Pulmonary thromboembolism (PTE)

Pulmonary thromboembolism, commonly abbreviated as PTE, is a serious and potentially fatal condition in cats that occurs when a blood clot blocks one or more arteries in the lungs. This obstruction prevents normal blood flow through the affected portion of the lung, severely impairing the cat's ability to oxygenate blood and leading to acute respiratory distress. PTE represents a medical emergency that requires immediate veterinary intervention to maximize the chance of survival. While less commonly discussed than some feline conditions, pulmonary thromboembolism is increasingly recognized as a significant cause of sudden respiratory compromise and death in cats.

The development of pulmonary thromboembolism involves the formation and migration of blood clots within the circulatory system. Clots typically form in the heart chambers, major veins, or other parts of the vascular system before breaking loose and traveling through the bloodstream to lodge in the pulmonary arteries. Several underlying conditions predispose cats to abnormal clot formation, including heart disease, cancer, protein-losing kidney or intestinal diseases, and various inflammatory conditions. The clot blocks blood flow to the downstream lung tissue, preventing gas exchange in the affected area and forcing the remaining healthy lung tissue to compensate for the loss.

The impact of pulmonary thromboembolism on affected cats is immediate and severe. Cats experience sudden onset of respiratory distress as oxygen exchange is dramatically reduced. The severity of symptoms depends on the size and location of the clot or clots, with larger clots causing more extensive blockage and more severe symptoms. Small clots may cause subtle symptoms that are easily overlooked, while large clots can cause cardiovascular collapse and death within minutes. Even cats that survive the initial event face the risk of additional clots and require identification and treatment of the underlying condition that caused clot formation.

Pulmonary thromboembolism is treatable if recognized quickly and managed aggressively, though the prognosis depends heavily on the underlying cause and the extent of pulmonary vascular obstruction. Treatment focuses on supporting respiratory function, preventing additional clot formation, and addressing the predisposing condition. Anticoagulant medications help prevent new clots while the body gradually dissolves the existing obstruction. The importance of early detection cannot be overstated, as delays in treatment allow further deterioration and reduce survival chances. Cat owners with pets known to have conditions predisposing to clot formation should be aware of PTE risk and watch for sudden breathing changes.

The primary cause of pulmonary thromboembolism is the formation of blood clots that travel through the circulation and become lodged in the pulmonary arteries. These clots most commonly originate from the heart, particularly in cats with heart disease that causes blood to pool and stagnate in the cardiac chambers. Hypertrophic cardiomyopathy, the most common heart disease in cats, is a leading predisposing factor for thrombus formation. Clots may also form in the systemic veins and travel through the right side of the heart to reach the lungs. In some cases, clots form directly in the pulmonary arteries themselves. Any condition that alters blood flow, damages blood vessel walls, or changes the composition of blood to favor clotting can predispose to PTE.

Several disease conditions create the hypercoagulable state that predisposes to pulmonary thromboembolism. Cardiac disease, particularly cardiomyopathy with left atrial enlargement, is perhaps the most well-recognized predisposing factor in cats. Neoplasia (cancer) activates clotting cascades and is commonly associated with thromboembolic events. Protein-losing conditions including protein-losing nephropathy and protein-losing enteropathy alter the balance of procoagulant and anticoagulant proteins in the blood. Immune-mediated hemolytic anemia causes red blood cell destruction that promotes clotting. Pancreatitis, sepsis, and other severe inflammatory conditions increase clot risk. Hyperadrenocorticism (Cushing's disease) and hyperthyroidism have been associated with increased thromboembolic risk in some species.

Genetic factors may contribute to pulmonary thromboembolism risk through their role in predisposing conditions. Certain cat breeds have genetic predisposition to hypertrophic cardiomyopathy, which in turn increases PTE risk. Maine Coons, Ragdolls, and British Shorthairs carry known mutations for cardiomyopathy. Other hereditary conditions affecting blood vessel integrity or clotting factor function could theoretically increase risk, though specific genetic mutations causing hypercoagulability have not been well characterized in cats. The hereditary component of PTE is therefore primarily through inherited predisposition to the underlying conditions that cause abnormal clot formation.

Risk factors for pulmonary thromboembolism include advanced age, sedentary lifestyle, recent surgery or trauma, and certain medications. Older cats are more likely to have developed the underlying conditions that predispose to clot formation. Cats that are immobile for extended periods, whether due to illness, injury, or confinement, have reduced blood flow that can promote clot formation. Surgical procedures and traumatic injuries cause tissue damage and inflammation that activate clotting cascades. Central venous catheters provide a surface for clot formation. Corticosteroid medications may increase clotting tendency in some cats. Cats with multiple predisposing factors face cumulative risk.

The mechanism by which pulmonary thromboembolism develops follows a predictable pathophysiological sequence. A clot forms in response to abnormal blood flow, vessel wall damage, or altered blood composition, which together constitute Virchow's triad. Once a clot reaches a certain size, all or part of it may break free and travel as an embolus through the bloodstream. The clot travels through the right side of the heart and into the pulmonary arterial system, where vessels become progressively smaller. When the clot reaches an artery smaller than its diameter, it becomes lodged and obstructs blood flow. The downstream lung tissue receives no blood for gas exchange, creating a ventilation-perfusion mismatch. If the obstruction is large enough, right heart failure may develop as the heart struggles to pump against increased resistance. Inflammatory responses to the clot can worsen the obstruction and may cause additional damage to lung tissue.

Early warning signs of impending pulmonary thromboembolism are often absent or extremely subtle, as the underlying conditions causing clot formation may produce few obvious symptoms. Cats with heart disease may have slightly increased resting respiratory rates or mild exercise intolerance before developing PTE. Those with cancer or other predisposing conditions may show gradual weight loss, decreased appetite, or lethargy in the weeks preceding the event. However, in many cases, PTE occurs without any warning, striking cats that appeared completely healthy just hours earlier. This unpredictable nature makes prevention and early intervention challenging and underscores the importance of managing known risk factors.

When pulmonary thromboembolism occurs, the onset of symptoms is typically sudden and dramatic. Affected cats develop acute respiratory distress, often within seconds to minutes. Rapid, labored breathing is the most consistent sign, with cats taking shallow, quick breaths and showing visible effort with each breath. Some cats may vocalize in distress or appear panicked. Collapse may occur if the obstruction is severe enough to significantly compromise oxygen delivery or cause right heart failure. The sudden nature of symptom onset, in a cat that may have appeared normal moments before, is characteristic of PTE and helps differentiate it from more gradually developing respiratory conditions.

Behavioral changes in cats experiencing pulmonary thromboembolism reflect severe distress and oxygen deprivation. Affected cats typically stop all normal activity immediately, refusing to walk, eat, or interact. They may seek out their owners or hide, depending on individual temperament. Extreme restlessness and inability to find a comfortable position is common as cats struggle to breathe. Some cats display open-mouth breathing, which is always abnormal in cats and indicates severe respiratory compromise. Vocalization ranging from distressed meowing to panting may occur. Affected cats generally resist being handled and may become aggressive due to distress and pain.

Physical signs visible during a pulmonary thromboembolism event include respiratory changes and signs of cardiovascular compromise. Gum color may change from healthy pink to pale, gray, or blue-tinged, indicating poor oxygenation and circulation. The tongue may show similar color changes. Breathing is rapid and shallow, with visible chest movement and often abdominal effort as well. The cat may stand or sit with elbows abducted and neck extended to maximize airway opening. Weak or rapid pulse may be detected. Body temperature may drop as circulation becomes compromised. In severe cases, loss of consciousness may occur as oxygen delivery to the brain becomes critically impaired.

The progression of symptoms in pulmonary thromboembolism can be frighteningly rapid. A cat may deteriorate from appearing relatively normal to being in respiratory failure within minutes to hours, depending on the size and number of clots. Small clots may cause only mild symptoms that could be missed initially, while massive clots can cause immediate cardiovascular collapse. Once symptoms begin, they typically worsen without treatment as oxygen deprivation affects organ function and additional complications develop. Cardiogenic shock may develop as the heart fails under increased workload. The trajectory can be so rapid that some cats die before reaching veterinary care.

Emergency symptoms requiring immediate transport to a veterinary facility include any sudden onset of difficulty breathing, collapse, open-mouth breathing, blue or purple discoloration of the tongue or gums, loss of consciousness, and inability to stand or walk. If PTE is suspected, the cat should be transported with minimal handling and kept as calm as possible, as stress increases oxygen demand and can precipitate further decompensation. Oxygen support during transport, if available, can be life-saving. Time is critical in PTE cases, and owners should proceed directly to the nearest emergency veterinary facility without delay.

The initial examination of a cat with suspected pulmonary thromboembolism prioritizes stabilization over diagnostic procedures. Cats presenting in acute respiratory distress are immediately provided oxygen support while the veterinary team observes from a distance, minimizing handling that could worsen respiratory compromise. Once the cat is somewhat stabilized, brief physical examination may reveal rapid heart rate, weak pulses, abnormal lung sounds, and altered mentation. The history, including any known underlying conditions, recent surgery, or previous similar episodes, helps raise suspicion for PTE. The combination of sudden-onset respiratory distress in a cat with known risk factors strongly suggests pulmonary thromboembolism.

Diagnostic imaging plays a crucial role in identifying pulmonary thromboembolism, though findings may be subtle or nonspecific. Thoracic radiographs may show areas of abnormally lucent (dark) lung where blood flow is reduced, regional differences in blood vessel size, or signs of right heart enlargement. However, radiographs can appear normal in many PTE cases, particularly early in the course. Computed tomography angiography (CTA) provides the most definitive imaging diagnosis, allowing direct visualization of clots within the pulmonary arteries. This specialized imaging requires anesthesia, which carries significant risk in unstable patients, and is not available at all veterinary facilities. Echocardiography can identify right heart enlargement and dysfunction, visualize clots in the heart, and detect pulmonary hypertension, all of which support a PTE diagnosis.

Additional diagnostic tests help confirm the diagnosis and identify underlying causes. Blood gas analysis reveals low oxygen levels and may show abnormalities consistent with respiratory failure. D-dimer testing, which measures a breakdown product of blood clots, may be elevated in cats with PTE, though results can be nonspecific. A complete blood count and chemistry panel evaluate overall health and may reveal abnormalities pointing to underlying conditions. Cardiac biomarkers like troponin may be elevated due to right heart strain. Coagulation testing helps identify clotting abnormalities. Screening for underlying conditions includes evaluation for heart disease, cancer, and protein-losing disorders depending on clinical suspicion.

Differential diagnosis for acute respiratory distress in cats includes several conditions that must be distinguished from pulmonary thromboembolism. Congestive heart failure with pulmonary edema causes breathing difficulty with distinct imaging findings. Feline asthma can cause acute respiratory distress, typically with more gradual onset and response to bronchodilators. Pneumothorax (air in the chest cavity) causes sudden breathing difficulty with characteristic examination and radiographic findings. Pleural effusion accumulates fluid around the lungs. Diaphragmatic hernia can cause acute respiratory compromise. Trauma to the chest may cause various respiratory problems. The diagnosis of PTE is often presumptive, based on compatible clinical signs, exclusion of other causes, identification of risk factors, and supportive diagnostic findings rather than definitive imaging in many cases.

Emergency treatment of pulmonary thromboembolism begins with respiratory stabilization and support. Oxygen therapy is initiated immediately using whatever method causes least stress to the patient, typically an oxygen cage or flow-by oxygen. Sedation may be administered to reduce anxiety and the associated increase in oxygen demand, though drugs must be carefully selected to avoid further cardiovascular depression. Intravenous access is established for medication and fluid administration, though fluid therapy is approached cautiously as excessive fluids can worsen right heart failure. The immediate goal is to maintain adequate oxygen delivery to vital organs while more specific treatments are initiated.

Anticoagulant therapy forms the cornerstone of medical treatment for pulmonary thromboembolism. Unfractionated heparin or low-molecular-weight heparin is typically started immediately once PTE is suspected or confirmed. These medications do not dissolve existing clots but prevent formation of new clots and extension of existing ones, allowing the body's own fibrinolytic system to gradually break down the obstruction. Anticoagulant therapy is continued for weeks to months depending on the underlying cause and risk of recurrence. Oral anticoagulants or antiplatelet medications like clopidogrel may be used for long-term prevention in cats at high risk for recurrent thromboembolism. Careful monitoring is required as anticoagulants carry risk of serious bleeding.

Thrombolytic therapy, which actively dissolves blood clots, is used in human medicine for severe pulmonary embolism but is less commonly employed in cats. Drugs like tissue plasminogen activator (tPA) can rapidly break down clots but carry significant risk of life-threatening bleeding. The decision to use thrombolytics requires careful consideration of the severity of obstruction, bleeding risk, and potential benefit. In life-threatening cases where other treatments have failed, thrombolytic therapy may be attempted despite the risks. Surgical removal of clots from the pulmonary arteries (pulmonary thrombectomy) is technically possible but rarely performed in cats due to the high surgical risk in unstable patients and limited availability of the required expertise and equipment.

Supportive care during the treatment of pulmonary thromboembolism addresses the many complications that can develop. Cardiovascular support may include judicious fluid therapy and medications to support blood pressure and heart function. Pain management is important as PTE can cause significant discomfort. Thermoregulation prevents hypothermia in compromised patients. Nutritional support becomes important once the cat is stable enough to eat. Treatment of any concurrent conditions, particularly heart failure, proceeds alongside PTE management. Close monitoring of respiratory status, heart rate and rhythm, blood pressure, and oxygenation guides treatment adjustments.

Addressing the underlying cause is essential for preventing recurrence and improving long-term outcomes. Cats with heart disease require appropriate cardiac medications. Those with cancer face decisions about oncological treatment. Protein-losing conditions need specific management. Inflammatory conditions require anti-inflammatory therapy. Without treatment of the predisposing condition, the risk of recurrent thromboembolism remains high. In some cases, the underlying cause may not be identifiable despite thorough investigation, and long-term anticoagulant therapy may be continued empirically.

Treatment decisions in pulmonary thromboembolism involve consideration of multiple factors including severity of the current episode, underlying cause, overall patient status, and practical considerations. The prognosis for severe, acute PTE is guarded regardless of treatment intensity. Costs can be substantial, particularly with intensive care hospitalization and specialized diagnostics. Veterinarians work with owners to determine the most appropriate level of care based on the individual situation. Honest discussion of expected outcomes helps owners make informed decisions about treatment versus humane euthanasia in severe cases.

The recovery timeline for cats surviving pulmonary thromboembolism varies dramatically depending on the severity of the initial event and the underlying cause. Cats that survive the acute phase typically require several days of hospitalization with intensive monitoring and continued anticoagulant therapy. Improvement in respiratory status occurs gradually as the body's own mechanisms break down the clot and blood flow is restored to affected lung areas. Some cats show significant improvement within twenty-four to forty-eight hours, while others require a week or more of intensive support. Complete resolution of the clot may take weeks to months, though clinical improvement typically precedes complete resolution.

Post-treatment care for cats recovering from pulmonary thromboembolism includes ongoing anticoagulant therapy, management of underlying conditions, and careful monitoring for recurrence. Most cats are discharged on injectable or oral anticoagulant medications that must be given consistently. Activity restriction may be recommended initially to reduce the risk of dislodging any remaining clot material. Follow-up appointments within one to two weeks assess recovery and adjust medications. Imaging studies may be repeated to evaluate resolution of clots and assess for complications. Management of the underlying predisposing condition becomes the focus of long-term care.

Several factors influence the prognosis for cats recovering from pulmonary thromboembolism. The extent of pulmonary vascular obstruction significantly impacts survival, with cats who have massive clots facing higher mortality. The underlying cause strongly affects long-term outlook, with conditions like cancer carrying a poorer prognosis than more treatable conditions. How quickly treatment was initiated matters, as earlier intervention generally improves outcomes. The presence of complications such as right heart failure or respiratory failure worsens prognosis. Response to initial therapy provides prognostic information, with cats showing rapid improvement having better outlooks than those who remain critically ill despite aggressive treatment.

The long-term outlook for cats surviving pulmonary thromboembolism depends primarily on management of the underlying cause. Cats with treatable conditions and good response to anticoagulant therapy may live for months to years after the event. However, the risk of recurrence remains significant, particularly if the predisposing condition cannot be fully controlled. Cats with heart disease face ongoing risk of both PTE recurrence and other complications of their cardiac condition. Those with cancer have prognoses determined largely by their oncological disease. Long-term anticoagulant therapy reduces but does not eliminate recurrence risk. Regular veterinary monitoring and owner awareness of warning signs of recurrence optimize long-term outcomes.

Primary prevention of pulmonary thromboembolism focuses on identifying and managing the underlying conditions that predispose to clot formation. Regular veterinary examinations help detect heart disease, the most common predisposing factor, in its early stages. Cats diagnosed with cardiomyopathy, particularly those with left atrial enlargement, should be considered for prophylactic antiplatelet therapy with medications like clopidogrel to reduce clot formation risk. Early diagnosis and treatment of cancer, kidney disease, and other conditions associated with hypercoagulability may reduce PTE risk. Prompt treatment of inflammatory conditions minimizes the hypercoagulable state associated with systemic inflammation.

Environmental and lifestyle factors can be modified to reduce thromboembolism risk in predisposed cats. Encouraging activity and preventing prolonged immobility helps maintain normal blood flow that discourages clot formation. Cats recovering from surgery or illness should be encouraged to move as soon as safely possible. Maintaining adequate hydration prevents blood from becoming concentrated and more prone to clotting. Avoiding unnecessary surgical procedures and minimizing central venous catheter placement reduces exposure to thromboembolic triggers. Careful monitoring of cats during and after any hospitalization helps detect early signs of clot formation.

Dietary approaches to preventing pulmonary thromboembolism focus on supporting cardiovascular health and managing underlying conditions. Heart-healthy nutrition appropriate for cats with cardiac disease may reduce disease progression and associated clot risk. Omega-3 fatty acid supplementation has been investigated for potential antiplatelet effects. Taurine adequacy is essential for cardiac function. Appropriate dietary management of conditions like kidney disease and protein-losing enteropathy helps control the underlying drivers of hypercoagulability. Maintaining healthy weight reduces overall cardiovascular strain.

Regular health monitoring for cats with known risk factors provides the best opportunity to detect and address clot formation before pulmonary embolism occurs. Cats with heart disease should receive cardiac monitoring per their cardiologist's recommendations. Those on anticoagulant or antiplatelet therapy require regular blood testing to ensure appropriate medication effect. Owners of at-risk cats should be educated about the signs of both arterial and pulmonary thromboembolism so they can seek immediate care if symptoms develop. Screening echocardiograms can detect intracardiac thrombi before they embolize.

Early intervention when warning signs appear offers the best chance of preventing life-threatening pulmonary thromboembolism. Any change in breathing pattern, exercise intolerance, or sudden weakness in a cat with heart disease or other risk factors warrants prompt veterinary evaluation. Cats showing signs of possible arterial thromboembolism, such as sudden hindlimb weakness or pain, require immediate attention as they are at high risk for concurrent or subsequent PTE. Veterinarians and owners should have a low threshold for investigating potential early thromboembolism before catastrophic events occur.

Daily management of a cat surviving pulmonary thromboembolism centers on consistent medication administration and vigilant monitoring for recurrence. Most cats require daily anticoagulant or antiplatelet medications, and consistency is crucial for maintaining protective effects. Owners must learn proper medication administration techniques and understand the importance of not missing doses. Daily observation of respiratory rate, effort, and overall behavior helps detect any changes that might indicate recurrence or complications. Keeping a log of vital signs and any concerning observations provides valuable information for veterinary visits and helps identify trends over time.

Home environment considerations for cats recovering from PTE focus on reducing stress and facilitating recovery. A calm, quiet environment helps minimize physiological stress that could increase oxygen demand. Easy access to food, water, and litter boxes reduces the need for exertion. Comfortable resting areas at ground level prevent the need for jumping during the recovery period. Temperature should be kept moderate and stable. Once recovery progresses, gradual return to normal activity is encouraged, but owners should monitor for any signs of respiratory difficulty with exertion.

Maintaining quality of life for cats with conditions predisposing to thromboembolism requires balancing medical management with normal activities. Many cats can return to enjoying their usual activities once stabilized on appropriate therapy, though some modifications may be necessary. Gentle play and interaction support mental wellbeing without excessive physiological stress. Affection and routine help reduce anxiety, which is beneficial for cardiovascular health. Appetite should be monitored and addressed if declining, as adequate nutrition supports recovery and overall health. Quality of life assessment becomes an ongoing process, particularly for cats with serious underlying conditions.

Ongoing monitoring and veterinary care are essential components of long-term management. Follow-up appointments allow assessment of response to therapy, adjustment of medications, and monitoring for recurrence or complications. Echocardiograms may be performed periodically to evaluate heart function and check for intracardiac thrombi. Bloodwork monitors organ function and medication effects. Coagulation testing may be performed in cats on anticoagulant therapy. Any change in respiratory status between scheduled appointments should prompt immediate veterinary evaluation. Open communication between owners and the veterinary team optimizes care.

Caregiver support is particularly important for owners of cats with life-threatening conditions like pulmonary thromboembolism. The experience of witnessing a cat in acute respiratory distress can be traumatic, and owners may struggle with ongoing anxiety about recurrence. Connecting with support resources, including online communities and counseling services, can help process these experiences. Understanding the nature of the condition and realistic expectations for the future helps owners cope with uncertainty. Veterinary teams can provide guidance on emergency planning, quality of life assessment, and end-of-life decisions if the disease progresses. Being prepared emotionally and practically for various outcomes reduces stress and allows owners to be fully present for their cats.

While pulmonary thromboembolism can occur in any cat, certain breeds face elevated risk due to their predisposition to heart disease, the primary underlying cause of feline thromboembolism. Maine Coon cats carry genetic mutations associated with hypertrophic cardiomyopathy and are at increased risk for both cardiac disease and its thromboembolic complications. Ragdolls similarly have breed-specific cardiomyopathy mutations and should be considered high-risk for PTE. British Shorthairs, Persians, and Sphynx cats have been reported to have increased prevalence of cardiomyopathy, indirectly increasing their PTE risk. Any cat breed with genetic predisposition to heart disease carries corresponding risk for thromboembolism.

Beyond specific breeds, other categories of cats face increased risk for pulmonary thromboembolism. Male cats develop hypertrophic cardiomyopathy more frequently than females and at younger ages, making them a higher-risk demographic. Middle-aged to older cats are more likely to have developed heart disease or other conditions predisposing to clot formation. Cats with diagnosed heart disease, regardless of breed, are at significantly elevated risk, particularly those with left atrial enlargement visible on echocardiography. Cats with cancer, protein-losing disorders, or chronic inflammatory conditions face increased risk from these underlying diseases. Mixed-breed cats with heritage from high-risk breeds may carry genetic predisposition without obvious breed characteristics.

Screening recommendations for at-risk cats focus on early detection of heart disease and appropriate prophylaxis. Breeds with known cardiomyopathy mutations should undergo screening echocardiograms starting at one to two years of age and continuing periodically throughout life. Any cat with a heart murmur or arrhythmia detected on examination warrants cardiac evaluation. Genetic testing is available for certain breed-specific mutations and can identify at-risk cats before clinical disease develops. First-degree relatives of cats with cardiomyopathy should be screened. Cats diagnosed with conditions predisposing to thromboembolism should discuss prophylactic antiplatelet or anticoagulant therapy with their veterinarian. Owners of at-risk cats should be educated about the signs of thromboembolism and instructed to seek immediate care if they occur.

Arterial thromboembolism (ATE) is the condition most closely related to pulmonary thromboembolism in cats, as both result from abnormal blood clot formation and share the same underlying causes. In ATE, clots typically lodge at the aortic bifurcation causing hindlimb paralysis and pain, a condition commonly called saddle thrombus. Cats with heart disease may experience both arterial and pulmonary thromboembolism, either simultaneously or at different times. The management approach for both conditions centers on anticoagulant and antiplatelet therapy along with treatment of the underlying cause. Cardiomyopathy, the most common cause of feline thromboembolism, frequently coexists with both types and determines much of the long-term prognosis.

Several conditions present with clinical signs similar to pulmonary thromboembolism and must be considered in the differential diagnosis. Acute congestive heart failure with pulmonary edema causes sudden respiratory distress and may occur in the same population of cats at risk for PTE. Feline asthma can cause acute respiratory difficulty, though typically with less sudden onset and different underlying pathophysiology. Pneumothorax from trauma or spontaneous causes presents with acute dyspnea. Pleural effusion of any cause can cause respiratory compromise. Diaphragmatic hernia may cause acute respiratory distress if abdominal organs suddenly herniate into the chest. Accurate differentiation through appropriate diagnostics enables targeted treatment.

Complications that may develop with pulmonary thromboembolism include several serious conditions. Right heart failure can develop acutely as the heart struggles to pump against increased pulmonary vascular resistance, or chronically if pulmonary hypertension persists. Concurrent arterial thromboembolism may occur, as the same hypercoagulable state predisposes to clots in both circulations. Chronic thromboembolic pulmonary hypertension may develop if clots do not fully resolve, leading to persistent elevation of pulmonary artery pressure. Recurrent thromboembolism is a significant risk if the underlying cause is not adequately addressed. Respiratory failure may progress despite treatment in severe cases. Organ dysfunction from prolonged hypoxemia can affect the brain, kidneys, and other vital organs.