Heart (2) Flashcards
What type of action potential happens in Myocytes?
Fast-response AP
Phases of a Fast-response action potential
0) Upstroke
1) Partial repolarization
2) Plateau
3) Complete Repolarization
4) Em
Duration of a Fast response AP
200 ms
What type of action potential happens in Nodal cells?
Slow-response AP
Duration of a Slow-response AP
400 ms
Slow vs Fast-response AP
- Slow does not have Phase 1&2, partial repol. & plateau
- More negative Em in fast AP
- Much greater slope&litude in fast
Automaticity
Spontaneous depolarization and generation of an AP
(SA, AV nodes)
(I)f
- HCN4 (non-selective cation ch.)
- Na+ in
- Pre/pacemaker potential generation
(<-50 hyperpol, cAMP)
(I)Ca T
- T-type VDCC
- Na+ & Ca2+ in
- Initial depol.
(Transient= temporary/short-lived)
(I)Ca L
- L-type VDCC
- Ca2+ in
- Depolarization
- ~ -30mV
(I)k
- VG types (several)
- K+ out
- Repolarization
(I)k,ach
- GIRK1 / GIRK4
- K+ out
- Hyperpolarization
(Ach, Vagus n, m2-R)
Does HCN channel inactivate?
No
HCN channel Inhibitor
Ivabradine
T-type VDCC Inhibitor
Verapamil
Chronotropic effect
Effect on the Heart Rate
Dromotropic effect
Effect on the Speed of conduction
Role of Gβγ in M2-R
Activation of GIRK channels
Sympathetic heart regulation
- NE on B1-AR
- Gs, more cAMP
Threshold is reached faster with (I)f, so faster AP rate
Parasympathetic heart regulation
- Right Vagus: SA
- Left Vagus: AV
- Ach on M2-R
- Gi, less cAMP
- Gγβ, hyperpol.
Does the Vagus nerve innervate the ventricles in Humans?
No
Hormone effects on HR (Epi, and TH)
- Epineph: similar to NE
- Hyperthyroidism: Tachycardia
- Hypothyroidism: Bradycardia
B1-R blocker
Propranolol
Blocks sympathetic effect
M2-R blocker
Atropine
Blocks parasymp. effect
Much stronger effect on parasymp. compared to B1-R blockers
What happens if we use both B1-R and M2-R blockers?
Propranolol & Atropine
Produce the intrinsic pacemaker frequency of the SA node
= 100 bpm
SA Node Intrinsic pacemaker freq.
100 bpm
AV Node/Bundle of His Intrinsic pacemaker freq.
40-60 bmp
Purkinje fibers Intrinsic pacemaker freq.
20-40 bpm
Myocytes Intrinsic pacemaker freq.
None
Under physiological conditions
(may happen in path.)
What affects conduction velocity?
- Size of current: higher current = faster conduction
- Resistance: Low R in gap junctions, thicker branches conduct faster
Why does AV node have slowest conduction?
Very thin fibers, slower cond.
To delay ventricular contraction
Effective / Absolute refractory period
Unresponsive after activation due to inactivated ion channels
Relative refractory period
Additional stimulus produces another AP, but needs stronger stimulus
ECG Depolarization and Inflection
- Positive direction= Positive inflection
- Negative direction= Negative inflection
ECG Repolarization and Inflection
- Positive direction= Negative inflection
- Negative direction= Positive inflection
Segment vs Interval on ECG
- Segment: Between waves where line is isoelectric
- Interval: Includes waves
PR (PQ) interval
- Conduction from atria to ventricles
- 0.12 - 0.20 s
QRS interval
- Ventricular depol.
- 0.06 - 0.1 s
QT interval
- Ventricular depol. and repol.
- 0.36 s
Unipolar lead
Measures the electric impulse of a point relative to a reference point
Bipolar lead
Measures electrical difference between 2 electrodes
(+ & -)
Augmented limb leads (Goldberger)
- Unipolar lead: active/exploring electrode & indifferent/reference electrode
- In Eindhoven’s Triangle
Angles of Leads on Hexaxial system
- I: 0°
- II: 60°
- III: 120°
3 bipolar leads in Eindhoven Triangle
- AVR: R.Arm -150°
- AVL: L.Arm -30°
- AVF: Left leg +90°
1st Heart Sound
- AV valve closure
- Longer, louder, lower frequency
2nd Heart Sound
- AO valve closure
- Shorter, weaker, higher pitch
Length of Cardiac cycle
0.8 s
Systole time vs electrical
- Time: Bw First and second heart sounds
- Electrical: Beginning of Q wave till end of T wave
Diastole time vs electrical
- Time: After 2nd heart sound till right before 1st heart sound
- Electrical: Isoelectric interval after T and right before P
Rules for construction of Cardiac cycle
- Liquid is incompressible
- Pressure gradient determines flow
- Valves open with blood flow
- No back-flow through closed valves
Stroke Volume (SV)
Amount of blood transported to Aorta in Systole
EDV - ESV
140 - 60 = 80ml
Ejection Fraction (EF)
Fraction of ventricular blood ejected
SV / EDV
0.5 < EF < 0.75
EDV
140 ml
ESV
60 ml
Atrium pressure
4 - 8 mmHg
Ventricle pressure
4 - 120 mmHg
Aortic pressure
80 - 120 mmHg
Systole duration
0.27 s
Diastole duration
0.53 s
Incisure/Dicrotic Notch
Small rise in pressure during diastole representing closure of AO valve
Cardiac Output (CO)
Volume of blood being pumped by L.Ventricle into Aorta / min
= 5.6 L/m (rest)
HR x SV (70 x 80)
Total Peripheral Resistance (TPR)
Total resistance that must be overcome to push the blood through the circulatory system and create flow
(P.art. - P.ven.) / CO
1/tpr = 1/Parm + 1/Pleg + 1/Pbrain
Mean arterial B.P
93 mmHg
CO x TPR
(Psys * 2xPdia) / 3
Why when calculating MABP we use 2x the Pdiastolic
Because since Diastole (0.53s) lasts almost 2x longer than Systole (0.27s), we give it a larger weighing by doing this
Regulation of CO
- Heterometric Reg.
- Homometric Reg.
Heterometric Regulation
How different initial fiber lengths impact contraction force
Otto Frank’s Experiment
- Proves Heterometric regulation.
- Higher preload, stronger contraction
- Greater fiber length, more forceful contraction