Abstract
436
Background: Pulmonary congestion is an important finding in heart failure. It can be assessed invasively by the PICCO method using transpulmonary thermodilution to measure extravascular lung water content (EVLW) and preload by global end-diastolic volume (GEDV), and pulmonary wedge pressure (PCWP) by pulmonary catheterization. However, at present, no reliable non-invasive methods are available for quantitatively measuring EVLW and preload. Using water labeled with oxygen-15 and positron emission tomography (PET) could be a viable alternative for thermodilution. The aim of this study was to develop methodology to measure EVLW and preload using standard dynamic 15O-water perfusion PET scans and to validate these methods in porcine model of pulmonary congestion.
Methods: Eight anesthetized and ventilated pigs were studied. Pulmonary congestion was induced by a combination of beta-blockers (BB), angiotensin-2 agonist (AT-2a) and saline infusion. Right heart catheterization, PICCO, computerized tomography (CT) and dynamic 15O-H2O-PET was performed. Transcardiac and transpulmonary transit times were measured by PET to calculate EVLW and GEDV. A 15O-water scan was performed at baseline, after AT-BB (AB) infusion and after infusion of 3L (AB-3L) and 10L (AB-10L) of saline.
Results: PCWP progressively increased from 8±2 mmHg at baseline to 29±5 mmHg during AB-10L (p < 0.001). MBF of both the left and right ventricle were increased (LV: 1.23±0.38 mL∙min-1∙g-1 to 2.54±0.58 mL∙min-1∙g-1, p=0.001; RV: 0.66±0.20 mL∙min-1∙g-1 to 1.32±0.31 mL∙min-1∙g-1, p = 0.003). EVLW increased from 521±76 mL to 973±325 ml (p<0.001) and GEDV from 1068±170 ml to 1254±85 ml (p<0.001). 15O-H2O PET measures of EVLW increased from 566±151 ml to 797±231 ml (p<0.001) whereas GEDV was lower than by PICCO but increased from 364±60 ml to 524±92 ml (p<0.001). Both EVLW and GEDV measured with PICCO and 15O-H2O-PET correlated (r2=0.40, p<0.001; r2=0.40, p<0.001, respectively). EVLW correlated positively with Hounsfield units by CT (PICCO: r2=0.36 p<0.001, PET: r2=0.46 p<0.001) and GEDV with PCWP (PICCO: r2=0.20 p=0.01, PET: r2=0.29 p=0.002). Conclusions: This study shows that preload and extravascular lung water content can be measured simultaneously and quantitatively during myocardial perfusions assessment using 15O-H2O-PET. Importantly, these parameters are generated during standard myocardial perfusion imaging with 15O-H2O and do not presuppose additional PET examinations. The prognostic implications of these quantitative measures can now be assessed non-invasively in outpatient settings.