lecture 19 - ischaemia & the heart Flashcards
What parts of the heart does the right coronary artery (RCA) supply?
Right ventricle, parts of spetum, posterior wall of left ventricle
What parts of the heart does the left coronary artery (LCA) supply?
Anterior left ventricle, atria, parts of septum
Issues with which coronary artery are most likely to cause issues with heart rhythm, and why?
Right coronary artery, because it supplies tissue close to the SA Node
Which part of the walls of the heart are most vulnerable to decreased blood flow?
The sub-endocardial regions (innermost part of the wall), particularly of the thick left ventricle which is furthest from the large supply vessels
What are the 2 ways that coronary blood flow is increased?
Dilation of coronary blood vessels, reduced resistance to flow
what is the most important mechanism in triggering increased flow in the coronary circulation?
Local metabolic control
What metabolite is the most important in regulating coronary blood flow?
Adenosine
Which scenarios trigger the release of adenosine in cardiomyocytes?
breakdown of ATP during
- exercise
- hypoxia
- ischaemia
What is the process via which ischaemia leads to contractile/heart failure?
Reduced o2 > Reduced contractility > Reduced SV > Increased end-diastolic pressure > compression of sub-endocardial tissue > ischaemia
Why does ischaemia cause reduced myocardial contractility?
Depleted ATP, accumulation of lactic acid from anaerobic metabolism, increased extracellular K+ (change to membrane potential)
What is the effect of high extracellular potassium on the cardiac action potential?
Slower onset, reduced amplitude, shorter = reduced contractility
What is the ‘current of injury’?
Current that flows from normal/healthy to ishchaemic heart tissue
What are the ECG changes seen due to the current of injury during myocardial iscahaemia?
ST segment elevation/depression
Which leads show ST segment elevation during an MI?
Leads that ‘look at’ the infarcted parts of the heart
Which leads show ST segment depression during an MI?
Leads opposite the infarct
