Subsegmental PEs


J Thromb Haemost. 2010 Mar;8(3):533-9. doi: 10.1111/j.1538-7836.2009.03724.x. Epub 2009 Dec 14.
Prospective multicenter assessment of interobserver agreement for radiologist interpretation of multidetector computerized tomographic angiography for pulmonary embolism.
Courtney DM1, Miller C, Smithline H, Klekowski N, Hogg M, Kline JA.
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Emergency physicians rely on the interpretation of radiologists to diagnose and exclude pulmonary embolism (PE) on the basis of computerized tomographic pulmonary angiography (CTPA). Few data exist regarding the interobserver reliability of this endpoint.
To quantify the degree of agreement in CTPA interpretation between four academic hospitals and an independent reference reading (IRR) laboratory.
Hospitalized and emergency department patients who had one predefined symptom and sign of PE and underwent 64-slice CTPA were enrolled from four academic hospitals. CTPA results as interpreted by board-certified radiologists from the hospitals were compared against those from the IRR laboratory. CTPAs were read as indeterminate, PE(-) or PE(+), and percentage obstruction was computed by the IRR laboratory, using a published method. Agreement was calculated with weighted Cohen's kappa.
We enrolled 492 subjects (63% female, age 54 +/- 1 years, and 16.7% PE(+) at the site hospitals). Overall agreement was 429/492 (87.2%; 95% confidence interval 83.9-90.0). We observed 13 cases (2.6%) of complete discordance, where one reading was PE(+) and the other reading was PE(-). Weighted agreement was 92.3%, with kappa = 0.75. The median percentage obstruction for all patients was 9% (25th-75th percentile interquartile range: 5% to -30%). For CTPAs interpreted at the site hospitals as PE(-) or indeterminate but read as PE(+) by the IRR laboratory, the median of percentage obstruction was 6% (4-7%).
We found in this sample a good level of agreement, with a weighted kappa of 0.75, but with 2.6% of patients having total discordance. Overall, a large proportion of clots were distal or minimally occlusive clots.

Incidental PE. Subsegmental PE. Do You Treat?

There is growing evidence of over-diagnosis of Pulmonary Embolism; there has been an 80% rise in the incidence of PE in the US after the introduction of CTA, without a significant impact on mortality (1-4).

The incidental discovery of clinically unsuspected PE on CT is an increasingly frequent problem, occurring in up to 5% of thoracic CT scans performed for non-PE indications, most often in patients with cancer, but also among those with paroxysmal atrial fibrillation or heart failure and history of atrial fibrillation (1,5). There are no robust data to guide the decision on how to manage unsuspected PE, but most experts agree that patients with cancer and those with clots at the lobar or more proximal level should be treated with anticoagulants (1,6).

By 2012, the proportion of all PE diagnosed in symptomatic patients that are confined to subsegmental arteries had increased from 4.7% to 15% with the use of multi-row detector CTA. The clinical significance of isolated SSPE on CTA is currently up for debate and the optimal management of these patients is unclear. The positive predictive value is low and inter-observer agreement is poor at this distal level (1,7). The definition of sub-segmental PE has yet to be standardized and a single sub-segmental defect probably does not have the same clinical relevance as multiple, sub-segmental thrombi (1).

Although a recent study showed similar outcomes for SSPE and more proximal PE (8) and some guidelines recommend anticoagulation for all PE, other guidelines acknowledge that anticoagulation may not be warranted in all cases because of uncertainty about the balance of benefits and harms for treating isolated SSPE (1,2). Some authors suggest withholding anticoagulation for stable patients with isolated SSPE with adequate cardiopulmonary reserve and a negative ultrasound for DVT (2,7).

(1) Konstantinides S, et al. Eur Heart J 2014 Aug 29. [Epub ahead of print].
(2) Wiener RS, et al. BMJ 2013;347. f3368.
(3) Tsai J, et al. Arch Intern Med 2012;172(12):960-961.
(4) Wiener RS, et al. Arch Intern Med 2011;171(9):831-837.
(5) Condliffe R, et al. Thorax 2014 Feb;69(2):174-80.
(6) Kearon C, et aL Chest 2012;141(2 Suppl):e419S-e494S.
(7) Stein PD, et al. Clin Appl Thromb Hemost 2012;18(1):20-26.
(8) den Exter PL, et al. Blood 2013 Aug 15;122(7):1144-9.

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