You can still defibrillate v tach (synchronized cardio version if there is a pulse). V tach is more uniform, regular in nature and is wide complex. V fib looks like little squiggly lines some complexes larger than others. Look at several pictures of rhythm strips in books. Also, don't forget about Torsades de pointes as the treatment is a little different that vtach/ vfib!
Is the patient responsive??? LOL - never forget that you're caring for the whole human being, not an isolated organ.
I have seen many instances of patients experiencing (what seemed to be) "lethal arrhythmias" as they were awake and talking. In those cases, discretion should always rule. Never shock an aware patient. Never make decisions based on only one data source (EKG). Check LOC, hemodynamic status, etc.... what appears to be V-tach may be rapid rate with new BBB - or even a loose lead flapping in the breeze.
OTOH, if this question is referring to a 'test' rather than an actual situation - just systematically apply the decision algorhythm you were told to use.
To understand this better, you have to understand cardiac conduction in general.
Remember that an EKG shows you the path the electrical impulse takes as it travels through the heart. Take a look at the diagram of the normal conduction system. That will help you visualize better.
Most muscle cells cannot contract without some sort of electrical stimulus telling them to. Cardiac muscle cells are a little different; they can generate their own little electric jolt and pass it along cell-to-cell to their neighbors IF the normal impulse doesn't come through the normal conduction pathway often enough. Remember that for later.
1)The normal impulse starts in some specialized cells in the sinoatrial (SA) node, a little patch of tissue that has the ability to do this by itself 'way up in the atria.
2) This impulse spreads thru conduction pathways in the atria, making the muscle cells contract as it goes, in a nice even pattern that empties the atria thru the tricuspid valve (right heart) and mitral valve (left heart) into the ventricles to give them something to do. That's diastole. This electricity looks like a nice round little bump, the P wave, on EKG.
3) There's a teeny pause while the impulse is gathered up in the atrioventricular (AV) node, then spreads in a nice pattern thru the ventricles, their muscle wringing like a washcloth. (The electrical signature of this action is the QRS, the big spiky deflection on the EKG.) The pressure thus developed closes the mitral and tricuspid valves but opens the pulmonic valve (right side) and aortic valve (left side) and blood gets pushed into the pulmonary artery and aorta. That's systole, and we have...a blood pressure.
If the tissue at the AV node is on strike for some reason, like it's dead after infarct (good reason), when the impulse comes down to it from the atria, it's unable to pass it along to the ventricular conduction pathway, so there is no longer a nice P wave->QRS, P->QRS, P->QRS happening. After a bit the ventricles notice that they are not getting any direction from up above. They are big and strong, but not that smart, so they only get it together to generate their own contraction slowly after one of their cells takes it upon itself to contract. Because the impulse driving them does not come down that nice dedicated pathway but has to spread cell-to-cell from there, it takes longer and doesn't look like it knows where it's going, so the QRS is wider and funny-looking.
Now if you look at the tracing for this, you see a nice regular march of P waves, indicating the atria are working they way they are supposed to, and then, at a totally different rate and not playing nice and holding hands with their friends, the ventricles tooling along on their own, slower rate. It may be fairly regular but it won't have any relationship at all to the P waves. THAT's complete heart block (3rd degree AV block).
The question is, “What’s the difference between defibrillation and cardioversion?”
I liked the answer that said, "A pt with afib is alive, but the pt with vfib is dead or almost there with an ETA of five minutes."
True enough. But I think that to help you answer your own question you need to be solid on the basics of normal cardiac cycle and the conduction system that makes it happen.
1) teeny electrical impulse starts in the sinoatrial (SA) node, a little patch of tissue that has the ability to do this by itself 'way up in the atria.
2) impulse spreads thru conduction pathways in the atria, making the muscle cells contract as it goes, in a nice even pattern that empties the atria thru the tricuspid valve (right heart) and mitral valve (left heart) into the ventricles to give them something to do. That's diastole. This electricity looks like a nice round little bump, the P wave, on EKG.
3) Impulse is gathered up in the atrioventricular (AV) node, then spreads in a nice pattern thru the ventricles, their muscle wringing like a washcloth. (The electrical signature of this action is the QRS, the big spiky deflection on the EKG.) The pressure thus developed closes the mitral and tricuspid valves but opens the pulmonic valve (right side) and aortic valve (left side) and blood gets pushed into the pulmonary artery and aorta. That's systole, and we have...a blood pressure.
SO now can you see the diference between an atrial event and a ventricular one? They occur in different places. So their consequences are radically different.
Cardiac muscle is better off in terms of efficiency if it uses those organized conduction pathways to develop coordinated muscle contractions. But the conduction system can be stretched out too much, like it can be in mitral disease, because the atria have really high pressures in them (think: high-pressure systolic backflow thru the mitral valve if it doesn't close all the way OR higher pressures in the atria if the valves don't OPEN all the way when they should). Or it could lose some of its useful cells with an MI. Whatever. What happens then is that the individual cells all think they have to take over, and the atria becomes a quivering, uncoordinated mess. You no longer see a nice little round P wave, because there's no longer the nice organized flow thru the atria to make one. That's atrial fibrillation. Some people get a decrease in BP with this (this has more to do with how the ventricles behave with the varying amts of blood presented to them in "diastole", but I digress...), but blood continues to flow into the ventricles and so there is still some BP to make in systole .
VF is something else. As I mentioned above, the cardiac muscle cell has an interesting quality that no other muscle cell in the body has: it can, if conditions are right, contract on its own without an external stimulus. (To get an idea of how remarkable this is, imagine what would happen if all the muscle cells in, say, your thigh could do this without waiting for instruction from your CNS.)
Unsuccessfully treated VF is a terminal event, because a ventricle that is fibrillating is not circulating any blood out the aorta...and we all know what that means. VF on the EKG looks like a wiggly, squiggly line with small irregular points-- sorta like a very quiet EEG line. Nothing neat, nothing organized, nothing regular...because that's what the ventricle is doing: nothing neat, nothing organized, and nothing regular. All the cells are firing off in an uncoordinated fashion, and even if there are normal impulses coming thru the AV node the conduction system isn't working.
The way a defibrillator works is sorta like what happens in the old Western movie when the Sheriff finds an ugly, rowdy mob on the front porch of the jail. This is VF-- uncoordinated, unpredictable, and deadly. What does he do? He fires off his rifle, ka-BLAM! and this stops all the rabblerousing in its tracks so they can now listen to reason. Defibrillation makes all those rowdy cells discharge all at once, and while they're getting their breath back, so to speak, the normal conduction pattern can take up its work of making them orderly again. Well, we hope so, anyway. If other conditions are right (cell oxygenation, chemistries, cell wall integrity...) it will.
When you shock a fibrillating ventricle, that's called "defibrillation." When you shock a fibrillating atrium (in hopes of accomplishing the same thing: an end to chaos and a return to order) it's called "cardioversion," and has to be synchronized with the pt's own QRS (the machine does this for you, but you have to tell it to). This is because a jolt that lands in the wrong time in the ventricular conduction sequence can make for VT or VF itself, and you don't want to make extra work for yourself in this way .