In the absence of a right ventricular outflow tract obstruction, the right ventricular systolic pressure is an estimate of systolic pulmonary arterial pressure and, thus, can help identify and stratify pulmonary hypertension. Normal systolic pulmonary arterial pressure is < 25 mm Hg, mild systolic pulmonary arterial hypertension is 30 to 50 mm Hg, moderate systolic pulmonary arterial pressure is 50 to 80 mm Hg, and severe systolic pulmonary arterial pressure is > 80 mm Hg.¹³

6. (Click photo for caption)

The maximum pulmonary insufficiency velocity estimates the diastolic pressure gradient across the pulmonary valve, or the pressure difference between the pulmonary artery and right ventricle. The pressure gradient can be calculated by applying the measured maximum pulmonary insufficiency velocity to the modified Bernoulli equation. The right ventricular pressure in diastole is assumed to be 0 mm Hg. Thus, the pressure gradient across the pulmonary valve in diastole equals the diastolic pulmonary arterial pressure. Normal diastolic pulmonary arterial pressure is < 15 mm Hg, and any value higher than that supports a diagnosis of diastolic pulmonary arterial hypertension.¹³

The assessment of the pulmonary artery velocity profile types is not always accurate, and veterinary and human studies suggest that up to 50% of patients with documented pulmonary hypertension may not have pulmonary artery velocity profile changes consistent with pulmonary hypertension.¹³ However, one study in dogs found that the short acceleration times and earlier peak velocities associated with type II and III pulmonary artery velocity profiles have 80% sensitivity and specificity for diagnosing pulmonary hypertension.¹⁴

In patients with right ventricular outflow tract obstruction, such as in pulmonic stenosis, tricuspid regurgitation, and pulmonary insufficiency, maximum velocity measurements are not accurate estimates of pulmonary arterial pressure and cannot be used to diagnose pulmonary hypertension. Human literature cites that in patients with tricuspid regurgitation or pulmonary insufficiency who are otherwise normal, maximum velocity measurements may overestimate or underestimate pulmonary arterial pressure by 20 mm Hg.¹³

Pulmonary arterial pressure can be overestimated if regurgitation jets overlap and color-flow and spectral Doppler placement is incorrect. In human medicine, there is evidence that adding estimated right atrial pressure may overestimate systolic pulmonary arterial pressure.¹⁵ Pulmonary arterial pressure may be underestimated if there is poor Doppler signal strength, poor jet alignment, or right ventricular myocardial failure or if tricuspid regurgitation and pulmonary insufficiency jets cannot be identified.^15,16

Other diagnostic tools

More advanced echocardiographic techniques can be used to diagnose pulmonary hypertension but are not commonly used. These techniques include calculating a Tei Index, which assesses myocardial function.^2,14 Tissue Doppler and right ventricular systolic time intervals can also be evaluated.¹⁴

In human medicine, right heart catheterization is the gold standard for diagnosing pulmonary hypertension.^17,18 In veterinary patients, this procedure requires general anesthesia and is a high-risk procedure given most patients' clinical signs. Right heart catheterization is also expensive and not commonly used in the clinical veterinary setting to diagnose pulmonary hypertension. Computed tomographic angiography, pulmonary function testing, and ventilation perfusion scans are also used in people.¹⁹