Monitoring the response to therapy for pulmonary arterial hypertension, part 2
Despite the recent development of several new therapies, pulmonary arterial hypertension (PAH) remains an incurable disease. Careful monitoring of disease progression is vital to ensuring that patients receive maximal medical therapy before the onset of overt right-sided heart failure. In part 1 of this article, I reviewed the role of the history and physical examination, chest radiography, electrocardiography, echocardiography, and pulmonary artery catheterization. In part 2, I focus on MRI, cardiopulmonary exercise testing (CPET), the 6-minute walk test, and biomarkers.
Despite the recent development of several new therapies, pulmonary arterial hypertension (PAH) remains an incurable disease. Careful monitoring of disease progression is vital to ensuring that patients receive maximal medical therapy before the onset of overt right-sided heart failure. In part 1 of this article, I reviewed the role of the history and physical examination, chest radiography, electrocardiography, echocardiography, and pulmonary artery catheterization. In part 2, I focus on MRI, cardiopulmonary exercise testing (CPET), the 6-minute walk test, and biomarkers.
MRI
This diagnostic test combines several advantages of pulmonary artery catheterization and transthoracic echocardiography (TTE). Like TTE, MRI is noninvasive and can be done repeatedly with little harm to the patient. At the same time, it can provide most of the hemodynamic measurements obtained by catheterization. Its ability to more precisely visualize right ventricular (RV) structures allows accurate measurements of RV end-diastolic and end-systolic dimensions, and computer processing of multiple cross-sectional areas provides ventricular volume and mass.
The RV ejection fraction can be calculated as the difference between RV end-diastolic volume and RV end-systolic volume. The RV stroke volume can be measured by examining volumetric flow in the pulmonary artery, and RV output can be calculated from the product of RV stroke volume and heart rate. Maximal systolic cross-sectional area and mean systolic blood flow velocity over the main pulmonary artery can be used to calculate the mean pulmonary artery pressure (PAP). Studies of patients with PAH have shown good agreement between mean PAP measured by MRI and by pulmonary artery catheterization.1
MRI can also assess RV function by generating pressure-volume loops from measurements of ventricular volumes and pressures.2 RV myocardial contractility can be assessed by the slope of the end-systolic pressure-volume relationship, a load-independent parameter of myocardial contractility.
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