Multimodality Imaging of Pulmonary Hypertension: Prognostication of Therapeutic Outcomes

There are many causes of pulmonary hypertension (PH). The new clinical classification system for PH relies on grouping the causes of this disorder by treatment paradigm. In the western world, PH is most commonly related to left heart disease/ischemic heart disease or due to chronic lung diseases. Pulmonary arterial hypertension (PAH) is a rare condition characterized by remodeling of the distal pulmonary vasculature. Commonly patients with PAH present late in their disease course after severe damage to the distal vasculature has occurred and the current treatment of PAH depends on the use of pulmonary vasodilators. Chronic thromboembolic pulmonary hypertension (CTEPH), which occurs in 1–3% of patients following acute pulmonary embolism, are treated with pulmonary endarterectomy and/or balloon pulmonary angioplasty provided the disease is accessible; patients with inaccessible disease require pulmonary vasodilators. For most causes of PH, the onset of right ventricular failure is rapid with death occurring within 5 years of diagnosis. Herein, we review the ability of ultrasound, nuclear medicine, and MRI for the diagnosis and follow up this group of diseases. Transthoracic ultrasound is the main tool to diagnose PH due to its portability, access, familiarity of use, and its ability to estimate mean pulmonary artery pressure from the velocity of the tricuspid regurgitation jet using the modified Bernoulli equation. For nuclear medicine, SPECT ventilation with ¹³³Xe gas and ^99mTc-MAA perfusion imaging is quite useful for the diagnosis of CTEPH. The key cardiovascular MRI metrics found to relate to right ventricular volume and function along with pulmonary arterial pulsatility. While there are a number of noninvasive methods for the diagnosis and follow-up of PH and PAH, there is no current replacement for the intra-arterial pressure measurements of right heart catheterization.