Lecture 3/4 (Arrhythmias) Flashcards
Ectopic pacemakers:
- pacemakers cells in the atrium that are not SA nodal.
- lead to premature atrial contraction.
What causes sinus tachycardia or sinus bradycardia?
- rate of SA nodal firing is increased or delayed.
- SNS/PSNS input.
- HCN channels (slow depolarization of pacemaker).
What arrythmia is this?
- Sinus tachycardia.
- Sinus rhythm (PQRST; only one P per QRS).
- HR > 100.
What arrythmia is this?
- Sinus bradycardia.
- Sinus rhythm (PQRST; only one P per QRS).
- HR < 60.
What kind of rhythm is this?
- normal sinus rhythm
- Sinus rhythm (PQRST; only one P per QRS).
- HR between 60-100
Primary heart block cause and ECG manifestation:
- Cause: delayed conduction through AV node or bundle of His.
- ECG: increased/lengthened PR interval.
What arrythmia is this?
- Primary heart block.
- note increased PR interval.
Secondary heart block cause and ECG manifestation:
- Cause: increased AV nodal refractory time; Not every atrial impulse is conducted through the AV node, His-Purkinje.
- ECG: more than one P wave per QRS complex.
What kind of arrythmia is this?
- Secondary heart block.
- >1 P wave per QRS complex.
Tertiary (complete) heart block cause and ECG manifestation:
-
Cause: Atrial impulses are not conducted through AV node.
- Atria beat at one rate and rhythm and ventricles beat at another.
- Ventricular contraction is driven by escape rhythm.
- ECG: P and QRS waves at regular intervals, but not coordinated.
What drives ventricular depolarization in tertiary (complete) heart block?
- escape rhythm.
- pacemaker cells in either AV node, bundle of his, or in ventricuar myocardium itself.
The three pacemakers of the heart:
-
SA node.
- Normal rate.
-
AV junctional.
- Moderate rate.
-
Ventricular (his, purkinje, myocardium itself).
- Very slow rate - not sustainable.
Normal sequence of electrical conduction through myocytes:
- Impulse travels unidirectionally in direction of excitable myocytes.
- Refractory myocytes behind impulse prevent immediate reexcitation.
- Impulse can only either:
- continue forward or
- collide with itself and extinguish.
An ectopic pacemaker is:
- any pacemaker that forms in the heart outside of the SA node.
Steps in formation of a reentry loop/circus rhythm:
- Impulse reaches healthy and damaged cells.
- Damaged cells only allow retrograde conduction, not anterograde.
- Anterograde conduction through healthy cells.
- Retrograde conduction through damaged cells.
- Time for retrograde conduction longer than effective refractory period of previously excited healthy cells.
- Healthy cells re-excited by retrograde conduction through damaged cells.
- Reentry loop/circus rhythm formed.
How does a reentry loop/ectopic pacemaker lead to the formation of an ectopic pacemaker?
- circus rhythm created by reentry loop exits reentrant loop and depolarizes
adjacent myocardium and spreads. - APs and contractions become uncoordinated, fibrillation can result.
When does relative refraction of the fast Na+ channels involved in plateau potentials and myocardium depolarization occur on an ECG?
- mid-end T wave.
- cell may be prematurely depolarized by rogue circus rhythm during relative refraction.
What causes atrial fibrillation?
- circus rhythm (formed from reentry loop) occurs in the atria and spreads.
- atrial myocardium depolarize and contract randomly.
- fibrillation results.
Atrial fibrillation ECG manifestation (2):
- No P waves.
- Irregularly irregular rhythm.
What arrhythmia is this?
A-Fib
- no P waves
- Irregularly irregular
Why does the ventricular depolarization rate remain relatively low in comparison to atrial depolarization rate in atrial fibrillation?
- AV nodal delay.
- AV node pacemaker cells experience refraction, and so all atrial impulses are not relayed through the AV node to the ventricles.
Atrial flutter ECG manifestation (4):
- Sawtooth appearance.
- rapid and regular P waves.
- P waves before QRS.
- >1 P wave per QRS.
Primary difference between A-Fib and atrial flutter:
- Atrial flutter has:
- P waves (>1 per QRS).
- rapid and regular rhythm (PQRS).
- slower rate.
What arrhythmia is this?
Atrial flutter w/ 2:1 ventricular response
(2 P waves per QRS)
What kind of arrhythmia is this?
Atrial flutter w/ variable ventricular response
Cause of ventricular fibrillation:
- Ectopic pacemaker forms in ventricle and stimulates ventricular myocytes in relative refraction (downslope of T wave) to depolarize.
- Ventricle does not contract simultaneously, it just quivers.
- Cardiac ventricular output decreases / does not occur.
What type of arrhythmia is this?
- Normal rhythm
- Event occurs
- Ventricular tachycardia
- Ventricular fibrillation
Cause of ventricular tachycardia:
- Scarred/injured myocardium allows reentrant phenomoenon.
- Ectopic pacemaker forms in the ventricles fires at a very high rate causing ventricles to enter tachycardia.
- 300 BPM
Cardiac output is impaired in V-Tach because:
- there is not enough time between ventricular contractions to allow for diastole.
There are no P waves in V-tach or any other waves besides QRS because:
- they are masked by the sheer size of ventricular depolarization.
- they are still occurring.
What arrhythmia is this?
V-Tach
- regular and rapid
- wide QRS
Cause of bundle branch block:
- Delayed/blocked conduction within a right or left bundle branch.
- Conductance relayed from the unaffected ventricle to impaired side via interventricular septum myocytes (SLOW).
- Widened QRS.
What causes the wide QRS complex on bundle branch block ECGs?
- Delayed/blocked conduction within a bundle branch.
- Conductance relayed from the unaffected ventricle to impaired side via interventricular septum myocytes, which have slow conduction rates.
- Ventricular depolarization is longer, widened QRS complex.
Right BBB ECG manifestation:
widened QRS on lead III, V1 and V2.
Left BBB ECG manifestation:
widened QRS on lead I, lead II, and V5 and V6.
What arrhythmia is this?
BBB
widened QRS
What arrhythmia is this?
BBB
widened QRS
Split R waves on an ECG (see image) are indicative of what type of arrhythmia?
BBB
What type of arrhythmia is this?
right BBB
- Split R waves
- Lengthened QRS complex
- V1 and V2 analyze right ventricle
Premature ventricular contractions (PVCs) are:
(include ECG manifestation)
- rogue ventricular contractions that arise from ectopic pacemaker in ventricle.
- Widened QRS complex; no P waves associated with QRS complexes.
What kind of arrhythmia is this?
premature ventricular contractions
- widened QRS
- no P wave
- random QRS complexes
