What causes a Heart Attack?

Rupture of a stable plaque in a coronary artery is the initial pathological event leading to a heart attack. When the rupture occurs, a clot suddenly forms in the lumen (channel) of the artery at the site of the rupture. Bleeding into the plaque often accompanies the rupture. The clot then blocks (occludes) the artery and thereby decreases the blood flow to the heart. This sequence of events in the coronary arteries is the basic problem in over 75% of people who suffer a heart attack. In some patients, more often women, there is just an erosion or ulceration of the plaque surface, rather than a full rupture that leads to clot formation in the coronary artery. Figure 3 shows an atherosclerotic plaque rupture and a clot in a coronary artery.


Figure 3: Rupture of Atherosclerotic Plaque in Coronary Artery
Cross-sectional Microscopic View


What happens to the heart muscle after a person survives a Heart Attack?

According to medical studies, 50% to 75% of people survive their first heart attack The others die during the heart attack because the decreased coronary blood flow causes a severe abnormal heart rhythm or extensive death of heart muscle. Figure 4 shows the heart of a patient who died 5 days after a heart attack. The photos show his myocardial infarction as it appears on the surface of the left ventricle and when the heart is sliced to view the muscle wall. About 90% of myocardial infarctions involve only the left ventricle (LV), which pumps oxygen-rich blood that comes from the lungs to the entire body. The other 10% also involve the right ventricle (RV), which pumps the blood to the lungs.


Figure 4: Myocardial Infarction Caused by Heart Attack
Views of Heart Surface and Slice Across Heart


If a person survives a heart attack, the heart muscle may return to normal or become a region of dead heart muscle (the myocardial infarction). The amount and health of the remaining heart muscle is the major determinant of the future quality of life and longevity for a patient after a heart attack. A heart attack can interrupt the normal electrical wiring of the heart, leading to abnormal heart rhythms. The heart attack can also weaken the pumping action of the heart causing shortness of breath due to heart failure. Each of these complications of a heart attack can occur at any time during the recovery period as a result of dead, dying, or scarring heart muscle.