A patient comes into the ED and you have to give them a shock. During what point of the ECG should you NOT shock them?
You shouldn't shock them during the relative refractory period. If you do that, you could cause an arrhythmia. You should shock them during the absolute refractory period (the early part of the T wave)
What are the 3 types of atrioventricular blocks?
1st degree: delayed conduction but all P waves conduct to the ventricles
2nd degree: Some p waves conduct but others do not
3rd degree: no P waves conduct to the ventricles, so a ventricular pacemaker takes over.
T or F?
When there is a left bundle branch block, there is QRS widening with delayed conduction to the right ventricle
There will be QRS widening in either left or right bundle branch blocks, but since this is the left one there will only be delayed conduction the left ventricle
An elderly lady comes in to your office and you discover she has a SA node block. What are potential findings?
"Sick sinus syndrome" resulting in slow sinus rates or takeover by other pacemakers which may be too slow or too fast.
T or F?
The greater the muscle mass, the less voltage produced by that muscle.
The greater the muscle mass, the greater the voltage.
You perform an ECG on someone and notice that the QRS and T waves are in the same direction. Is this normal?
Si señor. The QRS and T waves should always be in the same direction (positive and positive, negative and negative).
What does a QRS and a T wave facing opposite directions indicate?
Discordance between the two is pathological and could indicate abnormalities such as ischemia or ventricular hypertrophy.
In what 2 locations does the action potential tend to be slower in the heart?
The SA node and the AV node.
What is atrial repolarization typically not seen in the ECG?
It occurs around the same time as ventricular depolarization, which pretty much drowns out that repolarization signal on the ECG.
What does the P wave represent in cardiac conduction?
Depolarization of the atria
What does the QRS wave represent in cardiac conduction?
Depolarization of the ventricles. Phase 0, which is due to the fast sodium current.
What does the isoelectric segment between S and T on the ECG represent?
This corresponds to phase 2 of the cardiac AP, when there is a long plateau with little change in voltage when calcium influx and potassium efflux is balanced.
What does the T wave represent?
Ventricular repolarization, Phase 3 of the AP when there is still a great amount of potassium efflux occuring.
What does the isoelectric segment after the T wave represent?
This represents Phase 4 of the AP.
What does the PR interval represent?
The index of conduction time across the AV node.
What does the QT interval represent?
The total time of ventricular depolarization and repolarization.
T or F?
The QRS is positive on right sided leads.
Depolarization moving TOWARDS a positive electrode produces a positive deflection.
Since conduction moves from right downwards to left, the right sided leads are negative (downward peaks) and the left sided leads are positive (upward peaks)
T or F?
In the activation of the ventricles, the upward portion of the septum is depolarized from left to right
This is the first step.
T or F?
Depolarization is from epicardium to endocardium?
Depolariation is from endocardium to epicardium.
That electric feeling starts inside and then moves outwards.
T or F?
The apices of the ventricles are depolarized before the bases of the ventricles?
It starts in the septum, moves down to the apices, then moves back up towards the bases. This makes it so that the ventricles contract and force the blood upwards and out through the different arteries (pulmonary, aorta).
What are the three major mechanisms whereby abnormal tachyarrhythmias may arise?
1) Re-entry: Usually caused by a uni-directional block, this is the most common cause.
2) Abnormal automaticity (Ectopic foci): a focus of myocardium outside of the normal conduction pathways gains automaticity and its rate exceeds that of the normal pathway.
3) Triggered Activity: Afterpolarizations (EADs DADs) are triggered by the precding action potential.