Lecture #4 Flashcards
What is reentry?
In certain pathological conditions, a wave of depolarization may (instead of dying out) keep going on brancing or circular pathways in the myocardium
In the loop of muscle setting, what three conditions favor re-entry?
Long Pathway
Reduced Conduction Velocity
Shortened Refractory Period
Reentry in the heart typically occurs under what 4 conditions?
Long Pathways
Variable Conduction Rates
Altered Repolarization Rates
Aberrant Pathways
Example of long pathways in a heart
Dilated atria/ventricles
What might cause variability in conduction rate of the heart?
Ischema/Injury
Hyperkalemia/Cocaine
Altered repolarization tends to lead to what effect? What might cause it?
Shortened refractory period
Catecholamines
What might cause an abberant pathway in the heart?
A tract (bunde of kent) that bypasses AV
Relationship of ischemia/injury/fibrosis to reentry?
Can form a slowly conducting region that holds charge while surrounding tissue repolatizes, causing an ectopic beat
A series of ectopic beats can lead to a…
ventricular tachycardia
What is AV nodal reentry? What pathways are included?
Two pathways develop in AV
Slowly conducting with a short refractory
Rapidly conducting with a long refractory
Describe the process of AV renodal reentry.
Conduction through fast pathway
Slow conduction pathway can retrograde up repolarized fast path
Slow conduction pathway restimulated by restim fast path
AV reentrant tachycardia
What EKG findings for wolf-parkinson-white syndrome?
Short P-R and pre-excitation wave slurring the upstroke of the QRS
What happens in WPW syndrome?
an aberrant muscular bridge, the Bundle of Kent, connects the atria and ventricles, bypassing AV
Causes tachycardia that impairs ventricular filling
Dizziness, Faiting, and Angina
What is a delta wave?
A pre-excitation wave on the upstroke of QRS.
Shows rapid ventricular activation.
If premature atrial depolarization occurs with the accessory pathway still refractory, but AV not…
Causes….
first impulse passes antergrade through the excitable AV and vent, accesory recovers and causes delayed atrial stim
Inverted P-Wave, Paroxysmal supraventricular tachycardia
EKG findings in Lown-Ganong-Levine syndrome
Short PR
Normal ORS
What are triggered events?
Abnormal depolarizations always coupled to preceding action potential.
Difference between early-afterpolarization and delayed afterpolarization.
EAD’s occur before the cell is fully repolarized
DAD’s occur after the cell is fully repolarized.
When would you see EAD’s?
LQTS (often from mutation or drug use)
What are DAD’s assocaited with?
Calcium Overload
Seen in high HR, digitalis toxicity, high extracellular Ca ion conc, prolonged catecholamines
How does calcium overload trigger DADs?
Activates Ca/Na antiporter
Large amount of Na driven in depolarizes mem
How do you inhibit DADs?
Ca channel blockers, beta blockers, ryanodine
Review EKG notes.
Because you’re worth it too.
How might one use an EKG to identify the culprit artery in a myocardial infarction?
Use extra leads
Move V3-5 right, add V7-9 on back, etc.
What will increase the height of R Wave?
Hypertrophy of Ventricle (from high MAP or aortic stenosis, or hypertension)
What will cause decreased voltage on EKG? (3)
- decreased muscle mass (old heart attack)
- Shunting out of current (fluid in pericardial space)
- Changes of intrathoracic resistance (emphysema)
What do vector arrows point to (electrically)
Area to be depolarized
What are vectors?
Arrows that depict direction and megnitude of equivalent dipoles
Explain cardiac vector loop
Instantaneous cardiac vector inscribes a loop as the tissue is depolarized
Why is ventricular repolarization the same direction as R wave?
Outer/Apical surfaces of the heart repo before the inner/basal due to high pressure inhibiting coronary flow to endo and repo.
(Vector is always pointing bottom left, so always positive)
The form of the EKG in the precordials is determined by….
Cardiac axis in the transverse plane
What do you see in an EKG transition point?
Equal positive and negative waves in QRS
Not counting precordials, all other leads are in the _____ plane.
Frontal
A net positive QRS means that the axis is directed where?
toward the positive pole of the lead
Transition point means axis is….
at right angles to the lead
Alternate method of reading an EKG?
two leads with QRS of equal size
Axis is in the middle
What is normal axis deviation?
-30 to 120
What might cause someone to be left axis deviated? (5)
COPD Extreme Obesity Left Anterior Hemiblock Pathologic Q Waves Left Ventricular Hypertrophy (Only in transverse plane)
Causes of right axis deviation?
Right ventricular hypertrophy
Left anterolateral myocardial infarction
Leads associated with lateral heart (L Circumflex and LAD)?
I, AVL, V5, V6
Leads associated with septum?
V1, V2
Leads associated with anterior heart?
V2, V3, V4
Leads associated with inferior heart (Right Coronary)?
II, III, aVF
What does ST elevation in II, III, and aVF indicate?
Inferior Wall Infarction
What would be required to really see a true posterior infarction?
V7-9
Why is seeing this infarction not necessarily a huge concern?
Posterior infarction typically accompanied by infarctions elsewhere, often inferior wall
