Catheter-Directed Interventions for Acute Pulmonary Embolism

To the Editor:

The paucity of prospective data regarding catheter-directed interventions for the treatment of acute massive or submassive pulmonary embolism (PE) is well recognized,¹ and Kuo and colleagues² are to be commended for presenting the first prospective registry of such patients, to our knowledge, in this issue of CHEST (see page 667). Their use of a composite clinical success outcome is important as the combination of hemodynamic stabilization, echocardiographic improvement, and survival increases the face validity of this more patient-centric outcome compared with radiographic improvement alone.

The authors’ conclusion that standard catheter-directed thrombolysis may be equivalent to ultrasound-accelerated thrombolysis is also an astute one, considering that many retrospective studies examine the latter one alone.³ The comparative effectiveness of these two methods is a consideration that we also have questioned, with similar results, and will be of importance as catheter-directed PE interventions continue to mature.⁴

However, the pragmatic interpretation of this study within the broader scope of practice remains unclear, as the lack of a comparison arm limits analysis against anticoagulation or systemic thrombolysis for either the composite end point or outcomes such as mortality. Many retrospective series have demonstrated the relative safety and efficacy of these procedures for immediate improvement of hemodynamics; this study, though prospective, may not be unique.³

The inclusion of subjects in the study is unclear; though consecutive patients were enrolled, there is no mention of exclusions, withdrawals, or deviations from standard protocol. No subjects were included who failed first-line anticoagulation therapy, which is unusual in our experience. Cause of death, especially in those with submassive PE, was also not reported. In addition, the absence of quantitative echocardiogram measures such as the right ventricular to left ventricular diameter ratio, and reliance on institution-specific, nonblinded, single-reader echocardiogram interpretation may introduce bias for the primary outcome.⁵

Although 101 patients were enrolled, the low average number of yearly cases per participating institution (six) may increase sampling error. The absence of major complications aside from minor bleeding, especially in those with absolute contraindications to thrombolytics, is a surprising finding, suggesting that these excellent early results are unlikely to be sustained.

Finally, as the authors themselves noted, no postdischarge follow-up was included, limiting generalizability outside the immediate periprocedural period and preventing long-term evaluation including development of chronic thromboembolic pulmonary hypertension. Despite the prospectively collected nature of the data, these considerations suggest that for PE intervention, the jury is still out: Cautious interpretation of these results may be prudent until a larger sample and comparative data are available for analysis.