What is a re entrant arrhythmia?
A reentry arrhythmia is a self-sustaining cardiac rhythm abnormality in which the action potential propagates in a manner analogous to a closed-loop circuit. It is a disorder of impulse conduction and is discrete from disorders of impulse generation such as automaticity or triggered activity.
What is a re entry of an electrical impulse?
Reentry, due to a circuit within the myocardium, occurs when a propagating impulse fails to die out after normal activation of the heart and persists as a result of continuous activity around the circuit to re-excite the heart after the refractory period has ended; it is the electrophysiologic mechanism responsible for …
What is re entry phenomenon?
Re-entry ventricular arrhythmia is a type of paroxysmal tachycardia occurring in the ventricle where the cause of the arrhythmia is due to the electric signal not completing the normal circuit, but rather an alternative circuit looping back upon itself.
Is avnrt micro reentry?
Pathophysiology. AVNRT and AVRT are electrical aberrancies that occur mainly as a result of reentry. Less commonly, increased automaticity or triggered activity can be the mechanism and usually results in a narrow complex tachycardia.
How do you prevent reentry arrhythmia?
Drugs that depress AV nodal conduction, such as adenosine, beta-blockers and calcium channel blockers, are very effective in terminating these these reentry supraventricular tachycardias.
How long is the PR interval in first degree block?
First-degree atrioventricular block. The PR interval is 0.24 seconds (240 ms) in a patient with asymptomatic first-degree atrioventricular block.
What is early Afterdepolarization and delayed Afterdepolarization?
Afterdepolarizations and Triggered Activity. Triggered activity (TA) refers to abnormal impulse initiation from membrane depolarization that occurs during Phase 2 or 3 early afterdepolarizations (EADs) or during Phase 4 delayed afterdepolarizations (DADs), of a previous spontaneous or driven AP (12–14) (Figure 41.2A,B) …
What is the undershoot of an action potential?
The voltage-gated potassium channels stay open a little longer than needed to bring the membrane back to its resting potential. This results in a phenomenon called “undershoot,” in which the membrane potential briefly dips lower (more negative) than its resting potential.
What is thithreshold potential?
Threshold potential is the minimum potential difference that must be reached in order to fire an action potential. For most neurons in humans, this lies at -55 mV, so a signal to a resting cell must raise the membrane potential from -70 mV. The signal will have to overcome an even greater potential difference…
What happens when a cell reaches threshold for action potential?
Once the cell reaches threshold, voltage-gated sodium channels open and being the predictable membrane potential changes describe above as an action potential. Any sub-threshold depolarization that does not change the membrane potential to -55 mV or higher will not reach threshold and thus will not result in an action potential.
How does the action potential behave upon the all or none law?
It is important to know that the action potential behaves upon the all-or-none law. This means that any subthreshold stimulus will cause nothing, while threshold and suprathreshold stimuli produce a full response of the excitable cell.
How does an action potential travel through a block?
In such a block, impulses can travel retrograde (from branch 3 into branch 2) but not orthograde. When this condition exists, an action potential will travel down the branch 1, into the common distal path (branch 3), and then travel retrograde through the unidirectional block in branch 2 (blue line).