Introduction to ECGs Flashcards
what is the fireing rate of the SA node?
60-100 beats per minute
what is the conduction speed of the SA node?
2 meters/second
what is the conduction speed of the AV node?
0.05 meters/ second
what is the conduction speed of the bundle of his?
4 meters/ second
what is the conduction speed of the contractile muscle cells?
1 meter/ second
what is chronotropy?
the heart rate
what is dromotropy?
the conduction speed
what is Ionotropy?
the contractile strength
Absolute refractory period (ARP)
no new action potentials can be initiated regardless of the stimulus stength.
effective refractory period
includes the ARP plus a short segment of phase 3. a stimuli may cause cells to depolarize but not create an action potential
releative refractory period
a greater than normal stimuli will depolarize cells and cause an action potential leading to abnormal beats or arrythmias
supranormal period
a hyperexcitable period during which weaker than normal stimuli wil depolarize thee cells which could cause extra/premature beats
how many seconds does a small 1mm box represent?
0.04 seconds
how much seconds does a large box represent
0.2 seconds
how many milivolts does a small box respresent?
0.1 millivolts
what is the standard paper speed?
25mm per second aka 5 big boxs per second
what is the normal time for the PR interval?
0.12-0.2 or 3-5 small boxes
what does the PR interval represent?
the delay of conduction at the AV node
why is there a delay of conduction at the AV node?
to allow for an atrial kick so 30% more blood canbe passed through to the ventricles
how does the speed of the heart rate effect the PR interval?
a increased HR shortens the PR interval. a decrease in HR lengthens the PR interval
what does the Q wave represent?
depolarization of the ventricular septum
the depolarization of the ventricular septum moves in what direction
left to right, posterior to anterior
what is the duration of a physiological or normal Q wave?
0.03 second
what is the duration of a pathological Q wave?
longer than 0.03 seconds and has a 30% greater dip than R wave
what does a pathological Q wave indicate?
a MI either from the past or ongoing
what does the R wave represent?
ventricular depolarization and includes both the rise and decent on the ecg
what does the s wave represent?
also depolarization of ventricles
what is the normal duration of the QRS complex?
0.075 - 0.12 (less than 3 small boxes)
what does a narrow QRS complex indicate? <0.12
- fast ventricular depolarization and that the electrical impulse followed the correct conduction pathway
what does a wide QRS indicate? >0.12
slow ventricular depolarization and that the electrical impulses had issues with the conduction pathway
gender difference of the QRS complex
can be 0.005 to 0.008 (milliseconds) faster in women than in men
what does the ST segment represent?
early repolarization of the ventricles
what does the uwave represent?
late repolarization of the ventricles/purkinjie
what plane does the standard limb leads and augmented limb leads view the heart?
the verticle plane
whate plane does the precordial leads view the heart?
horizontal plane
when placing the leads the should be _____cm away from the heart to avoid distortion
10cm
