Cardiac Conduction Flashcards
What is the value for a first degree AV block?
greater than 0.2 ms
What order does AP spread? (general)
- SA node
- AV node
- Purkinjie fibers
- bundle of his
- r/l bundle branches
- smaller purkinjie fibers
Which contracts first:
- RA or LA
- Epicardium or Endocardium
- LV epicardium or RV epicardium
- RA before left
- Endocardium before epi
- RV epicardium before LV
What are second degree AV blcoks?
- AV recieves signal and drops it, then receieves second signal and passes it on
- Drop signal and pass every time
- Random
Phase 4?
RMP, maintained by Na/K ATPase
What is phase 0 of the cardiac fast AP?
- Results from reaching threshold
- Incrased conductance of Na
- Opening voltage gated fast Na channels (activation gate)
What is cardiac fast action potential phase 1?
- Closure of voltage gated Na channels, Inactivation gates are closed (Ina)
- Opening of transient outward K current (Ito)
What is the cardiac fast AP phase 2?
- Opening of voltage gated L type Ca channels (Ica)
- CLlosure of inward rectifying K channels (Ik1)
- Closure of channels causing Ito
WHat is the cardiac fast AP phase 3?
Repolarization
- CLosure of voltage gated L type Ca channels
- Opening inward rectifying K channels
- Opening of vooltage gated K channels (Ikr, Iks) these do start to open during phase 2 but largely contribute to phase 3
What happens if phase 3 is disrupted?
- Ikr and Iks are not acting properly and Long QT syndrome result
- transition from phase 2 to 3 is lengthened
- can be ocngenital or acquired
What is cardiac slow AP phase 4?
- Resting mem pot gradually depolarizes until it reaches threshold, intrinsic spontaneous depolarization acts as the pace maker
- Due to the slow influx of Na through “funny” voltage gated Na channels (Inaf) that open upon complete repolarization of membrane
What is phase 0 of the cardiac slow AP?
- Opening of voltage gated Ca channels
- Rather than fast voltage gated Na channels
- Closure of inward rectiying K channels
- Phase one and two are absent in cardiac slow AP
What is phase 3 of the slow cardiac AP?
- Reversal of phase 0
- Closure of votage gated Ca channels
- Opening delayed rectifying K channels
- Closure of inward rectifying K channels
Parasympathetic stimuli to the heart is carried by ___ to the: __
Parasympathetic stimuli to the heart is carried by Vagus to the:
- SA and AV node
- Modest but physiologically insignifacant to atrial myocytes
- Ach
- Receptos M2/M3
- Also special K ach channel
What is a negative chronotropic effect?
- Slower entry of Na through funny Na channels during phase 4
- Hyperpolarizationi of SA node by increasing outward K current via special K ach channels
- NO influence on contractility
- Takes longer to reach threshold and fire (slowing heart rate!)
Where does SNS go?
- SA and AV node and ventricular myocytes
- Not relevant in atrial myocytes
- Norepi
- Receptor B1 adrenergic
What is a positive chronotropic effect?
- Speeding up heart rate via rapid influx of Na through funny Na channels
- allows threshold to be reached quicker
- Increases contractilitiy (positive iontropic effect)
- increases ca into myocytes
What is a positive dromotropic and lusitropic effect?
- Increased conduction velocity and relaxation velocity
- greater phase 0 slope more rapid and complete recycling of AP
What is the cardiac refractory period?
- Period when AP can’t be generated
- Refractory periods are longer to protect against arrhythmias and aid in rhythmic contraction
What is an absolute refractory period?
- No AP can be generated
- all voltage gated Na channels are inactivated
What is a relative refractory period?
- AP can be generated but will require greater stimulus or have abnormal conduction
- many but not all voltage gated Na channels have reset
What is a supranormal period?
- Cells are more excitable than normal and the AP will be abnormally conducted
- closer to threshold, many Na channels are reset
How does hyperkalemia impact cardiac AP?
- Slows phase 0
- Speeds up phase 3
- Some cells may already be at threshold and others are very close to it, can result in asynchronyous contraction
How does hypokalemia impact cardiac AP?
- Were further from threshold and more stimulus is needed to depolarize
How does S1 relate to EKG?
- Q wavebegins as mitral valve closes
How does S2 relate to EKG?
- Its at the end of the T wave when the aortic valve closes
How does S3 relate to the EKG?
- Mitral valve opens and blood enters ventricles
How does S4 relate to EKG?
PR segment
