Patient - ECG Flashcards
Which channels, when opened, cause the polarisation of membrane?
K+ cationic gated ion channels
Voltage gated can be Ca2+ and Na+
Describe Ca2+ induced Ca2+ release
1) Entry of Ca2+ during plateau phase
2) Drives the release of more Ca2+ from internal stores in sarcoplasmic reticulum
3) Ca2+ binds to troponin, exposing actin to myosin
4) Actin/myosin fibres contract, using ATP
Describe how troponin can be a sign of a heart attack (myocardial infarction)
If cardiac myocytes are damaged then cells open and leakage of troponin occurs, troponin then is in the blood which is a sign of an MI
What 3 things to contractile myocytes contain?
- proteins actin and myosin make contractile fibres
- protein troponin regulates the actin-myosin crossbridges
- Sarcoplasmic reticulum - an organelle which contains stores of Ca2+
What are contractile fibres made of?
Actin and myosin
What regulates actin-myosin crossbridges?
Troponin
Which organelle contains stores of Ca2+?
sarcoplasmic reticulum
Describe how excitation-contraction coupling occurs
- Calcium-induced calcium release during the plateau occurs. Calcium enters the cell (~5%) which triggers sarcoplasmic reticulum to release calcium (~95%)
- Contraction enabled when cytosolic Ca2+ binds to troponin, making it active and capable of interacting with myosin
- Repolarisation causes relaxation of actin-myosin fibres. Active transport of Ca2+ back to SR and extracellular fluid
- Fall in cytoplasmic Ca2+ renders troponin inactive and therefore the fibres relax
In which cell type is the action potential driven by the opening of “fast” Na+ channels?
Contractile myocytes
What is an ECG?
Electroencephalogram
Non-invasive, information-rich monitoring of cardiac electrical activity
Coordinated electrical currents in the heart create small voltage differences within the body
What do QRS waves correspond to?
Ventricular action potentials
The strength of an ECG signal depends on what?
direction of depolarisation travel
How many leads in an ECG?
12 leads
P, QRS, T shape corresponds to which tissue?
Contractile
What does the P wave signify?
Atrial depolarisation (start contraction)
What does the QRS complex/wave signify?
Ventricular depolarisation (start contraction)
What does the T wave signify?
Ventricular repolarisation (start relaxation)
What factors must one look at to analyse the ECG?
- Identify QRS complex (ventricular contraction)
- Heart rate - normal? tachycardic?
- Heart rhythm - look for the P wave - normal excitation cycle? (sinus rhythm?) , does the P wave precede each QRS by a constant interval?
- Conduction problems
How to measure heart rate?
Measure R–>R (seconds per beat)
Convert interval to rate (bpm)
Shortcut is 300/number of large squares
Name 3 things to look at when checking for conduction problems
- PQ (or PR) interval - May reveal AV block (too long) or Wolff-Parkinson-White syndrome (too short- unwanted pathways)
- QRS interval - may reveal right or left bundle block
- Q-T interval - May reveal QT prolongation - failure to repolarise quickly enough
PQ (or PR) interval is too long, what can this signify?
AV Block
PQ (or PR) interval is too short, what can this signify?
Wolff-Parkinson-White syndrome
Which part of the ECG can reveal right or left bundle block?
QRS interval
Which part of the ECG can reveal failure to repolarise quickly enough?
QT interval that is too prolonged
What can an ECG bpm diagnose?
sinus tachycardia
sinus bradycardia
What does no P wave in an ECG possibly signify?
Atrial fibrilation
as artial myocutes are ectopic pacemakers
What does a long P-Q interval possibly signify?
First degree heart block (AV block)
What do missed heart beats possibly signify?
Second degree heart block
What is STEMI?
ST segment elevated above baseline - sign of ischaemic tissue - worst type of myocardial infarction
