Vector lead rules - 12 lead

Question 1

RULE 1 - The leads pick up the SUM of impulses (voltage from different part of the conduction system from the waves you see).

RULE 2- If an impulse (A wave of depolarization) travels TOWARDS the (+) electrode a positive wave or complex wave will be seen.

RULE 3 - If an impulse (a wave of depolarisation) travels AWAY from the (+) electrode a NEGATIVE wave or complex will be seen.

-more muscle means more cells which means more voltage.

-Less muscle means less cells which means less voltage.

Question 2

THE VECTORS AND MECHANISMS OF CONTRACTION

• An ECG graph measures changed in voltage over a period of time.

Question 3

Depolarisation

• leads to a positive charge in voltage.
• The inside of the myocyte (cardiac muscle cells) becomes more positive compared to the outside due to the influx of sodium ions (Na+).
  Depolarisation therefore creates a positive (upright wave).

Question 4

Repolarisation

• Leads to a negative change in voltage.
• The myocyte cells return to their negative resting stat (Where it s more negative inside). The inside of the myocyte becomes more negative compared to the outside due to the outward movement of potassium ions (K+). Normally this would generate negative (downward waves) but the T wave is actually upright suggesting repolarisation to be positive.

Question 5

The p wave and QRS complex are upright in the lead II the waves are caused by the myocytes becoming more positive (depolarised).

The T wave is caused by ventricular myocytes becoming more negative (Repolarisation).

Question 6

Depolarisation = positive

Answer 6

Repolarisation = Negative

Question 7

The ECG is a graph of voltage over time. it records the electrical changes that occur in the heart during each beat.

The waves are an electrical representation of two processes: depolarisation and repolarisation.

• Any movement away from the baseline represents some cardiac event. I.E. the P wave represents atrial depolarization.

-The heart is a muscle that contracts to squeeze blood from the atria to the ventricles and then to the lungs and the body.

• Before the myocardium can contract and squeeze the blood to different areas od the heart is must first depolarise.
• Muscles only contract after they have been repolarised.
• Depolarisation allows certain electrolytes such as calcium to enter the muscle cells (myocyte) and allows it to contract.
• The movement of electrolytes (which are electrically charged) into muscle cells create the ECG waves.

Question 8

Depolarisation is positive as the muscle cells become more positively charged. #

Repolarisation is negative as the cells become more negatively charged (they return to their previous negative resting state).

-Atrial and ventricular depolarisation created positive upright waves - P wave and QRS complex in lead II.

• you would expect the T-WAVE to be negative as repolarisation is negative.