FAQ Ischemic Myocardial Infarction

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What factors influence myocardial oxygen supply and demand?

Myocardial supply is influenced by: coronary blood flow (diastolic time, blood pressure and blood vessel diameter) and the percentage of oxygen in blood. Remember, the more the diastolic time, the better for heart muscle because during diastolic time, the heart is filling with oxygenated blood. Myocardial demand is influenced by: heart rate, blood pressure and contractility.

Why is this balance altered in ischemic heart disease?

In heart disease, the heartís demand is not matched with the heartís supply of oxygen. Due to this, certain regions of the heart die and are replaced by nonfunctioning connective tissue. All this may be done due to decreased diastolic time, reduced blood vessel diameter, or increased blood pressure.

Describe the pain of acute myocardial infarction. Explain its distribution:

Patients with ischemic myocardial infarction experience pain in the chest, neck, chin, or down the left arm of elbow. This is called referred pain and is experienced indirectly because sympathetic nerves to the heart that carry afferents from T1 and T2 also supply cutaneous innervations of the upper left limb and nearby areas. Sometimes, these pains may not occur, which is more dangerous.

Why does a patient become sweaty, pallid and tachycardic during an acute myocardial infarction?

Sweaty: Sweating during a heart attach or angina is particularly due to cold sweat (secreted by apocrine glands) stimulated during emotional response. It should be noted that this cold sweating my even occur without sustained muscle action.

Pallid: Because oxygenated blood isnít reaching the skin

Tachycardic: Because the heart has become ineffective and more blood is remaining in the ventricles at the end of each cycle. To compensate for reduced blood volume pumped in circulation, heart rate increases.

These symptoms are caused by action of the autonomic nervous system, which promotes hemostasis.

List the common arrythmias that may occur after acute myocardial infarction:

Various types of tachycardia may occur. The important ones are:

• Heart Block.

• Flutter and fibrillation.

• Ventricular premature contraction.

What is an ectopic focus?

A section of the heart that gives rise to impulses separately from the SA node is called an ectopic focus.

What is heart failure? What is shock?

Heart failure is the inability of the heart to keep pace with the normal events of life like exercising, climbing stairs, walking etc. Shock is followed by a severe heart attack and many people die during this condition.

A patient suffers a myocardial infarction that damages a large area of his left ventricle. He develops left-sided heart failure. Why does he become pale, hypotensive and short of breath?

The left side of the heart is the main pump that sends blood throughout the body. An inefficient pump will not send enough blood resulting in low blood pressure, paleness and shortness of breath due to lack of oxygenation of blood in the lungs.

Additional Reading:

Basic Cardiology

1. Electrical Activity of the Heart
2. Heart Muscle Mechanics
3. Heart Sounds and Murmurs
4. Additional FAQ on Heart Sounds and Murmurs
5. Cardiac Conduction Diagram
6. Blood Pressures in Cardiac Chambers
7. What is Pulsus Paradoxus?
8. FAQ on Heart Murmurs and Mechanisms of Turbulent Flow
9. Notes on Fetal Circulation
10. FAQ on Ischemic Myocardial Infarction
11. FAQ on Electrocardiograms / ECG / EKG
12. FAQ on Cardiac Conduction
13. The Heart as a Pump, the Cardiac cycle and Cardiac Output
14. What are the most common causes of aortic stenosis?
15. What is Pulseless Electrical Activity?
16. Causes and Complications of Arteriovenous Fistulas
17. CHADS2 Score for Atrial Fibrillation Stroke Risk
18. How to Reduce Blood Pressure without Medications?
19. Types of Shock
20. Locations of Heart Murmurs on Chest Wall
21. Types of Heart Blocks

Electrocardiogram (EKG/ECG) Topics

1. EKG Chest Leads
2. EKG Limb Leads
3. Quick 12-Lead ECG/EKG Format

Cardiology Videos

1. Video of Cardiology Examination in a Clinical Setting

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

Related Topics

1. Thorax Anatomy
2. Vascular Disorders
3. Heart Disorders
4. Histology of the Cardiovascular System
5. Jugular Venous Distention Workup
6. ER Chest Pain Workup
7. Cardiac Examination for Internal Medicine
8. FAQ on Blood Pressure
9. FAQ on principles of fluid and flow dynamics of Blood

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