Role of Pulmonary Artery Wedge Pressure Saturation During Right Heart Catheterization: A Prospective Study

Diagnosis and proper classification of PH is challenging. Even when gold-standard right heart catheterizations (RHC) are performed, PH is often misdiagnosed, resulting in inappropriate and potentially harmful treatment approaches.¹ Additionally, the definition of PH has expanded recently, putting even more emphasis on accurate hemodynamic assessment during RHC.^2–4 A critical component of the hemodynamic evaluation is measurement of pulmonary artery wedge pressure (PAWP) since this is the sole parameter that delineates pre-capillary PH (PCPH) from PH due to left heart disease (PH-LHD), conditions with disparate therapeutic strategies. The PAWP is also a key determinant of pulmonary vascular resistance (PVR) that is used to delineate the two PH-LHD subgroups: isolated post-capillary PH (IpcPH) and combined pre- and post-capillary PH (CpcPH).² Importantly, PAWP only reflects left atrial pressure if a complete occlusion of the PA occurs. If the occlusion is incomplete, the measured pressure will include contributions from the PA, falsely elevating the recorded PAWP and possibly leading to misdiagnosis.⁵ To address this point, recently published consensus statements recommend confirming an elevated PAWP and complete occlusion by measuring the oxyhemoglobin saturation (SaO₂) of blood from the distal tip of the PA catheter when in the wedge position.² With complete occlusion, SaO₂ will approximate that of the left atrium whereas lower SaO₂ values may indicate incomplete occlusion and should prompt additional PAWP measurement attempts.

Accordingly, we instituted a standard of care clinical protocol at our institution as follows: SaO₂ level is measured from a wedge blood sample for all RHC where PAWP is >15mmHg. If the initial PAWP is confirmed to be occlusive (SaO₂ >90% or within 5% of systemic arterial saturation), it is the final reported value. However, if PAWP saturation suggests an incomplete occlusion, up to 2 additional attempts are made to obtain PAWP with an occlusive SaO₂. The final reported PAWP is the value associated with an occlusive SaO₂.

Because data regarding the feasibility and clinical impact of this method are lacking, we sought to prospectively study the overall success rate of obtaining an occlusive PAWP SaO₂, the differences between the initial and final reported hemodynamics, and any clinically-relevant PH re-classification. After Institutional Review Board approval, and several months after instituting the standard of care protocol, investigators not performing the RHC enrolled and observed subjects undergoing clinically-indicated RHC from September 2019 to June 2020. Demographic, clinical, echocardiographic, procedural and hemodynamic data were collected. Subjects undergoing routine post-transplant RHC and those with PAWP ≤15mmHg were excluded. All hemodynamics were measured in a standardized fashion and were reported by the proceduralists (not investigational observers). Initial and final hemodynamics were compared using the Signed-Rank Test.

A total of N=111 consecutive subjects were enrolled. One subject was excluded due to incomplete data. The cohort was 58±14 years old, 60% male, 60% Caucasian/35% Black race, and had body mass index of 31±7 kg/m². The average left ventricular ejection fraction (LVEF) was 41±23%, with 47/110(43%) having LVEF ≥50%. Clinical indications for RHC included assessment of advanced heart failure therapy candidacy (38%), uncertain volume/perfusion status (26%), pre-operative optimization/risk stratification (24%), and evaluation of known/suspected PCPH(12%). RHC were performed by interventional cardiologists (52/110; 47%) and heart failure cardiologists (58/110; 53%).

Despite apparent confirmation of PAWP occlusion by fluoroscopy and/or typical hemodynamic waveform appearance, an occlusive PAWP SaO₂ was obtained on the first attempt only 50% of the time (55/110; Figure). There was no difference in initial success rate between interventional and heart failure cardiologists or based on LVEF. With up to two additional attempts, an occlusive PAWP SaO₂ was obtained in 91% of subjects. In subjects in whom additional attempts were successful in obtaining occlusive PAWP SaO₂ (n=45; initial SaO₂ 68.8±14.3% vs 94.5±2.7%; p <0.001), 29 had a lower final PAWP compared to the initial PAWP [20±6 vs. 25±7 mmHg; p<0.001], and 14 of the 45 subjects (31%) had ≥4 mmHg difference between final and initial PAWP values. This also led to significant differences in final vs. initial PVR (3.8±3.5 vs. 2.4±1.8 WU; p<0.001). Re-classification from PH-LHD to PCPH was made in 6 subjects and from IpcPH to CpcPH in 4 subjects. Additionally, of the 10 subjects without an occlusive PAWP SaO₂ after three attempts, 5(50%) were noted to have a lower final reported PAWP compared to the initial PAWP, which resulted in re-classification of three additional subjects. This suggests that even the attempt to obtain a PAWP saturation, with deflation and re-inflation of the balloon, may lead to lower and likely more accurate PAWP values. In total, 13 subjects (12%) were ultimately re-classified. There were no observed complications.

Figure.

Study Flow Chart. * = p < 0.001, # = p > 0.05, PH-LHD = pulmonary hypertension due to left heart disease, PCPH = pre-capillary pulmonary hypertension, IpcPH = isolated post-capillary pulmonary hypertension, CpcPH = combined pre- and post-capillary pulmonary hypertension

In this prospective, single-center study, half of initial PAWP measurements were not occlusive when the initial measured PAWP was >15mmHg. The practice of obtaining a PAWP saturation resulted in significantly lower PAWP, higher PVR, and clinically-relevant disease re-classification. A PAWP saturation is a simple, safe and effective technique to verify complete PAWP occlusion during RHC and should be considered in clinical practice.