Biorhythms

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Causes of Fatigue Slideshow Pictures

Heart attack

Over one million Americans suffer a heart attack annually. Over four hundred thousand of these heart attack victims die as a result. Many of the heart attack deaths are due to sudden ventricular fibrillation occurring before the patient can reach any medical assistance or the emergency room. Ventricular fibrillation and other heart electrical disturbances can be treated with medications once the patient reaches the hospital. Therefore, 90% to 95% of those heart attack patients who make it to the hospital survive.

Heart attack (myocardial infarction) is the irreversible death of heart muscle due to complete blockage of a coronary artery, usually by a blood clot forming on a cholesterol plaque.

  • A coronary artery is an artery supplying blood to the heart muscle.
  • A cholesterol plaque is an abnormal, hard thick deposit on the artery wall.
  • The condition whereby cholesterol plaque deposits on coronary arteries is called coronary artery disease (CAD).
  • CAD leads to narrowing of these coronary arteries, thus impairing the normal oxygen supply to the heart.
  • Coronary artery narrowing can cause angina, chest pain or pressure due to an insufficient supply of oxygenated blood (ischemia) to the heart muscle.
  • During a heart attack, heart muscle dies when a diseased coronary artery becomes completely blocked by a blood clot. Heart attack can cause chest pain, heart pump failure, and electrical disturbances in the heart.
  • Electrical disturbances in the heart can cause ventricular fibrillation (a chaotic heart rhythm). A heart undergoing ventricular fibrillation simply quivers, and is incapable of pumping oxygenated blood to the rest of the body and the brain. Permanent brain damage usually occurs unless oxygenated blood is restored to the brain within minutes.

Numerous studies, including the classic Framingham study, have shown that the incidence pattern of sudden cardiac death parallels those of hypertension, heart muscle ischemia, angina, and heart attack - a 70% greater risk between the hours of 7 a.m. and 9 a.m., compared to the rest of the day.

Stroke resulting from ischemia occurs more frequently in the morning than at any other time of day. Like heart attack, ischemic stroke refers to permanent death of brain tissue because of blockage of the artery supplying blood to the brain, usually by a blood clot.

Medically Reviewed by a Doctor on 6/18/2015

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