratio <0.98 best predicted LA pressure ≥20 mm Hg with 77% sensitivity and 71% specificity. In conclusion, systolic PV flow velocity immediately increased in response to mitral regurgitation reduction during MitraClip procedure. PV flow velocity, specifically systolic to diastolic ratio, was useful to evaluate invasively determined LA pressure.

Longitudinal left ventricular function is globally depressed within a week of STEMI

Sixty percent of stroke volume (SV) is generated by atrioventricular plane displacement (AVPD) in a healthy left ventricle (LV). The aims were to determine the effect of ST-elevation myocardial infarction (STEMI) on AVPD and contribution of AVPD to SV and to study the relationship between AVPD and infarct size (IS) and location. Patients from CHILL-MI and MITOCARE studies with cardiovascular magnetic resonance within a week of STEMI (n = 177, 59 ± 11 years) and healthy controls (n = 20, 62 ± 11 years) were included. Left ventricular volumes were quantified in short-axis images. AVPD was measured in six locations in long-axis images. Longitudinal contribution to SV was calculated as AVPD multiplied by the short-axis epicardial area. Patients (IS 17 ± 10% of LV) had decreased ejection fraction (48 ± 8%) compared to controls (60 ± 5%, P<0·001). Global AVPD was decreased in patients (11 ± 2 mm versus 15 ± 2 mm in controls, P<0·001) and this held true for both infarcted and remote segments. AVPD contribution to SV was lower in patients (58 ± 9%) than in controls (64 ± 8%) (P<0·001). There was a weak negative correlation between IS and AVPD (r2 =0·06) but no differences in global AVPD linked to infarct location. Decrease in global and regional AVPD occur even in remote myocardium within 1 week of STEMI. Global AVPD decrease is independent of MI location, and MI size has only minor effect. Longitudinal pumping is slightly lower compared to controls but remains to be the main component to SV even after STEMI. These results highlight the difficulty in determining infarct location and size from longitudinal measures of LV function.

Evaluation of left ventricular diastolic function: state of the art after 35 years with Doppler assessment

Left ventricular (LV) diastolic function can be evaluated by echocardiographic indices of LV relaxation/restoring forces, diastolic compliance, and filling pressure. By using a combination of indices, diastolic function can be graded and LV filling pressure estimated with high feasibility and good accuracy. Evaluation of diastolic function is of particular importance in patients with unexplained exertional dyspnea or other symptoms or signs of heart failure which cannot be attributed to impaired LV systolic function and to assess filling pressure in patients with heart failure and reduced LV ejection fraction. Furthermore, grading of diastolic dysfunction can be used for risk assessment in asymptomatic subjects and in patients with heart disease.

The role of Ivabradine in Diastolic Heart Failure with preserved Ejection Fraction. A Doppler-Echocardiographic study

Background:

Ivabradine (IVA) is effective in patients with coronary artery disease (CAD) or systolic heart failure in sinus rhythm. Its action consists in reducing heart rate (HR) and improving the time of left ventricular (LV) diastolic filling. The aim of this study was to evaluate the effects of IVA added to conventional therapy on patients with diastolic heart failure (DHF) and preserved ejection fraction (HFpEF).

Methods:

We evaluated 25 patients with DHF in the New York Heart Association (NYHA) Class II-III and sinus rhythm. In these, IVA per os (5 mg/twice a day) was added to the conventional medical therapy and given for 12 weeks. Immediately before the beginning of IVA therapy and 3 months later, patients underwent echocardiographic evaluation by two-dimensional (2D) ultrasound and tissue Doppler imaging (TDI). The patterns of diastolic mitral inflow and pulmonary venous flow were recorded using 2D echocardiography, while the diastolic phase of mitral flow was recorded by TDI, from the lateral mitral annulus.

Results:

Three months after the addition of IVA to conventional treatment, HR significantly decreased in comparison to the baseline values. On the contrary, the echocardiographic indexes of LV diastolic dysfunction improved.

Conclusions:

These results testify that the addition of IVA to conventional therapy in patients with HFpEF can improve LV diastolic function evaluated by 2D and tissue Doppler-echocardiographic patterns. These Doppler-echocardiographic results match with the clinical improvement of patients evaluated.

Dynamic cycling in atrial size and flow during obstructive apnoea

Objective

Obstructive sleep apnoea (OSA) is strongly associated with cardiovascular disease. However, acute cardiovascular effects of repetitive airway obstruction are poorly understood. While past research used a sustained Mueller manoeuver to simulate OSA we employed a series of gasping efforts to better simulate true obstructive apnoeas. This report describes acute changes in cardiac anatomy and flow related to sudden changes in intrathoracic pressure.

Methods and results

26 healthy, normal weight participants performed 5–6 gasping efforts (target intrathoracic pressure −40 mm Hg) while undergoing Doppler echocardiography. 14 participants had sufficient echocardiographic images to allow comparison of atrial areas during the manoeuver with baseline measurements. Mitral and tricuspid E-wave and A-wave velocities postmanoeuver were compared with baseline in all participants. Average atrial areas changed little during the manoeuver, but variance in both atrial areas was significantly greater than baseline. Further, an inverse relationship was noted with left atrial collapse and right atrial enlargement at onset of inspiratory effort. Significant inverse changes were noted in Doppler flow when comparing the first beat postmanoeuver (pMM1) with baseline. Mitral E-wave velocity increased 9.1 cm/s while tricuspid E-wave velocity decreased 7.0 cm/s; by the eighth beat postmanoeuver (pMM8) values were not different from baseline. Mitral and tricuspid A-wave velocities were not different from baseline at pMM1, but both were significantly higher by pMM8.

Conclusions

Repetitive obstructive apnoeas produce dynamic, inverse changes in atrial size and Doppler flow across the atrioventricular valves. These observations have important implications for understanding the pathophysiology of OSA.

Effect of viscosity on the wave propagation: Experimental determination of compression and expansion pulse wave velocity in fluid-fill elastic tube

The velocity by which the disturbance travels through the medium is the wave velocity. Pulse wave velocity is one of the main parameters in hemodynamics. The study of wave propagation through the fluid-fill elastic tube is of great importance for the proper biophysical understanding of the nature of blood flow through of cardiovascular system. The effect of viscosity on the pulse wave velocity is generally ignored. In this paper we present the results of experimental measurements of pulse wave velocity (PWV) of compression and expansion waves in elastic tube. The solutions with different density and viscosity were used in the experiment. Biophysical model of the circulatory flow is designed to perform measurements. Experimental results show that the PWV of the expansion waves is higher than the compression waves during the same experimental conditions. It was found that the change in viscosity causes a change of PWV for both waves. We found a relationship between PWV, fluid density and viscosity.