Myocardial Ischaemia and Infarction Flashcards
Phases of Myocardial Ischemia/Infarction
Subclinical phase (asymptomatic).
Stable angina pectoris.
Unstable angina.
Acute myocardial infarction. (STEMI and NSTEMI)
How does ischaemia cause cell death
All cells need oxygen to survive
Oxygen deprivation alters cellular function
Creates anaerobic metabolism
Creates the state of acidosis
Build up of harmful metabolites in the cell
Results in cell death
What are the main coronary arteries
Main coronary arteries ;
Left Coronary Artery
Left Main Stem;
Left Anterior Descending
Left Circumflex
Right Coronary Artery
ACS flowchart
ACS
STE - positive cardiac markers - STEMI (Qwave MI)
NSTElevation - positive cardiac markers (NSTEMI Non-Qw MI)
- Negative cardiac markers (unstable angina)
What is the ST segment?
The ST segment is the flat, isoelectric section of the ECG between the end of the S wave (the J point) and the beginning of the T wave.
It represents the interval between ventricular depolarization and repolarization.
Forms of ST abnormality
ST Depression – this represents ischaemia which occurs when there is not enough oxygen provided to the heart for the cells to work properly.
ST Elevation – this represents myocardial injury on the ECG. During myocardial injury, there is no oxygen getting to the heart cells so therefore this zone does not repolarise completely and remains positive.
Q Waves – this represents an infarcted region of heart muscle ie dead tissue. Therefore there is no action potential so the electrode sees the opposite wall (electrophysiological window).
What is the most common cause of ST segment abnormality
cause of ST segment abnormality (elevation or depression) is myocardial ischaemia or infarction
Types of ST depression
Horizontal
Downsloping - this and horizontal = indicates ischemia
Upsloping
STEMI ECG progression
Peaked T wave (mins)
Progression of STsegment elevation (mins to hrs)
Loss of R wave, Qwave formatiom (hrs to days)
T wave inversion (days)
T wave normalisation, persisting Qwave
Which location are most MIs?
Inferior
Generally have a more favourable prognosis than anterior myocardial infarction
Up to 40% of patients with an inferior STEMI will have a concomitant right ventricular infarction. These patients generally have a worse prognosis due to increased area of myocardium at risk.
Up to 20% of patients with inferior STEMI will develop significant bradycardia due to second-or third-degree AV block. These patients have an increased in-hospital mortality (>20%).
Lateral MI
The lateral wall of the LV is supplied by branches of the left anterior descending (LAD) and left circumflex (LCx) arteries.
Infarction of the lateral wall usually occurs as part of a larger territory infarction, e.g. anterolateral STEMI.
Isolated lateral STEMIs are less common, but may be produced by occlusion of smaller branch arteries that supply the lateral wall, e.g. the first diagonal branch (D1) of the LAD, the obtuse marginal branch (OM) of the LCx
Lateral extension of an anterior, inferior or posterior MI indicates a larger territory of myocardium at risk with consequent worse prognosis.
Posterior MI
Posterior infarctionaccompanies 15-20% of STEMIs, usually occurring in the context of an inferior or lateral infarction.
Isolated posterior MI is less common (3-11% of infarcts).
Posterior extension of an inferior or lateral infarct implies a much larger area of myocardial damage, with an increased risk of left ventricular dysfunction and death.
Isolated posterior infarction is an indication for emergent coronary reperfusion. However, the lack of obvious ST elevation in this condition means that the diagnosis is often missed
Posterior ECG positions
V7 - posterior axillary line, same horizontal line as V4-V6
V8 - midscapular line, same horizontal line as V7-V9
V9 - left spinal border, same horizontal line as V4-V6
How to differentiate benign early repolarisation vs pericarditis
BER STe = limited to precordial leads, no PR depression, fish-hook J wave appearance in V4
Pericardial STe - generalised, PR depression
