Data Reveals How Pulmonary Embolism Can Lead To Pulmonary Hypertension

According to recent data, there is a direct correlation between pulmonary emboli that result in the onset of pulmonary hypertension (PH) — an under recognized condition that researchers and medical practitioners alike hope to address in the PH patient population.

Pulmonary embolism is the clinical condition marked by a  blockage or an interruption in blood flow through the pulmonary artery, which interferes with the blood flow and exchange of gases between the heart and the lungs. This is caused mainly as a result of deep vein thrombosis, a condition where there is a blood clot present in the deep veins of the leg or pelvis, and this clot migrates from the vein and is deposited in the pulmonary vasculature, interrupting blood flow. This condition is called pulmonary thromboembolism.

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Chronic thromboembolic pulmonary hypertension (CTEPH) is a result of continued or persistent thromboembolism. The emboli (clots) continue to form more clots and increase difficulty in circulation. This increases pressure on the lungs and the right side of the heart (as this side is responsible for pumping out deoxygenated blood via the pulmonary artery into the lungs), medically termed as hypertension.  This is a rare condition, but has been on the rise in a number of cases in the recent past (around 4%). According to reports by the World Council of Pulmonary Embolism, only 5,000 cases of CTEPH are reported annually in the United States.

However, not all people with an underlying embolism will develop CTEPH — about half of the people with pulmonary embolism progress to developing CTEPH in later stages.

Pulmonary hypertension (PH) refers to increase in blood pressure in the lung vasculature due to interrupted blood flow from the heart to the lung and insufficient oxygen being passed on. Another cause of there disease can be the incomplete closing of the ductus arterioles or foramen oval during transformation from the fetal stage to the postnatal stage, due to incomplete circulatory transformation. This can either lead to PH in childhood, or become more pronounced in adulthood.

From Pulmonary Embolism To Pulmonary Hypertension: The Progression

There are no specific symptoms for PH, which makes diagnosis in the early stages even more difficult. Of the few non-specific symptoms in CTEPH, the commonly reported ones include shortness of breath with exercise or intense body movements (dyspnea), chest discomfort, and fatigue. Late-stage symptoms include fainting; signs of right heart failure, including cyanosis (the tips of fingers turning blue due to lack of oxygen); and pulmonary edema among others.

Diagnosis of CTEPH begins with imaging techniques like transthoracic echocardiogram (TTE) and ventricular perfusion scanning, which helps in detecting the presence of blood clots or checking for any obstructions to blood-flow through the arteries, degree of arterial dysfunction, and rate of ventricular filling, all of which are affected during pulmonary hypertension. It also helps in detecting the presence of a right-to-left shunt, which is one of the primary reasons for PH. Pulmonary angiography is another confirmatory imaging technique which uses X-rays to check for abnormalities in pulmonary and cardiac circulation, once an abnormal ventricular perfusion scan report is obtained. Computed tomography scanning (CT scan) can help in observing sections of the pulmonary artery and ruling out conditions which mimic CTEPH like fibrous mediastinitis, sarcoma of the pulmonary artery, tumor emboli into the pulmonary artery, hydatic emboli, or pulmonary arteritis such as Behcet’s arteritis or Takayashu’s arteritis among others.

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Right heart catheterization is regarded as the ‘Gold Standard’ in case of a suspicious case of PH. It measures the right heart pressures and measures pulmonary vascular resistance, which gives a surer idea of the severity of the condition.

After diagnosis, a surgical procedure called a pulmonary thromboendarterectomy is performed on the patient. It is an invasive procedure where an incision is made in the chest and is performed through a period of cardiopulmonary arrest, where the heart is made to stop beating and an artificial heart-lung machine provides respiratory support. The surgeon works on the right and left pulmonary arteries, working his way into the small arterioles of the pulmonary vascular tree, clearing the blockage and ensuring a near-to-normal condition of the heart with a clear passage for oxygenated and deoxygenated blood. The rates of success with this process are very high, with a low death rate of 5% to 10%, depending on the patient’s health, comorbidities, and hemodynamic status. If the pulmonary vascular resistance is below 900 dynes.s.cm-5, the rate of death is around 4%. It increases to 10% in patients with resistance between 900 and 1200 dynes.s.cm-5, and to 20% for resistance higher than 1200 dynes.s.cm-5.4 Hence, it is advisable to perform pulmonary endarterectomy early in the course of the disease to limit the operative risk.

Survival rates improve significantly with the successful surgical procedures. From a poor median survival period of 12 to 24 months and a mere 10% survival chance after 5 years of living with the condition ,for people with untreated PH, surgery improves this to as much as 75% after 10 to 15 years of surgery. The complications arising from this are limited only till dyspnea in certain people but no major consequences are reported. Supportive anti-coagulation therapy is necessary to maintain a healthy arterial blood-flow and prevent thrombosis.