Characterization of regional diastolic pressure gradients in the right ventricle

Peak Oxygen Consumption (V̇O 2peak ) Recovery Delay in a Pediatric Fontan Population

PURPOSE

The purpose of this study is to identify predictors and correlates of VO2RD in youth with Fontan.

METHODS

Cardiopulmonary exercise test data was used from a single center, cross-sectional study of children and adolescents (age, 8-21 yr) with Fontan physiology. The VO2RD was determined using time (s) to <90% of V̇O 2peak and categorized as "low" (≤10 s) or "high" (≥10 s). t Tests and χ 2 analysis were used to compare continuous and categorical variables, respectively.

RESULTS

The analysis sample included 30 adolescents with Fontan physiology (age, 14.2 ± 2.4 yr; 67% male) with either right ventricular (RV) dominant (40%) or co/left ventricular (Co/LV) dominant (60%) systemic ventricular morphology. There were no differences in V̇O 2peak between the high and low VO2RD groups (high = 1.3 ± 0.4 L·min -1 ; low = 1.3 ± 0.3 L·min -1 ; P = 0.97). VO2RD in participants with RV dominance was significantly greater than in patients with Co/LV dominance (RV = 23.8 ± 15.8 s; Co/LV = 11.8 ± 16.1 s; P = 0.03).

CONCLUSIONS

V̇O 2peak was not correlated with VO2RD when analyzed as high/low VO2RD groups. However, morphology of the systemic single ventricle (RV vs Co/LV) may be related to rate of recovery in V̇O 2 after a peak cardiopulmonary exercise test.

Non-invasive left ventricular pressure-volume loops from cardiovascular magnetic resonance imaging and brachial blood pressure: validation using pressure catheter measurements

Aims

Left ventricular (LV) pressure-volume (PV) loops provide gold-standard physiological information but require invasive measurements of ventricular intracavity pressure, limiting clinical and research applications. A non-invasive method for the computation of PV loops from magnetic resonance imaging and brachial cuff blood pressure has recently been proposed. Here we evaluated the fidelity of the non-invasive PV algorithm against invasive LV pressures in humans.

Methods and results

Four heart failure patients with EF < 35% and LV dyssynchrony underwent cardiovascular magnetic resonance (CMR) imaging and subsequent LV catheterization with sequential administration of two different intravenous metabolic substrate infusions (insulin/dextrose and lipid emulsion), producing eight datasets at different haemodynamic states. Pressure-volume loops were computed from CMR volumes combined with (i) a time-varying elastance function scaled to brachial blood pressure and temporally stretched to match volume data, or (ii) invasive pressures averaged from 19 to 30 sampled beats. Method comparison was conducted using linear regression and Bland-Altman analysis. Non-invasively derived PV loop parameters demonstrated high correlation and low bias when compared to invasive data for stroke work (R2 = 0.96, P < 0.0001, bias 4.6%), potential energy (R2 = 0.83, P = 0.001, bias 1.5%), end-systolic pressure-volume relationship (R2 = 0.89, P = 0.0004, bias 5.8%), ventricular efficiency (R2 = 0.98, P < 0.0001, bias 0.8%), arterial elastance (R2 = 0.88, P = 0.0006, bias -8.0%), mean external power (R2 = 0.92, P = 0.0002, bias 4.4%), and energy per ejected volume (R2 = 0.89, P = 0.0001, bias 3.7%). Variations in estimated end-diastolic pressure did not significantly affect results (P > 0.05 for all). Intraobserver analysis after one year demonstrated 0.9-3.4% bias for LV volumetry and 0.2-5.4% for PV loop-derived parameters.

Conclusion

Pressure-volume loops can be precisely and accurately computed from CMR imaging and brachial cuff blood pressure in humans.

Left and right ventricular hemodynamic forces in healthy volunteers and elite athletes assessed with 4D flow magnetic resonance imaging

Intracardiac blood flow is driven by hemodynamic forces that are exchanged between the blood and myocardium. Previous studies have been limited to 2D measurements or investigated only left ventricular (LV) forces. Right ventricular (RV) forces and their mechanistic contribution to asymmetric redirection of flow in the RV have not been measured. We therefore aimed to quantify 3D hemodynamic forces in both ventricles in a cohort of healthy subjects, using magnetic resonance imaging 4D flow measurements. Twenty five controls, 14 elite endurance athletes, and 2 patients with LV dyssynchrony were included. 4D flow data were used as input for the Navier-Stokes equations to compute hemodynamic forces over the entire cardiac cycle. Hemodynamic forces were found in a qualitatively consistent pattern in all healthy subjects, with variations in amplitude. LV forces were mainly aligned along the apical-basal longitudinal axis, with an additional component aimed toward the aortic valve during systole. Conversely, RV forces were found in both longitudinal and short-axis planes, with a systolic force component driving a slingshot-like acceleration that explains the mechanism behind the redirection of blood flow toward the pulmonary valve. No differences were found between controls and athletes when indexing forces to ventricular volumes, indicating that cardiac force expenditures are tuned to accelerate blood similarly in small and large hearts. Patients’ forces differed from controls in both timing and amplitude. Normal cardiac pumping is associated with specific force patterns for both ventricles, and deviation from these forces may be a sensitive marker of ventricular dysfunction. Reference values are provided for future studies.

NEW & NOTEWORTHY Biventricular hemodynamic forces were quantified for the first time in healthy controls and elite athletes (n = 39). Hemodynamic forces constitute a slingshot-like mechanism in the right ventricle, redirecting blood flow toward the pulmonary circulation. Force patterns were similar between healthy subjects and athletes, indicating potential utility as a cardiac function biomarker.

Estimation of maximum intraventricular pressure: a three-dimensional fluid-structure interaction model

Background

The aim of this study was to propose a method to estimate the maximum pressure in the left ventricle (MPLV) for a healthy subject, based on cardiac outputs measured by echo-Doppler (non-invasive) and catheterization (invasive) techniques at rest and during exercise.

Methods

Blood flow through aortic valve was measured by Doppler flow echocardiography. Aortic valve geometry was calculated by echocardiographic imaging. A Fluid–structure Interaction (FSI) simulation was performed, using an Arbitrary Lagrangian–Eulerian (ALE) mesh. Boundary conditions were defined as pressure loads on ventricular and aortic sides during ejection phase. The FSI simulation was used to determine a numerical relationship between the cardiac output to aortic diastolic and left ventricular pressures. This relationship enabled the prediction of pressure loads from cardiac outputs measured by invasive and non-invasive clinical methods.

Results

Ventricular systolic pressure peak was calculated from cardiac output of Doppler, Fick oximetric and Thermodilution methods leading to a 22%, 18% and 24% increment throughout exercise, respectively. The mean gradients obtained from curves of ventricular systolic pressure based on Doppler, Fick oximetric and Thermodilution methods were 0.48, 0.41 and 0.56 mmHg/heart rate, respectively. Predicted Fick-MPLV differed by 4.7%, Thermodilution-MPLV by 30% and Doppler-MPLV by 12%, when compared to clinical reports.

Conclusions

Preliminary results from one subject show results that are in the range of literature values. The method needs to be validated by further testing, including independent measurements of intraventricular pressure. Since flow depends on the pressure loads, measuring more accurate intraventricular pressures helps to understand the cardiac flow dynamics for better clinical diagnosis. Furthermore, the method is non-invasive, safe, cheap and more practical. As clinical Fick-measured values have been known to be more accurate, our Fick-based prediction could be the most applicable.

Delayed improvement of right ventricular diastolic function and regression of right ventricular mass after percutaneous pulmonary valve implantation in patients with congenital heart disease

BACKGROUND

Percutaneous pulmonary valve implantation (PPVI) has been introduced as therapy for right ventricular (RV) to pulmonary artery conduit dysfunction in patients with congenital heart disease. It has been shown that RV systolic function improved early after PPVI. The effects of PPVI on RV diastolic function and RV hypertrophy have not yet been studied.

PURPOSE

The objective of this study is to assess early and late changes in systolic and diastolic RV function and RV mass after PPVI.

MATERIALS AND METHODS

Fourteen patients underwent PPVI (7 male, median age 15 years). Cardiac magnetic resonance imaging was performed before and at 2 time points after PPVI (at 1 and 16 months). Right ventricular volume and systolic and diastolic function as well as RV mass were assessed.

RESULTS

At 1 and 16 months after PPVI, the RV mass decreased from 28.6 +/- 2.1 to 25.6 +/- 2.2 g/m(2) (P = .03) and to 22.3 +/- 2.1 g/m(2) (P = .002). E/A volume ratio increased from 1.91 +/- 0.4 to 2.6 +/- 0.4 (not significant [NS]) and to 3.3 +/- 0.4 (P = .01). E/A peak flow ratio increased from 1.34 +/- 0.14 to 1.48 +/- 0.16 (NS) and to 1.73 +/- 0.14 (P = .04). E-wave deceleration time increased from 142 +/- 25 to 160 +/- 27 milliseconds (NS) and to 211 +/- 26 milliseconds (P = .007). At 1 month, RV end-diastolic volume decreased from 124 +/- 8 to 113 +/- 8 mL (P = .01) and RV ejection fraction increased from 36% +/- 2% to 46% +/- 2% (P = .001) without further improvement at 16 months.

CONCLUSION

After PPVI, in contrast to rapid improvement of RV systolic function, the improvement of RV diastolic function is delayed. The reduction of RV mass appears to be the underlying mechanism for improvement of RV diastolic function. Long follow-up for patients with PPVI is recommended.

RV instantaneous intraventricular diastolic pressure and velocity distributions in normal and volume overload awake dog disease models

Intraventricular diastolic right ventricular (RV) flow field dynamics were studied by functional imaging using three-dimensional (3D) real-time echocardiography with sonomicrometry and computational fluid dynamics in seven awake dogs at control with normal wall motion (NWM) and RV volume overload with diastolic paradoxical septal motion. Burgeoning flow cross section between inflow anulus and chamber walls induces a convective pressure rise, which represents a "convective deceleration load" (CDL). High spatiotemporal resolution dynamic pressure and velocity distributions of the intraventricular RV flow field revealed time-dependent, subtle interactions between intraventricular local acceleration and convective pressure gradients. During the E-wave upstroke, the total pressure gradient along intraventricular flow is the algebraic sum of a pressure decrease contributed by local acceleration and a pressure rise contributed by a convective deceleration that partially counterbalances the local acceleration gradient. This underlies the smallness of early diastolic intraventricular gradients. At peak volumetric inflow, local acceleration vanishes and the total adverse intraventricular gradient is convective. During the E-wave downstroke, the strongly adverse gradient embodies the streamwise pressure augmentations from both local and convective decelerations. It induces flow separation and large-scale vortical motions, stronger in NWM. Their dynamic corollaries on intraventricular pressure and velocity distributions were ascertained. In the NWM pattern, the strong ring-like vortex surrounding the central core encroaches on the area available for flow toward the apex. This results in higher linear velocities later in the downstroke of the E wave than at peak inflow rate. The augmentation of CDL by ventriculoannular disproportion may contribute to E wave and E-to-A ratio depression with chamber dilatation.

Influence of ventricular morphology on aerobic exercise capacity in patients after the Fontan operation

OBJECTIVES

This study investigated the influences of ventricular morphology, hemodynamics and clinical findings on exercise capacity in patients after the Fontan operation.

BACKGROUND

Determinants of exercise capacity after the Fontan operation remain unclear.

METHODS

Peak oxygen uptake (PVo2) was determined in 105 patients by exercise test and compared to hemodynamics and clinical findings. Patients were divided into three groups based on ventricular morphology: those with a right ventricle (group RV), a biventricle (group BV) and a left ventricle (group LV).

RESULTS

Ten patients with atrioventricular valve regurgitation (AVVR) or hypoxia exhibited a low PVo2. After excluding these patients, although PVo2 did not correlate with hemodynamics, except ventricular ejection fraction (p < 0.02), it correlated with age at the Fontan operation and exercise test (p < 0.002). The PVo2 was higher in group LV (63+/-9%) than in groups RV (55+/-9%) and BV (55+/-12%) (p < 0.01), while an inverse correlation between PVo2 and age at operation was demonstrated only in group RV (p < 0.05). Groups RV or BV and age at exercise test were associated with a lower PVo2, whereas group LV was an independent predictor of a higher PVo2 (p < 0.01). During 4.2 years of follow-up, a decrease in peak heart rate was related to a decrease in PVo2 (p < 0.05). The PVo2 decreased in group RV (p < 0.01).

CONCLUSIONS

In addition to AVVR, hypoxia, and heart rate response, ventricular morphology is related to exercise capacity. Early Fontan operation may be beneficial in terms of exercise capacity, especially in the group RV patients.

Spatio-temporal mapping of intracardiac pressure gradients. A solution to Euler's equation from digital postprocessing of color Doppler M-mode echocardiograms

Doppler assessment of intracardiac pressure gradients using the simplified Bernoulli equation is inaccurate in the absence of a restricted orifice. The purpose of this study is to develop a new general method to map instantaneous pressure gradients inside the heart using Doppler echocardiography. Color Doppler M-mode recordings are digitally postprocessed with a software algorithm that decodes flow velocity and fits a bivariate spatio-temporal tensor-product smoothing spline. Temporal and spatial accelerations are then calculated by analytical derivation of the fitted velocity data, allowing solution of both inertial and convective terms of Euler's equation. A database of 39 transmitral inflow and transaortic outflow color Doppler M-mode recordings from 20 patients with a number of cardiac conditions was analysed, along with matched pulsed-wave spectral recordings. A close agreement was observed between the spectral and postprocessed color Doppler velocity values (error = 0.8 +/- 11.7 cm/s), validating the data decoding and fitting process. Spatio-temporal pressure-gradient maps were obtained from all studies, allowing visualisation of instantaneous pressure gradients from the atrium to the apex during left ventricular filling, and from the apex to the outflow tract during ejection. Instantaneous pressure differences between localised intracardiac sample points closely matched previously published catheterization findings, both in magnitude and waveform shape. Our method shows that intracardiac instantaneous pressure gradients can be analysed noninvasively using color Doppler M-mode echocardiography combined with image postprocessing methods.

Importance of left ventricular function and systolic ventricular interaction to right ventricular performance during acute right heart ischemia

To determine whether modulation of systolic ventricular interaction influences right ventricular performance during right heart ischemia, the effects of septal ischemia and inotropic stimulation were studied in 15 dogs in an open chest preparation. Right coronary branch occlusions led to right ventricular dilation and free wall dyskinesia, reversed septal curvature and reduced left ventricular diastolic volume. In systole, the septum thickened but bulged paradoxically into the right ventricle generating an active but depressed right ventricular systolic pressure (28.9 +/- 5.5 to 22.1 +/- 4.5 mm Hg), with associated decreases in right ventricular stroke work (5.66 +/- 0.94 to 1.92 +/- 0.53 g.m/m2) and left ventricular systolic pressure (123 +/- 11 to 80 +/- 10 mm Hg). Septal ischemia induced systolic septal thinning, left ventricular dilation and decreased left ventricular systolic pressure (80 +/- 10 to 55 +/- 10 mm Hg) and stroke work. Although the extent of paradoxic septal displacement increased, there were further decrements in right ventricular systolic pressure (22.1 +/- 4.5 to 18.7 +/- 4.3 mm Hg) and stroke work (1.92 +/- 0.53 to 0.7 +/- 0.2 g.m/m2). Dopamine infusion augmented left ventricular free wall contraction and increased left ventricular systolic pressure (55 +/- 10 to 172 +/- 17 mm Hg) and stroke work. Although systolic septal thinning persisted, the extent of paradoxic septal displacement increased strikingly and, despite continued right ventricular free wall dyskinesia, right ventricular systolic pressure increased (18.7 +/- 4.3 to 39.6 +/- 6.2 mm Hg) as did right ventricular stroke work (0.7 +/- 0.2 to 7 +/- 1.6 g.m/m2).(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term assessment of right ventricular diastolic filling in patients with pulmonic valve stenosis successfully treated in childhood

Patients with severe pulmonic stenosis (PS) have right ventricular (RV) diastolic filling abnormalities detectable by tricuspid valve pulsed Doppler examination. To determine if these abnormalities persist long term after successful therapy of PS, 19 patients were examined 8 +/- 3 years after PS therapy. At the time of follow-up Doppler examination, the PS gradient was 15 +/- 8 mm Hg. From the tricuspid valve inflow Doppler study, the following measurements were obtained at peak inspiration: peak velocities at rapid filling (peak E) and during atrial contraction (peak A), ratio of peak E to peak A velocities, RV peak filling rate normalized for stroke volume, deceleration time, the fraction of filling in the first 0.33 of diastole as well as under the E and A waves, and the ratio of E to A area. Data from PS follow-up patients were compared with our previously reported data from 12 age-related control subjects and 14 untreated patients with PS. Patients with PS who were followed up had higher peak E velocity (0.75 +/- 0.14 vs 0.59 +/- 0.21 m/s), lower peak A velocity (0.47 +/- 0.09 vs 0.64 +/- 0.28 m/s), higher E/A velocity ratio (1.65 +/- 0.33 vs 1.11 +/- 0.52), higher 0.33 area fraction (0.52 +/- 0.08 vs 0.34 +/- 0.14), lower A area fraction (0.29 +/- 0.06 vs 0.45 +/- 0.21) and higher E/A area ratio (2.48 +/- 0.82 vs 1.73 +/- 1.05) than PS patients without treatment (p less than 0.03). All Doppler indexes of the patients with PS who were followed up were the same as those of the control subjects except for the peak E velocity that was slightly higher (0.75 +/- 0.14 vs 0.63 +/- 0.11 m/s), the peak A velocity that was slightly higher (0.47 +/- 0.09 vs 0.38 +/- 0.09 m/s) and the E/A area ratio that was slightly lower (2.48 +/- 0.82 vs 3.50 +/- 1.25) (p less than 0.03). Thus, at long-term follow-up, all RV diastolic filling indexes in successfully treated patients with PS improved compared with the untreated patients and approached values found in normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)