Ultrasound for Predicting Pulmonary and Cardiac Pressures

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Ultrasound for Predicting Pulmonary and Cardiac Pressures

Abstract and Introduction

Abstract


Aims Quantification of linear lung ultrasound (LUS) artefacts (B-lines) represents a novel, non-invasive approach to assess pulmonary congestion. We investigated the relationship between the number of B-lines (vertical artefacts arising from the pleural line) and intracardiac pressures.
Methods and results Prior to scheduled right heart catheterization (RHC), 100 subjects underwent LUS of eight zones. A reviewer blinded to the haemodynamic data quantified the number of sonographic B-lines. Of 92 subjects who completed RHC, 79 had adequate LUS data of all zones [median age 61 years, 26 women, median left ventricular ejection fraction (LVEF) 58%, 35 with history of heart failure; 22 postcardiac transplantation]. The number of B-lines correlated with measured right atrial (r = 0.32), pulmonary artery diastolic (PADP) (r = 0.34), mean pulmonary artery (mPAP) (r = 0.43), pulmonary artery systolic (PASP) (r = 0.48) pressures, and pulmonary vascular resistance (PVR) (r = 0.51) (P < 0.005 for all), but not with pulmonary capillary wedge pressure. There was a graded association between tertiles of B-line number and increasing PADP, mPAP, PASP, and PVR (P for trend ≤0.001 for all). Each additional B-line was associated with an increase in PASP of 1 mmHg and an increase in PVR of 0.1 Wood units. These associations remained robust after multivariable adjustment (P = 0.002). Assessment of two inferior lateral zones resulted in similar correlations to the eight-zone method.
Conclusions Easily obtainable, LUS may be useful in the estimation of right-sided cardiac pressures and PVR. Further evaluation of lung ultrasound as an adjunct to heart failure diagnosis, monitoring, and prognosis is warranted.

Introduction


Management of heart failure and avoidance of heart failure hospitalization depends largely on correct assessment of volume status and cardiac filling. The latter has been described as 'haemodynamic congestion'. Bedside assessment of filling pressures in patients with heart failure remains challenging, with accuracies for assessment by expert cardiologists of right-sided and left-sided filling pressures of 71% and 60%, respectively. Although intracardiac pressures can be directly measured using invasive haemodynamic monitoring, the bedside evaluation remains the cornerstone of clinical assessment in the ambulatory setting. Augmentation of the clinical assessment by non-invasive testing using chest radiography, echocardiography, measurement of intrathoracic impedance, natriuretic peptides, and pulse pressure variation has been explored, but many of these have limitations or are challenging to implement in the clinic setting. Accordingly, there is a clinical need for alternative, non-invasive markers of volume status.

Lung ultrasound represents a novel, quantitative approach to assessment of pulmonary congestion. This technology is readily available in many acute care settings, and the technique is simple and can be applied rapidly and non-invasively at the bedside. Sonographic assessment of extravascular lung water is based on reverberation artefacts that arise from the pleural line and are thought to originate from interlobular septa thickened by fluid. These artefacts are known as 'B-lines' (also 'comet tails' or 'lung comets'). The number of B-lines has been reported to correlate with the amount of extravascular lung water and decreases within hours of haemodialysis or within days of treatment for acute heart failure.

Most heart failure exacerbations are related to a progressive rise in cardiac filling pressures (haemodynamic congestion) that precipitates pulmonary congestion. In the absence of a gold standard, right atrial pressure (RAP) and pulmonary capillary wedge pressure (PCWP) are commonly used as markers of pulmonary congestion. Small previous studies have suggested a possible correlation between the number of lung ultrasound artefacts and PCWP. Data regarding the association between more comprehensive haemodynamic measurements and lung ultrasound are lacking. We sought to assess the relationship between the number of B-lines on lung ultrasound and directly measured cardiac pressures in patients undergoing right heart catheterization (RHC).

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