Chapter 25 Disorders of Cardiac Conduction and Rhythm Flashcards
What does the conduction system of the heart control?
rate and direction of the electrical impulse conduction in the heart
Where are impulses generated in the heart?
SA node
Are there specialized cells of the conduction system?
yes – they help maintain conduction
What is the order of conduction for the heart?
SA node, AV node, bundle of His, R/L bundle branches, purkinje fibers
What are the 2 types of conduction disorders?
disorders of rhythm and impulse conduction
What is a disorder of impulse conduction?
somewhere along the pathways of nerve cardiocytes it is damaged
What are disorders of rhythm?
too fast or too slow
What causes arrhythmias and conduction disorders?
Congenital defects or degenerative changes in the conduction system
Myocardial ischemia and infarction
Fluid and electrolyte imbalances
Effects of drug ingestion
What are the sinus node arrhythmias?
sinus bradycardia, tachycardia, and arrest
What is the normal heart beat?
60-100 beats a minute
What is sinus bradycardia?
heart rate slower than 60 beats a minute
Where does sinus bradycardia originate?
in the SA node
Can sinus bradycardia be normal?
yes for elite athletes it can be a baseline for them – their heart beats are generally slower than a regular persons
What is sinus tachycardia?
increased rate of electrical discharge from the SA node - higher heart rate over 100 beats a minute
What is vagal tone?
balance of activity between the parasympathetic and sympathetic nervous systems through the vagus nerve
What is sinus arrest?
Failure of the SA node to discharge and causes an irregular pulse → other places in the heart can fire, if the SA node is not fired then the cardiocytes will decide to fire a pulse on their own
What is respiratory arrhythmia?
regular arrhythmias that occurs with breathing, because breathing puts pressure on the vagus nerve, the rate is higher, then on expiration when the pressure is lifted the rate is slower
What are premature atrial complexes?
when Ectopic foci in the atria fire before the SA node does
what is Paroxysmal Supraventricular Tachycardia?
Causes HR of 140-240 beats per min
Signal re enters atria before the SA node fires
May be asymptomatic
how do you treat Paroxysmal Supraventricular Tachycardia?
Treated with ablation: destruction where they’ll damage the cardiocytes that are allowing the signal to occur, so it will stop it
What is atrial flutter?
ectopic tachycardia of 240-400 beats/min
What is Atrial Fibrillation?
Disorganized atrial depolarization resulting in an atrial rate of 300-600 beats/min
Persistent fibrillation may require cardioversion (using the paddles to reset the heart to encourage it to work properly again)
What is Long QT Syndrome and Torsade’s de Pointes
Highly unstable rhythm that may result in ventricular fibrillation or revert to sinus rhythm and Long QT: repolarization is prolonged – it takes so long that some cells are depolarized for so long that they start to repolarize = inefficient contraction
Rate of tachycardia is 100 to 180 beats/min and can result in sudden cardiac death
What is long QT syndrome and Torsade’s de Pointes linked to?
various drugs, electrolyte imbalances, MI and infections, and can be congenital
What are Premature ventricular complexes (contractions) PVC?
Ectopic pacemaker in the ventricles and fires before the SA node
Not significant in a healthy heart
A lot of ppl have this – it’s where the heart skips a beat every now and again
What is Ventricular Tachycardia?
Rhythm originating in the ventricle of 70-150 beats per min
May decrease filling time cardiac output to dangerous levels
What is Ventricular Fibrillation?
No cardiac output and fatal within minutes requires defibrillation
Common side effect of an MI
What are examples of disorders of Atrioventricular conduction?
1st, 2nd, and 3rd degree AV block
What is 1st degree AV block?
Delayed AV conduction and a prolonged PR interval
The SA node is not firing
What is 2nd Degree AV block?
Failure of one or more of the impulses from the atria to ventricles
Generally due to damage/death of the heart (like in an MI)
What is 3rd Degree Av block?
Loss of the atria to ventricle impulses
Results in bradycardia and requires a pacemaker
Different pacemakers for the atria and ventricles
What is the treatment for arrhythmias?
Drugs, electronic pacemaker, cardioversion (defibrillation or synchronized) ablation, surgical interventions
What are the pharmacological treatments for arrythmias?
Class 1 drugs:
Block fast sodium channels: block conduction pathways used to treat ectopic foci and reentrant arrhythmias
Class 2 Agents:
Beta andergenic blocking drugs: reduce sympathetic nervous system stimulation, used to treat supraventricular arrhythmias and tachyarrhythmias
Class 3 Drugs:
Inhibit K+ movement and repolarization: extend the action potential and refractoriness. Used to treat ventricular arrhythmias
Class 4 Drugs:
Block the slow calcium channels: reduce the force of contraction and slow the SA and AV nodes which slows the ventricles
