Module 8 ECGs Flashcards
Conductivity
The ability of cells to transmit electrical current
Contractility
The ability of muscle fibres to respond to electrical stimulus by shortening and contracting
Conductivity
The ability of the cells to transmit electrical current
Contractility
The ability of muscle fibers to respond to electrical stimulus by shortening and contracting
Conduction System of the heart
Sa Node
AV node
Bundle of His
Purkinje Fibres
Pacemaker Potential
A self-initiating action potential that occurs in the condition system of the heart and triggers action potentials (and thus contraction)in the cardiac cells.
why would a QRS complex be inverted?
Ischemia
Ventricular hypertrophy
Basically, whenever blood flow is restricted (lack of O2)
What are the 5 rules for analyzing ECG’s/heart rhythms?
Regularity
Rate
P wave
PR Interval
QRS
How PR intervals are measured?
when they measure between 0.12 and 0.20 seconds.
Expected QRS range?
Less than 0.12 seconds.
indicates time between atrial and ventricle contraction
Innervations of the heart by the autonomic system: what does the sympathetic branch effect?
- The atria and ventricles
- It increases:
-HR
-Conduction
-Irritability
Innervations of the heart by the autonomic system: what does the parasympathetic branch effect?
- only the atria
- decreases:
-HR
-Conduction
-Irritability
Elements of Sinus Arrhythmia
-SA Node is the pacemaker, impulses are irregular.
-RR increases with inspiration/expiration
-Each beat is conducted normally
Characteristics of: Accelerated Junctional Rhythm
-Short waves but regular rhythm
-The AV node takes over.
Inherent Rates for: SA Node
60 - 100 BPM
Inherent Rates for: AV Node
40 - 60 BPM
Inherent Rates for: Ventricles
20 - 40 BPM
How do you calculate a regular rhythm from a ECG?
Count the number of large squares between the R waves and divide into 300.
OR
Count small squares and divide into 1500 (more accurate)
ECG Recordings: How much is one small square in terms of time?
0.04 s
ECG Recordings: 5 large squares is equal to how many seconds?
1 second
ECG Recordings: How many seconds are in 5 small squares?
0.20 seconds
ECG Interpretation: what does the ST segment represent? (Lead II)
Depression = possible ischemia
Elevation = acute myocardial injury (MI)
What do inverted T Waves (lead II) suggest?
Ischemia
ECG Interpretation: What are QT intervals?
Vulnerable refractory period of ventricles
What do Digoxin and Amiodarone do?
They treat heart failure/heart related rhythm irregularities associated with ventricular contractions.
Ectopic Beat
Any electrical activation of the heart that originates outside of the SA node.
Ectopic Focus
Refers to the location that rise to the ectopic bea
i.e atrial or ventricular ectopic beat
Escape beat
Any beat that initiates an impulse because the faster pacemaker failed to do so.
i.e SA node fails, atria stimulates the next beat
What is the dominant pacemaker?
SA node
Which would fall under the category of “escape” pacemakers?
AV node -> AV junction
Bundle of his -> purkinje network
Rate for SA node?
60-100/min
AV junction rate?
40-60/min
Bundle Branches Rate?
30-40/min
Purkinje network rate?
30-40/min
Terminology: Automaticity or autorhythmicity
The ability of the pacemaker cells to generate an action potential without external stimulation.
Terminology: Excitability or irritability?
The ability of a cell to reach its threshold potential, then respond to stimulus.
Refer back to slide 15 on polarized myocardial cells (resting state)
What are 5 types of Arrhythmias?
- Sinus Arrhythmias
- Atrial Arrhythmias
- Junctional Arrhythmias
- Heart Blocks (Conduction Defects)
- Ventricular Arrhythmias
Why do Sinus Arrhythmias Arise?
Sinus Arrhythmias arise because of problems with the SA Node
Why do Atrial Arrhythmias Arise?
Atrial arrhythmias arise due to either irritability or escape
Why do junctional Arrhythmias Arise?
Junctional arrythmias arise due to either irritability or escape/
Why do Heart Blocks Arise?
(heart blocks = conduction defects)
Heart blocks occur because of delays/defects in the way of the AV junction conducts the impulses from the atria to the ventricles.
AV junction = AV node or Bundle of his
Why do Ventricular Arrhythmias Arise?
Ventricular Arrythmias arise due to either irritability or escape
Normal ECG: What does the P-Wave Reflect?
depolarization of the atria (initial contraction)
Normal ECG: What does the QRS complex Reflect?
Depolarization of the ventricles (contraction)
note repolarization of atria occurs when the ventricles contract, so its hidden in the QRS
Normal ECG: What does the T-Wave Reflect?
Repolarization of the ventricles
What is the RR interval
time between qrs complexes (peaks)
How many boxes are in 6 seconds?
30.
5 big boxes are 1 second.
ECG: how many seconds are in 1 small box?
Each small box has 0.20 seconds.
3 factors that affect validity of ECGS are:
1. lead placement
2. Chest wall factors
3. Artifacts
What are artifacts?
Artificial electrical impulses such as:
-Patient motion (causes irregular appearance)
-muscle tremors/shivering
-electrode contact (when it gets loose)
-other machines
Characteristics of Atrial Fibrillation
-Regularly irregular rhythm
(distance between r intervals are different)
No definite P-waves (quivering)
Idioventricular rhythm?
Regularity: usually regular, slows more and more irregular as heart dies.
Rate: 20 - 40bpm (<20 as the heart dies)
P waves: none
PR interval: no pwave = no prI
QRS complex: wide and bizzare
Rules for premature ventricular contractions (PVC)
Regularity: depends on rhythm; PVC interrupts rhythm
Rate: depends on rhythm
P wave: do not precede ectopic
PR Interval: no p wave = no PRI
QRS: wide and bizarre
**T Wave: frequently in opposite direction of QRS **
Heart block general rules (between 1-3)
Key points:
P-P always regular
R-R usually regular but can become irregular for second degree.
PRI and Conduction are the main indicators
Names for second degree heart blocks (type 1 and 2)
1 = wenkebench
2 = mobitz
Rank the severity of heart blocks
First, second, third.
The higher the degree, the worse the block.
Rates for the following:
Sinus tachy
Atrial Tachy
Atrial flutter
junctional tachy
supraventrical tachy
Sinus Tachycardia 100 – 160 bpm
Atrial Tachycardia 150 – 250 bpm
Atrial Flutter (atrial rate) 250 – 350 bpm
Junctional Tachycardia 100 – 180 bpm
Supraventricular = > 150
What ECG type has a inverted P wave?
Junctional tachycardia;
note. p wave could be invisible if <0.12
Atrial Fibrillation vs. Atrial flutter
In atrial fibrillation, the atria beat irregularly.
In atrial flutter, the atria beat regularly, but faster than usual and more often than the ventricles, so you may have four atrial beats to every one ventricular beat.
Atrial arrhythmia main characteristic/rule
SA node is no longer the pacemaker, atria have taken over.
P waves = abnormal
Most likely from irritation
