Week 5 Flashcards
ECG
automaticity
are able to discharge/depolarize without stimulation from a nerve, as is typical in other striated muscle cells
They automatically discharge
cardiac myocytes have 3 unique properties
Automaticity, rhythmicity, and conductivity
rhythmicity
Depolarization occurs at regular intervals
Cardiac muscle cells can therefore depolarize at regular intervals (rhythm to their firing or depolarization)
Hierarchy of rhythmicity
rhythmicity creates the
sinus rhythm
conductivity
The ability to spread impulses to adjoining cells very quickly without nerve involvement
p wave
the first waveform of the electrocardiogram, reflects depolarization of the atria
QRS complex
The second waveform seen
corresponds to the depolarization of the right and left ventricles of the human heart
Q, R, and S waves occur in rapid succession, do not all appear in all ECG leads, and reflect a single event, and thus are usually considered together. Greater amplitude because of greater muscle mass
t wave
the T wave represents the repolarization of the ventricles.
The interval from the beginning of the QRS complex to the apex of the T wave corresponds to the absolute refractory period
In most leads, the T wave is positive (upward deflection) and reflects the repolarization of the myocytes.
ECG consists of tracing from
6 limb leads and 6 chest leads
leads 1-6
are monitored from six electrodes placed on the chest wall
Show gradual changes in all the recordings
Record in a horizontal plane
1st degree AV block
First-degree AV block occurs when the impulse is initiated in the SA node but is delayed on the way to the AV node
The delay may be initiated in the AV node itself, and the AV conduction time is prolonged
second degree heart block
Transient disturbance that occurs high in the AV junction and prevents conduction of some of the impulses through the AV node
wenckeback/ mobitz 1
Initially a P wave precedes each QRS complex, but eventually a P wave may stand alone (conduction is blocked).
Progressive lengthening of the P-R interval occurs in progressive order
As the P-R interval increases, a QRS complex will eventually be dropped i.e. P wave not associated with a QRS complex
“Longer, longer, drop, then you have Wenckeback”
mobitz 2
Intermittent non-conducted p waves without progressive prolongation of PR interval.
P waves “march through” at a constant rate.
RR interval surrounding the dropped beats is an exact multiple of preceding RR interval
“If some p’s don’t get through, then you have Mobitz II”
third degree AV block
No impulses that are initiated above the ventricles are conducted to the ventricle
Atria fire at their own inherent rate
Ventricles fire at their own inherent rate
“If Ps and Qs don’t agree, then you have 3rd degree”
