Continuing Education March, 2001 ISCHEMIA Continuing Education March, 2001

GOALS: Upon completion of this offering, the participant will be able to: define ischemia discuss its significance, and recognize major S-T segment changes in the ECG

Lesson Outline (Objectives): Review of coronary circulation Review of ECG components Definition of ischemia Causes of ischemia Corresponding ECG changes with coronary ischemia S-T segment elevation S-T segment depression Examples of ST changes Diagnosis of ischemia Study questions

Review of Coronary Artery Circulation The heart is a muscular organ composed of four chambers: the two upper (smaller) chambers are called atria and the two lower (larger) are known as ventricles. The four chambers work together to pump blood throughout the body, bringing oxygenated blood to the cells. Since the heart is a muscle, it too must have oxygen and nutrients to do its job. The heart’s blood supply comes from its own arteries, the coronary arteries, which form a network over the surface of the heart much like the branches or roots of a tree. NOTE: Aorta tell you that although the heart pumps blood to the body during ventricular contraction (systole), the blood to its own arteries is circulated during rest (diastole)

Review of Coronary Artery Circulation The coronary circulation is provided by two arteries that branch off from an area close to where the aorta leaves the heart. They are known as the right and left coronary arteries. Although each person has his or her own unique pattern of circulation, for most persons the arteries supply the heart in the following manner: The LEFT CORONARY ARTERY divides into the left anterior descending (LAD) and the circumflex arteries. The LAD provides oxygen and nutrients down the front of the heart, to both (but primarily the left) ventricles. The circumflex branch winds around the back (posterior) part of the heart. The RIGHT CORONARY ARTERY (RCA) is the conduit for blood flow to the right heart, inferior (lower) portion of the ventricle and a portion of the left lateral wall of the ventricle. Both arteries continue to branch out into many “limbs” to supply the heart muscle with oxygen and nutrients.

Review of ECG Components Correlation between ECG components and heart activity: the P-R interval represents atrial activity, the QRS represents systole (contraction), and ST repolarization (diastole or rest).

Review of ECG Components ECG components are measured in time and distance. Each small horizontal square equals 0.04 seconds. Each small vertical square is the equivalent of 0.1 millivolt, or more commonly, 1 mm. The above diagram shows the electrical activity in one heart beat. (More on this in next month’s lesson.)

What is Ischemia? Ischemia is the result of loss or decrease of blood supply to a tissue or organ, particularly the heart muscle. Untreated, ischemia will lead to death of the muscle or organ tissue. Heart or myocardial ischemia occurs when the demand for oxygen by the heart is not met, or when the work of the heart muscle (myocardium) exceeds available oxygen. Pain that is the result of diminished blood supply is referred to as “angina”. If the lack of oxygen continues, the heart muscle will die and the patient will suffer a myocardial infarction (death of myocardium).

What causes Ischemia? BLOCKAGE Any process that impedes the circulation of heart arteries can cause ischemia. Impaired flow of blood and oxygen to heart muscle is usually due to a blockage in one of the arteries that serve the heart itself. A blockage can be composed of substances such as lipids (blood fats), tar and nicotine from cigarette smoking, or blood components such as sticky platelets or red blood cells. CONSTRICTION The arteries themselves may be narrowed because of spasm or constriction, which in turn lessens blood flow and oxygen. BLOOD DEFICIENCY Low blood volumes, such as a person suffering from massive bleeding or severe anemia, can lead to ischemia because of the lack of sufficient blood to carry oxygen to the myocardium, resulting in ischemia.

ST Segment Changes with Ischemia Electrical conduction going through the heart muscle that is ischemic is altered: if the normal pathway for electrical conduction is affected, the electrical impulse will go around the area, with corresponding changes on the ECG. The new pathway will result in either ST segment depression or elevation. Generally, four millimeters (four small vertical blocks on the ECG) of depression or elevation indicate ischemia. Normally, ST segments are in the isoelectric line or no more than 1 mm (one small block) above or below it. ST segment changes are the earliest indication on the ECG of myocardial ischemia or impending damage. Note how the electrical conduction circumvents the area of ischemia, resulting in ST segment elevation on the ECG (normal ECG in green) Isoelectric line

Examples of Abnormal ST Segment Changes The green line represents the isoelectric, or base, line

Coronary Arteries and Related ECG Changes Ischemia, injury or death involving the right coronary artery (RCA) most often result in changes in the inferior surface of the heart: Leads II, III, AVF Obstruction of blood flow in the circumflex artery is associated with lateral changes from ischemia or infarction: Leads I, AVL, V5, V6 Left anterior descending branch (LAD) of the left coronary artery (LCA) flow obstructions are associated with anterior wall and/or septal changes: Leads V1 and V2 (septal)…Leads 2,3,4 (anterior wall)

Diagnosing Ischemia Cardiac ischemia must be verified by a 12 lead ECG. A rhythm strip or one lead will show only a single view of the heart, and as was seen in the preceding slide, different blockages will affect different areas of the heart and thus different areas of the ECG. Cardiac angiography (dye inserted into the arteries of the heart via leg vein) can pinpoint anatomical areas of blockage. See Fig. 4 Fig. 4 The above picture represents a blockage in the left anterior descending artery as seen via angiography. This is not a good situation for the patient. Stress testing via treadmill or bike may demonstrate ischemic changes. Laboratory blood tests can also determine whether heart muscle has been affected. Cardiac enzymes, myoglobin and troponin if present can help pinpoint diagnosis of ischemia in the emergency room.

Treatment Treatment of ischemia/angina is dependent upon the underlying cause. For a narrowing or blockage in a coronary artery, surgery can bypass the blockage by implanting a blood vessel to go around the affected area (coronary artery bypass graft - CABG) An angioplasty (informally called a Roto Rooter) allows the surgeon to remove some of the material blocking the inside of the artery to improve blood flow. A small wire frame can also be placed inside an artery to keep the vessel from re-occluding (stenting). Medical treatment can include various medications or combinations thereof, such as nitrates, which dilate the arteries and reduce work of the heart. This group of medication includes nitroglycerin, which patients put under their tongues to relieve angina from ischemia. Aspirin should be given immediately when ischemia is suspected. Supplemental oxygen is also frequently given. Other groups of medications such as calcium channel blockers or beta blockers may be prescribed as well. Cholesterol lowering medication can help prevent further blockages. If the ischemia is due to low blood volume, replacement of blood can relieve the lack of oxygen.

REMEMBER…… Untreated myocardial ischemia can lead to a heart attack and death. Ischemia is reversible.

Study Questions 1. Ischemia is defined as a. Heart attack b. Blockage in an artery c. Lack of oxygen to heart muscle d. Rapid heart rate 2. ST segment changes of ischemia should be at least _______ mm from the isoelectric (base) line. a. One b. Two c. Three d. Four 3. The CardGuard products that can be used in detection of ischemia are: a. Rhythm check b. CG 6560 disclosure c. Micro12 ECG d. King of Hearts e. A and D f. B and C 4. Persons experiencing signs of ischemia or heart attack should immediately take: a. red wine b. aspirin c. strong coffee d. ibuprofen

Extra Credit: What part of the heart is depicted here? Study Questions 5. Indicate whether the ST segments in the following ECG demonstrate a. Elevation b. Depression c. Horizontal d. Normal Extra Credit: What part of the heart is depicted here?

Study Questions 6. The main arteries of the heart are: a. Top and bottom coronary arteries b. Right and left coronary arteries c. Front and back coronary arteries d. Interior and exterior coronary arteries 7. The number of ECG leads needed to diagnose heart attack or ischemia are: a. Six b. Twelve c. Four d. Eight 7. Nitroglycerine is used by patients to a. Alleviate headache b. Constrict the arteries of the heart c. Relieve angina d. Blow up the back yard 9. When the electrical activity of the heart travels over damaged heart tissue, the electrical impulse will a. Go through it at a rapid rate b. Stop completely c. Go around the area d. Return to its point of origin

Study Questions 10. Chuck, an avid golfer aged 55, had been experiencing intermittent pressure between his shoulder blades for several weeks. At first he dismissed it as a muscle strain, but the fact that he had a history of high cholesterol and cigarette smoking compelled him to visit a cardiologist. He did not experience any pressure on the treadmill stress test nor did it show any abnormalities; however, the pressure continued to present itself on and off, particularly when he walked up the steep eighteenth fairway at his home club. What device(s) in your bag of products would you recommend that the cardiologist try with Chuck? a. King of Hearts b. MicroER c. Rhythm Check d. Micro 12 ECG e. CG 6550 Disclosure