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33 Cards in this Set

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the ---and ----also has an ERP, however, the channels that remain closed during this phase are the L-type calcium channels
The AP of the SA node
Briefly, when AP’s are generated in the heart, there is a period in which the tissue will not respond to excitation. This is known as
the absolute refractory period (ARP).
The -----includes a very short time beyond the ARP in which stimulation produces a localized depolarization that does not propagate – in other words and AP will not propagate.
effective refractory period (ERP)
In what? does the effective refractory period starts at the upstroke of the action potential and ends in the first half of repolarization, and during this period the sodium channels undergo several conformational changes that do not allow the passage of Na+ ions.
the Purkinje fiber
During what period does stimulation of the heart cells occur, but it produces a weak action potential that does not propagate as fast.
the relative refractory (RRP)
why does a relative refractory period occurin teh heart
cellsThis is because some of the sodium channels have recovered from the inactivated state and they can respond again to excitation
The refractory period of a heart cell is what?
a function of how rapidly sodium channels recover from inactivation.
ARP=Absolute Refractory period =
unexcitable to stimulation
ERP = Effective Refractory period =
brief period beyond ARP where stimulation produces weak depolarization that does not propagate
RRP = Relative Refractory period =
stimulation produces a weak PA that does propagate but more slowly than usual
P wave =
atrial dpolarization
QRS wave =
ventricle depolarization
T wave =
ventricle repolarization
PR interval =
time between depolarization of atria and the spread of the impulse across the atria and through the AV node, bundle of His, bundle branches and Purkinje fibers.
QT interval =
time from ventricle depolarization to repolarization, and measures ventricular activity.
ST segment = measures time between end of ventricular depolarization and beginning of ventricular repolarization
Many factors can precipitate arrhythmias: name some
• ischemia, as a result of a myocardial infarction,
• hypoxia, acidosis or alkalosis, electrolyte disturbance, excess catecholamines,
• drug toxicity,
• overstretching of the cardiac fibers, and scarred or diseased tissue.
Although the factors are variable for precipitating arrhythmias, all arrhythmias result from alterations in:
• impulse formation
• impulse conduction
• both impulse formation and conduction
where can they originate
• specialized conduction system: SA node, AV node, His bundle, Purkinje fibers
• atrial muscle
• ventricular muscle
beating too rapidly – can be either a ? or ? or ? or ?
sinus or ventricular tachycardia; atrial or ventricular premature depolarization; or atrial flutter or fibrillation
The two main mechanisms that are primarily responsible for abnormal impulse formation that lead to arrhythmias are
1) altered automaticity (i.e pacemaker rate):
• of the sinus node, of latent pacemakers within the specialized conduction pathway,
• abnormal automaticity in atrial or ventricular myocytes

2) Afterdepolarizations – also known as triggered activity
Under certain situations when an action potential is generated it triggers
an additional depolarization in the ventricle heart tissue, known as afterdepolarizations
self-sustaining depolarizations result in
extra heart beats (ectopic beats) or rapid arrhythmias
There are two types of self sustaining depolarization, what are they
Early after depolarizations – beginning of Phase 2/3
Late after dpolarizations- appear after repolarization of the an action potential
Why do self sustaining depolarization happen?
They are believed to be the result of abnormal calcium influx during or immediately after phase 3 repolarization.
what does digitalis toxicity do to the heart
digitalis toxicity, causes calcium overload inside the heart tissue, which results in a type of arrhythmia known as a digitalis-induced arrhythmia (bigeminy), where an extra beat of the heart occurs
When impulse conduction in the heart tissue is altered it can result
in arrhythmias
?__ is when a propagating impulse is blocked when it encounters an electrically unexcitable region of the heart. what is an example
• Conduction block – AV block
In 1st degree heart block the impulse is
On the EKG this can be observed by
prolonged beyond the normal delay at the AV-node. a prolonged P-R interval
2nd degree heart block is where there is
On the EKG this is observed as
intermittent failure of atrioventricular conduction.
some P-waves not follwed by a QRS complex
In 3rd degree heart block there is .
on the EKG this can be observed by
complete failure of impulses between the atria and the ventricles. There are many P waves not followed by QRS waves. The intermittent QRS waves that develop are result of latent pacemakers in the ventricles
? is when there is re-excitation of an area of cardiac tissue by the same impulse occurs again and again. where can this occur
Re-entry –
Re-entry of an impulse can occur in a small region near the AV node, or in large sections of the atria or ventricle walls, or because of an anatomical abnormality (Wolff-Parkinson-White syndrome) that creates an additional AV connection - “bypass tract.
In type II, most beats are conducted with a constant PR interval, but occasionally atrial depolarization is not followed by ventricular depolarization (see Figure 6). Type II is pathological and indicates disease of the conduction system where
distal to the AV node.
The heart’s ability to increase its CO is dependent on four main factors: