Title: T4 / MDBI / Moment 1 / Klinisk Fysiologi / Membranpotential till EKG

Q: Vad gör EKG maskinen?
A: - EKG maskinen analyserar rörelsen av elektrisk kraft genom hjärtat från 12 olika riktningar
- Avledningarna printas på papper och då kan den ge oss information om sjukdomar i olika delar av hjärtat och upptäcka skillnader i dessa

Q: När ses en rak linje på EKG?
A: En platt linje syns på ett EKG när det inte finns någon net current som flödar i dess riktning - kallas isoelektrisk linje

Q: Hur uppstår topparna och dalarna på ett EKG?
A: - Alla avledningar på EKG är uppsatta så att en depolarisation som rör sig mot en avledning producerar en deflektion på EKG ovan den isoelektiska linjen - en positiv deflektion
- Medan en depolarisation, som rör sig från avledningen, producerar en deflektion under den isoelektiska linjen - en negativ deflektion

Q: What does the deflection of a repolarising current look like?
A: Repolrising current has the opposite polarity to depolarisating current, therefore, repolarising current moving towrds the lead produces a negative deflection, while repolarising current moving away from the lead is producing a positive current

Q: How big are the deflections in a normal EKG?
A: In an standard 12 lead EKG, the sensitivity of the machine is set at a level so that 1mV of current moving towards or away from the lead produces a deflection of 10mm

Q: What can we do when the de- and repolarising currents move throughout the heart?
A: As the depolarisation and repolarisation waves spread through the heart in a well defined and constant pattern, meaning that if we know the perspektive of the EKG lead of electrial events in the heart we can predict the readout

Q: How does the artial depolarising wave spread and what does it look like on the EKG readout?
A: The atrial depolarisation wave spreads downwards and to the left and outwards towrads the front of the chest and chestleads and as it is moving towards the leads it produces a positive deflection on the EKG paper, this is the P-wave

Q: What happens after atrial depolarisation?
A: After a short delay of which no current is flowing the AV-node allows the depolarisation to travel into the ventricles

Q: How does the depolarising wave spread after passing the AV-node and what does that look like on the EKG read out?
A: - The depolarising current is first released from the left bundle branch of the conducting system into the interventricular septum -> this s the first piece of ventricular muscle to depolarise and does so by the signal spreading across the septum from the left to the right
- This depolarisation signal is moving towards V1 and produces a positive deflection in the V1 read, however moving away from V6 and producing a negative deflection in the V6 read

Q: How does the depolarisation spread after passing the septum?
A: As the septum continues to depolarise, the depolarisation wave is released from the terminal fibers of the conducting system into the main muscle mass of the ventricles

Q: How does the depolarising wave spread in the muscle mass of the ventricles and what does that look like on the EKG read out?
A: - The left ventricle has a greater muscle mass than the right and dominates the electrial signal of ventricular depolarisation in all leads
- Therefore, after release of the depolarisation wave from the conducting system into the main muscle mass of the ventricles, the subcardial to epicardial movement of the current in the left ventricle overwhelms all other signals and as its moving away from V1 that deflection becomes negative (EKG), while it becomes positive in the V6, since it's moving towards it

Q: As what is the flow of depolarizing current around the ventricles recorded?
A: The flow of the depolarising current around the ventricles is recorded as the QRS-complex and the morphology of the QRS-complex differs in the EKG leads depending on their position in relation to the heart

Q: What happens after ventricular depolarisation?
A: When ventricular depolarisation is complete there is a brief period when no current is flowing and the recording returns to the isoelectric line, this period ends with the onset of ventricular repolarisation

Q: How does the repolarising wave behave in the ventricles?
A: - Repolarising current has opposite polarity to the depolarisation wave so when its moving towards a lead it produces a negative deflection moving towards a lead and a positive one moving away from it (lead)
- Repolarisation spread through the ventricles in the opposite direction to the depolarisation wave - going from epicardium to endocardium
- The deflection produced on a EKG by ventricular repolarsation is dominated by the left ventricle

Q: What does the repolarising current in the ventricles look like on the EKG?
A: - As this repolarsing current is moving toward V1 the deflection is negative in this lead, and in V6 positive since it's moving away from it, this is the T-wave
- Cardiac repolarisation spreads slowly through the myocardial muscle mass utside the conducting system, so the T-wave is logner in duration and broader on the EKG paper than the QRS-complex

Q: Why is the T-wave wider than the QRS-complex?
A: Cardiac repolarisation spreads slowly through the myocardial muscle mass utside the conducting system, so the T-wave is longer in duration and broader on the EKG paper than the QRS-complex

Q: What corrolation can be spotted on the EKG readout?
A: The fact that repolarising current moves through the ventricles in the opposite direction to the depolarisation wave means that in leads with a positive QRS-complex, the positive deflection is lager than the negative deflection and the T-wave also tends to be positive, while in leads with a negative QRS-complex the T-waves are also under the isoelectric line (negative)
- The QRS-complex and T-waves tend to be concordant

Q: Can atrial repolarisation be seen in the EKG readout?
A: Artial repolarisation produces a relatively weak electrial signal which is burried in the QRS-complex and is normally not detected in an EKG

Q: What is the magnitude of the depolarising muscle proportional to?
A: The magnitude of the electrial signal generated by depolarising muscle is directly propotional to the mass of the muscle generating it - the more muscle present the more electrial signals are generated and the more signals the EKG machine detects