Pathophysiology Flashcards
What are auto-rhythmic cells?
Generate action potentials spontaneously
1% of myocardial cells
Do not contribute to contractile force
ANS innervates the heart
What is the conducting pathway of the Heart?
1) SA node (pacemaker)
2) AV node
3) AV bundle ( bundle of HIS
4) Right and left bundle branches
5) Purkinje fibers
Electrical Pathway of the SA node
1) SA depolarizes
2) Moves rapidly to the AV node via inter nodal pathway
3) Depolarization spreads more slowly across atria (so atria can finish filling) Conduction is slow though AV node
Electrical Events of the Cardiac Cycle
P wave
P wave: Atrial depolarization
PR segments
time between end of atrial depolarization and onset of ventricular depolarization
Conducting through the AV nose and continuing atrial contraction
Q wave
R wave
S wave
Down the apex
Up from the apex
Up the ventricle
ST segment
time between end of ventricular depolarization and onset of ventricular repolarizaton
Continuing ventricular contraction
PR Interval (combination of waves and segments)
time between onset of atrial depolarization and ventricular depolarization
AV blocks
QT interval
Time between onset of ventricular depolarization and end of repolarization
long QT syndrome (abnormality of ion channel on the cardiac cells)
What is a normal HR
60-100 bpm
average 70 bpm
What is tachycardia?
fast resting heart rate
greater than 100 bpm
What is bradycardia?
Slow resting heart rate
less than 60 bpm
Some endurance athletes have bradycardia but is a physiological advantage
What is Primary AV Block?
increase duration of PR interval
increase delay between contraction
What is secondary AV block?
Slowed conduction through AV node
lose 1 to 1 P wave and QRS complex
lose 1 to 1 atrial to ventricular contraction
What is tertiary AV block?
loss of conduction through AV node
P wave is independent of QRS
Atrial and ventricular and contractions are independent
ECG interpretations
Shape, timing, duration of wave segments These may indicate changes in - conduction velocity - enlargement of heart - tissue damage
Arrhythmia (abnormal heart rhythm)
electrical problems in the generation or conductance of action potentials Seen as : -missed or extra beats - atrial fibrillation -premature ventricular contraction
What is atrial fibrillation?
SA node is not acting as pacemaker
Absence of P wave and irregular rate
May be no symptoms
What is premature ventricular contractions (PVC)
Extra beats under the influence of auto-rhythmic cells other than SA node
QRS and T waves look abnormal
Felt like a skipped heart beat, strong beat or suction
Cause chest pain, fainting, fatigue or hyperventilation
Several in a row becomes ventricular tachycardia
Need to be treated if greater than 6bpm
What is ventricular fibrillation?
Uncoordinated contraction
Cause of cardiac arrest
ST Elevation
Indicate myocardial infraction
ST depression
indicate myocardial ischemia
What are some treatments of conduction abnormalities?B
Bradycardia
Pacemaker- put in where contraction starts and the AV node because that is the only pathway
Conduction Abnormality Treatments
Tachycardia
medication (calcium blockers)
Cadrioversion (overriding the heart)
- Electrical shock (sets heart to regular ryhthm
- Emergency cardioversion = defibrilation
Conduction Abnormality Treatments
Ablation Therapy
Destroy cardiac tissue = electrical block along pathway to prevent arrhythmia
Other Treatments for Arrhythmia
Surgery
-Bypass for CAD (plaque build up)
-Maze procedure to correct electrical pathway
-Implantable cardioverter-defibrillator (ICD)
(monitors heart rhythm, sends out electrical shock to set heart back to normal)
What do ECG represent?
The summed electrical activity of all cells recorded from the surface of the body
