ecg

[rbrowne42]

Im a firs year medical student and its all going fine, but i just cant seem to get the hang of the ECG and heart cycle. Also general nervous impulses and depolarisation etc confuses me so if anyone could shed any light...??

[MissB]

This baffled me too. U will need to understand nervous impulses & depolarisation b4 attempting the heart cycle & ECGs as this is fundamentally what they r based upon. Simply put, action potentials r the movement of ions across membranes creating a difference in the charges on either side of the membrane, resulting in cell excitation. http://www.cvphysiology.com/Arrhythmias/A003.htm This site is a little heavy in places but the more u read, the better u'll understand.

Don't get 2 caught up in it, except 2 recall which ions r involved & in what phase, such as Na+, Ca2+ and K+. Knowing this will assist u when it comes 2 understanding the consequence of chemical imbalances and the indication of certain drugs.

[MissB]

RE: the heart cycle. Excitation of nodes & fibres in the following order SA-> AV->His bundles->Purkinje fibres results cardiac muscle contraction causing movement of blood around the chambers. The atria fill with blood- venous return is assisted by inspiration (which increases thoracic pressure, I think though am not sure) and skeletal muscular contraction assisting which can push blood against gravity. There is a third reason but I can't remember it. Maybe something to do with diaphragmatic contraction and how that acts as a pump to move blood in the IVC.

SA then AV node excitation causes contraction of the atria (previously relaxed and filling with blood), hence moving blood to the ventricles. As the electrical impulse continues to travel through the heart, ventricular contraction occurs. As the contraction occurs, pressure increases (as the volume decreases) thereby closing the tricuspid and bicuspid (a.k.a. mitral) valves and opening the pulmonary and aortic valves. Increased pressure and appropriately opened or closed valves consequently pushes blood into either the pulmonary or systemic circulations.

The ECG interpretation is not the easiest. Not many people can interpret them well. Basic forms to recognise are A Flutter, atrial fibrillation, supraventricular tachycardias, V Tach and asystole. Get a textbook especially for this one. There are many different ECG machines with different numbers of leads placed on the chest. Depending on what you are looking for and where the location of it is in the heart, along with the ECG device used, determines which lead to monitor from. Textbooks tell you to use Lead 2 and aVF a lot. Like I said it depends what you are expecting to see. Otherwise monitor in the leads that are the most appropriate for the condition.

Good luck.

[rassling]

Get 'The ECG Made Easy' - great little book, trick is to keep rereading it until it makes sense. It got me through this topic and now ECGs are pretty intuitive.