Absolute refractory period questions...

[Kiwi, BSN, RN]

I am learning cardiac rhythms and I have some questions about the absolute refractory period. Why is it important? What special considerations should be made in viewing extopy during this period, and why is it considered important when defibrillation is being done?

Thanks! I'm a little confused.

[louloubell1]

I am learning cardiac rhythms and I have some questions about the absolute refractory period. Why is it important? What special considerations should be made in viewing extopy during this period, and why is it considered important when defibrillation is being done?

Thanks! I'm a little confused.

The absolute refractory period describes a point in the contraction cycle in which the cell can not be stimulated to depolarize again. The relative refractory period, however, describes a point where the cell may be stimulated to depolarize again in the presence of a strong enough stimulus. This is important to know because stimulation of the heart during the relative refractory period can lead to life-threatening dysrhythmias. The refractory period is really an important consideration in synchronized cardioversion, not defibrillation. It's also important to know when pacing a patient - i.e. if you see pacer spikes on the downslope of the T wave the pacer is not sensing correctly & could stimulate R on T phenomenon.

[traumahawk99]

I am learning cardiac rhythms and I have some questions about the absolute refractory period. Why is it important? What special considerations should be made in viewing extopy during this period, and why is it considered important when defibrillation is being done?

Thanks! I'm a little confused.

the absolute refractory period ensures that your heart's individual cells fire off in a highly cordinated pattern, in one direction. it is caused by the fact that na+ channels cannot open until they are reset by a negative membrane potential. if these channels don't open, there is no firing of the cell.

i wouldn't worry much about this period per se, other than you need to understand the process of a cardiac cell firing, with the na+, k+ and ca++ channels in the membrane reacting to and controlling the membrane's potentials. memorize this to the nth degree!

as far as cardiology, if you're trying to understand what's truly going on, you need to take a class in 12 lead and learn how the machines tracings on various leads can give you information about what's going on in their heart. this means a thorough understanding of the hexaxial system and the precordial leads.

the heart is a marvelously complex organ, with a specialized cells organized into a conduction system that controls the way it fires. you need to have a thorough understanding as to how the conduction system normally works. then you can appreciate what's going on when this system isn't working properly. there are many things that can malfunction, from ectopic sites to conduction blocks.

during defib (v fib and pulseless v tach are the only times you defib), the refractory period, relative or absolute is irrelevant. there is no regular wave, and cells are just firing without syncrony. the paddles fire when you press the button, no timing is needed.

during cardioversion or transcutaneous paciing, it's essential to sync up with the r waves. lifepacks have a sync setting. shocking someone on top of a t wave during the relative refractory peroid can throw them into v fib and kill them. this means you need to be sure that the monitor is syncing properly with the wave before you shock. the syncing process is not totally foolproof, and sometimes you need to adjust the size, lead or electrode.