CV Part 2 Flashcards
AV node allows for ______ from the _____ to the ______
Unidirectional conduction
Atria
His bundle
His-Purkinje is the bridge between _____ and ______
AV nodal relay
Ventricular myocardium
The refractory period of Purkinje fiber AP is
Inversely related to HR
Order of events starting with SA node → Purkinje
SA node → atrial myocardium → AV node → bundle of His → left and right bundle branches → Purkinje fibers
What’s the direction of ventricular depolarization in the myocardium?
From apex to base
Upward deflections in ECG mean
Depolarization moving towards + electrode
Repolarization moving away from + electrode
Negative deflections in ECG mean
Depolarization moving away from + electrode
Repolarization moving towards + electrode
P wave
1st half = RA depol
2nd half = LA depol
PR interval
Atrial depol
End of ventricular repol
QRS complex
Ventricular depol
S
End phase of ventricular depol
ST segment
End of ventricular depol
Beginning of ventricular repol
T
Ventricular repol
TP
Isoelectric line
Electrically silent myocardium
The cardiac electrical axis falls between
0 and 90 degrees
2 common causes for axis deviation is
Hypertrophy
Pregnancy
Supraventricular arrhythmias are problems in (3)
SA nodal
Atrial
AV junctional
(Anything before hitting the bundle branches)
Ventricular arrhythmias originate in (2)
Bundle branches
Ventricular myocardium
When are narrow QRS complexes formed? Why?
Supraventricular arrhythmias
Ventricular depol can still use fast conducting pathways
When are widened QRS complexes formed? Why?
Ventricular/bundle branch arrhythmias
Signal has to go through the myocardium cell by cell
Sinus tachycardia
HR > 100 bpm
Decrease P-P interval
Increase SA node AP
Sinus bradycardia
HR < 60
Increase P-P interval
Decrease SA node AP
What is atrial flutter and what is it the result of?
Rapid and regular atrial activity
Reentry
Ventricular rate depends on
Degree of AV delay
Premature atrial contractions (PAC) causes
Premature depol leading to atrial contraction
AV node dysfunction is known as _____ and is based on ______
Heart block
Degree of severity
Primary heart block:
How is the ECG affected?
What is it caused by?
Prolonged PR interval
Longer conduction time in AV node/bundle of His
Second degree heart block:
How is the ECG affected?
What is it caused by?
Ratio of P:QRS is greater than 1
Increased refractory period of AV node/bundle of His → less excitable
Third degree heart block?
How is the ECG affected?
What is it caused by?
Messy- P waves can be before, within or after QRS complex
No atrial impulses reach the ventricles
What is an escape rhythm?
Pacemakers that take control of cardiac rate and rhythm when the relay system doesn’t work properly
AV Junctional
Escape rhythm if the block is in the AV node
40-50 bpm
Can maintain hemodynamic stability
Ventricular (think AV node)
Escape rhythm when block is distal to AV node
30-40 bpm
Unstable and slow rhythm
What is fibrillation?
Arrhythmia hat prevent effectual contraction of atria/ventricles
Atrial Fibrillation (4)
Rapid twitches or contractions of muscle fibrils
No discernable P wave
Irregularly irregular HR and pulse
Lose atrial contribution to CO
Ventricular fibrillation
Blood not effectively pumped from the ventricles
Apply electric current to defibrillate myocardium for a brief period of refraction
Hope to get SA node in control again
Bundle branch block
Cause widened QRS
Have to use myocyte-myocyte conduction
Premature ventricular contraction (PVC)
Uncoordinated ventricular depol
Widened QRS
No P wave associated with aberrant QRS
Ventricular tachycardia
Wide QRS complex
Vary in shape and rhythm
Antiarrhythmic drugs targets _____ and prevents ________
SNS
Activation of Ca, Na or K channels
