Cor Pulmonale

Introduction
Background

Cor pulmonale is defined as an alteration in the structure and function of the right ventricle caused by a primary disorder of the respiratory system. Pulmonary hypertension is the common link between lung dysfunction and the heart in cor pulmonale. Right-sided ventricular disease caused by a primary abnormality of the left side of the heart or congenital heart disease is not considered cor pulmonale, but cor pulmonale can develop secondary to a wide variety of cardiopulmonary disease processes. Although cor pulmonale commonly has a chronic and slowly progressive course, acute onset or worsening cor pulmonale with life-threatening complications can occur.
Pathophysiology

Several different pathophysiologic mechanisms can lead to pulmonary hypertension and, subsequently, to cor pulmonale. These pathogenetic mechanisms include (1) pulmonary vasoconstriction due to alveolar hypoxia or blood acidemia, (2) anatomic compromise of the pulmonary vascular bed secondary to lung disorders (eg, emphysema, pulmonary thromboembolism, interstitial lung disease), (3) increased blood viscosity secondary to blood disorders (eg, polycythemia vera, sickle cell disease, macroglobulinemia), and (4) idiopathic primary pulmonary hypertension. The result is increased pulmonary arterial pressure.

The right ventricle (RV) is a thin-walled chamber that is more a volume pump than a pressure pump. It adapts better to changing preloads than afterloads. With an increase in afterload, the RV increases systolic pressure to keep the gradient. At a point, a further increase in the degree of pulmonary arterial pressure produces significant RV dilation, an increase in RV end-diastolic pressure, and RV circulatory collapse. A decrease in RV output with a decrease in diastolic left ventricle (LV) volume results in decreased LV output. Since the right coronary artery, which supplies the RV free wall, originates from the aorta, decreased LV output diminishes blood pressure in the aorta and decreases right coronary blood flow. What ensues is a vicious cycle between decreases in LV and RV output. Genetic investigations have confirmed that morphogenesis of the right and left ventricle originated from different sets of progenitor cells and sites. This polymorphism could explain the differing rates of hypertrophy of the right and left ventricles.1

Right ventricular overload is associated with septal displacement toward the left ventricle. Septal displacement, which is seen on echocardiography, can be another factor that decreases LV volume and output in the setting of cor pulmonale and right ventricular enlargement. Several pulmonary diseases cause cor pulmonale, which may involve interstitial and alveolar tissues with a secondary effect on pulmonary vasculature or may primarily involve pulmonary vasculature. Chronic obstructive pulmonary disease (COPD) is the most common cause of cor pulmonale in the United States. (For related information, see Medscape's COPD Resource Center.)
Cor pulmonale usually presents chronically, but 2 main conditions can cause acute cor pulmonale: massive pulmonary embolism (more common) and acute respiratory distress syndrome (ARDS). The underlying pathophysiology in massive pulmonary embolism causing cor pulmonale is the sudden increase in pulmonary resistance. In ARDS, 2 factors cause RV overload: the pathologic features of the syndrome itself and mechanical ventilation. Mechanical ventilation, especially higher tidal volume, requires a higher transpulmonary pressure. In chronic cor pulmonale, right ventricular hypertrophy (RVH) generally predominates. In acute cor pulmonale, right ventricular dilatation mainly occurs.
Frequency
United States

* Cor pulmonale is estimated to account for 6-7% of all types of adult heart disease in the United States, with chronic obstructive pulmonary disease (COPD) due to chronic bronchitis or emphysema the causative factor in more than 50% of cases.
* At present, cor pulmonale accounts for 10-30% of decompensated heart failure related admissions in the United States.2
* Although the prevalence of COPD in the United States is about 15 million, the exact prevalence of cor pulmonale is difficult to determine because it does not occur in all cases of COPD, and the physical examination and routine tests are relatively insensitive for the detection of pulmonary hypertension.
* In contrast, acute cor pulmonale is usually secondary to massive pulmonary embolism.
* Acute massive pulmonary thromboembolism is the most common cause of acute life-threatening cor pulmonale in adults.
* In the United States, 50,000 deaths are estimated to occur per year from pulmonary emboli and about half occur within the first hour due to acute right heart failure.

International

The incidence of cor pulmonale varies among different countries depending on the prevalence of cigarette smoking, air pollution, and other risk factors for various lung diseases.
Mortality/Morbidity

Development of cor pulmonale as a result of a primary pulmonary disease usually heralds a poorer prognosis. For example, patients with COPD who develop cor pulmonale have a 30% chance of surviving 5 years. However, whether cor pulmonale carries an independent prognostic value or it is simply reflecting the severity of underlying COPD or other pulmonary disease is not clear. Prognosis in the acute setting due to massive pulmonary embolism or ARDS has not been shown to be dependent on the presence or absence of cor pulmonale.
Clinical
History

Clinical manifestations of cor pulmonale generally are nonspecific. The symptoms may be subtle, especially in early stages of the disease, and mistakenly may be attributed to the underlying pulmonary pathology.

* The patient may complain of fatigue, tachypnea, exertional dyspnea, and cough.
* Anginal chest pain also can occur and may be due to right ventricular ischemia (it usually does not respond to nitrates) or pulmonary artery stretching.
* Hemoptysis may occur because of rupture of a dilated or atherosclerotic pulmonary artery. Other conditions, such as tumors, bronchiectasis, and pulmonary infarction, should be excluded before attributing hemoptysis to pulmonary hypertension. Rarely, the patient may complain of hoarseness due to compression of the left recurrent laryngeal nerve by a dilated pulmonary artery.
* A variety of neurologic symptoms may be seen due to decreased cardiac output and hypoxemia.
* In advanced stages, passive hepatic congestion secondary to severe right ventricular failure may lead to anorexia, right upper quadrant abdominal discomfort, and jaundice.
* Syncope with exertion, which may be seen in severe disease, reflects a relative inability to increase cardiac output during exercise with a subsequent drop in the systemic arterial pressure.
* Elevated pulmonary artery pressure can lead to elevated right atrial pressure, peripheral venous pressure, and then capillary pressure and by increasing the hydrostatic gradient, it leads to transudation of fluid, which appears as peripheral edema. Although this is the simplest explanation for peripheral edema in cor pulmonale, other hypotheses explain this symptom, especially in a fraction of patients with COPD who do not show increase in right atrial pressure. A decrease in glomerular filtration rate (GFR) and filtration of sodium and stimulation of arginine vasopressin (which decreases free water excretion) due to hypoxemia play important pathophysiologic roles in this setting and may even have a role for peripheral edema in patients with cor pulmonale who have elevated right atrial pressure.

Physical

Physical findings may reflect the underlying lung disease or pulmonary hypertension, RVH, and RV failure.

* On inspection, an increase in chest diameter, labored respiratory efforts with retractions of the chest wall, distended neck veins with prominent a or v waves, and cyanosis may be seen.
* On auscultation of the lungs, wheezes and crackles may be heard as signs of underlying lung disease. Turbulent flow through recanalized vessels in chronic thromboembolic pulmonary hypertension3 may be heard as systolic bruits in the lungs. Splitting of the second heart sound with accentuation of the pulmonic component can be heard in early stages. A systolic ejection murmur with sharp ejection click over the region of the pulmonary artery may be heard in advanced disease, along with a diastolic pulmonary regurgitation murmur. Other findings upon auscultation of the cardiovascular system may be third and fourth sounds of the heart and systolic murmur of tricuspid regurgitation.
* RVH is characterized by a left parasternal or subxiphoid heave. Hepatojugular reflux and pulsatile liver are signs of RV failure with systemic venous congestion.
* On percussion, hyperresonance of the lungs may be a sign of underlying COPD; ascites can be seen in severe disease.
* Examination of the lower extremities reveals evidence of pitting edema. Edema in cor pulmonale is strongly associated with hypercapnia.4

Causes

* A general approach to diagnose cor pulmonale and to investigate its etiology starts with routine laboratory tests, chest radiography, and electrocardiography. Echocardiography gives valuable information about the disease and its etiology. Pulmonary function tests may become necessary to confirm the underlying lung disease. Ventilation/perfusion (V/Q) scan or chest CT scan may be performed if history and physical examination suggest pulmonary thromboembolism as the cause or if other diagnostic tests do not suggest other etiologies. Right heart catheterization is the most accurate but invasive test to confirm the diagnosis of cor pulmonale and gives important information regarding the underlying diseases. Any abnormal result in each of these tests may need further diagnostic evaluation in that specific direction.
* Laboratory investigations are directed toward defining the potential underlying etiologies as well as evaluating complications of cor pulmonale. In specific instances, appropriate lab studies may include the following: hematocrit for polycythemia (which can be a consequence of underlying lung disease but can also increase pulmonary arterial pressure by increasing viscosity), serum alpha1-antitrypsin if deficiency is suspected, and antinuclear antibody level for collagen vascular disease such as scleroderma. Hypercoagulability states can be evaluated by serum levels of proteins S and C, antithrombin III, factor V Leyden, anticardiolipin antibodies, and homocysteine.
* Arterial blood gas tests may provide important information about the level of oxygenation and type of acid-base disorder.
* Elevated brain natriuretic peptide (BNP) level alone is not adequate to establish presence of cor pulmonale, but it helps to diagnose cor pulmonale in conjunction with other noninvasive tests and in appropriate clinical settings. An elevated BNP level may actually be a natural mechanism to compensate for elevated pulmonary hypertension and right heart failure by promoting diuresis and natriuresis, vasodilation of systemic and pulmonary vessels, and reduction of circulating levels of endothelin and aldosterone.

Source : http://emedicine.medscape.com/article/154062-overview