The

complex (wave) represents the sum of all ventricular muscle cell depolarizations

The left ventricle is responsible for pumping oxygenated blood out of the heart and into systemic circulation, which requires generating enough pressure to overcome the resistance of the systemic blood vessels. Therefore, the left ventricle has thicker and more muscular walls than the right ventricle and can generate higher pressures during contraction. In contrast, the right ventricle pumps deoxygenated blood to the lungs, which have lower resistance compared to the systemic circulation, and therefore do not need to generate as high pressures.

A pulmonary embolism (PE) occurs when a blood clot, typically originating from the deep veins of the legs or pelvis, travels through the bloodstream and lodges in one of the pulmonary arteries in the lungs.

Deep venous thrombosis (DVT) is the most common source of pulmonary emboli. DVT occurs when a blood clot forms in the deep veins of the legs, pelvis, or arms, and can develop due to prolonged immobility, surgery, trauma, cancer, pregnancy, hormone therapy, or genetic factors.

Endocarditis, valvular heart disease, and left heart failure are not typical sources of pulmonary emboli. Endocarditis is an infection of the heart valves and lining, which can lead to valve damage and heart failure, but does not usually cause blood clots. Valvular heart disease, which includes conditions such as aortic stenosis and mitral regurgitation, can cause blood flow disturbances and increase the risk of thrombosis, but does not directly cause blood clots. Left heart failure, which occurs when the left ventricle of the heart is unable to pump effectively, can cause fluid buildup in the lungs, but does not typically cause blood clots to form.