Discordance between Imaging Modalities in the Evaluation of Chronic Thromboembolic Pulmonary Hypertension: A Combined Experience from Two Academic Medical Centers

CTEPH: A Kaiser Permanente Northern California Experience

INTRODUCTION

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare and life-threatening form of pulmonary hypertension and the only potentially curable form of the World Health Organization Pulmonary Hypertension classes. Thus, the prompt and accurate diagnosis of this condition is imperative. Despite widespread chronic symptoms following acute pulmonary embolism (PE), the condition is rarely considered, and an externally validated inexpensive diagnostic algorithm is lacking.

METHODS

A long-term, retrospective cohort study was conducted to assess the incidence of CTEPH following acute PE in a real-world study population. Additional data were collected regarding the practice patterns of diagnostic testing and imaging, particularly in patients with persistent or recurrent symptoms. Amongst diagnosed CTEPH patients, previously established risk factors were evaluated for degree of risk and commonly used diagnostic tests (electrocardiogram [ECG] right ventricular hypertrophy [RVH] pattern, B-type natriuretic peptide [BNP] elevations) employed during this period were evaluated and assessed for feasibility as screening tests. The study population was obtained from the MAPLE study cohort, comprised of patients presenting with acute PE in 21 community medical centers across the Kaiser Permanente Northern California system from January 2013 to April 2015. Diagnosis of CTEPH was confirmed via pulmonary vascular imaging (ventilation/perfusion [V/Q] scanning, computed tomography angiography, pulmonary angiography) and diagnostic right heart catheterization (RHC). Probable diagnoses were defined as a combination of suggestive echocardiographic and RHC findings. Additional inclusion criteria included age (≥18 years) with at least 2 years follow up and no previous diagnosis of CTEPH or PE during the prior 30 days.

RESULTS

There were 1973 patients who met inclusion criteria (mean age 62.4 years). Despite 75 % of patients developing symptoms consistent with CTEPH >3 months following acute PE, only 5.6 % of these symptomatic patients underwent V/Q scanning. There was overall a very low cumulative incidence of CTEPH (2.3 %), which was significantly higher amongst patients with symptoms compared to those without symptoms. When controlled for confounding in the multivariate analysis, only recurrent PE (HR 19.3, P < 0.001) and pulmonary artery systolic pressure >50 mmHg (HR 10.4, P < 0.001) were statistically significant predictors of CTEPH. Of the non-invasive diagnostic tests, ECG criteria for RVH were found to be poorly sensitive (2.6 %), but very specific (98.8 %) for CTEPH. Elevated levels of BNP alone were more sensitive than RVH ECG criteria (76.3 %) but poorly specific (44.4 %).

CONCLUSIONS

The diagnosis of CTEPH is uncommonly made following acute PE. Despite the frequency of persistent symptoms consistent with CTEPH following acute PE, the appropriate diagnostic work-up is rarely undertaken as evidenced in this cohort. This suggests that CTEPH is underappreciated and rarely considered, likely underestimating the true incidence in this cohort. Future studies are needed to elucidate the true prevalence of CTEPH and further investigate both the optimal diagnostic tools and timing of appropriate screening. These discoveries may help guide future development of diagnostic algorithms that can effectively rule out and accurately identify this potentially curable disease in a timely manner.

A Clinical Approach to Multimodality Imaging in Pulmonary Hypertension

Pulmonary hypertension (PH) is a clinical condition characterized by progressive elevations in mean pulmonary artery pressures and right ventricular dysfunction, associated with significant morbidity and mortality. For resting PH to develop, ~50-70% of the pulmonary vasculature must be affected, suggesting that even mild hemodynamic abnormalities are representative of advanced pulmonary vascular disease. The definitive diagnosis of PH is based upon hemodynamics measured by right heart catheterization; however this is an invasive and resource intense study. Early identification of pulmonary vascular disease offers the opportunity to improve outcomes by instituting therapies that slow, reverse, or potentially prevent this devastating disease. Multimodality imaging, including non-invasive modalities such as echocardiography, computed tomography, ventilation perfusion scans, and cardiac magnetic resonance imaging, has emerged as an integral tool for screening, classifying, prognosticating, and monitoring response to therapy in PH. Additionally, novel imaging modalities such as echocardiographic strain imaging, 3D echocardiography, dual energy CT, FDG-PET, and 4D flow MRI are actively being investigated to assess the severity of right ventricular dysfunction in PH. In this review, we will describe the utility and clinical application of multimodality imaging techniques across PH subtypes as it pertains to screening and monitoring of PH.

Clinical and imaging outcomes after intermediate- or high-risk pulmonary embolus

Long-term outcomes after acute pulmonary embolism vary from complete resolution to chronic thromboembolic pulmonary hypertension (CTEPH). Guidelines after acute pulmonary embolism are generally limited to anticoagulation duration. We assessed patients with estimated prognosis >1 year in our pulmonary hypertension clinic 2–4 months after treatment for intermediate- or high-risk acute pulmonary embolism. At follow-up, ventilation–perfusion scan and echocardiogram were offered. The aim of this study was to assess for recurrent symptomatic disease, residual imaging defects or right ventricular dysfunction, and functional disability after acute management of pulmonary embolism. After treatment for acute intermediate- or high-risk pulmonary embolism, 104 patients followed up in pulmonary hypertension clinic. Of those, 55% of patients had self-reported limitation in activity. No patients had symptomatic recurrence of pulmonary embolism. Forty-eight percent of patients had residual perfusion defects on perfusion imaging, while 91% of patients had either normal or only mildly enlarged right ventricles. We identified heart failure preserved ejection fraction, iron deficiency, and obstructive sleep apnea as significant contributors to breathlessness. Treatment of these conditions was associated with improvement. Surprisingly, we diagnosed CTEPH in nine patients; for some, chronic thrombus may already have been present at the time of index evaluation. Our findings suggest that follow-up in a dedicated pulmonary hypertension clinic 2–4 months after acute intermediate- or high-risk pulmonary embolism may add value to patient care. We identified treatable comorbidities that could be contributing to post-pulmonary embolism syndrome as well as CTEPH.