Coronary Artery Disease and Associated Complications

Coronary artery disease (CAD) describes complications that arise from a compromised blood flow to the cardiac muscle. Over time, deposits of cholesterol and fatty acids, calcium and other minerals form plaques. Plaque creates a rough, rigid surface that ultimately reduces the diameter of the intima of the coronaries, and elasticity of the vessel is lost (Atherosclerosis).  In some conditions, plaques can become dislodged from the surface and become trapped in a distal region of an artery, causing a clot to form, ultimately starving the myocardium from its oxygen (blood) supply, causing infarction and tissue death.

1. The coronary arteries supply blood, oxygen and nutrients to the heart muscle and conduction system.

 

2. The consequences of impaired blood supply to the conduction system are variable:

    

   • Blockage of posterior branch of the RCA will typically cause transient changes in the conduction system through the AV node;

    

   • Impairment of circulation of the LAD usually results in a large myocardial infarction that may damage the bundle branches;

    

   • Tissue death in bundle branches leads to permanent conduction delay. A heart block occurring at this level requires a permanent pacemaker- a device that stimulates contraction of the heart muscle.

    

 

3. Coronary blood flow is dependent on blood pressure and the vascular resistance of the vessels.

 

4. Because the left ventricle muscle mass exceeds that of the RV, the LV requires more blood supply

 

5. Arteries are compressed by the contracting myocardium during systole, increasing the resistance to blood flow.  Flow is restored during diastole.

 

6. During exercise, there are many demands placed on the heart to provide enough oxygen to the myocardium.

 

• increased heart rate- diastolic filling time decreases which decreases coronary flow

 

• increased blood pressure – vascular resistance increases, which decreases blood flow

 

• increased contractility of the ventricle

 

7. Collateral circulation:

    

   • The coronary arteries are located on the epicardial surface of the heart, while smaller branches of these arteries are embedded into the middle (myocardial) and inner (subendocardial) surfaces of the heart muscle.

    

   • These are end vessels which communicate freely to supply the cardiac muscle with blood.

    

   • Many small anastomoses are normally found which are benign until an area of the heart is deprived of blood- they then enlarge to meet the demand and provide a collateral blood supply to the affected muscle

    

8. Atherosclerosis– the most frequent pathological process involved in the reduction of blood flow

 

• Disorders of the coronaries are the most common cause of death in affluent countries and are responsible for much disability

 

• Half of people afflicted with this disease will die because of it; 45% of the deaths occur within two hours of onset of symptoms (Sudden cardiac death)

 

9. Ischemia– coronary circulation is inadequate to supply myocardial oxygen demands.

 

• Development of myocardial ischemia depends on:

 

 a. location and severity of the stenosis

 b.   presence or absence of collateral vessels

 c.   demands of the myocardium

 d.   coexistence of risk factor

 

• Clinical manifestations:

a.  angina pectoris- chest pain or discomfort resulting from transient and reversible ischemia (reduced blood flow)

b. myocardial infarction-results from total occlusion- cell death

c.  sudden death