Pulmonary Hypertension

Dana Point Classification of Pulmonary Hypertension

DEFINITION:

• A resting mean pulmonary arterial pressure of 20 mmHg or less is considered normal. 
• Pulmonary hypertension is defined as a resting mean pulmonary arterial pressure of 25 mmHg or more at catheterization of the right side of the heart, a hemodynamic feature that is shared by all types of pulmonary hypertension in the Dana Point classification system
• Use of the term pulmonary arterial hypertension is restricted to those with a hemodynamic profile in which high pulmonary pressure is a result of elevated precapillary pulmonary resistance and normal pulmonary venous pressure and is measured as a pulmonary wedge pressure of 15 mmHg or less, a hemodynamic profile that is shared by groups 3, 4, and 5 in the Dana Point classification system, which was updated during the 4th World Symposium on Pulmonary Hypertension held in Dana Point, California, in 2008 
• A diagnosis of pulmonary arterial hypertension is made only in the absence of other causes of precapillary pulmonary hypertension such as that resulting from lung disease (group 3), chronic thromboembolic pulmonary hypertension (group 4), and disease resulting from multifactorial mechanisms (group 5).

Pathophysiology:

 

• The normal adult pulmonary vascular bed is a low-pressure, low-resistance system that is able to accommodate increases in blood flow with minimal elevation in pulmonary arterial pressure.
• In patients with pulmonary hypertension, pulmonary arterial pressure and vascular resistance are chronically elevated, leading to right ventricular dilatation and hypertrophy .
• Normal right ventricles have a thin wall and, when viewed in cross section, a crescent shape that is appropriate for pumping blood across the pulmonary vascular system 
• Pulmonary hypertension results in right ventricular hypertrophy, followed by dilatation and right atrial enlargement . Initially, these changes are compensatory mechanisms that allow the right ventricle to produce a larger stroke volume and maintain cardiac output. 
• In patients with severe pulmonary hypertension, the hypertrophied right ventricle has a spherical shape that has a greater cross-sectional area than that of the left ventricle, resulting in abnormal septal motion that impairs left ventricular function . 
• Eventually, the demand of the right ventricle for oxygen exceeds the available supply, causing chamber dilation that leads to tricuspid regurgitation, a result of tricuspid annular dilatation and incomplete valve closure. These processes eventually result in decreased cardiac output and right-sided heart failure
• The ability of the right ventricle to cope with the progressive increase in pulmonary arterial pressure is the main determinant of patients’ functional capacity and survival .
• Morphologic and functional assessment of the right ventricle plays a central role in both diagnosing pulmonary hypertension and performing serial follow-up examinations. The most useful noninvasive parameters for assessing right ventricular size and function are right ventricular volumes and ejection fraction, which are most accurately measured at cardiac MR imaging.

   Chest Radiography

Chest radiography is usually the initial imaging study performed and may depict features of pulmonary hypertension that are indicative of its underlying cause, such as interstitial lung disease, emphysema, chest wall deformities, and left-sided heart disease.

The classic radiographic findings of pulmonary hypertension are evident only late in the disease process.

findings include:

1.central pulmonary arterial dilatation; pruning of the peripheral arteries;

 2.increased diameter (15 mm in women and 16 mm in men) of the right interlobar artery, measured from its lateral aspect to the interlobar bronchus;

 3.and reduced retrosternal air space on lateral views, a result of right ventricular dilatation

Multidetector CTPA

Vascular Signs.—The classic CTPA findings of pulmonary hypertension may be divided into three categories: vascular, cardiac, and parenchymal.

Vascular signs

1.On transverse images, the main pulmonary artery is evaluated at the level of its bifurcation, orthogonal to its long axis . A pulmonary artery with a diameter of 29 mm or more has a positive predictive value of 97%, sensitivity of 87%, and specificity of 89% for the presence of pulmonary hypertension . However, it is important to emphasize that a diameter of less than 29 mm does not necessarily exclude pulmonary hypertension.

2.The diameters of the segmental pulmonary arteries should also be equal to those of adjacent bronchi. In the presence of a dilated (29 mm or more) main pulmonary artery, a segmental artery–to-bronchus diameter ratio of 1:1 or more in three or four lobes has a specificity of 100% for the presence of pulmonary hypertension

3.At CTPA, a main pulmonary arterial diameter larger than that of the ascending aorta is also a sign of pulmonary hypertension, with a positive predictive value of 96% and specificity of 92%, especially in patients younger than 50 years old.

 Cardiac Signs.—

Findings of adaptation and failure of the right side of the heart that may be seen at ECG-gated CTPA include

1.right ventricular hypertrophy, which is defined as wall thickness of more than 4 mm;

2.straightening or leftward bowing of the interventricular septum;

3. right ventricular dilatation (as a right ventricle–to–left ventricle diameter ratio of more than 1:1 at the midventricular level on axial images);

4.decreased right ventricular ejection fraction;

5.dilatation of the inferior vena cava and hepatic veins;

6. pericardial effusion

Parenchymal Signs

1.Centrilobular ground-glass nodules are a feature of pulmonary hypertension and are especially common in patients with idiopathic pulmonary arterial hypertension

Cardiac MR Imaging

Cardiac MR imaging is used to assess ventricular volume, morphologic characteristics, mass, function, and changes in pulmonary circulation

It is the modality of choice for studying the right ventricle because no geometric assumptions are required, and its three-dimensional, anatomic,morphologic measurements are unaffected by body habitus, lung disease, and chest wall deformity

REFERENCE

Radiographics   JAN-FEB 12-13