Lecture 13- Arrhythmias Flashcards
abnormal rhythms (arrhythmias) may arise from
the atria
the ventricels
what are arythmias called if they occur in the atria
supraventricular arrythmia
where can arrhythmias arise from int he atria
SAN
atrium itself
AV node
what are arrhythmias that arise in the vetricels called
ventricular arrythmias
name the three main types of arrhythmias
- Atrial fibrillation
- Ventricular ectopic beats
- Ventricular fibrillation
All arrhythmias originate
somewhere outside of the normal conduction system of the heart- atria or ventricles.
you can determine where an arrhthmia originates from by looking
at the width of the QRS complex
if the QRS complex is narrow
rhythm is originating in the atria and traveling down the ventricles via the normal conduction path
if the QRS complex is broad
rhythm is originating in the ventricles and not travelling via the normal conduction path (taking longer for ventricles to depolarise)
Two ways abnormal rhythm can start to cause arrhythmia
- Ectopic focus
- Re-entry loop
1) Ectopic focus
Many tachycardic rhythms are caused by ectopic beats. These are impulses that are generated by an area (focus) in the myocardium, not the SAN. Ectopic impulses can be generated by a small area of highly excitable myocardium which can spontaneously depolarise and cause a wave of depolarisation.
Features seen on ECG depends on where the ectopic impulse originates: Atrial ectopic
an abnormally shaped P wave that appears early and is usually followed by a QRS complex due to the impulses being conducted to the ventricles e.g. atrial fibrillation is caused by an ectopic foci
Features seen on ECG depends on where the ectopic impulse originates: Atrioventricular junctional ectopics
these ectopics can activate the ventricle by travelling via the His-Purkinje system- normal QRS.
Impulses can also retrogradely activate the atria (impulse travels backwards from the AV node to spread across the atria) to give an inverted P wave- however this can be masked by the QRS complex as two events happen at the same time
Features seen on ECG depends on where the ectopic impulse originates: Ventricular ectopics
impulses generated by ectopics in the ventricles do not travel via the His-Purkinje system, and instead spread comparatively slowly over the myocardium. Therefore these ectopics give a broad QRS complex as the time taken for the impulse to travel is longer. There can be a compensatory pause as the ventricles have to repolarise before contracting again when the SA node next fires. E.g. ventricular tachycardia
Supraventricular vs ventricular arrythmias
2) re-entry loops
In the conduction system of the myocardium, there are areas in the pathway where electrical impulses can split and travel down two paths. This usually isn’t a problem because when the two impulses meet each other again, they cancel each other out. This allows the myocardium to contract in an even and efficient way.
However, problems arise when there is damage to areas of myocardium that disrupt the normal pathway of electrical impulses, or there are structural abnormalities. In the case of re-entry loops, there is an area of myocardium that is damaged and causes a unidirectional conduction block (electrical impulses can only travel one way through the damaged tissue, and one direction is blocked). Therefore electrical impulses will be able to retrogradely travel through the damaged tissue.
The impulse in a re-entry loop will travel back on itself and take alternative routes thorough the myocardium, causing abnormal contraction of the heart. This is best shown in the diagram below.
If there are re-entry loops, patient can have:
AV nodal re-entry
Atrioventricular re-entry
Atrial flutter
AV nodal re-entry
if there are ‘fast’ and ‘slow’ pathways in the AV node, there can be a re-entry loop which can cause a supra-ventricular tachycardia.
Atrioventricular re-entry
an accessory pathway between atria and ventricles leads to a re-entry loop. E.g. Wolff-Parkinson-White syndrome.
Atrial flutter can be caused by
can be caused by a re-entry loop in the atria.
atrial arrythmias 93)
Atrial tachycardia
Atrial flutter
Atrial fibrillation
atrial tachycardia is defined as a heart rate above
100bpm
how may atrial tachycardia appear on an ECG
As the heart is beating so fast, the T waves and P waves can be occurring at the same time and merge on the ECG
