Cardiac Flashcards
Resting membrane potential
-90
Primarily regulated by K+
Hypokalemia decreases RMP
Hyperkalemia raises RMP
Threshold potential
-70 mV
primarly regulated by calcium
Hypocalcemia decreases TP
Hypercalcemia increases TP
Cardiac myocytes contain _____ _______ than skeletal muscle cells
More mitochondria
What serves as low resistance pathways in cardiac myocyte?
Tight junctions (also called gap junctions or nexi)
RMP established by what mechanisms?
- Chemical force
- Electrostatic counterforce
- Na/K ATPase
Na/K pump is an ______ ______ ______ that requires energy in the form of ATP
Active transport mechanism
Note Absolute refractory vs Relative refractory period
Absolute:
- From 1 to halfway through 3
- Longest in phase 2
- about 0 mV in phase 2
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Current that is primary determinant of pacemakers intrinsic rate?
- I-f (funny current)
- Sets rate of spont. phase 4 depolarization in SA node
Rates of cardiac nodes
- SA 70-80
- AV 40-60
- Purkinjes Fibers 15-40
Nornal mL/min values for 70kg adult:
CaO2
DO2
VO2
CvO2
- CaO2 - 20
- DO2 - 1000
- VO2 - 250
- CvO2 - 15
Frank starling mechanism relates?
Examples?
ventricular volume to ventricular output
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Functional unit of contractile tissue in heart?
Sarcomere
Decreases contractility
- ischemia
- hypoxia
- acidosis
- hypercapnia
- hyperkalemia
- hypocalcemia
- volatile anesthetics
- propofol
- B.blockers
- CCB
Initiates myocardial contraction?
initiates relaxation?
- Calcium binds to troponin C
- Unbinds
Role of calsequestrin?
- Binds to calcium inside Sarcoplasmic reticulum for storage
- think “sequesters calcium”
What areas of heart are supplied by what coronary arteries?
(Picture)
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Identify valvular disorders
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Best > Worst leads for intraoperative ST changes?
With CAD?
V3 > V4 > V5 > III > aVF
CAD: V3 > aVF > MCL5 or III
Note: Lead II is good for dysrhythmias with narrow QRS where P analysis is critical - junctional, a-flutter, a-fib
CCBs that impair contractility from highest to lowest
V-Nif-D-Nic
Verapamil > Nifedipine > diltiazem > Nicardipine
CCB thats useful coronary antispasmotic?
Nicardipine
Only CCB proven to reduce M&M from cerebral vasospasm?
Nimodipine
Period of highest awareness during CPB?
Sternotomy
(second is rewarming)
protamine dosing
1 mg per 100 units of heparin
Clamping distal tissue results in:
- ^ lactic acid –> metabolic acidosis
- ^ prostaglandins
- ^ activated compliment
- ^ myocardial depressant factors
- v Tempurature
After clamp removal:
Decreased:
- Preload
- SVR
- DBP
- CO
- Sv02
Increased:
- PAOP
- PAP
- PVR
Thoracic cross clamp times greater than ____ pose significant risk for cord ischemia
30 minutes
Spinal cord protection strategies?
- Moderate hypothermia
- CSF drainage
- Proximal HTN during Xclamp
- Avoid Hyperglycemia
- SSEP/MEP monitor (SSEP only posterior cord - sensory)
- Partial CPB
- Drugs - corticosteroids, CCBs, Mannitol