EXAM #1: MYOCARDIAL ISCHEMIA AND INFARCTION Flashcards
What layer of the heart is the most susceptible to ischemia?
Subendocardial
What are the three main determinants of myocardial oxygen demand?
1) HR
2) Contractility
3) Myocardial wall tension
What is the relationship between heart size and the myocardial wall tension?
Bigger the heart = more wall tension
Outline the sequelae of increased oxygen demand in the setting of reduced coronary blood flow?
- Rest= blood flow is adequate
- Exercise= increased demand with constant supply
Results in ST (depression) and T-wave changes (inversion)
Describe the type of T-wave inversion seen in ischemia.
Symmetric
When there is TRANSMURAL ischemia, what is the first ECG change?
T-waves that become tall and peaked i.e. “hyperacute”
Note that this is the very first thing that occurs in transumural infarction and it is relatively transient
What is the ECG manifestation of transmural ischemia?
ST segment elevation
What is a myocardial infarction?
Prolonged infarction resulting in injury/ necrosis
Where does the necrosis begin in MI?
Subendocardium
What is the initial indication of a MI on ECG?
ST elevation
What is the late sign of MI?
Pathologic Q-waves
What is the definition of a pathologic Q-wave?
Greater than 0.03 sec in duration i.e. one small box or bigger
What is the best way to review the ECG leads to diagnose ischemia? List the leads associated.
Inferior= II, III, aVF Septal= V1, V2 Anterior= V3, V4 Lateral= I, aVL, V5 and V6
“I See All Leads”
What is the most common cause of an inferior wall MI?
RCA occlusion
How often does the RCA supply the right inferior wall?
90%
The other part of the time, there is a dominant left circumflex
