ECG, cardiac cycle, cardiac output Flashcards
(23 cards)
What is an ECG?
A simple test to determine heart rythm, rate and electrical activity
What is the cardiac dipole?
Vector
extracellular fluid around myocardium-negatively charged due to Ca and Na leaving to go into myocytes
Depolarised region remains more positive
Rotating battery
Vectors and electrodes
Vector moving towards electrode- positive deflection
Vector moving away-Negative deflection
What speed is an ECG recorded at
25 mm/sec (5 large squares=sec)
Each smal 1 mm box represents 0.04 sec
What is the P wave
Atrial depolarisation
sa node throughout atria
brief isoelectric (flat) line equals impulse travelling in AV node and bundle of his)
PR interval
P wave to QRS complex
if more than 0.20= AV conduction block
QRS complex
Ventricular depolarisation0.06-0.010
ST segment
both ventricles completely depolarised time
Can help identify Ischemia or hypoxia if ST segment depressed or elevated
T wave
Ventricular repolarisation
(positive deflection)
Last cells to depolarise and first to repolarise
QT interval
time for both ventricular depolarization and repolarization to occur
Is atrial repolarization represented by q wave?
NO
Cardiac cycle
Pressure control
Diastole
relaxed ventricles (blood passively flowing from atrium to ventricle)
How is aortic pressure measured?
Pressure measuring catheter from peripheral artery into aorta
Cardiac cycle is split into
7
Phases
1) P wave of ECG
2-4) Systole
5-7) early and mid diastole
Phases: more depth
1) Atrial systole(contraction)
2)Isovolumetric contraction (all valves closed)
3) Aortic and pulmonic valves open (rapid ejection)
4) Reduced ejection
5) Isovolumetric relaxation (all valves closed)
6)Rapid ventricular filling (a v valves open)
7) Diastasis
What is cardiac output?
Amount of blood heart pumps in one minute
determined by stroke volume and no. of beats per minute
Stroke volume
Ventricular stroke volume is the amount of blood in mL ejected per beat by left or right ventricle
