Getting specific
ECGs can evaluate for the presence of right atrial enlargement, right-axis deviation, and RV hypertrophy. While demonstrating some sensitivity, the ECG lacks specificity. In a study by Ahearn et al, findings on ECG showed no definite correlation with echocardiographic or right heart catheterization findings. Their study actually showed that 13% of the patients referred for further treatment with significant pulmonary hypertension had normal ECGs.9 The diagnosis or exclusion of pulmonary hypertension should not be based solely on ECG findings as the ECG is an inadequate screening tool.
A chest x-ray allows the clinician to determine cardiac and pulmonary artery size and to evaluate the lung fields. Findings seen in PAH include an enlarged RV (often filling the retrosternal space on the lateral view film) and enlarged pulmonary arteries.10 The lung fields should be examined for the assessment of other possible diseases, such as chronic obstructive pulmonary disease (COPD) or PF.
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Exercise capacity is evaluated, typically with the six-minute walk test. In this test, the patient walks (unprompted) for six minutes while oxygen saturation, heart rate, and BP are monitored. At the end of the six minutes, the total distance is evaluated and recorded. The patient’s degree of breathlessness is also assessed using the Borg dyspnea score, which ranges from 0 to 10, with 0 indicating no shortness of breath and 10 indicating maximal shortness of breath. A six-minute walk <332 meters has been associated with a poorer prognosis in the presence of PAH.
Echocardiography, if done correctly, can be the most reliable noninvasive test for indirectly evaluating the pulmonary artery systolic pressure (PASP). This is often the first test done when pulmonary hypertension is suspected. Findings typical of PAH include the previously mentioned RV hypertrophy, RV dilation, and tricuspid regurgitation (Figure 1), as well as RV systolic dysfunction and an elevated right ventricular systolic pressure (RVSP). In the early stages of PAH, the RV hypertrophies, but as the disease progresses, the RV enlarges and the septum becomes D-shaped and impinges on the left ventricle. The impingement continues as the disease worsens, and the left ventricular cavity becomes smaller. This decrease in size and subsequent decrease in volume contributes to a reduced cardiac output. The echocardiogram can also help to distinguish other potential causes for elevated pulmonary pressures, such as mitral or aortic valvular disease, left ventricular dysfunction, or intracardiac shunting. The RVSP, which is estimated based on the tricuspid regurgitation jet and a modified Bernoulli’s equation, should be confirmed with right heart catheterization.
Right heart catheterization is the gold standard for the diagnosis of pulmonary hypertension. This test allows for evaluation of not only the pulmonary artery pressures but also cardiac function (cardiac index, PVR, and right atrial pressure). A poor prognostic indicator is a cardiac index <2 L/min and a right atrial pressure >20 mm Hg. Without aggressive treatment, patients with these findings may not survive for six additional months; even so, treatment may come too late. Vasodilator testing is done while the catheter is in place to assess vasoreactivity. One of three medications is given (inhaled nitric oxide or an IV infusion of prostacyclin or adenosine) while hemodynamics are measured. A response to the medication is defined as a drop in the mean pulmonary artery pressure >10 mm Hg to a value <40 mm Hg with no decrease in cardiac output. If this is seen with any of the previously mentioned medications, the patient is said to be a “responder.” Responders are not seen often; the numbers vary from 5% to 15%. Some responders may be candidates for treatment with a calcium channel blocker (diltiazem, nifedipine, or amlodipine) to address their pulmonary hypertension. Consideration must be given to the patient’s overall condition and other diagnoses. Close monitoring is essential, as long-term response to calcium channel blockers has been reported to be as low as 6.8%.11
MRI is currently being used in some patients as a noninvasive way to assess the pulmonary vasculature and the myocardium. New techniques that involve tagging blood cells to monitor flow through certain vessels can evaluate flow patterns in the pulmonary vasculature. What may offer significant benefit is the evaluation of the RV. The MRI can yield accurate determinations of pulmonary pressures, as the measurements obtained are determined from the evaluation of mass, contractility, and volume observed, not geometrical assumptions used in echocardiography. Also taken into consideration is the condition of the interventricular septum and the degree of bowing into the left ventricle from RV overload.
Determining severity
Once all the testing has been done and PAH confirmed, patients should be categorized as to their WHO functional class. This classification assesses the patients’ symptoms with exertion and is highly suggestive of their long-term prognosis (Table 2), as are the hemodynamics and six-minute walk distance. The WHO functional class is similar to the New York Heart Association classification for heart failure.
