Up to 17% of patients die within three months of diagnosis of venous thromboembolism (VTE), although many of these deaths may be due to associated comorbidities rather than direct causation. More recent large RCTs show a 2% all-cause mortality at 3 months. The increased sensitivity of imaging modalities has doubled rates of hospital admission for pulmonary embolism over the past decade, and case-fatality rates remain stable or are declining. [1]
VTE will affect up to 5% of all people at some stage during their life.
Recall the Right-ventricular strain pattern:
- T-wave inversion in V1 and V2
- At least one of the following:
- T-wave inversion in lead III
- The precordial lead with deepest T-wave inversion is V1 or V2
The combination of TWI in V1 and lead III is quite specific for PE (Kosuge, 2014; Witting, 2012). By combining the criteria of maximal TWI in V1-V2 and/or TWI in V1 and III increases the sensitivity for PE to 98% while maintaining a specificity of 92%, compared to MI.
Clinical (pre-test) low risk, including PERC negative: rule out PE without need for D-dimer:
Pulmonary Embolus Rule-out Criteria (PERC): sensitivity 97% (0.96-0.98), specificity 23%, LR+ 1.22 (1.16-1.29), LR- 0.17 (0.13-0.23) [2]
Rules out PE if no criteria are present in patient with a low pre-test probability (≤ 15%):
- < 50 years old
- PR < 100 bpm
- SpO2 > 94%
- no unilateral leg swelling
- no haemoptysis
- no surgery or trauma within 4 weeks of presentation
- no history of DVT or PE
- no oral hormone use (OCP / MHT)
Patients meeting all eight criteria have a pre-test probability low enough to defer a D-dimer test. Missed pulmonary embolus in 0.5% (1 in 500).
Clinical (pre-test) low to intermediate risk: check D-dimer
- D-dimer < 250 mcg/L (negative) >> nil further
- D-dimer > 250 mcg/L (positive) >> CTPA + lower limb venous ultrasound scan (USS)
Refining the interpretation of the D-dimer in patients over 50 years old: Because D-dimer concentrations increase with age, an age-adjusted D-dimer approach improves its specificity further: patient’s age in years × 10 mcg/L, for patients over age 50 years [3]. Although limited data exist for a D-dimer threshold set at 250 ng/mL (i.e. the unadjusted D-dimer laboratory threshold is usually 230-250), retrospective studies suggest using instead “age per 5” rule: e.g. can essentially rule out PE in a 60-year old patient if their D-dimer is less than 300 ng/mL. A prospective trial to determine D-dimer threshold for suspected VTE is ongoing. [4]
High clinical (pre-test) risk: start anticoagulation and perform CT Pulmonary Angiography (CTPA) + Lower Limb USS (venous duplex). If imaging negative, consider V/Q scan.
Inconclusive D-dimer (or imaging): V/Q scan
Fifty per cent of venous thromboembolism events are associated with a transient risk factor, such as recent surgery or hospital admission for medical illness, [while] 20% are associated with cancer, and the remainder are unprovoked.
References
- Duffett L., Castellucci L. A., Forgie M. A. “Pulmonary embolism: update on management and controversies.” BMJ 370; 2020: m2177. doi:10.1136/bmj.m2177.
- Singh, Balwinder; Mommer, Shannon K., Erwin, Patricia J., Mascarenhas, Soniya S. and Parsaik, Ajay K. “Pulmonary embolism rule-out criteria (PERC) in pulmonary embolism—revisited: A systematic review and meta-analysis.” Emerg Med J 30: 2013: 701–706. doi:10.1136/emermed-2012-201730.
- Urban K, Kirley K, Stevermer JJ. “PURLs: It’s time to use an age-based approach to D-dimer.” J Fam Pract 63(3); 2014: 155-158..
- Righini, Marc P. Age-Adjusted D-dimer for Venous Thromboembolism (VTE). MD+ calc.
- Doherty, Steven. “Pulmonary embolism: An update.” Aus Fam Phys 46(11); 2017.
- Farkas, Joshua. Submassive & Massive PE. Internet Book of Critical Care (IBCC). Sep 5, 2019. Available at https://emcrit.org/ibcc/pe/#top.
