Thrombosis and Atrial Fibrillation

The diagnosis of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia seen in clinical practice, affecting approximately 4.5 million people in the EU and 2.2 million people in the US.²² This arrhythmia is characterised by an irregular supraventricular rhythm with a variable ventricular rate.²²

Atrial fibrillation (AF) can be intermittent or persistent or permanent. Symptoms include palpitations, chest pain, fatigue, dyspnoea, lightheadedness, and syncope.^{33, 34} Some patients have no symptoms, and the diagnosis is made incidentally during a medical evaluation conducted for other reasons. Cardiovascular causes of AF include hypertension, coronary artery disease, valvular heart disease, pericarditis, and pulmonary embolism. Other causes include hyperthyroidism, alcohol intoxication, and pneumonia.^{22, 34}

People with AF have an irregular heart rate that may be rapid.⁴ The diagnosis is confirmed by electrocardiography. Once the diagnosis is established, medical management involves identifying and addressing the cause of the AF and, when possible, restoring a normal cardiac rhythm.^{4, 33} When restoration of a normal heart rhythm is not feasible, the main goals of treatment include controlling the heart rate and minimising the risk of stroke by preventing thrombus formation in the heart.

ECG showing atrial fibrillation

Virchow’s triad in atrial fibrillation and the risk of stroke

Thrombus formation in patients with AF results from stagnant blood in the atria, combined with other physiological derangements.²⁸⁰ These abnormalities are consistent with the 3 factors first identified by Virchow as contributing to DVT formation. In AF, Virchow’s triad consists of:

Stagnant blood flow in the left atrium, visible on an echocardiogram as spontaneous echocontrast
Anatomical cardiac wall defects, such as progressive atrial dilatation
Abnormal platelet activation and changes in coagulation factors, contributing to an increased propensity for blood clot formation²⁸⁰

Without anticoagulant therapy, patients with AF are at high risk of stroke, as a thrombus that forms in the atria can embolise to block blood flow to the brain.^{4, 18}

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Article references

22 - Fuster V, Rydén LE, Cannom DS, et al. ACC/AHA/ESC 2006 Guidelines for the Management of Patients with Atrial Fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients With Atrial Fibrillation): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society. Circulation. 2006;114(7):e257-e354.
33 - Padanilam BJ, Prystowsky EN. Atrial fibrillation: goals of therapy and management strategies to achieve the goals. Med Clin North Am. 2008;92(1):217-235, xii-xiii.
34 - Kannel WB, Benjamin EJ. Status of the epidemiology of atrial fibrillation. Med Clin North Am. 2008 ;92(1):17-40, ix.
4 - Lip GY, Tse HF. Management of atrial fibrillation. Lancet. 2007;370(9587):604-618.
280 - Watson T, Shantsila E, Lip GY. Mechanisms of thrombogenesis in atrial fibrillation: Virchow’s triad revisited. Lancet. 2009;373(9658):155-166.
18 - Waldo AL. Anticoagulation: stroke prevention in patients with atrial fibrillation. Med Clin North Am. 2008;92(1):143-159, xi.

Arrhythmia: Any variation from the normal rhythm of the heart beat (e.g., sinus arrhythmia, premature beat, heart block, atrial fibrillation, atrial flutter, pulsus alternans, and paroxysmal tachycardia).
Coronary artery disease: Coronary artery disease (CAD) is the end result of the accumulation of plaques within the walls of the arteries that supply the muscle of the heart with oxygen and nutrients. The process by which the coronary arteries become narrowed or completely occluded is known as atherosclerosis.
Hypertension: Persistently high arterial blood pressure. Hypertension may have no known cause (essential or idiopathic hypertension) or be associated with other primary diseases (secondary hypertension). This condition is considered a risk factor for the development of heart disease, peripheral vascular disease, stroke, and kidney disease.
Coagulation factors: Group of plasma protein substances (Factor I to XIII) contained in the plasma, which act together to bring about blood coagulation.
Platelet: (Thrombocyte) Cell circulating in the blood that is involved in the cellular mechanisms of primary haemostasis leading to the formation of blood clots. When a blood vessel is injured, platelets gather at the site of injury and stick together to form a plug, thereby preventing blood loss.