Mechanisms Of Cardiac Arrhythmias Flashcards
Generated by rapid inward Na+ current and are responsible for fast conduction in the atria
Fast response APs
Slow response APs are generated by slow inward Ca2+ current and are responsible for slow conduction in
Sinus and AV nodes
Abnormal impulse generation that results in increased normal automaticity and enhanced automaticity of latent pacemakers
Arrhythmias
Found in the primary pacemaker, the SA node, as well as in certain subsidiary or latent pacemakers that can become the main pacemaker under certain conditions
Normal automaticity
The cause of normal automaticity in the sinus node and in latent pacemakers is a spontaneous decline in the membrane potential during
Diastole or Phase 4
The maximum negativity attained after repolarization of the action potential
Maximum Diastolic Potential (MDP)
The level of threshold potential for initiation of phase 0 of the action potential is a determinant of the rate of
Impulse initiation
The rate of change of phase 4 of the action potential
Slope of Spontaneous Diastolic Depolariztion (SDD)
The rate of impulse initiation by pacemaker cells is controlled by four specific characteristics of the transmembrane potential. What are the 4?
MDP, TP, SDD, and APD
The autonomic nervous system modulates the
Sinus Rate
Electronic interactions can suppress latent
Pacemakers
When a cell is activated at faster than intrinsic rates, more Na+/K+ ATPase activity is seen, which results in
More negative MDP
Arrhythmias can be due to alterations in normal automaticity. This can happen with
Sinus tachycardia or bradycardia
When cells that don’t normally exhibit automaticity are depolarizer, they may develop automaticity. This is called
Abnormal automaticity
Working myocardial cells have the ion channels that cause SDD in pacemakers. However, in working cells, these channels do not cause
Automaticity
In working myocardial cells, opposes any inward depolarizing currents during diastole that might lead to SDD
IK1 (outward K+ current)
When the resting potentials of working myocardial cells are reduced significantly, SDD can occur and cause impulse initiation by the mechanism of
Abnormal automaticity
The second form of abnormal impulse initiation
Triggered Activity
The term used to describe impulse initiation that is dependent on afterdepolarizations
Triggered Activity
Oscillations in membrane potential that follow the primary depolarization phase (0) of an action potential
Afterdepolarizations
Oscillations in membrane potential that occur during repolarization
Afterdepolarizations
Oscillations in membrane potential that occur after repolarization of the action potential
Delayed afterdepolarizations
More likely to develop in conditions which prolong the
AP duration
Clinically, prolongation of the QT interval is associated with the development of a ventricular arrhythmia called
Tornado de Pointes
Pacing at faster rates increases the amplitude of
-When they reach threshold, they may result in spontaneous repetitive depolarizations
Delayed Afterdepolarizations
Occurs when the propagating impulse encounters a region of the heart that is electrically unexciteable
-Tissue is refractory
Conduction Block
When the AV node is stimulated at faster rates, the conduction velocity through the AV node
Decreases
When the AV node is stimulated at faster rates, the conduction velocity through the AV node decreases. This phenomenon is known as
Decremental Conduction
This is seen in tissue such as the AV node, that is principally dependent on the slow inward Ca2+ current
Decremental Conduction
Prevents normal propagation of the cardiac impulse from the sinus node to the ventricles
Conduction block w/in AV node or His-Purkinje system
Removes the normal overdrive suppression that keeps latent pacemakers in the AV node and His-Purkinje system in check
Conduction block
Usually results in the emergence of escape beats or escape rhythms in the AV node, His-Purkinje system, or ventricles
Conduction block
Directly related to the rate of rise of phase 0 of the action potential, which is a reflection of the magnitude of inward Na+ current
Conduction Velocity
Refers to the time during which a myocardial cell cannot be depolarized by an electrical stimulus
Refractory Period
Dependent on the action potential duration and the strength of the stimulus
Refractory Period
Characterized as the longest S1-S2 interval that fails to result in ventricular capture
Effective Refractory Period
Inactivates Na+ channels and slows conduction velocity
High K+
When an electrical impulse circulates repeatedly around the same pathway, recurrently depolarizing a region of cardiac tissue
Recently
Conduction block and slow conduction are necessary for the establishment of
Reentry
A measure of the spatial extent of refractoriness
Wavelength (gamma)
What are the two mechanisms of bradyarrhythmias?
Altered impulse formation and impulse conduction
Mechanisms that decrease phase 4 depolarization can lead to
Bradyarrhythmias
Triggered activity, i.e. EADs or DADs are mechanisms of
Tachyarrhythmias
Reentry is a mechanism of
Tachyarrhythmias
