COR PULMONALE

COR PULMONALE

Definitions

• Cor pulmonale is defined as enlargement or hypertrophy of the right ventricle (RV) in response to increased right ventricular afterload.
• Clinically, cor pulmonale presents as right heart failure, which is defined by a sustained increase in RV pressures combined with an inability to augment the cardiac output in response to exercise or other stimuli.
• Some authors exclude right heart failure due to increased left atrial pressures from definitions of cor pulmonale, however this distinction is of no clinical value and will not be used here.

Pathophysiology

• In normal individuals the right ventricle plays little role in augmenting circulatory flow with most of the driving pressure for flow coming from the left ventricle and the venous return. In fact, children with tricuspid atresia can be successfully treated by joining the right atrium to the pulmonary artery (Fontan procedure).
• When the right ventricle is exposed chronically to increased afterload it hypertrophies and assumes a more important role in maintaining flow through the pulmonary circulation.
• If the afterload elevation is severe enough, the right ventricle limits the overall cardiac output. RV afterload can increase due to (1) obstruction or destruction of the pulmonary circulation, (2) hypoxic pulmonary vasoconstriction, (3) cardiac disease, or (4) idiopathic causes.
• Obstruction or destruction of any part of the pulmonary circulation from the pulmonic valve to the left atrium results in increased RV afterload. Examples include (1) pulmonary arterial obstruction (acute or chronic pulmonary emboli), (2) destruction of the pulmonary microvasculature (emphysema, fibrotic lung diseases), or (3) obstruction of the pulmonary veins (pulmonary veno-occlusive disease, sickle cell disease, some chemotherapeutic agents).
• Hypoxic pulmonary vasoconstriction is the vasoconstriction of small pulmonary arteries and arterioles at oxygen tensions less than 60 torr. This response results in improved ventilation to perfusion matching at the expense of increased pulmonary vascular resistance. Chronic obstructive pulmonary disease, chest wall diseases, obstructive sleep apnea, and interstitial fibrosis all cause pulmonary hypertension via this mechanism.
• Idiopathic causes of pulmonary hypertension include
• Finally, cardiac disease can result in pulmonary hypertension either through increased left atrial pressures (mitral stenosis) or through chronic L to R shunting. Idiopathic proliferation of pulmonary arterioles and dropout of pulmonary capillaries eventually leads to irreversible increases in the pulmonary vascular resistance so repair of the underlying defect may not alleviate the right heart failure. In patients with chronic L to R shunts, R sided pressures may eventually exceed left sided pressures leading the R to L shunting (Eisenmenger physiology).

Clinical Presentation

• The most common presenting complaints of patients with cor pulmonale is dyspnea on exertion and fatigue.
• Syncope, near syncope, chest pain, palpitations and leg edema are also common.
• Physical findings may be subtle early. Jugular venous pressures are invariably increased. Cardiac palpation may reveal a right ventricular heave. P2 is increased and moves closer to A2 as the pulmonary pressures increase. Eventually S2 may be fixed and paradoxically split. Increased right atrial pressures may lead to dependent edema, hepatojugular reflux, and ascites.
• The chest x-ray may reveal right ventricular hypertrophy, manifest as filling of the retrocardiac space on the lateral film, and increased PA size.
• The ECG may be normal or show right atrial and ventricular enlargement as well as an R axis deviation. Supraventricular tachycardias are common.

Diagnosis

• Diagnosis is often expected based on clinical examination although findings may be subtle.
• Increasingly, the diagnosis of pulmonary hypertension is made with echocardiagraphy which demonstrates increased right ventricular size and wall thickness as well as evidence of ventricular interdependence (i.e. the septum moves with the RV instead of the LV). In the presence of tricuspid regurgitation (which is almost invariably present in R heart failure), pulmonary artery pressures can be estimated based on the velocity of the regurgitant jet.
• The diagnosis is confirmed with right heart catheterization which demonstrates elevated right atrial, ventricular and pulmonary artery pressures.
• Left atrial pressure is normal unless there is mitral stenosis or LV failure.
• In addition, measurement of chamber oxygen saturations during right heart catheterization can be diagnostic for L to R shunts.

Differential Diagnosis

·         Obstructive Lung Diseases

Emphysema
Chronic bronchitis
Bronchiectaisis
Cystic fibrosis

·         Chest Wall Disease

Kyphoscoliosis
Thoracoplasty

·         Hypoventilation Syndromes

·         Neuromuscular diseases 

·         Obstructive sleep apnea 

·         Interstitial Fibrosis 

·         Pulmonary Thromboembolism (deep venous, tumor, foreign body)

·         Cardiac Disease

Congenital L to R shunts with Eisenmenger physiology (especially atrial septal defect in adults)

Mitral stenosis

·         Idiopathic

Primary pulmonary hypertension
Pulmonary venoocclusive disease
Sickle hemoglobinopathies
Portal hypertension
Fibrosing mediastinitis

Treatment of Underlying Etiology

• Anticoagulation or vena caval interruption are effective for thromboembolic disease.
• CPAP or tracheostomy can be used for obstructive sleep apnea, and correction of cardiac abnormalities is effective if the pulmonary vascular resistance is not substantially elevated.

Afterload Reduction

• Medical therapy is aimed primarily at decreasing right sided afterload. This can be done most effectively with oxygen via reversal of hypoxic pulmonary vasoconstriction. Indeed, 2 large studies of patients with chronic hypoxia (SaO2<90%) and cor pulmonale secondary to COPD demonstrated marked survival benefits with long term oxygen therapy.
• Vasodilating agents used in left heart failure are generally ineffective at decreasing right sided afterload as systemic hypotension is usually encountered before significant decreases in pulmonary vascular resistance are achieved. One clear exception to this is inhaled nitric oxide. The rapid metabolism of this drug prevents systemic vasodilation and hypotension. Furthermore its distribution solely to ventilated regions prevents the worsened hypoxemia due to impaired V/Q mismatching encountered with systemic vasodilators. Investigation in this field is active.

Heart Failure

• Peripheral edema and ascites due to R heart failure can be treated with diuretics. This must be done with care as decreased right ventricular filling can be associated with a catastrophic fall in cardiac output.
• Digoxin is not effective for treating R heart failure.

Lung Transplantation

• Lung transplantation should be considered for patients with end stage COPD, fibrotic lung diseases and primary pulmonary hypertension who have severe symptoms despite 
  • maximal medical therapy. Dramatic reversals in pulmonary hypertension and clinical symptoms are seen with this procedure, however, it carries the side effects of long term immunosuppression.