Cardiac arrhythmias Flashcards
Where does each heart beat originate from?
SA node.
What is the average beat from the SA node?
70 beats a minute.
When will you see bradycardia (slowing of HR)?
Sleep.
When will you see tachycardia (fast HR)?
- Emotion.
- Exercise.
- Fever.
- Other stimuli.
When does the heart rate accelerate?
Inspiration - impulses in the vagi from the stretch receptors in the lungs inhibit the cardio-inhibitory area in the medulla oblongata. There is a decrease in tonic vagal discharge (that keeps the HR slow) so the HR rises.
When does the heart rate decelerate?
Expiration.
What is sinus arrhythmia due to?
Normal phenomenon - fluctuations in parasympathetic output to the heart.
What happens in sick sinus syndrome?
Disease process that affects the SA node -> marked bradycardia -> dizziness and syncope.
What is complete (third-degree) heart block?
Interruption to conduction from the atria to the ventricles.
What happens in a complete heart block?
The ventricles beat at a low rate independent of the atria.
What can cause complete heart block?
- Disease in AV node - AV nodal block.
- Disease in the conducting system below the node - infranodal block.
in AV nodal block what tissue becomes the pacemaker?
Remaining nodal tissue - will roughly beat 45bpm.
In infranodal block what tissue becomes the pacemaker?
Ventricular pacemaker (located peripherally) - 35bpm on average.
What else can occur in patients with infranodal blocks?
Periods of asystole lasting >1 minute. This can result in cerebral ischaemia which can cause dizziness and fainting (stokes-adams ysndrome).
What is incomplete heart block?
Conduction between atria and ventricles is slowed but not completely interrupted.
What will you see on the ECG in first degree heart block?
PR interval is abnormally long - all the atrial impulses reach the ventricles.
What will you see on the ECG in second degree heart block?
Not all atrial impulses are conducted to the ventricles. So a ventricular beat may follow every second or third atrial beat (2:1 block, 3:1 block).
What is the wenckebach phenomenon?
Repeated sequences of beats with the PR interval lengthening progressively until a ventricular beat is dropped. The PR interval of the cardiac cycle that follows the dropped beat is usually normal or only slightly prolonged.
What is a bundle branch block?
When one branch of the bundle of His is interuppted. Right or left bundle branch block.
What occurs in a bundle branch block?
Excitation normally goes down the bundle on the intact side and then goes back through the muscle to activate the ventricle on the blocked side.
What will you see on the ECG in a bundle branch block?
- Prolonged QRS complex and deformed.
- normal ventricular rate.
What is a fascicular block?
Block in the anterior or posterior fascicle of the left bundle branch.
What will you see in a left anterior fascicular block on an ECG?
Abnormal left axis deviation.
What will you see in a left posterior fascicular block on an ECG?
Abnormal right axis deviation.
What happens when His-purkinje fibres may discharge spontaneously?
There is increased automaticity of the heart and an ectopic beat can occur (beat that occurs before the expected next normal beat).
What are the type of ectopic beats?
- Atrial.
- Nodal.
- Ventricular - extrasystole or premature.
What happens if ectopics fire repeatedly at a rate higher than the SA node?
Produces a rapid regular tachycardia - atrial, ventricular, or nodal paroxysmal tachycardia or atrial flutter.
What is a circus movement?
Where there is a block on one side of the conducting system. So when impulses spread in both directions, one side is blocked. The other side continues around and when it reaches the blocked area, the impulse on the other side is in its refractory stage. The a impulse then continues going around in a circular position.
What happens in a bundle of Kent?
There is an extra bundle of conducting tissue that connects the atria to the ventricles. This will allow for a re-entrant pathway to occur.
What happens with atrial extrasystoles?
Another area in the atria will stimulate the AV node prematurely, hence the ventricles are conducted prematurely.
What will you see on the ECG with atrial extrasystoles?
- Abnormal P waves.
- Normal QRS complex.
What is atrial tachycardia?
When an atrial focus discharges regularly or there is reentrant activity. You will get atrial rates of up to 220/min.
What is the atrial rate in atrial flutter?
200-350/min.
What happens in atrial flutter?
Large counterclockwise circus movement in the right atrium.
What will you see with atrial flutter on the ECG?
Sawtooth pattern of flutter waves.
Why will you see sawtooth appearance
