Compression of interventricular septum during right ventricular pressure loading

Perioperative Right Ventricular Dysfunction and Abnormalities of the Tricuspid Valve Apparatus in Patients Undergoing Cardiac Surgery

Right ventricular (RV) dysfunction frequently occurs after cardiac surgery and is linked to adverse postoperative outcomes, including mortality, reintubation, stroke, and prolonged ICU stays. While various criteria using echocardiography and hemodynamic parameters have been proposed, a consensus remains elusive. Distinctive RV anatomical features include its thin wall, which presents a triangular shape in a lateral view and a crescent shape in a cross-sectional view. Principal causes of RV dysfunction after cardiac surgery encompass ischemic reperfusion injury, prolonged ischemic time, choice of cardioplegia and its administration, cardiopulmonary bypass weaning characteristics, and preoperative risk factors. Post-left ventricular assist device (LVAD) implantation RV dysfunction is common but often transient, with a favorable prognosis upon resolution. There is an ongoing debate regarding the benefits of concomitant surgical repair of the RV in the presence of regurgitation. According to the literature, the gold standard techniques for assessing RV function are cardiac magnetic resonance imaging and hemodynamic assessment using thermodilution. Echocardiography is widely favored for perioperative RV function evaluation due to its accessibility, reproducibility, non-invasiveness, and cost-effectiveness. Although other techniques exist for RV function assessment, they are less common in clinical practice. Clinical management strategies focus on early detection and include intravenous drugs (inotropes and vasodilators), inhalation drugs (pulmonary vasodilators), ventilator strategies, volume management, and mechanical support. Bridging research gaps in this field is crucial to improving clinical outcomes associated with RV dysfunction in the near future.

Systolic reserve maintains left ventricular-vascular coupling when challenged by adverse breathing mechanics and hypertension in healthy adults

Augmented negative intrathoracic pressures (nITP) and dynamic hyperinflation (DH) are adverse breathing mechanics (ABM) associated with chronic obstructive pulmonary disease (COPD) that attenuate left ventricular (LV) preload and augment afterload. In COPD, hypertension (elevated systemic arterial load) commonly adds additional afterload to the LV. Combined ABM and hypertension may profoundly challenge ventricular-vascular coupling and attenuate stroke volume (SV), particularly if LV systolic reserve is limited. However, even in the healthy heart, the combined impact of ABM and systemic arterial loading on LV function and ventricular-vascular coupling has not been fully elucidated. Healthy volunteers (10 M/9 F, 24 ± 3 yr old) were challenged with mild (-10 cmH₂O nITP and 25% DH) and severe (-20 cmH₂O nITP and 100% DH) ABM, without and with postexercise ischemia (PEI) at each severity. LV SV, chamber geometry, end-systolic elastance (E_es), arterial elastance (E_a), and ventricular-vascular coupling (E_es:E_a) were quantified using echocardiography. Compared with resting control (58 ± 13 mL), SV decreased during mild ABM (51 ± 13 mL), mild ABM + PEI (51 ± 11 mL), severe ABM (50 ± 12 mL), and severe ABM + PEI (47 ± 11 mL) (P < 0.001); similar trends were observed for LV end-diastolic volume. The end-diastolic radius of septal curvature increased, indicating direct ventricular interaction, during severe ABM and severe ABM + PEI (P < 0.001). Compared with control (1.99 ± 0.41 mmHg/mL), E_a increased progressively with mild ABM (2.21 ± 0.47 mmHg/mL) and severe ABM (2.50 ± 0.56 mmHg/mL); at each severity, E_a was greater with superimposed PEI (P < 0.001). However, well-matched E_es increases occurred, and E_es:E_a was unchanged throughout. ABM pose a challenge to ventricular-vascular coupling that is accentuated by superimposed PEI; however, in healthy younger adults, the LV has substantial systolic reserve to maintain coupling.NEW & NOTEWORTHY In healthy younger adults, combined dynamic hyperinflation (DH) and negative intrathoracic pressures (nITP) attenuate left ventricular filling, but through different mechanisms at different severities. DH and nITP contribute to increased left ventricular afterload through mechanical effects in addition to presumed reflexive regulation, which can be further increased by elevated arterial loading. However, within this demographic, the left ventricle has substantial reserve to increase systolic performance, which matches contractility to afterload to preserve stroke volume.

Three-dimensional biventricular strains in pulmonary arterial hypertension patients using hyperelastic warping

BACKGROUND AND OBJECTIVE

Evaluation of biventricular function is an essential component of clinical management in pulmonary arterial hypertension (PAH). This study aims to examine the utility of biventricular strains derived from a model-to-image registration technique in PAH patients in comparison to age- and gender-matched normal controls.

METHODS

A three-dimensional (3D) model was reconstructed from cine short- and long-axis cardiac magnetic resonance (CMR) images and subsequently partitioned into right ventricle (RV), left ventricle (LV) and septum. The hyperelastic warping method was used to register the meshed biventricular finite element model throughout the cardiac cycle and obtain the corresponding biventricular circumferential, longitudinal and radial strains.

RESULTS

Intra- and inter-observer reproducibility of biventricular strains was excellent with all intra-class correlation coefficients > 0.84. 3D biventricular longitudinal, circumferential and radial strains for RV, LV and septum were significantly decreased in PAH patients compared with controls. Receiver operating characteristic (ROC) analysis showed that the 3D biventricular strains were better early markers (Area under the ROC curve = 0.96 for RV longitudinal strain) of ventricular dysfunction than conventional parameters such as two-dimensional strains and ejection fraction.

CONCLUSIONS

Our highly reproducible methodology holds potential for extending CMR imaging to characterize 3D biventricular strains, eventually leading to deeper understanding of biventricular mechanics in PAH.

Biventricular diastolic dysfunction, thrombocytopenia, and red blood cell macrocytosis in experimental pulmonary arterial hypertension

Pulmonary arterial hypertension is a fatal disease, where death is associated with right heart failure and reduced cardiorespiratory reserve. The Sugen 5416, hypoxia and normoxia Fischer rat model mimics human pulmonary arterial hypertension, although the cause(s) of death remains incompletely understood. Here, we hypothesized that these animals develop biventricular diastolic dysfunction that contributes to tissue hypoperfusion coincident with severe pulmonary arterial hypertension. We performed comprehensive echocardiographic and hematologic assessments. Serial echocardiogram at 3-5 weeks was performed followed by blood sampling via aortic or cardiac puncture. Echocardiogram revealed pulmonary arterial hypertension in pulmonary artery Doppler waves, including notched wave envelopes, and decreased pulmonary artery acceleration time/pulmonary artery ejection time ratio and right ventricular outflow tract velocity time integral. Impaired right ventricular systolic function, assessed by decreased tricuspid annular plane systolic excursion and tricuspid tissue Doppler systolic positive wave velocity, was observed in pulmonary arterial hypertension. Tricuspid and mitral pulsed wave and tissue Doppler findings suggested biventricular diastolic dysfunction, with dynamic changes in early and late diastolic filling waves, their fusion patterns, and a decrease in e' velocity. Heart rate and ejection fraction did not change, but cardiac output, stroke volume, and end-diastolic volume were decreased, and inferior vena cava respiratory variation was decreased. Blood electrolyte values were suggestive of intravascular volume expansion early in the disease followed by volume contraction and tissue hypoperfusion in the latter stages of disease. Complete blood count showed thrombocytopenia and non-anemic macrocytosis with reticulocytosis and an increase in red blood cell distribution width. Thus, pulmonary, cardiac, and hematological findings in Fischer animals with pulmonary arterial hypertension are characteristic of humans and provide an insightful experimental platform to resolve mechanisms of disease progression.

Echocardiographic evaluation of diastolic function in the setting of pulmonary hypertension

Heart failure due to diastolic dysfunction and pulmonary hypertension are frequent comorbid conditions with significant morbidity and mortality. Identifying the presence and etiology of diastolic dysfunction in the setting of pulmonary hypertension remains challenging despite profound therapeutic and prognostic implications. Additionally, there is little guidance in identifying and parsing etiology of diastolic dysfunction in patients found to have pulmonary hypertension. This review discusses the complex interplay between left ventricular diastolic dysfunction and pulmonary hypertension. With an explicit focus on the use of echocardiography for determination of diastolic dysfunction and etiology of pulmonary hypertension, this review also provides a comprehensive review of the literature and provides a framework by which to assess diastolic dysfunction echocardiographically in the setting of pulmonary hypertension.

Ventricular Dysfunction, Interdependence, and Mechanical Dispersion in Newborn Infants with Congenital Diaphragmatic Hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is an important cause of mortality and morbidity in the neonatal period. Pulmonary hypertension and pulmonary hypoplasia are key pathological findings. Cardiac function may also be an important determinant of disease severity, prognostic indicator, and therapeutic target in CDH.

OBJECTIVE

The aim of this study was to assess ventricular mechanics and synchrony in infants with CDH and controls using speckle tracking echocardiography (STE).

METHODS

Retrospective analysis was performed of echocardiograms obtained in the first 48 h of life in 27 infants with CDH and 20 controls. STE-derived longitudinal strain (LS) was measured in the right and left ventricles (RV, LV). Circumferential strain (CS) and radial strain (RS) were additionally measured in the LV. Mechanical dispersion (MD), a measure of synchrony, was assessed by calculation of the standard deviation of time to peak systolic strain in six ventricular segments.

RESULTS

RV LS and LV LS, LV CS, and LV RS were significantly reduced in CDH compared to controls. In the LV free wall, LS and RS were significantly reduced in CDH. LV LS correlated significantly with RV LS in CDH cases (r2 = 0.37, p = 0.002), but not controls (r2 = 0.19, p = 0.06). LV LS also correlated with LV MD in CDH (r2 = 0.25, p = 0.01) but not controls (r2 = 0.02, p = 0.54).

CONCLUSIONS

Global impairment of RV and LV systolic function are present in newborn infants with CDH and are associated with primary left ventricular dysfunction, ventricular interdependence, and MD.

Right Ventricular Fiber Structure as a Compensatory Mechanism in Pressure Overload: A Computational Study

Right ventricular failure (RVF) is a lethal condition in diverse pathologies. Pressure overload is the most common etiology of RVF, but our understanding of the tissue structure remodeling and other biomechanical factors involved in RVF is limited. Some remodeling patterns are interpreted as compensatory mechanisms including myocyte hypertrophy, extracellular fibrosis, and changes in fiber orientation. However, the specific implications of these changes, especially in relation to clinically observable measurements, are difficult to investigate experimentally. In this computational study, we hypothesized that, with other variables constant, fiber orientation alteration provides a quantifiable and distinct compensatory mechanism during RV pressure overload (RVPO). Numerical models were constructed using a rabbit model of chronic pressure overload RVF based on intraventricular pressure measurements, CINE magnetic resonance imaging (MRI), and diffusion tensor MRI (DT-MRI). Biventricular simulations were conducted under normotensive and hypertensive boundary conditions using variations in RV wall thickness, tissue stiffness, and fiber orientation to investigate their effect on RV pump function. Our results show that a longitudinally aligned myocardial fiber orientation contributed to an increase in RV ejection fraction (RVEF). This effect was more pronounced in response to pressure overload. Likewise, models with longitudinally aligned fiber orientation required a lesser contractility for maintaining a target RVEF against elevated pressures. In addition to increased wall thickness and material stiffness (diastolic compensation), systolic mechanisms in the forms of myocardial fiber realignment and changes in contractility are likely involved in the overall compensatory responses to pressure overload.

The assessment of septal wall motion in patients undergoing CABG by myocardial perfusion-gated SPECT

PURPOSE

In this study, we aimed to assess the presence and prevalence of paradoxical septal motion (PSM) by myocardial perfusion-gated single-photon emission computed tomography (SPECT) imaging in patients undergoing coronary artery bypass grafting (CABG).

METHODS

A total of 172 patients (145 men and 27 women, with a mean age of 64.81 ± 8.93 years) undergoing CABG surgery were included in the study. All selected scintigraphic studies of the patients undergoing CABG were reprocessed. Semiquantitative interpretation of septal perfusion, wall motion, and wall thickening was performed with QPS and QGS programs. Phase analysis parameters were also obtained using the Emory Cardiac Toolbox. According to myocardial perfusion-gated SPECT results, the patients were trichotomized as follows: group 1 (nonischemic PSM): regular perfusion and thickening of the septal wall and abnormal motion of the septal wall; group 2 (ischemic PSM): abnormal perfusion, motion, and thickening of the septal wall; group 3 (non-PSM): normal perfusion, motion, and thickening of the septal wall. The data in each of the three groups were compared using Student's t-test and one-way analysis of variance.

RESULTS

No PSM (normal perfusion, motion, and thickening of the septal wall) was observed in 19.2% of patients undergoing CABG, whereas nonischemic PSM (regular perfusion and thickening of the septal wall and abnormal motion of the septal wall) was observed in 60.5% of patients and ischemic PSM (abnormal perfusion, motion and thickening of the septal wall) was seen in 20.3% of patients.

CONCLUSION

According to our study results, PSM is fairly common in patients undergoing CABG. It will be beneficial to use myocardial perfusion scintigraphy-gated SPECT, which is a noninvasive examination method, to identify the presence of PSM and investigate whether it is accompanied by ischemia or infarction.

Pericardial fat is associated with impaired lung function and a restrictive lung pattern in adults: the Jackson Heart Study

BACKGROUND

Impaired lung function has been linked to obesity and systemic inflammation. Pericardial fat has been shown to be associated with anomalies in cardiac structure, function, and atherosclerosis. We hypothesized that pericardial fat may have a similar role in the impairment of lung function.

METHODS

Cross-sectional associations of pericardial fat volumes, quantified by multidetector CT scan, with FEV(1) and FVC assessed by spirometry, were investigated in 1,293 participants (54.5 ± 10.8 years; 66.4% women) in the Jackson Heart Study. We also examined whether these associations were independent of visceral adipose tissue (VAT).

RESULTS

Pericardial fat was associated with impaired lung function after multivariable adjustment, but these associations generally did not remain after adjustment for VAT. An exception was the FEV(1)/FVC ratio. Higher pericardial fat volumes were associated with higher odds of a restrictive lung pattern and lower odds of airway obstruction. Participants in the highest quartile had the highest odds of a restrictive lung pattern (OR, 1.85; 95% CI, 1.22-2.79, compared with quartile 1), even after adjustment for VAT. The odds of obstruction decreased across increasing quartiles of pericardial fat. These relationships were generally graded, suggesting dose-response trends.

CONCLUSIONS

Pericardial fat is generally associated with lower lung function and independently associated with a restrictive lung pattern in middle-aged and elderly adults. Further research is needed to fully understand the mechanisms through which pericardial fat contributes to pulmonary anomalies.

Noninvasive assessment of pulmonary vascular resistance and pressure in patients with congenital heart disease: a new method using M-mode echocardiography

BACKGROUND

The accurate evaluation of pulmonary vascular resistance (PVR) and mean pulmonary artery pressure is important to determine the optimal management and therapeutic strategy for patients with congenital heart disease (CHD). We evaluated the PVR and mean pulmonary artery pressure in 46 patients with several CHD types using the interventricular septum (IVS) motion determined by M-mode echocardiography.

METHODS

We divided the patients into 2 groups according to the different IVS motions. We measured the maximum anterior displacement from the baseline during early systole (a) and the maximum posterior displacement from the baseline during early diastole (b). We defined type A to be a/b greater than or equal to 1.0, and type B to be a/b less than 1.0.

RESULTS

The PVR and mean pulmonary artery pressure in type A patients were significantly higher than those in type B patients (p < 0.05). Type A IVS motion predicted patients with high PVR (>2.5 unit/m(2)) and high mean pulmonary artery pressure (>25 mmHg) (sensitivity 89%, specificity 89% and sensitivity 70%, specificity 91%, respectively).

CONCLUSIONS

Our method can noninvasively separate high and low PVR among patients with CHD. This noninvasive method is therefore considered to be useful in the management of patients with CHD in a clinical setting.

Review of Movahed's sign (D shaped left ventricle seen on gated SPECT) suggestive of right ventricular overload

Recently, D shaped ventricle seen on gated SPECT imaging (Movahed's sign) has shown to correlate with right ventricular overload similar to the D shape ventricle seen on echocardiography. Right ventricle (RV) imaging during gated SPECT studies is challenging because of the low tracer uptake due to relatively smaller right ventricular myocardial mass and lower coronary flow to the RV. Increased mass or workload causes higher tracer uptake in the RV wall secondary to increase in RV wall thickness and higher coronary flow. Furthermore, increased RV volume or pressure load can cause displacement of the septum towards the left ventricle causing septal flattening and a D shaped configuration of the left ventricular septum. This is an important finding that should be a part of nuclear gated SPECT interpretation.

Biventricular function at high altitude: implications for regulation of stroke volume in chronic hypoxia

The myocardium is well protected against chronic hypoxia. In chronic hypoxia stroke volume falls both at rest and on exercise. The fall in stroke volume is associated with reduction in left ventricular dimensions and filling pressure. An obvious explanation for this is the reduction in plasma volume observed at high altitude, but this does not appear to be the whole story. Neither is left ventricular systolic function abnormal even at the summit of Mount Everest. Hypoxia itself may have a direct effect on impairing myocardial relaxation. Increased pulmonary vascular resistance leads to right ventricular pressure overload. This may impair right ventricular function, and reduce stroke volume and venous return to the left atrium. Interaction between the right and left ventricles, which share a common septum and are potentially constrained in volume by the pericardium, may impair diastolic left ventricular filling as a consequence of right ventricular pressure overload, and hence reduce stroke volume. It is questionable how clinically significant is this left ventricular diastolic dysfunction. The relative importance of different mechanisms which reduce stroke volume probably depends whether hemodynamics are measured at rest or on exercise. Intervention with sildenafil to ameliorate hypoxic pulmonary vasoconstriction is associated with both an increase in exercise capacity and stroke volume in hypoxia. Whether these have a causal association remains to be demonstrated.

Cardiac arrest with continuous mechanical chest compression during percutaneous coronary intervention

Mechanical chest compression may be necessary to make coronary intervention possible during resuscitation. We report our experience using the Lund University Cardiac Arrest System (LUCAS, Jolife, Lund, Sweden) which is a gas-driven sternal compression device that incorporates a suction cup for active decompression. During the last 13 months LUCAS has been used in our catheterisation laboratory to maintain adequate organ perfusion pressure in 13 patients with cardiac arrest or severe hypotension and bradycardia (male/female ratio 1.6, mean age 59+/-19). The mean compression time was 105+/-60min (range 45-240), and the mean systolic and diastolic blood pressure obtained was 81+/-23 and 34+/-21mmHg, respectively. Angiography and eventually percutanous coronary intervention was possible in all cases during ongoing automatic chest compression. Three patients survived the procedure, but no patients were discharged alive. In two cases we found inadequate flow in the anterior descending artery, and in one case the invasive measurements revealed inadequate coronary perfusion pressure. There were no excessive intra-thoracic or intra-abdominal injuries. We conclude that the LUCAS device is suitable during cardiac catheterisation and intervention, and the device ensures an adequate systemic blood pressure in most patients without life-threatening injuries.

Cardiac Effects of Pulmonary Disease

Pulmonary hypertension (PHT) is the primary cardiac consequence of pulmonary disease. It develops as alveolar hypoxia of pulmonary disease, coupled with vasoactive and mitogenic substances released from pulmonary endothelial and vascular smooth muscle cells damaged by the primary disease process, mediates arterial vasoconstriction and vascular remodeling to raise pulmonary vascular resistance. Independent of the underlying pulmonary disease, PHT produces clinical signs of respiratory distress, exercise intolerance, syncope, and right heart failure. Diagnosis of PHT is made by estimation of pulmonary artery pressures by means of continuous-wave Doppler echocardiographic assessment of tricuspid or pulmonic regurgitant flow velocity. Treatment of PHT is directed at the underlying pulmonary disease but may also aim to attenuate pulmonary artery pressure and limit the clinical sequelae of PHT. No treatments are of proven benefit in veterinary patients; irrespective of the nature of the inciting pulmonary disease, the prognosis is often grave.

The potential role of the pericardium on diastolic filling in endurance-trained athletes under conditions of physiological stress

In this review, we examine the growing body of evidence suggesting that the pericardium plays an important role in modulating cardiac function during conditions of physiological stress. Specifically, we discuss the effects of the pericardium on left ventricular filling and compliance. Furthermore, we reveal that there is increasing evidence to support the contention that the pericardium is capable of adaptation in response to volume loading. We also provide data that suggests endurance-training is a good example of a physiological stressor capable of causing pericardial remodelling. These adaptations appear particularly beneficial during exercise and may explain (in part) the common finding of stroke volume increasing during exercise to a greater extent in endurance-trained athletes. However, this adaptation may also partially explain the increased susceptibility to orthostatic intolerance in endurance athletes.

Diastolic ventricular interactions in endurance-trained athletes during orthostatic stress

Enhanced left-ventricular (LV) compliance is a common adaptation to endurance training. This adaptation may have differential effects under conditions of altered venous return. The purpose of this investigation was to assess the effect of cardiac (un)loading on right ventricular (RV) cavity dimensions and LV volumes in endurance-trained athletes and normally active males. Eight endurance-trained (Vo(2max), 65.4 +/- 5.7 ml.kg(-1).min(-1)) and eight normally active (Vo(2max), 45.1 +/- 6.0 ml.kg(-1).min(-1)) males underwent assessments of the following: 1) Vo(2max), 2) orthostatic tolerance, and 3) cardiac responses to lower-body positive (0-60 mmHg) and negative (0 to -80 mmHg) pressures with echocardiography. In response to negative pressures, echocardiographic analysis revealed a similar decrease in RV end-diastolic cavity area in both groups (e.g., at -80 mmHg: normals, 21.4%; athletes, 20.8%) but a greater decrease in LV end-diastolic volume in endurance-trained athletes (e.g., at -80 mmHg: normals, 32.3%; athletes, 44.4%; P < 0.05). Endurance-trained athletes also had significantly greater decreases in LV stroke volume during lower-body negative pressure. During positive pressures, endurance-trained athletes showed larger increases in LV end-diastolic volume (e.g., at +60 mmHg; normals, 14.1%; athletes, 26.8%) and LV stroke volume, despite similar responses in RV end-diastolic cavity area (e.g., at +60 mmHg: normals, 18.2%; athletes, 24.2%; P < 0.05). This investigation revealed that in response to cardiac (un)loading similar changes in RV cavity area occur in endurance-trained and normally active individuals despite a differential response in the left ventricle. These differences may be the result of alterations in RV influence on the left ventricle and/or intrinsic ventricular compliance.

Evaluation of right ventricular Tei index (index of myocardial performance) in healthy dogs and dogs with tricuspid regurgitation

Right ventricular (RV) Tei index (index of myocardial performance) has been demonstrated to be clinically useful in estimating RV function in various human cardiac diseases. The purposes of this study were to validate the correlation between RV Tei index and RV function obtained by cardiac catheterization in healthy dogs, and to evaluate the RV Tei index in dogs with tricuspid regurgitation (TR). In healthy dogs, the RV Tei index significantly correlated with the RV peak +dP/dt (r=-0.80, p<0.0001) and -dP/dt (r=0.69, p=0.0001). In normal dogs, the RV Tei index was not significantly correlated with heart rate, body weight, and age. The RV Tei index significantly increased in dogs with moderate to severe TR (0.39 +/- 0.35, p=0.0015), filariasis (0.46 +/- 0.16, p=0.0131), and trivial to mild TR and severe mitral regurgitation (MR; 0.61 +/- 0.14, p=0.0017) when compared with the normal dogs (0.17 +/- 0.10). In addition, the RV Tei index in dogs with TR significantly increased in association with pulmonary hypertension [PH(-), 0.19 +/- 0.09; PH(+), 0.65 +/- 0.14; respectively p<0.0001]. Our study has demonstrated that RV Tei index is a feasible approach to estimate RV function in dogs and is not influenced by heart rate, body weight, and aging. Further investigations are required to clarify the clinical significance of RV Tei index in dogs with right-sided cardiac diseases.

Coupling of a 3D finite element model of cardiac ventricular mechanics to lumped systems models of the systemic and pulmonic circulation

In this study we present a novel, robust method to couple finite element (FE) models of cardiac mechanics to systems models of the circulation (CIRC), independent of cardiac phase. For each time step through a cardiac cycle, left and right ventricular pressures were calculated using ventricular compliances from the FE and CIRC models. These pressures served as boundary conditions in the FE and CIRC models. In succeeding steps, pressures were updated to minimize cavity volume error (FE minus CIRC volume) using Newton iterations. Coupling was achieved when a predefined criterion for the volume error was satisfied. Initial conditions for the multi-scale model were obtained by replacing the FE model with a varying elastance model, which takes into account direct ventricular interactions. Applying the coupling, a novel multi-scale model of the canine cardiovascular system was developed. Global hemodynamics and regional mechanics were calculated for multiple beats in two separate simulations with a left ventricular ischemic region and pulmonary artery constriction, respectively. After the interventions, global hemodynamics changed due to direct and indirect ventricular interactions, in agreement with previously published experimental results. The coupling method allows for simulations of multiple cardiac cycles for normal and pathophysiology, encompassing levels from cell to system.

A 2D FE model of the heart demonstrates the role of the pericardium in ventricular deformation

During pulmonary artery constriction (PAC), an experimental model of acute right ventricular (RV) pressure overload, the interventricular septum flattens and inverts. Finite element (FE) analysis has shown that the septum is subject to axial compression and bending when so deformed. This study examines the effects of acute PAC on the left ventricular (LV) free wall and the role the pericardium may play in these effects. In eight open-chest anesthetized dogs, LV, RV, aortic, and pericardial pressures were recorded under control conditions and with PAC. Model dimensions were derived from two-dimensional echocardiography minor-axis images of the heart. At control (pericardium closed), FE analysis showed that the septum was concave to the LV; stresses in the LV, RV, and septum were low; and the pericardium was subject to circumferential tension. With PAC, RV end-diastolic pressure exceeded LV pressure and the septum inverted. Compressive stresses developed circumferentially in the septum out to the RV insertion points, forming an arch-like pattern. Sharp bending occurred near the insertion points, accompanied by flattening of the LV free wall. With the pericardium open, the deformations and stresses were different. The RV became much larger, especially with PAC. With PAC, the arch-like circumferential stresses still developed in the septum, but their magnitudes were reduced, compared with the pericardium-closed case. There was no free wall inversion and flattening was less. From these FE results, the pericardium has a significant influence on the structural behavior of the septum and the LV and RV free walls. Furthermore, the deformation of the heart is dependent on whether the pericardium is open or closed.

Compression induced by RV pressure overload decreases regional coronary blood flow in anesthetized dogs

Pulmonary artery constriction (PAC), a model of right ventricular (RV) pressure overload, flattens or inverts the septum and may flatten the left ventricular (LV) free wall. Finite element (FE) analysis predicts that such deformations may cause substantial compression. This study tests the hypothesis that deformation-induced myocardial compressive stress impedes coronary blood flow (CBF). Colored microspheres (∼2 × 106) were injected into the left atrium of 13 open-chest, anesthetized dogs under control conditions and during PAC, which decreased the end-diastolic transseptal pressure gradient (LV − RV) from 1.6 ± 1.3 to −3.4 ± 1.7 mmHg. Septal and LV deformation was assessed with the use of two-dimensional echocardiography, and by FE analysis, the hydrostatic component of stress was assessed. Postmortem, a 2.5-cm wide, LV equatorial ring was divided into 16 endocardial and epicardial samples. PAC decreased CBF in the FE-predicted compression zones, areas with the greatest compression having the greatest reductions in CBF. During PAC, compression reached a maximum of 25.3 ± 1.8 mmHg on the (LV) endocardial sides of the RV insertion points, areas that saw CBF decrease from 1.05 ± 0.08 to 0.68 ± 0.05 ml·min−1·g−1 ( P < 0.001), more than 30%. CBF decreased (from 1.08 ± 0.07 to 0.81 ± 0.07 ml·min−1·g−1; P < 0.001) on the RV side of the midseptum, an area with as much as 16.0 ± 1.0 mmHg of compression. Overall, average compressions of 10 mmHg decreased CBF by ∼30%. We conclude that acute RV pressure overload deforms the septum and LV and induces compressive stresses that reduce CBF substantially. This may help explain why some patients with pulmonary hypertension and no critical coronary disease have chest discomfort indistinguishable from angina pectoris.

Finite element modelling and simulations in cardiovascular mechanics and cardiology: A bibliography 1993–2004

The paper gives a bibliographical review of the finite element modelling and simulations in cardiovascular mechanics and cardiology from the theoretical as well as practical points of views. The bibliography lists references to papers, conference proceedings and theses/dissertations that were published between 1993 and 2004. At the end of this paper, more than 890 references are given dealing with subjects as: Cardiovascular soft tissue modelling; material properties; mechanisms of cardiovascular components; blood flow; artificial components; cardiac diseases examination; surgery; and other topics.

Adaptation to mechanical load determines shape and properties of heart and circulation: the CircAdapt model

With circulatory pathology, patient-specific simulation of hemodynamics is required to minimize invasiveness for diagnosis, treatment planning, and followup. We investigated the advantages of a smart combination of often already known hemodynamic principles. The CircAdapt model was designed to simulate beat-to-beat dynamics of the four-chamber heart with systemic and pulmonary circulation while incorporating a realistic relation between pressure-volume load and tissue mechanics and adaptation of tissues to mechanical load. Adaptation was modeled by rules, where a locally sensed signal results in a local action of the tissue. The applied rules were as follows: For blood vessel walls, 1) flow shear stress dilates the wall and 2) tensile stress thickens the wall; for myocardial tissue, 3) strain dilates the wall material, 4) larger maximum sarcomere length increases contractility, and 5) contractility increases wall mass. The circulation was composed of active and passive compliances and inertias. A realistic circulation developed by self-structuring through adaptation provided mean levels of systemic pressure and flow. Ability to simulate a wide variety of patient-specific circumstances was demonstrated by application of the same adaptation rules to the conditions of fetal circulation followed by a switch to the newborn circulation around birth. It was concluded that a few adaptation rules, directed to normalize mechanical load of the tissue, were sufficient to develop and maintain a realistic circulation automatically. Adaptation rules appear to be the key to reduce dramatically the number of input parameters for simulating circulation dynamics. The model may be used to simulate circulation pathology and to predict effects of treatment.

Quantification of the curvature and shape of the interventricular septum

The interventricular septum (IVS) occupies a unique position within the heart, lying between the left (LV) and right (RV) ventricular cavities. Changes in its normal geometry may signify not only abnormalities of the septal myocardium, but also abnormal pressure differences between the LV and RV. Flattening of the IVS has been noted with cross-sectional imaging in association with pulmonary hypertension, but the septal curvature and shape have not previously been measured in three dimensions. This paper describes a method to model the RV surface of the IVS from spatially registered cross-sectional images for measurements of curvature. A smoothing 2D spline surface is constructed through the RV septal surface at regular times during the cardiac cycle, and the principal curvatures, as well as the Gaussian and mean curvatures, shape index, and curvedness, are calculated. Vector and color surface maps and graphs of average curvature and shape indices are constructed. Consistent curvature patterns were observed in four normal subjects. This method of measuring septal geometry can provide potentially useful new information on the effects of RV disease. We examine the problem of describing septal motion, and describe a simple measure of septal curvature that may be of clinical value.

Effects of acute left ventricular unloading on right ventricular function in normal and chronic right ventricular pressure-overloaded lambs

OBJECTIVE

Right ventricular pressure overload occurs in several types of (congenital) heart disease, as well as in pulmonary disease. Clinical outcome in some of these patient groups might in part be related to left ventricular loading conditions. The effects of left ventricular unloading on the function of the hypertrophic right ventricle have not been studied. We aimed to study the effects of left ventricular unloading on right ventricular hemodynamics and contractility in an animal model of chronic right ventricular pressure overload.

METHODS

In lambs the pulmonary artery was chronically banded to increase right ventricular pressure to systemic levels. After 8 weeks, right ventricular contractility and hemodynamic function were assessed in these lambs, as well as in age-matched control animals, by using a combined pressure-conductance catheter in the right ventricle during baseline conditions and during complete bypass of the left ventricle.

RESULTS

In both groups acute left ventricular unloading significantly decreased left ventricular pressure to low levels while aortic pressure was maintained. In the right ventricle of the control group, both end-systolic and end-diastolic volumes increased with left ventricular unloading (P <.01) while end-systolic pressure was maintained. Cardiac output was unchanged despite decreased right ventricular contractility. In the banding group acute left ventricular unloading also decreased right ventricular contractility but increased cardiac output. During acute left ventricular unloading, diastolic stiffness was unchanged in the control group, whereas it was significantly decreased in the banding group.

CONCLUSIONS

Both in normal hearts and in hearts subject to chronic right ventricular pressure overload, acute left ventricular unloading decreases right ventricular contractility. Although no effects on cardiac output are encountered in normal hearts during left ventricular bypass, cardiac output is improved in right ventricular pressure-overloaded hearts, most likely related to improved right ventricular diastolic compliance.