m7 + 8 lab - EKG Flashcards
what does an ECG do?
ECG
electrocardiogram (ECG or EKG) = takes .80 sec per beat = 75bpm
- measures the electrical activity of the nodal system + the myocardium
—> determines activity or inactivity due to damage or ischemia to the myocardium
what is the nodal system?
ECG
- initiated by the intrinsic conduction system —> initiates heart contractions independently of all CNS activity (reason why brain dead patient has a heart beat - bc heart has O2 + nutrient supply)
- made from autorhythmic cells
what do autorhythmic cells do in the nodal system?
ECG
- spontaneously depolarize to trigger contraction - called pacemaker potential (set @ 100 bpm)
- some regulation by the ANS
1. SNS = cardioacceletory —> increased HR
2. PSNS = cardioinhibitory —> decreased HR
=> thru vagus nerve stim.
=> vagal response - stimulate vagus nerve to decrease HR 1)valsalva
2) carotid
aspects of the myocardium:
ECG
- connected by gap-junctions
- two units: atria + ventricles
what happens during isovolumetric time?
valves + filling of blood
volume in ventricle is not changing due to valve action
- depo. (right after Q wave)
- repo. (right before T wave)
when do the AV and semilunar valves open + close?
valves + filling of blood
AV valves
- closes at beginning of depo. at the Q-wave
- opens at the end of repo. at the T-wave
semilunar valves
- opens at the end of depo. at the Q-wave
- closes at the beginning of repo. at the T-wave
what happens at the beginning of the P-wave?
valves + filling of blood
- SA node initiates atrial depo. leading to contraction (helps fill ventricles)
what happens at the beginning of the Q-wave?
valves + filling of blood
- signal is conducted to purkinje fibers
what happens between the Q-wave (depo.) and the T-wave (repo.)?
valves + filling of blood
blood is ejected from the ventricles creating:
- circulation
- pressure
- BP: systole (120mmHg) = contraction
what happens between the end of the T-wave and the Q-wave?
valves + filling of blood
ventricles are refilling (this is occuring durring the SA node initiating atrial contraction)
- 80% is by gravity and circulation
- 20% is by the atrial contraction occuring at the P-wave by the SA node
- BP: diastole (80mmHg) = relaxation
what happens at the sinoatrial node (SA node)?
cardiac intrinsic conduction
- called the pacemaker
- largest
- initiates depolar. leading to contraction of atria @ 100bpm
- depo. wave starts + spreads out to both atria through intercolated discs –> atria contract at the same time
what happens at the atrioventricular node (AV node)?
cardiac intrinsic conduction
delays signal by 0.1 second to allow blood to drain from atria into ventricles
what happens at the atrioventricular (AV) bundle? (bundle of His)
cardiac intrinsic conduction
- carries electrical impulses from the atrioventricular (AV) node to the ventricles
- bundle of His and Purkinje fibers work together to create ventricular contractions in the heart
—> descends down the interventricular septum, which separates the right and left ventricles.
what happens at the purkinje fibers?
cardiac intrinsic conduction
- initiates ventricular depo. = then a contraction occurs = ejecting blood = creating pressure and circulation
- ventricles pump same volume
—> RV = pumps deoxygenated blood to lungs
—> LV = pumps oxygenated blood thru the aorta and to the rest of the body
what happens at the P-wave?
electrocardiography
initated by SA node - atrial depo. = then atrial contraction
what happens during the QRS complex?
electrocardiography
stimulated by purkinje fibers = causes ventricular depo. = then contraction = ventricles eject blood
- atrial repo. occurs during QRS complex
what happens during P-Q interval?
electrocardiography
- point of conduction from SA node to Purkinje
- atria are depo. = then contracting = filling the last 20% of the the ventricles
- normal time: .12 - .20 sec
- > = heart block
- < = tachycardia or fibrillation
what happens during the Q-T interval?
electrocardiography
- ventricles depo. at Q-R wave = causing a contraction
- during S-T interval, ventricles are ejecting blood = circulation + pressure
- then ventricular repo. at T-wave
- normal time: .31 - .41 sec ( < or > = problems w/ circulation)
- < = dec. filling + ejection = tachycardia
- > = dec. ejection, dec. flow = long Q-T , genetic condition
when do systole and diastole occur?
electrocardiography
systole - during Q-T interval (120mmHg)
- blood is ejected from ventricles by contraction
diastole - during T-Q interval (80mmHg)
- ventricles are refilling with blood - relaxation period
- 80% by gravity + circulation, 20% by atrial contraction
what is einthoven’s triangle?
standard limb leads
lead I = RA - LA
lead II = RA - LL
lead III = LA - LL
what is a normal ECG cycle length?
ECG cycle
.8 seconds long
what are the two divisions of an ECG cycle?
ECG cycle
diastole = relaxation
- ventricular filling (passive + active refilling)
- from T-Q wave
systole = ejection
- ventricular contraction + ejection = circulation
- from QRS to end of T-wave
what happens during the P-Q interval?
ECG cycle
- AV node delays signal .1 sec to allow ventricular filling
- normal time: .12-.20 sec
- > .20 sec = heart block (usually at AV node)
what happens at the Q-T interval?
ECG cycle
- all ventricular activity (systole=contraction)
- normal time: .31-.41 sec
- stays around the same even during exercise
- if it elongates, could cause syncope or fibrillation
what are the two ways to cause a vagal response?
lower BP
1) rectum - straining can cause fainting
2) carotid sinus - massaging can cause fainting
how long are each square on a ECG?
ECG examples - sinus rhythms
each square = .20 sec
1/5 of the square = .04 sec
find average by adding three sections together / by 3 = average
ex.) .76 + .70 + .76 / 3 = .74
normal sinus rhythm: 60 / average = HR
ex.) 60 / .74 = 81 bpm
what indicates sinus bradycardia and sinus tachycardia?
ECG examples - sinus rhythms
bradycardia - HR is below 60 bpm
tachycardia - HR is above 100 bpm
what indicates atrial fibrillation?
ECG examples - fibrillation
no P wave
what indicates ventricular fibrillation?
ECG examples - fibrillation
no pattern visible
