- This study examined the phenomenon of "partial wedging," in which an incompletely occluded pulmonary artery (PA) yields an overestimation of true pulmonary capillary wedge pressure (PCWP) by reflecting both left atrial and PA pressures
- In partial wedging it appears that as the balloon is deflated before transition from PCWP to PA, the catheter can move into a small branch of the PA, creating more complete occlusion and therefore a lower, more accurate alternative wedge pressure
- Researchers at Massachusetts General Hospital re-reviewed hemodynamic tracings for 182 patients who underwent right and/or right and left heart catheterization
- They identified alternative wedge pressures (≥3 mmHg lower than the initial PCWP) in 26 patients (14.3%)
- Eleven of the 26 patients (42%) had alternative wedge pressure ≤15 mmHg with a calculated alternative pulmonary vascular resistance ≥3 Wood units; 10 of them (38.5%) were re-classified from a post-capillary to pre-capillary pathology
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Accurate estimates of pulmonary capillary wedge pressure (PCWP) during right heart catheterization are crucial to correctly classifying and managing cardiopulmonary conditions. According to the World Health Organization (WHO), PCWP ≤15 mmHg and pulmonary vascular resistance ≥3 Wood units are two of the measurements that distinguish pulmonary arterial hypertension from pulmonary hypertension due to left heart failure.
Physicians should be alert to the potential for "partial wedging," in which partial occlusion of the pulmonary artery (PA) results in falsely elevated wedge pressures. It's thought that in this scenario, as the balloon is deflated prior to the transition from PCWP to PA, the catheter moves briefly into a smaller branch vessel, inadvertently creating more complete occlusion and therefore a more accurate, lower alternative wedge pressure.
Researchers at Massachusetts General Hospital have found that this phenomenon is common even for the experienced catheterization operators at their high-volume institution. Shelsey W. Johnson, MD, physician in the Department of Internal Medicine at Mass General, and colleagues report the details in Pulmonary Circulation and provide tips for improving the accuracy of reporting.
The researchers queried a database for all patients who underwent right and/or right and left heart catheterization between January 2015 and June 2017. They selected for review 182 reports in which a computer-generated PCWP was ≥20 mmHg and a tracing of the transition from PCWP to PA was recorded.
An alternative PCWP was defined as a PCWP tracing ≥3 mmHg lower than the initial PCWP during balloon deflation prior to transition from PCWP to PA.
The PCWP ≥20 mmHg threshold was selected, rather than PCWP of 15–20 mmHg, to improve the chance of identifying patients in whom an alternative PCWP would change the WHO diagnostic group.
Frequency of Alternative PCWP
- An alternative wedge pressure was identified for 26 patients (14.3%; 95% CI, 9.6%–20.2%; P≤0.0001)
- 14 of those patients (54%) had a negative diastolic pulmonary gradient (diastolic PA pressure lower than reported PCWP), suggesting the operator didn't understand the relationship between these variables well enough to appreciate the inadequacy of the PCWP
- In all eight of the 26 patients who had left heart catheterization data available, left ventricular end-diastolic pressure was closer to the alternative PCWP than to the reported PCWP, supporting the accuracy of the alternative PCWP
Frequency of Reclassification
Eleven of the 26 patients (42%) had alternative wedge pressure ≤15 mmHg with a calculated alternative pulmonary vascular resistance ≥3 Wood units. Ten of them (38.5% of the 26 patients) were re-classified from a post-capillary to pre-capillary pathology.
Guidance for Physicians
The transition from PCWP to PA is an important procedural time point. The operator should be aware that the initial PCWP could represent a partial or incomplete wedge. To ensure the accuracy of PCWP reporting:
- Advance the catheter with a fully inflated balloon
- Before transitioning from PCWP to PA, deflate the balloon slowly to allow the catheter to fall further forward, with attention to the possibility of identifying an alternate PCWP
- Consider additional techniques (e.g., use of smaller balloon volumes, wedge saturation or wedge angiography) if the initial PCWP obtained is incongruent with the clinical scenario, the tracing does not demonstrate the anticipated atrialization or the relationship between diastolic PA pressure and PCWP deviates from expected results
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