Dysrhythmias Flashcards
(34 cards)
What is the normal resting membrane potential in nonpacemaker cardiac cells?
Approximately −90 mV
Resulting from differential concentrations of Na+ and K+ across the cell membrane.
What role does the Na+ K+ exchange pump play in cardiac cells?
Maintains the resting membrane potential
It facilitates the concentration-dependent flow of K+ out of the cell.
What occurs during depolarization in nonpacemaker cells?
Membrane potential becomes less negative
Initiated by an electrical stimulus.
At what membrane potential do specialized Na2+ channels open?
−70 mV
This causes a rapid influx of positive charge into the cell.
What is the effective refractory period in nonpacemaker cells?
When the membrane potential remains more positive than −60 mV
During this period, depolarization from a second electrical stimulus is not possible.
What is the intrinsic impulse-generating rate of the AV node?
45 to 60 beats/min
This rate is lower than that of the SA node.
What does the P wave represent on an ECG?
Atrial depolarization
It is the first wave in the normal ECG cycle.
What is the normal range for the PR interval on an ECG?
0.10 to 0.20 seconds
Represents the time it takes to conduct an impulse from the atria to the ventricles.
What does the QRS complex represent on an ECG?
Ventricular depolarization
Normally lasts 0.09 seconds or less.
What is enhanced automaticity?
Spontaneous depolarization in nonpacemaker cells or low-threshold depolarization in pacemaker cells
Common in conditions like hyperkalemia or digoxin toxicity.
What is triggered activity in cardiac dysrhythmias?
Abnormal impulses from afterdepolarizations
These can occur early or delayed after the resting potential is restored.
What characterizes reentry dysrhythmias?
Repetitive conduction of impulses through a self-sustaining circuit
Requires differing refractory periods in the conduction pathways.
Fill in the blank: The SA node has a typical rate of _______ beats/min.
60 to 90
It is considered the dominant pacemaker in healthy adults.
What does the T wave represent on an ECG?
Ventricular repolarization
Its duration can vary depending on multiple factors.
What can cause PR interval prolongation?
Nodal or supranodal conduction system disease
This condition may indicate underlying cardiac issues.
What is the role of the His-Purkinje system in cardiac conduction?
Delivers impulses to myocardial tissues for coordinated ventricular contraction
Ensures effective heart function.
What can lead to aberrant conduction in cardiac impulses?
Premature impulse arrival
Associated with bundles that are relatively refractory.
What is the significance of the QT interval?
Represents the total time of ventricular depolarization and repolarization
Important for assessing QT prolongation in syncope or dysrhythmia cases.
True or False: The left anterior descending artery typically supplies the left posterior-inferior bundle.
False
The LPIB may be supplied by the RCA or LCA.
What are Class I antidysrhythmic drugs?
Sodium (fast) channel blockers that slow depolarization with varying effects on repolarization
These drugs have membrane-stabilizing effects.
What characterizes Class IA antidysrhythmic drugs?
Moderate slowing of depolarization and conduction; prolong repolarization and action potential duration.
Class IA agents slow conduction through the atria, AV node, and HisPurkinje system and suppress conduction in accessory pathways. As
such, they slow both depolarization and repolarization.
Class IA agents
also exhibit anticholinergic and mild negative inotropic effects.
Examples include Procainamide, Quinidine, and Disopyramide.
When can you use Procainamide and what is the dose?
- Only agent to be used in emergency rx of vent. and supravent. arrythmias
- Can alter normal and accesory pathway conduction
- Preferred agent in WPW syndrome
Dose: 20-30 mg/min until
dysrhytmia terminated
hypotension occurs( 5-10% of cases due to vasodilatory effect)
QRS widens by more 50% of pretreatment width
What is the effect of Class IB antidysrhythmic drugs?
Minimally slow depolarization and conduction; shorten repolarization and action potential duration rather than prolonging it
Little effect on accesory pathway conduction
Examples include Lidocaine, Phenytoin, Tocainide, and Mexiletine.