The unprecedented breakout of Covid-19 pandemic has not only crippled the health care system but also created panicness in our mind. Though the symptoms are respiratory initially, it affects the multi-system of our body with an array of clinical presentation. The haematological affection is also a devastating complication particularly in serious patients in ICU. Blood clots may lead to clogging of blood vessels compromising flow to vital organs like heart and brain leading to serious complications.
Usually the external injury incites the endothelium of blood vessel injury leading to blood clot formation(thrombus). But in Corona virus infection without external injury the haematological mechanism leads to thrombus formation which ultimately cause end organ damage manifesting as stroke, heart attack, pulmonary thromboembolism, deep vein thrombosis.
Possible mechanisms of blood clot formation in COVID–
1. The corona virus binds to the ACE2 protein expressed in the endothelial cells causing damage to the endothelial cells triggering platelet activation, activation of coagulation pathway and thrombus formation. The microthrombi clog the blood vessels like veins and arteries leading to thrombosis. It ultimately cause poor blood and oxygen supply to the visceral organs like heart, brain, liver, kidney.
John Hopkins study found the viral spike protein binds to heparan sulfate which checks Factor H. Factor H helps in regulating the inflammation process and damage to the host cells. With the inhibition of Factor H , the inflammatory processes go unchecked leading to more damage to cells, further aggravating the thrombosis and damage to vital organs.
2. Activation of cytokines cause inflammatory cascade further damaging the end organ.
3. Immobilisation, mechanical ventilation flare up the thrombotic mechanism.
Lancet study with meta analysis shows thromboembolic events are high in COVID infection. Overall venous thromboembolism was 21%, deep vein thrombosis was 28%,pulmonary embolism rate was 19%, arterial thromboembolism rate was 2%.
The microthrombi affect almost all vital organs like brain, heart, liver, kidney, muscle.
Complications of blood clot
Stroke
The micro thrombus can clog the cerebral vessels decreasing the blood flow to the vital organ like brain. It can result in ischemia or decreased blood supply and infarction ultimately leading to stroke. Stroke or paralysis can involve single limb or both upper limb and lower limb. It is called hemiplegia when one side hand and leg is affected. Monoplegia when a single limb is affected.
Heart attack
When the blood vessels of the heart are affected by thromboembolism it can result in heart attack. The d-dimer levels are markedly increased in covid-19 potentiating the effect.
According to new research data, covid has long term deleterious effect on our cardiovascular system. Arterial stiffness is the marker of ageing and post covid complication. It is a sequelae to post covid infection that has impact in peripheral vascularisation.
Paul Harrison, Professor of Psychiatry and Head of Translational Neurobiology Group at Oxford University quotes ” Covid-19 markedly increases the risk of CVT(Cerebral venous thrombosis)”.
In almost all ICU set up therefore it is been an usual practice of using LMW heparin as a matter of prophylaxis to tackle the cases of thrombosis related complications. The patients with high D-dimer level was associated with poor prognosis and increased risk of morbidity and mortality.
D-dimer is is a product of coagulation mechanism. High levels indicates severity and more aggressive thromboembolic phenomena. It is mandatory to regularly check the D-dimer values to anticipate the complications related to thrombosis.
Potential aggravating factors in Covid 19 for blood clots
1. Bedridden or hospitalization
Less ambulatory activities or hospitalization increases the propensity for thromboembolism. ICU setup or critical care conditions aggravate the already immunocompromised event.
2. Obesity
Obesity is home to many metabolic syndromes like hypercholesterolemia or diabetes. They have higher body mass index indicating less lean muscle mass.
3. Patients having diabetes or chronic kidney or liver diseases
4. Immunocompromised patients like cancer, AIDS or tuberculosis or chronic obstructive pulmonary disease have more risk of having complications.
