Class 9 Flashcards
What is the phenomenon of pacemaker cells with higher intrinsic rhythm preventing latent pacemakers in the heart from firing
Overdrive Suppression
Pacemaker cells with higher intrinsic rhythm tend to suppress what?
Latent pacemaker’s automaticity
When is the automaticity of pacemaker cells depressed?
When they are forced to fire faster than their intrinsic rate
What is the mechanism of overdrive suppression?
The activity of the Na/K ATPase increased when Na has a higher rate of influx, creating a higher rate of Na efflux than K influx
When overdrive suppression has happened it is more (negative, positive) in the cell
Negative, hyperpolarization
When it is more negative in the pacemaker cell, what happens to the pacemaker’s automaticity?
It is suppressed
When a pacemaker cell is hyperpolarized, the diastolic potential is changed how?
More negative maximum diastolic potential
When a pacemaker cell is hyperpolarized, what happens to the threshold value?
It is increased, thus slowing automaticity
What is a phenomenon that cardia impulses may re-excite the myocytes through which it had passed previously within same cardia cycle?
The re-entry loop
What is a direct consequence of conduction disturbance?
Onset of tachycardia or fibrillation
3 essential conditions required for the re-entry loop:
1) Must be closed conduction loop
2) Must be region of unidirectional block
3) Slow conduction of impulse around the loop
What does the re-entry loop cause physically to happen?
An extra heart beat
SA node controls the cardiac rhythm describes what?
Sinus rhythm
Sinus rhythm with a rate less than 60 bpm describes what?
Sinus bradycardia
Sinus rhythm with a rate greater than 100 bpm describes what?
Sinus tachycardia
Defined as the onset of abnormal heart rhythms is what?
Arrhythmia
Prolonged impairment of SA node allows latent pacemaker (AV node) to initiate escape beat is what?
Escape rhythm
Continuation of escape beats gives ride to what?
Escape rhythm
What is more sensitive to parasympathetic activity? SA and AV nodes or ventricular conducting system
SA and AV nodes
What is the ventricular conduction system?
bundle of His or bundle branches
During intense parasympathetic activity what becomes the latent pacemaker? When would this happen?
Ventricular conduction system, this is an escape rhythm
In intense parasympathetic activity, is the HR high or low?
Low
Ischemia of the SA node can trigger what?
Onset of junctional escape beat and thus junction rhythm
What is an ectopic beat?
A heartbeat generated by impulse other than from the SA node
Junctional escape beat is a form of what?
Ectopic beat
Impulse from latent pacemaker travels in two driections:
1) Towards the ventricular contractile myocytes
2) Towards the atrial contractile myocytes
What happens to an ECG when there is an impulse from a latent pacemaker in junctional escape rhythm?
Inverted P wave
What happens to ECG when impulse from a latent pacemaker in a ventricular escape rhythm?
Absent QRS complex
What is an absent QRS complex an indication of?
An AV block
When the AV node is blocked, what is the latent pacemaker?
bundle of His or bundle branches
Ventricular tachycardia on a ECG:
Normal ECG, but fast heart rate, may have a wider QRS complex
What can ventricular tachycardia lead to?
Ventricular flutter (over 200 bpm)
What can ventricular flutter lead to?
Ventricular fibrillation
What is ventricular fibrillation?
Form of nonfunctional muscle contraction, produces no cardiac output
Impaired conduction through the AV conduction system describes what?
Heart block
What is included in the AV conduction system?
AV node, bundle of His, bundle branches
Delay between atrial and ventricular depolarization is what degree of heart block?
First
Intermittent failure of AV conduction is what degree of heart block?
Second
First degree heart block on ECG:
Prolong PR interval
What are the symptoms of a first degree heart block?
Usually asymptomatic, could get worse
What are the 2 types of second degree heart blocks?
1) Mobitz I - Wenckebach
2) Mobitz II
Mobitz I second degree heart block on ECG:
PR interval progressively lengthens until one QRS complex is absent, repeats
What are the symptoms of Mobitz I second degree heart block?
AV node problem, increased vagal tone
Mobitz II second degree heart block on ECG:
QRS complex absent every few PR intervals, may lose two or more in a row
What is often the cause of Mobitz II second degree heart block?
Septal infarct or His-Purkinje system degeneration
Third- degree heart block on ECG:
Total dissociation between P wave and QRS complex
What can cause a third degree heart block?
Myocardial infarction or degeneration of the AV conduction system
Complete hear block with complete failure of conduction between atria and ventricles is what degree of heart block?
Third
Symptoms of third degree heart block?
Low HR, light headedness
Occurs when the electrical impulse from the bundle of His does not conduct along the right bundle branch is what?
Right bundle branch block
In a right bundle branch block what happens to the right ventricle?
The right ventricle depolarizes later and is slower
Occurs when transmission of impulse is delayed or fails along the main left bundle branch or in both left anterior and posterior fascicles is what?
Left bundle branch block
In left bundle branch block, what happens to the left ventricle?
The left ventricle depolarizes slowly by cell-to-cell conduction that spreads from right v to left v
