6.2 - Electrophysiology of the Heart Flashcards
Function of the Sinoatrial Node
- primary intrinsic pacemaker (bc it has highest spontaneous depolarization rate)
- at junction bw R atrium and superior vena cava
Function of Atrioventricular Node
- delays conduction to ensure that ventricles have filled with blood before they contract
- conducts AP through bundle of His
- purkinje fibers: terminal branches that spread electrical impulses thriugh ventricles/ initiate contractions
Propagation of Cardiac Action Potentials
Depolarization - activation of cardiomyocytes
Repolarization - deactivation of cardiomyocytes
Action Potential
- inside of cell is less (-)
- resting membrane potential reaches threshold
Threshold
- minimum membrane potential a cell must reach to initiate AP
Refractory Period
- now new AP’s ca be initiated
a. Absolute - Na and Ca channels reopen
b. Relative - stronger -than normal stimulus is required to trigger another depolarization
Automoticity Vs. Rythmiticty
Automaticity
- cells that can spontaneously depolarize
Rythmiticity
- generation of AP by hearts conduction system
P Wave
- atrial depolarization; activity of atria as it contracts to pump blood into ventricles
- indicates start of cardiac cycle: 1st small upward wave
- happens after atrial contraction
QRS Complex
- ventricular depolarization; activation of ventricles as they contract blood into heart
- larger wave (reflecting more force needed by ventricles)
ST Segment
- period bw ventricular depolarization (end of QRS) and ventricular repolarization (beginning of T wave)
ST Segment Depression
- below baseline
- result of ischemia
ST Segment Elevation
- above baseline
- signs of acute injury
T wave
- ventricular repolarization (ventricles returning to resting state)
- after QRS
Measures of Normal Sinus Ryhtmn
Rate: 60-100 bpm
P wave: positive and before QRS
PR interval: 0.12-0.2 sec
QRS: < 0.12 sec
How to Calculate Rate
- count # of R’s (big wave; middle of QRS) bw ticks x 10
Sinus Bradycardia
- rate < 60 bpm
Sinus Tachycardia
- rate > 60 bpm
How to Interpret Rhythm
PR Interval > 0.20 = AV block
QRS Interval >0.12 = Bundle Branch Block
PR interval
- represents the time it takes for the SA node stimulus to travel from atria to ventricle through the AV node
- # of squares between beginning of P and beginning of Q x 0.04
- if > 0.2 = AV block
- AV Block: when there is disruption in transmission of impulses from atria to ventricles through AV node
1st Degree AV Block: 1:1 P:QRS ration
2nd Degree AV Block: 2 P waves for every QRS
3rd Degree: P waves present, no QRS
QRS Complex
- time it takes for stimulus to spread through ventricles
- measure bw start of Q and end of S and x 0.04
- if > 0.12 = BBB
- Bundle branch block: when one of bundle branches is blocked
- characterizes by wide QRS complex
LBB - delay/blockage in electrical impulses travelling through LBB
- L ventricle is activated later than normal = wide QRS
RBB - delay/blockage in electrical impulses travelling through RBB
- R ventricle is activated later than normal = wide QRS
Atrial Fibrillation
Cause
- irregular, rapid heart rhythm
- hypertension and heart failure (aortic dilation)
- coronary artery disease
- valve disease
Patho
- abnormal electrical activity = chaotic depolarization = loss of atrial contraction = atrial quiver
- atrial quiver = decreased cardiac output
Types
1) Paroxysmal
- Temporary episodes
- Starts suddenly
2) Persistent
- Episodes > seven days
3) Permanent
Changes
- atrial enlargement: abnormal rhythm causes remodelling
- atrial fibrosis
- thrombus: bc of uncoordinated activity, blood pools in atria, clot formation = embolism = stroke
S&S
- palpitations, fatigue, SOB, chest pain, dyspnea
Complications
- thromboembolism = stroke
A Fib ECG
Rate: > 100 bpm
Rhythm: Irregular
P-wave: No P wave
- fibrillatory waves bc atria is quivering
PR Interval: NONE (No p wave)
QRS: normal
