Arrhythmia meaning
Abnormal rhythm (meaning without rhythm)
Rhythm of all automaticity foci
All pace with regular rhythm
Sinus arrhythmia
- present in humans at all times
- not a true arrhythmia
- because the autonomic system causes barely detectable rate changes in sinus pacing that relate to the phases of respiration (normal minimal variations in SA node pacing rate in association with phases of respiration)
Autonomic system effect in respiration that causes sinus arrhythmia
- inspiration activate sympathetic stimulation of the SA node = slight increase in HR during inspiration
- parasympathethetic inhibtion of the SA = slight decrease in pacing rate
Importance variability of sinus rhythm -what does it indicate
-absence of this variability = indicator of increased mortality 0 particularly after infarction
Three conduction pathways in the right atrium
Internodal pathways
- course from SA to AV noe
- Anterior, Middle and Posterior Internodal tracts
Bachman’s bundle
Originates in the SA node an distributes depolarization to the left atrium
What produces the P wave on the ECG
Depolarization of the atrial myocardium
Because depolarization passes too rapidly thrugh the atrial conduction system and therefore oes not record on ECG
PQ interval
- pause between atrial depolarization and AV node depolarization because conduction of depolarization slows within the AV node
- during this delay blood from the atria passes into the ventricles
- horizontal baseline on the ECG
What produces the QRS complex no ECG
Depolarization of the ventricular myocardium
(depolarization passing through the purkinje fibers of the ventricular conduction system is too weak to record on ECG = concealed conduction)
From the purkinje fibers where does the depolarization travel
To the endocardial surface of the ventricular myocardium
Left to right depolarization of the septum - why, in what sequence
- Occurs before the rest of the venricular myocardium depolarizes
- because the left bundle branch produces fine terminal filaments while the right bundle branch does not
Ventricular contraction on the ECG
Begins and ends during the QT interval
Repolarization of Purkinje fibers (T vs. U wave)
- takes longer than ventricular repolarization
- end of T wave makrs the end of ventricular repolarizatin but repolrization of Purkinje occurs a bit later - beyond end of T wave can sometimes see small hump = U wave
Irritable automaticity focus -characteristics
- may suddenly pace rapidly
- emergency rate 150-250 per minute is approximately the same for foci of all levels
Categories of arrhythmias
1) Irregular rhythms
2) Escape
3) Premature beats
4) Tachy-arrhythmias
Types of irregular rhythms
1) Wandering pacemaker
2) Multifocal atrial tachycardia
3) Atrial fibrilation
Irregularly irregular
Irregular chaotic rhythm with no predictable recurring pattern
Entrance block/parasystolic automaticity foci
- type of malfunctioning of automaticity foci
- any incoming depolarization is blocked - protecting them from passive depolarization b any other source
- by being insensitive to passive depolarization cannot be overdrive -suppressed
- when a automaticity focus has entrance block = parasystolic (the focus paces but can’t be over-drived suppresed)
Wandering pacemaker
An irregular rhythm produced by the pacemaker activity wandering from the SA node to nearby atrial automaticity foci
So the cycle lengths vary and P wave morphology (shape) varies as the pacemaking center moves
Multifocal atrial tachycardia
- rhythm experienced by patients with chornic obstructive pulmonary disease
- heart rate > 100 per minute
- P waves of various shapes because three + atrial foci are involved
- because atria are developing resistance to overdrive suppression (signs of parasystole) - no single focus achieves pacemaking dominance so all pace together
