Application Of ECG Flashcards
Describe normal sinus rhythm, what does it indicate?
Rate: 60-100 bpm, regular R-R interval- 5 small boxes
P waves present, upright in leads I, II, & III
QRS interval (width normal ~ 2.5 small boxes)
P:QRS ratio: every P associated with a QRS
P-R interval normal (<5 small boxes)
Mean electrical axis- normal
Indicates:
- electrical signal generated by SA node
- AV functioning (P-R interval)
- Signal conducted via normal pathways & normal velocity through heart
What are arrhythmias?
Abnormal rhythms of the heart
What arrhythmias involve the heart rate?
Bradyrhythmias(too slow)
Tachyrhythmias(too fast)
How can arrythmias be classified on site of origin?
Supraventricular (SA node, atria, & AV node) & ventricular
What mechanisms are used to classify types of arrhythmias ?
Automatic, triggered, or re-entrant (covered in pathyops)
What are the causes of arrhythmias?
Altered automaticity: SA node, AV node, or ectopic foci (new pacemakers)
Altered conduction: can occur anywhere along the conducting pathways, and may be partial or compelete. Several blocks are due to dysfunction of the AV node
What are the locations/sources of arrhythmias?
- Sinoatrial node(SA) node)- normal sinus arrhythmias
- Atrial arrythmias
- AV node- node/junctional/heart blocks
Since these 3 are above the ventricle, they are called supraventricular arrythmias
Ventricle- typically due to new pathological/ectopic foci generating electrical signals
What is a supraventricular arrythmias ?
Change in cardiac rhythm from the “normal sinus rhythm”
What is sinus arrhythmia?
Change in HR with the respiratory cycle (slight increase in HR in inspiration; slight decrease in HR in expiration). Due to Vagus nerve/parasympathetic effect on SA node), transplanted heart not have this response.
What is sinus bradychardia ?
Decreased HR. Athletes (increased vagal tone), hypothyroid, hypothermia
What is atrial fibrillation?
Ectopic foci/ pacemaker signals coming from cells other than the SA node
What are the supraventricular arrhythmias ?
Sinus arrhythmias
Sinus tachycardia
Sinus bradycardia
Atrial fibrillation
What is a sinus tachycardia?
SA node pacemaker generates impulse for HR, but at a faster pace than normal
Due to increased depolarization of phase 4 of SA node action potential
Describe sinus tachycardia showings on an ECG
Rate above 100 bpm
Rhythm: regular
P-wave: vusubke before each QRS
QRS interval: normal
Exercise, stress, fight, fever
Describe the showings of atrial fibrillation
Rate: 80-100 bpm
Rhythm: irregularly irregular
P wave: not distinguishable
QRS interval: usually normal
P-R interval: not measurable
What is the clinical significance if atrial fibrillation ?
Multiple sites generating electrical impulses in atria. Due to refractory period of AV node only some signals pass through AV node to ventricles. Thus HR irregular
- Frequency of generation of action potentials is so high that there is no coordinated contraction of the myocardium
- Atrial contraction contributes 10-20% of end diastolic blood volume
- Atrial fibrillation is well tolerated
- Common in the elderly
Complications: blood pools in parts of the atria forming clots
What mechanisms cause increased excitability of ventricular arrythmias?
-abnormal passage of signals through conducting pathways, or new/ectopic foci
-Damage to cells make them more excitable and automaticity e.g. ischemia
1. Reduced oxygen delivery to the damaged myocardium.
The decreased ATP synthesis results in the following cascade. Na/K ATPase pump less efficient, & intracellular [Na+] increases. Thus causes the resting membrane potential (RMP) to increase. Thus the RMP is closer to threshold & cells are more excitable
- Damaged cell membranes become leaky, allowing more Na+ to enter the cell
What are the types of ventricular fibrillation?
Tachycardia- very fast. Large/wide, frequent smooth QRS on EKG
Fibrillation—> 350. Many ectopic foci. Thus EKG QRS not regular, and at some times depolarize in direction opposite EKG lead-resulting in some inverted QRS as well
Describe ventricular tachycardia showing on ECG
Rapid deadly rhythm of the ventricles
Rate: 150-300 bpm
P wave: not seen
QRS shape: only wide, tall bizarre looking complexes. Prolonged QRS interval> 0.12 sec
Complications: can be a DEADLY rhythm
Ventricles cannot maintain thus rate. Poor cardiac output
Describe showing of ventricular fibrillation on ECG
Rapid, uncoordinated firing of ventricles
Rate: > 300+ bpm
DEADLY RHYTHM- irregular
Rhythm does not generate a pulse
QRS- No discernible QRS complexes. Disorganized electrical signals cause the ventricles to quiver instead of contracting in a rhythmic fashion
All waves are fibrillation waves
What occurs in ventricular fibrillation?
Electrical chaos: no coordinated ventricular contraction. Due to many ectopic foci generating depolarization signals.
Decreased CO, Decreased MAP, patient becomes unconscious as there in NO cardiac output
May be caused by myocardial infarct
What are conduction blocks?
Heart blocks/ junctional blocks/ AV blocks
Why does the AV node slow the signals?
- Small cells: the wave of depolarization has to jump many cell membranes and moves slowly. Greater resistance
- Few gap junctions between the cells.
- High resting membrane potential (RMP, -60mV). Thus most voltage gated Na channels are closed. AV node depolarization due to L type Ca2+ channels- which are slower (less step phase 0 in SA as compared to normal cardiomyocytes)
Describe importance AV node & effect on P-R interval
The atria are electrically separated from the AV node by a fibrous septum
- The only normal pathway for SA node signals to get to the ventricles is via the AV node(a window)
- The AV node delays the signal by 0.1 sec (P-R interval), giving atria time to contract and fill ventricles
What are 1st degree heart blocks?
Prolonged P-R interval
Conduction delayed through AV node.
PR interval long > 0.2 seconds
Each and every P wave is followed by a QRS wave
Longer interval
How is 1st degree heart block treated ?
NO treatment indicated for asymptomatic, isolated 1st degree Atrioventricular (AV) heart block
What is the cause of 1 st degree heart block?
Age, athletic training, surgery, some diseases, electrolyte disturbances, AV node blocking drugs, or normal variabt
How can 1st degree heart blocks be identified on ECG?
Rate: 60-100 bpm (normal), normal rhythm
P: QRS ratio: each P followed by QRS (1:1)
QRS shape: normal
P-R interval> 0.2 sec> 5 small boxes
What are the types of 2nd degree heart blocks?
Mobitz type 1p
Mobitz ty9e 2
What is a mobitz type 1, 2nd degree heart block?
Type- Wenckeback
Progressive lengthening of P-R interval beat dropped
Gradual increase in AV node refractoriness causes conduction block of some; not all atrial impulses get through to ventricles
Defect at AV node: P-R interval progressively longer
Benign condition. Children, athletes with increase vagal tone
In treatment necessary
Describe the showing of a mobitz type 1 (wenckback) on ECG
Progressive lengthening of P-R interval-beat dropped
Rate: normal or slow
P: QRS ratio: ALMOST every P followed byvQRS
QRS shape: normal
-P-R interval: progressively longer until QRS dropped (QRS and T waves absent)
Describe 2nd degree heart block -mobitz type 2 showing in ECG
Some beats dropped
Rate: 30-100 bpm depending on conduction ratio (2:1, 3:1, 4:1)
P: QRS ratio: ALMOST every P followed by QRS
P-R interval: constant and normal
Impulses blocked at A-V node- so some P waves stand alone
Defect below AV node- AV node working & P-R interval not change
Dangerous condition need a pacemaker
What causes the 2nd degree heart block, mobitz type II?
Due to loss of conduction beyond AV node.
P waves on time . Atria regular Ventricles irregular
How is a 3rd degree heart block treated?
Pacemaker
How does a 3 rd degree heart block show on ECG?
No relationship between P & QRS
Rate: P wave (atrial) 60-100 bpm (normal. Pacemaker is SA node)
QRS (ventricle) 20-40 bpm (ventricle generate their own impulse through an NON SA node pacemaker (e.g. AV node or conduction system)
P: QRS ratio; complete dissociation of P and QRS relationship
QRS may look narrow or wide and bizarre
P-R interval values because it is completely random and dissociated from QRS
CO & BP are compromised
What are bundle branch blocks?
Occurs when heart rate > critical level, conduction system fails. Inadequate time for repolarization of conduction system
Impulse spreads slowly through the ventricles- from one myocyte to the next (conducting system not working)
QRS complex is widened. No coordinated spread of APs. Contractions of the heart are weaker
