What causes heart attacks? Myocardial Infractions Explained

Heart attack

Heart attack, or myocardial infarction as they are commonly referred to by doctors, occur when blood flow to a part of the heart that  is blocked for an extended period of time leading to the damage or death of tissues in that area which can lead to the heart muscles getting damaged and dying. And that is what causes heart attacks.

The main cause of heart attacks is the blockage of the coronary arteries that deliver blood to the heart. This blockage is caused mainly by the buildup of a substance called plaque which is mainly made up of cholesterol and other cells along the walls of the arteries stopping the flow of blood to the muscles starving them of oxygen and causing them to die. The actual causes of heart attacks are not well known, but they can be triggered by heavy physical activity, being active outside in the cold weather or by severe emotional and physical stress.

Causes of heart failure:

One contributing factor for heart attacks is coronary heart disease. This is governed by your heart disease risk factor. These are habits or conditions that increase your risk of getting coronary heart disease and these factors also increase the risk of coronary heart disease worsening.

The main heart disease risk factors are high blood cholesterol, high blood pressure, obesity, diabetes, smoking, unhealthy diet and lack of physical activity. Any one of or any combination of these factors greatly increases your likelihood of getting coronary heart disease.

Heart problems are another factor that causes heart attacks. These are related to cardiac heart disease. The main one is the clogging of the coronary arteries due to the buildup of plaque.

Heart failure is when the heart stops functioning properly leading to the heart attack. It’s caused when blood flow is restricted to the cardiac muscles; this means the muscles are deprived of oxygen which they need to function. The muscles gradually stop working and may die, this means that the heart can’t pump blood properly and hence causing heart failure.

Heart failure is normally preceded by certain signs that if spotted in time, can be vital in preventing a heart attack. The most common signs are shortness of breath, coughing or wheezing, tightness around the chest, and buildup of fluids in body tissues, dizziness, nausea, fatigue and anxiety. These signs once seen should be acted upon immediately to avert any impending heart attack.

what causes heart attacks

Here are some facts about heart attacks that show how major an issue it is;

In the US in 2008, heart attacks accounted for 616000 deaths, almost 25% of the deaths, making it the leading killer in the US. It accounts for 25.1% of the deaths in whites making it the leading cause of death among white adults and is estimated to cost the US government $108.9 billion in treatment, medication and lost productivity.

Having answered the question what causes heart attacks with these causes and signs of an impending heart attack, one sees the need to change their lifestyle to lower their risk of heart attack and live a healthy productive life.

Reperfusion injury

Reperfusion injury has been defined as myocardial tissue blood supply after a period of ischemia. Whether reperfusion merely  accelerates the damage that would have occurred during the initial ischemia  or whether there is a additional injury caused by reperfusion itself is still researched. Although the crucial role of reperfusion injury in revascularization procedures has bees recognized, the etiology and pathogenesis of this phenomenon remain unknown.
Myocardial ischemia accompanied by reperfusion injury followed by complete normalization if it took 5 minutes, by diastolic and systolic dysfunction if ischemia took 15-20 minutes and without return contractile function if ischemia took more than one hour.
The most common cause found in patients who died after reperfusion is hemorrhagic infarction. In myocardial infarction of less than 3 days the cellular response is present throughout the myocardial infarction, in contrast to the distinct zones seen in the non- reperfused myocardial infarctions. Reperfusion itself may produce injury.

The mediators of reperfusion injury

Reperfusion injury

One of the mediators of reperfusion injury is oxygen free radicals. The possible role of reactive oxygen species in reperfusion injury has evolved from our knowledge. They elaborate enzyme systems that rapidly detoxify superoxide and peroxide. The metabolism of reactive oxygen also has damaging effects. The investigators of this event have suspected that even physiological quantities of peroxide may inhibit the aerobic oxidation of pyruvate and thus restrict cellular ATP formation.
Another mediator of reperfusion injury is endothelial dysfunction and microvascular injury. Recent reports indicate that endothelium-dependent relaxation  of coronary microvessels is markedly impaired after ischemia with reperfusion. This microvascular endothelium dysfunction may be caused by blood products or myocardial metabolites that are released during the reperfusion period or by oxygen free radicals.
One of the oldest hypotheses about reperfusion injury involved calcium overload. Other mediators involved in reperfusion injury are altered myocardial metabolism and endogenous protective mechanisms.
There are some cardiovascular risk factors influence reperfusion injury. This are  hypercholesterolemia, very high glucose and hypertension.

Pharmacological methods to attenuate reperfusion injury

There are a number of pharmacological methods for attenuate reperfusion injury. In the treatment of myocardial infarction, restoration of coronary flow as soon as possible is a very important thing to prevent and reduce myocardial necrosis and ischemia. By this treatment ensure a reduction of mortality,  complications and a good prognosis in infarction. Early myocardial reperfusion injury prevent necrosis; in this way systolic and diastolic functions are established and are preventable fatal arrhythmias. In the early hours of  infarction,  reperfusion injury offers the greatest benefits: higher thrombus lysis.
Anti-ischemic therapy and lytic therapy has an important role to reduce myocardial energy demand. There are three revascularizations methods: trombembolitic treatment,  coronary angioplasty and coronary bypass. To thrombolytic treatment add anticoagulant and antithrombotic treatment and GP IIb/IIIa blockers. Thrombolytic agents currently used are streptokinase, tissue plasminogen activator and urokinase.

Conclusion for reperfusion injury

In conclusion the beneficial effect of fast recanalization may be offset by reperfusion injury.