CV 3 Flashcards
3 causes of dysrhythmias
Alterations in resting potential
Channel malfunction
Conduction defects
What are the concentrations for: Na K Ca inside the cell?
Na 10 mM
K 135 mM
Ca 0.0001 mM
What are the equilibrium potentials for:
Na
K
Ca
Na +70 mV
K -94mV
Ca +132 mV
What is the normal resting potential?
-85 mV
What 2 factors contribute to the membrane potential?
Concentration gradient and membrane conductance of each ion
Phases of a fast AP
Upstroke (Na+ inward current) Initial repolarization (K+ outward current) Plateau Repolarization Stable resting potential
Absolute refractory period
No way to get another AP
From the rapid depol until about threshold level of stage 3
Relative refractory period
Greater than normal stimulus needed to get AP
From midway through part 3 to part 4
Funny current
Carried by HCN channels
Activated by hyperpolarization
Carried by both Na and K ions
Active during diastolic depolarization
L-type Ca current
Responsible for late phase of diastolic depolarization
Also primarily responsible for the slow AP upstroke
Delayed rectifier K current
Responsibel for slow AP repolarization
Ensures SA node myocytes return to a membrane potential at which the funny current and L-type Ca channels can be activated to initiate the next slow AP
How does sympathetic activation by norepinephrine work?
NOR acts at the beta-1 adrenergic receptors (as an agonist) to increase the spontaneous AP frequency by increasing the If and Ica-L which increases the slope of the diastolic depolarization
Moves at a faster rate up to threshold
How does parasympathetic activation by acetylcholine work?
M2 receptor agonist
- Decreases spontaneous AP frequency by decreasing If and Ica-L, which decreases the slope of diastolic depolarization
- Activates the ACh-sensitive K current, which hyperpolarizes the max diastolic potential and decreases spontaneous AP frequency
Intrinsic firing rate of the normal pacemaker
About 100 beats per min
But with innervation it is kept around 70
Latent pacemakers
Other cells of the conduction system normally suppressed
Can act as pacemaker if the normal pacemaker gets too low
5 things you can interpret from the ECG
Heart rhythm Heart rate Intervals Abnormalities of P wave, QRS, ST segment, and T wave Mean QRS axis
Tachycardia and bradycardia HRs
T: greater than 100 bpm
B: less than 60 bpm
First degree AV block
The impulse through the AV node is slightly longer
PR interval is lengthened
Second degree AV block
When one or more (but not all) of the atrial impulses fail to conduct to the ventricles due to impaired conduction
Third degree AV block
When the impulse generated in the SA node does not propagate to the ventricles
Accessory pacemakers then take over
Calculate HR from P waves and then from R-R, will see large differences
