Anti-arrhythmic agents Flashcards
The conduction system of the heart is through the:
SA node–> atria–> AV node–> bundle of His–> bundle branches–> purkinje fibers–> ventricles
The slow response action potential are for the
Pacemaker cells
Describe phase 0 of the action potential in cardiomyocyte cells:
Phase 0: rapid depolarization (fast sodium channels open; fast inward flow of Na+)
Describe phase 1 of the action potential in cardiomyocyte cells:
Begin repolarization (sodium channels close)
Describe phase 2 of the action potential of cardiomyocyte cells:
Plateau (slow calcium channels open; slow inward flow of Ca2+)
Describe phase 3 of the action potential of cardiomyocyte cells:
Repolarization (calcium channels close; potassium channels open; slow outward K+ current)
Describe phase 4 of the action potential of cardiomyocyte cells:
Pacemaker potential; return to resting membrane potentials
The absolute refractory period is the period when
another action potential cannot be generated
Pacemaker cells have
automaticity so they can self-excite
Describe phase 0 of the pacemaker cells:
upstroke, critical firing threshold is 40 mV, slower and Ca2+ mediated
Describe phase 3 of the pacemaker cells:
repolarization; inactivation of Ca2+ and Na+ channels; activation of K+ channels
Describe phase 4 of the pacemaker cells:
Gradual depolarization; slow inward Na+ and Ca2+ currents
The cardiac pacemaker is the
Sinoatrial node
Normal sinus rhythm is
60-100 beats/min.
Conduction slows through
the AV node
The P wave is the
atrial depolarization
The QRS complex is the
ventricular depolarization
The T wave is the
ventricular repolarization
An arrhythmia is a
disturbance in the electrical activity of the heart
Arrhythmias are classified according to:
site of origin of abnormality (atrial/junctional/ventricular)
Complexes on ECG (narrow/broad)
Heart rhythm (regular/irregular)
Heart rate is increased or decreased
Mechanisms of arrhythmia production include
altered automaticity, delayed after-depolarization, re-entry, and conduction block
A conduction block is
an impulse fail to propagate in non-conducting tissue
Re-entry is
refractory tissue reactivated repeatedly and rapidly due to unidirectional block, which causes abnormal continuous circuit
Delayed after-depolarization is
a normal action potential of cardiac cell triggers a train of abnormal depolarizations
Altered automaticity is
latent pacemaker cells take over the SA node’s role; escape beats
Factors underlying cardiac arrhythmias include
arterial hypoxemia, electrolyte imbalance, acid-base abnormalities, myocardial ischemia, altered SNS activity, bradycardia, administration of drugs, enlargement of a failing ventricle
When do cardiac arrhythmias require treatment?
They cannot be corrected by removing the precipitating cause
hemodynamic stability is compromised
the disturbance predisposes to more serious cardiac arrhythmias or co-morbidities
Acute non-pharmacological treatment of cardiac arrhythmias include
vagal maneuvers & cardioversion
Non pharmacological treatment of cardiac arrhythmias include:
pacing (external, temporary, and permanent) & prophylaxis- radiofrequency catheter ablation or implantable defibrillator
Antiarrhythmic agents are used to
prevent, suppress, or treat a disturbance in cardiac rhythm
Cardiac rhythm disturbances include:
atrial fibrillation, atrial flutter, SVT, ventricular tachycardia, ventricular fibrillation, bradyarrhythmias, heart block
If there is a new onset dysrhythmia
the surgery will most likely be cancelled
According to the Vaughan Williams classification of antiarrhythmic drugs, class 1:
are sodium channel blockers and they work at phase 0
According to the Vaughan Williams classification of antiarrhythmic drugs, class 2:
are beta adrenergic blockers and primarily work at phase 4
According to the Vaughan Williams classification of antiarrhythmic drugs, class 3 drugs:
are potassium channel blockers and act at phase 2 & phase 3
According to the Vaughan Williams classification of antiarrhythmic drugs, class 4 drugs:
are calcium channel blockers and act at phase 2
According to the Vaughan Williams classification of antiarrhythmic drugs, class 5 drugs:
are unclassified drugs
Class 1 drugs can further be subdivided into:
Class 1A, 1B, and 1C and they all work at phase 0
Class 1A drugs work by
causing moderate depression and prolonged repolarization
Class 1B drugs work by
weak depression and shortened repolarization
Class 1C drugs work by
strong depression with little effect on repolarization
