Cardio VII Flashcards
All the muscle cells in the heart are sorted into two classes of action potentials: […] and […].
fast and slow.
Where in the heart are slow and fast action potentials found respectively?
Slow: SA node, AV node
Fast: ventricular muscle, atrial muscles, bundle of His, bundle branches, Purkinje fibers
How does the upstroke rate compare between fast and slow action potentials?
Slow: 1-10 V/sec
Fast: 100-1000 V/sec
How does the speed of depolarization compare between fast and slow action potentials?
Fast: 0.5-5 m/sec
Slow: 0.01-0.05 m/sec
What is the physiological function of having both slow and fast action potentials in different parts of the heart?
The purpose is physiological delay between the depolarization of the atria and the ventricles. If the ventricles and the atria contracted at the same time, since the pressure of the ventricles is much stronger, it is likely that blood would squirt back up the atria.
At what point on the ECG does the upstroke of the atrial action potential occur?
Around halfway through the P-wave (line 1).
At what point on the ECG does the upstroke of the ventricular action potential occur?
Right before the peak of the QRS complex (line 2)
How does the duration of the ventricular action potential compare to that of the atrial action potential?
The duration of the atrial action potential is much shorter than the ventricular action potential.
What is normal sinus rhythm? State the range of values that fall within a normal rhythm.
It is the normal heart rhythm that creates the typical ECG wave. A heart rate between 60 bpm and 100 bpm (inclusive) is considered normal.
What is sinus bradycardia? Is it pathological or physiological?
It is when heart rate is less than 60 bpm. It can be physiological when we sleep, as the heart rate slows, or pathological otherwise
What is sinus tachycardia? Is it physiological or pathological?
It is when heart rate is greater than 100 bpm. We get a physiologic sinus tachycardia when we exercise. Athletes often have resting heart rates than are less than 60, which is technically a bradycardia. Otherwise, it is pathological.
What is sinus arrythmia? Is it physiological or pathological?
It is when heart rate increases on inspiration and decreases on expiration. This is completely normal (physiological). They gradually go away with age.
What is the appearance of the ECG when someone has a 2:1 atrioventricular block
Has very large QRS complex, only has QRS complex after every other P-wave
What is happening in the heart during a 2:1 atrioventricular block?
When another P-wave follows the T-wave (instead of a QRS complex), this means that the atria were activated, but that the action potential didn’t make it down to the ventricles. Only the atria beat. This occurs for every other beat.
Where are the possible locations of a block that can cause a 2:1 atrioventricular block?
- Could be in the AV node, where action potentials might enter but not be able to leave
- Bundle of His
- Both bundle branches.
Why is a 2:1 atrioventricular block problematic?
If there’s something wrong with the AV node, you can go from a 2:1 block to a 3:1 block etc. to eventually a complete block, where no APs will get through.
What does the ECG look like for a complete atrioventricular block?
Only P-waves are visible and there are no more QRS complexes.
What is happening during a complete atrioventricular block?
The ventricles are not contracting at all, only the atria.
What is the treatment for a complete atrioventricular block?
The solution would be to implant an electronic pacemaker that generates a current once per second and picks up the ECG. If it sees something abnormal for long enough, it will inject current into the ventricles of the heart, thus pacing the ventricles.
What is the ECG look like for a premature ventricular contraction?
You see a premature complex/ectopic QRS that is large and occurs before the previous beat is over.
What is happening during premature ventricular contraction?
The patient’s ventricles have an area that is sending off action potentials, causing premature ventricular contraction.
What is an ectopic beat? When does it occur?
An ectopic beat occurs when there is a pacemaker in the wrong place in the heart. You might see an ectopic beat during premature ventricular contraction.
What does the ECG look like for ventricular tachycardia?
There is an almost sinusoidal alternation as the ventricles beat extremely quickly (5 times per second(.
What is happening to the patient during ventricular tachycardia and fibrillation? What is the effect on blood circulation?
After a premature ventricular contraction, the Q, R, S, and T waves all merge together and the ventricles are beating several times per second. Because the ventricles have no time to fill with blood, the stroke volume and cardiac output go to zero, as will the blood pressure. The patient will faint.
