Many causes of high estimated systolic pulmonary artery pressure
Table 1 shows conditions associated with a high estimated systolic pulmonary artery pressure. Echocardiographic limitations, constitutional factors, and high cardiac output states can lead to an apparent elevation in systolic pulmonary artery pressure, which is not confirmed later during right heart catheterization.
Systolic pulmonary artery pressure increases with age and body mass index as a result of worsening left ventricular diastolic dysfunction.8 In fact, an estimated pressure greater than 40 mm Hg is found5 in 6% of people over age 50 and in 5% of people with a body mass index greater than 30 kg/m2. It can also be high in conditions in which there is an increase in cardiac output, such as pregnancy, anemia (sickle cell disease, thalassemia), cirrhosis, and arteriovenous fistula.
The estimated systolic value often differs from the measured value
Studies have compared the systolic pulmonary artery pressure measured during right heart catheterization with the estimated value on echocardiography.9,10 These studies noted a reasonable degree of agreement between the tests but a substantial variability.
Both underestimation and overestimation of the systolic pulmonary artery pressure by echocardiography were common, with 95% limits of agreement ranging from minus 40 mm Hg to plus 40 mm Hg.9,10 A difference of plus or minus 10 mm Hg in systolic pulmonary artery pressure between echocardiography and catheterization was observed in 48% to 51% of patients with pulmonary hypertension, particularly in those with higher systolic pulmonary artery pressure.9,10
An important reason for overestimation of systolic pulmonary artery pressure is the inaccurate estimation of the right atrial pressure by echocardiography.9,10 Indeed, this factor may account for half of the cases in which the systolic pulmonary artery pressure is overestimated.10 Although the traditional methods to estimate the right atrial pressure have been revisited,8,11 this estimation is less reliable for intermediate pressure values, for patients on mechanical ventilation, and for young athletes.8
Other explanations for the variability between measured and estimated systolic pulmonary artery pressure include suboptimal alignment between the Doppler beam and the regurgitant jet, severe tricuspid regurgitation, arrhythmias, and limitations inherent to the simplified Bernoulli equation.12 The estimated value is particularly inaccurate in patients with advanced lung disease, possibly owing to lung hyperinflation and alteration in the thoracic cavity and position of the heart—all factors that limit visualization and measurement of the tricuspid regurgitant jet.13
OTHER SIGNS OF PULMONARY HYPERTENSION ON ECHOCARDIOGRAPHY
Echocardiography provides information that is useful in assessing the accuracy of the estimated systolic pulmonary artery pressure, particularly right ventricular size and function.
As pulmonary hypertension progresses, the right ventricle dilates, and its function is compromised. Therefore, it is important to determine the right ventricular size and function by using objective echocardiographic findings such as right ventricular diameters (basal, mid, apical) and area, right ventricular fractional area change, tricuspid annular plane systolic excursion, myocardial performance index, and the pulsed tissue Doppler tricuspid annular peak systolic excursion velocity.8
Other echocardiographic features that suggest pulmonary hypertension include a dilated right atrial area, flattening of the interventricular septum, notching of the right ventricular outflow tract flow, and dilation of the main pulmonary artery. Interestingly, left ventricular diastolic dysfunction of the impaired relaxation type (grade I) is commonly observed in pulmonary hypertension14; however, more advanced degrees of diastolic dysfunction, ie, pseudonormalization (grade II) or restrictive left ventricular filling (grade III),15 particularly when associated with a left atrial enlargement, suggest pulmonary hypertension associated with left heart disease and not pulmonary artery hypertension.
WHAT TO DO IF ECHOCARDIOGRAPHY INDICATES PULMONARY HYPERTENSION
An algorithm showing the approach to an elevated systolic pulmonary artery pressure on echocardiography is presented in Figure 1.
In the appropriate clinical setting, if the systolic pulmonary artery pressure is 40 mm Hg or greater or if other echocardiographic variables suggest pulmonary hypertension, our practice is to proceed with right heart catheterization.
Clinical variables that suggest pulmonary hypertension include progressive dyspnea, chest pain, presyncope-syncope, lower extremity edema, hepatomegaly, jugular vein distention, hepatojugular reflux, sternal heave, loud second heart sound (P2), murmur of tricuspid or pulmonary regurgitation, and right ventricular third heart sound.16 These are of particular interest when associated with conditions known to cause pulmonary hypertension,2such as connective tissue disease, portal hypertension, congenital heart disease, HIV infection, and certain drugs and toxins.
Other tests that raise suspicion of pulmonary hypertension are an electrocardiogram suggesting a dilated right atrium or ventricle, an elevated brain natriuretic peptide level, a low carbon monoxide diffusing capacity on pulmonary function testing, and an enlarged pulmonary artery diameter on imaging.
Given the high prevalence of pulmonary hypertension, the Fifth World Symposium on Pulmonary Hypertension recommended first considering heart or parenchymal lung disease when an echocardiogram suggests pulmonary hypertension.6 If there are signs of severe pulmonary hypertension or right ventricular dysfunction, referral to a center specializing in pulmonary hypertension is recommended. Referral is also appropriate when there is no major heart or lung disease and the echocardiogram shows an elevated systolic pulmonary artery pressure, particularly when the clinical presentation or results of other testing suggest pulmonary hypertension.
In the appropriate context, a high systolic pulmonary artery pressure on echocardiography suggests pulmonary hypertension, but right heart catheterization is needed to confirm the diagnosis. Estimating the systolic pulmonary artery pressure with echocardiography has limitations, including false-positive results, predominantly when the pretest probability of pulmonary hypertension is low.