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BIOC33H3 Lecture Notes - Aortic Valve, Artificial Cardiac Pacemaker, Obstructive Lung Disease

Biological Sciences
Course Code
Stephen Reid

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BIOC34 Lec 3 - Jan. 13/14
Last week:
ECG: Standard Limb Leads
oHave P wave: atrial depolarization,
oQRS complex: ventricular contraction,
oT wave - repolarization of ventricles
oPR distance = time it takes to conduct electrical activity from SA node to AV node
oArrhythmias - wandering atrial pacemaker - get electrical activity of pacemaker
potentials from other areas of atria
Arrhythmias: heart beat originating from the ventricle
oCan come from other areas than SA node, or can come from SA node and be
faster or slower
oCan also have abnormal rhythms from the ventricles
Litmus test of looking at pacemaker activity is whether the QRS complex
is narrow or wide
Narrow (but normal) QRS complex = electrical activity is probably arising
from the atria
Abnormally wide/m-tooth/saw-tooth shape = electrical activity that caused
this is from the ventricle
Problematic; requires artificial pacemakers
Atrial and ventricular ectopic beats
oCan arise from atria or ventricle
oEctopic beat = electrical activity forming a pacemaker potential is coming from
somewhere other than the SA node
oAtrial ectopic beat - looks normal but it is coming too quickly; premature beat;
originating from certain foci
Overdrive: increased pump activity - hyperpolarization -- suppression
Termed ectopic pacemaker because it is being generated not at SA node
Beat comes prematurely because that foci location is closer to AV node;
therefore, it takes less time for electrical current to reach AV node

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oVentricular ectopic beat - abnormal, premature QRS complex with saw-tooth, M
shape. It is being generated at apex of ventricle functioning as a pacemaker
Case of advanced degree heart block
No electrical activity coming from atria into ventricle
Ventricle is creating its own pacemaker potentials
Arrhythmias: premature and late beats
oEctopic beats show up as early beats or late beats in atria or ventricle
oIn upper diagram of premature beat of atrial origin, can tell it is atrial because it
has a narrow QRS complex - looks like the other ones
Ectopic location
oAll narrow complexes are generated in the atria and produce a normal, stable
NOT a saw-tooth shape
oIn bottom case, have a premature contraction originating in ventricle
Wider QRS complex indicates it is happening in the ventricles
oIf it is a normal shape but kind of wide, it is not as bad as a saw-tooth shape
Arrhythmias: Impaired conductance
oCommon type: heart block
Start to get abnormal or absent electrical activity through the AV node
oNormal pacemaker activity produced in SA node but at some point, transmission
to AV node is slowed or abolished
oIn a normal case, see P wave, QRS, T wave
P-R distance = red lines = indicative of time it takes for electrical activity
in SA node to get to AV node and into ventricles
First-degree heart block
oIn most benign sense, conduction through AV node is slowed or delayed
oKey to identifying first degree heart block: look at P-R distance
Prolonged PR interval (>0.2 sec)

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oTop diagram - first degree heart block
P-R distance is longer than in a normal rhythm
Normally shaped P wave - not an ectopic pacemaker - still generated at SA
node, just taking longer to get to AV node
Not a very dangerous situation - happens under normal conditions
Enhanced vagal tone - parasympathetic innervation of the heart;
impinges on SA node and AV node and can slow down conduction
to the AV node
AV node disease
Electrolyte imbalance
Benign situation; no treatment
Second degree heart block
oIn this case, there is still some transmission from atria into AV node into
ventricles, but sometimes it is completely blocked
oMissing QRS complexes
Not all are missing, but have missing ones
oEvery now and then, electrical activity that has generated the P wave is not
generated to AV node and do not get a QRS complex
oStarting to become problematic
oProgressive increase in delay until a beat is skipped (Type I)
o2-4 P waves for every QRS complex (Type II)
Third degree heart block
oDangerous situation
oComplete inability of AV node to conduct electrical activity from atria to
oNormal pacemaker activity is not being transmitted down into ventricles
oSome region of the ventricles has to serve as a pacemaker to generate ventricular
oBegin to see saw-tooth or m-type pattern. These patterns of activity are indicative
of blockade
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