Pacemaker
o :# SA Node
Backup to SA node Impulse pauses to prevent simultaneous contraction of the atria and
ventricles
o :# AV Node
Why is the SA node the primary pacemaker?
o :# The SA node has the highest intrinsic rate of any cardiac tissue
Intrinsic rate of SA node
o :# 60-70 per minu...
Backup to SA node Impulse pauses to prevent simultaneous contraction of the atria and
ventricles
o :# AV Node
Why is the SA node the primary pacemaker?
o :# The SA node has the highest intrinsic rate of any cardiac tissue
Intrinsic rate of SA node
o :# 60-70 per minute
Intrinsic rate of AV node
o :# 50 per minute
Intrinsic rate of myocardium
o :# 30 per minute
The wave of contraction or depolarization moves from the endocardium to the
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o :# epicardium
What is absolute refractory state?
o :# that period when a muscle cell is not excitable
from phase 1 into phase 3
the relative refractory period is during phase 3 and the muscle cell might contract if the
stimulus is strong
Depolarization equals
o :# Contraction
Repolarization equals
o :# relaxation
P wave represents
o :# artrial systole
P-R interval represents
o :# from atrial to ventricular depolarization
QRS complex represents
, 2024/2025 3|Page
o :# ventricular systole
T wave represents
o :# ventricular diastole- repolarization
What is the normal duration for the QRS complex?
o :# less than 0.12 seconds
What is the frank-starling law?
o :# Increased volume-preload- equals increased contractility
increased myocardial fiber length equals increased tension or Rubber Band theory
Stroke volume increases in response to an
o :# increase in the volume of blood filling the heart or end diastolic volume
The greater the preload the greater
o :# the force of contraction-frank starling Law
Reasons for increased preload
o :# Regurgitation in all valves, ventricular and atrial septal defects, and fluid
overload.
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Does a PDA increase LV preload?
o :# Yes when the shunt is Left to Right.
Increased preload equals
o :# dilatation
Increased afterload equals
o :# hypertrophy
Resistance against which the ventricle must pump. Determines the tension of the
myocardium must generate.
o :# Afterload
Increased afterload is caused by
o :# Hypertension, Aortic stenosis, and pulmonic stenosis
End diastolic volume minus end systolic volume
o :# Stroke Volume
Normal stroke volume
o :# 70-110 ml
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