Novel, single-beat approach for determining both end-systolic pressure-dimension relationship and preload recruitable stroke work

The prognostic value of stroke work/end-diastolic volume ratio during stress echocardiography

BACKGROUND

The ventricular stroke work (SW) refers to the work done by the left ventricle to eject the volume of blood during one cardiac cycle. The cath-lab relationship between SW and end-diastolic volume (EDV) is the preload-recruitable SW (PRSW). Recently a non-invasive single-beat PRSW (SBPRSW) has been proposed. However, the single beat formula needs mathematical skillness, and extra software. Aim of this study was to compare the non-invasive SBPRSW with the simpler non-invasive SW/EDVratio in the stress-echo lab.

METHODS

We studied 692 patients, age 62 ± 12 years, ejection fraction 50 ± 17%, with negative stress echo (SE)(exercise, n = 130, dobutamine, n = 124, dipyridamole, n = 438) and follow-up data. The PRSW was estimated at rest and at peak stress by the SBPRSW technique and compared with the SW/EDV. All patients were followed-up. Event rates were estimated with Kaplan-Meier curves.

RESULTS

SBPRSW and SW/EDV were linearly correlated at rest (r = 0.842, p < .001) and at peak stress (r = 0.860, p < .001). During a median follow-up of 20 months (first quartile 8, third quartile 40 months), 132 major events were registered: at receiver operating characteristic (ROC) analysis rest SBPRSW vs. SW/EDV (AUC 0.691 vs. 0.722) and peak stress (AUC 0.744 vs. 0.800) demonstrated both a significant prognostic power (all p < .001) with non-inferior survival prediction of the simpler SW/EDV ratio at Kaplan-Meier curves (Chi-square rest = 38, peak = 56) vs. SBPRSW (Chi-square rest = 14, peak = 42).

CONCLUSIONS

The data obtained with the non-invasive SBPRSW and by the simpler SW/EDV are highly comparable. PRSW with either SB or SW/EDV approach is effective in predicting follow-up events.

Finite state machine implementation for left ventricle modeling and control

Background

Simulation of a left ventricle has become a critical facet of evaluating therapies and operations that interact with cardiac performance. The ability to simulate a wide range of possible conditions, changes in cardiac performance, and production of nuisances at transition points enables evaluation of precision medicine concepts that are designed to function through this spectrum. Ventricle models have historically been based on biomechanical analysis, with model architectures constituted of continuous states and not conducive to deterministic processing. Producing a finite-state machine governance of a left ventricle model would enable a broad range of applications: physiological controller development, experimental left ventricle control, and high throughput simulations of left ventricle function.

Methods

A method for simulating left ventricular pressure-volume control utilizing a preload, afterload, and contractility sensitive computational model is shown. This approach uses a logic-based conditional finite state machine based on the four pressure-volume phases that describe left ventricular function. This was executed with a physical system hydraulic model using MathWorks’ Simulink^® and Stateflow tools.

Results

The approach developed is capable of simulating changes in preload, afterload, and contractility in time based on a patient’s preload analysis. Six pressure–volume loop simulations are presented to include a base-line, preload change only, afterload change only, contractility change only, a clinical control, and heart failure with normal ejection fraction. All simulations produced an error of less than 1 mmHg and 1 mL of the absolute difference between the desired and simulated pressure and volume set points. The acceptable performance of the fixed-timestep architecture in the finite state machine allows for deployment to deterministic systems, such as experimental systems for validation.

Conclusions

The proposed approach allows for personalized data, revealed through an individualized clinical pressure–volume analysis, to be simulated in silico. The computational model architecture enables this control structure to be executed on deterministic systems that govern experimental left ventricles. This provides a mock circulatory system with the ability to investigate the pathophysiology for a specific individual by replicating the exact pressure–volume relationship defined by their left ventricular functionality; as well as perform predictive analysis regarding changes in preload, afterload, and contractility in time.

Single-Beat Estimation of Right Ventricular Contractility and Its Coupling to Pulmonary Arterial Load in Patients With Pulmonary Hypertension

Background

An accurate assessment of intrinsic right ventricular (RV) contractility and its relation to pulmonary arterial load is essential for the management of pulmonary hypertension. The pressure‐volume relationship with load manipulation is the gold standard assessment used for this purpose, but its clinical application has been hindered by the lack of a single‐beat method that is valid for the human RV. In the present study, we sought to validate a novel single‐beat method to estimate the preload recruitable stroke work (PRSW) and its derivative for ventriculoarterial coupling in the human RV.

Methods and Results

A novel single‐beat slope of the PRSW relationship (M_sw) was derived by calculating the mean ejection pressure when the end‐systolic volume was equal to volume‐axis intercept of the PRSW relationship. In addition, by using a mathematical transformation of the equation representing the linearity of the PRSW relationship, a novel index for ventriculoarterial coupling, M_sw/mean ejection pressure, was developed. RV pressure‐volume relationships were measured in 31 patients (including 23 patients with pulmonary hypertension) who were referred for right‐sided heart catheterization. In this cohort, the single‐beat M_sw was strongly correlated with the multiple‐beat M_sw (r=0.91, P<0.0001). Moreover, a significant correlation was observed between the single‐ and multiple‐beat M_sw/mean ejection pressure (r=0.53, P=0.002), with a stronger correlation in those with greater RV systolic pressure (r=0.70, P=0.003).

Conclusions

The novel single‐beat approach provided an accurate estimation of indexes for the PRSW relationship and ventriculoarterial coupling. It may be particularly useful in assessing RV adaptation to increased pressure overload.

Ventricular-vascular dynamics in pediatric patients with heart failure and preserved ejection fraction

OBJECTIVE

The details of the ventricular-vascular dynamics of heart failure with preserved ejection fraction (HFpEF) in children remain poorly understood. We tested the hypothesis that pediatric HFpEF patients have ventricular systolic, diastolic, and arterial stiffening at rest as well as impaired reserve function associated with coronary supply/demand imbalance.

METHODS

We studied the ventricular pressure-area relationship in 22 pediatric HFpEF patients and 22 control subjects before and after dobutamine infusion and during abdominal compression. Coronary supply/demand balance was assessed by subendocardial viability ratio (SEVR) calculated from the aortic pressure waveform.

RESULTS

Compared with controls, the HFpEF patients had significantly higher end-systolic (Ees) and arterial (Ea) elastance. Increased ventricular diastolic stiffness also occurred in the HFpEF patients, resulting in modest elevation of end-diastolic pressure (EDP) at rest (13.6±4.3 vs. 7.3±2.3mmHg, P<0.0001). The difference in EDP became more evident with a preload increase through abdominal compression, indicating a limited diastolic reserve in HFpEF patients (EDP changes; 11.3±6.2 for HFpEF vs. 3.4±0.6mmHg for controls, P=0.016). The HFpEF patients exhibited impaired beta-adrenergic reserve in ventricular contractility and ventricular-arterial coupling in response to dobutamine infusion. SEVR was significantly lower in the HFpEF (0.64±0.11) than in the control (0.79±0.07, P<0.0001) and was significantly correlated with LV diastolic stiffness and dobutamine-induced changes in ventricular contractility.

CONCLUSIONS

HFpEF in children involves higher ventricular-arterial stiffness at rest as well as impaired systolic and diastolic reserve, which closely correlate with impaired coronary supply/demand balance.