**7. D-dimer**

probability of this diagnosis may be utilized. Several clinical prediction rules (CPRs) are available for the assessment of the clinical pretest probability for PE including but not limited to the Wells (Wells 1998), modified Wells (Bahia 2011), Geneva, and modified Geneva scores. In a meta-analysis performed by Ceriani et al (Ceriani 2010) in 2010, nine different clinical prediction tools for PE were reviewed. This meta-analysis suggests that all rules have compa‐ rable accuracy; however, there were differences in the extent of validation testing. The most

**Figure 1.** Acute pathophysiologic responses of the right ventricle to pulmonary thromboembolism (Adapted from

Increased RV Wall Tension

has both short-term and long-term consequences. Additional evaluation and characterization of patients at risk to develop long

Figure 1. Acute pathophysiologic responses of the right ventricle to pulmonary thromboembolism (Adapted

Pulmonary Arterial Bed Occlusion

Pulmonary Arterial Vasoconstriction

Increased RV Afterload

Pulmonary Thromboembolism

> RV Dilation

Tricuspid Insufficiency

> Decreased LV Preload

> Decreased LV Output

Interventricular Septal Dysfiguration

term complications of pulmonary emboli is needed.

RCA/Endomyocardium Compression

RV Ischemia/ Infarction

Decreased Myocardial Oxygen Delivery

Piazza and Goldhaber 2005)

Systemic Hypotension

from Piazza and Goldhaber 2005)

124 Pulmonary Hypertension

The D-dimer antigen is a marker of fibrin degradation. It is formed by the sequential action of thrombin, Factor XIIIa and plasmin. D-dimer antigen can exist on fibrin degradation products derived from soluble fibrin before its incorporation into a fibrin gel or after the fibrin clot has been degraded by plasmin (Adam 2009). D-dimer has been found to be useful in evaluating outpatients for the presence of venous thromboembolism (VTE) (Wells 2001). D-dimer levels >500 ng/mL are considered elevated (Stein 2004). 95% of patients with proven PE will have an elevated D-dimer by ELISA assay (Stein 2004). Unfortunately, only 40-68% of patients without VTE have a negative D-dimer (Stein 2004). D-dimer elevation occurs in multiple other conditions besides PE including renal failure, surgery, cancer, sepsis, and pregnancy (Rathbun 2004). Thus, the use of d-dimer to evaluate VTE in hospitalized or otherwise chronically ill patients is limited. D-dimer is best used to exclude VTE in outpatients with low or moderate clinical suspicion for a thromboembolic event (Rathbun 2004, Wells 2000, Wells 2001, Stein 2006, Stein 2007).
