NBS Exam 1 Flashcards
normal length of the PR interval
.12 - .2 seconds
normal length of QRS complex
less than .1 seconds
if QRS is wide
you think of conduction problems int he ventricles
The MEA (mean electrical axis) of ventricular depolarization should be between
-30 and +120 degrees
definitiion of right axis deviation
+120-+180
definition of left axis devition
-30–90
causes of left axis deviation
LV hypertrophy, left bundle branch block, high diaphragm due to obesity, pregnncy or ascites, or a right sided infarct.
MEA shifts towrds ____ and away from ___
towards hypertrophy and away from infarction
causes of Right axis deviation
RV hypoertrophy, right bundle branch block , flat diaphragm, due to being thin, left side infarct
What is 1st degree block?
1st degree block is when there is a delay in impulse conduction at the level of the AV node leading to a prolonged PR segment
how do you diagnose 1st degree block
the PR segment will be >.2 seconds
What are some causes of 1st degree block
calcium channel blockers, bta blockers or increased Ach tone
What is second degree block: Mobitz type I
When every so often there is a P wave with no QRS following it, with progressively lenghtening PR segments up to that.
What is second degree block: Mobitz type I due to?
due to a block at the AV node from increased parasympathetic tone or a cardiosupressant drug
What is second degree block: Mobitz type II due to
anterior wall infarct where blockage occurs below the level of the AV, usually at the bundle branch
How do you diagnose second degree block: Mobitz type II
can be seen to frequently drop a QRS segment without PR lengthening prior to the dropped beat
What is third degree block?
When there is a complete block at the AV node so there is no coordination between the contraction of the atria and the ventricles. The PP and RR segments are normal but they are not coordianted. The ventricle takes on its own pacemaker
What determines the width of the QRS complex in third degree heart block?
How far the pacemaker is from the AV node. The farther from the AV node, the wider the QRS
Bundle Branch Block is seen on an ECG as?
an R and R’ wave. Where one ventricle contract normally to give the R wave and the ventricle with the damaged bundle branch conducts slower in cell:cell conduction to give an R’ wave
what is Delta Wave (Wolff-Parkinson-White Syndrome)
There is an accessory pathway of muscle cells that bypass’ the AV node so you do not get the normal delay
How does Wolff-parkinson0white syndomre look on EKG
have a delta wave where the PR segment has a positive slope (due to the early depolarization of the ventricles)
Atrial fibrillation is caused by what
when the tissue at the base of the pumlonary vein in the right atria becomes very excitable and will send impulses to the AV node. This results in asynchronous contraction of the atrial muscle and loss of the atrial kick during ventricular filling
What does atrial fibrillation look like on an EKG
- The atrial rate is increased and ventricular rate is variable, ventricular rhythym is variable.
- no identifiable P-waves with no measurable PR interval
What causes ventricular tachycardia
have fast Na channels on the ventricle that are randomly depolarizing: but if you have a depolarization at the wrong time during repolarization (during T-wave), you can end up initiating another action potential
-the SA node is no longer in control
What is R on T phenomenon
on T phenomenon: an ectopic beat during relative refractory period asynchronous contraction of ventricle
how to you treat Vtach
using a sodium channel blocker
The right coronoary artery perfuses
- the Rt atrium and rt ventricle
- the inferior and posterior L ventricle
- the SA and AV node
- the bundle of his