I just logged on and it opened up. Are you trying
Or try this
Also, here is another good site.
Just remember that what you are seeing is a representation of electricity moving through the heart. The horizontal plane represents time and the vertical plane represents voltage. With the leads placed in a certain pattern (either a 3 lead, 5 lead or 12 lead pattern) we can see how the electricity is moving through the heart and thus how the heart is working or not working. For basic rhythm interpretation ie. is the pt in sinus brady, afib, having frequent PVCs etc we look at lead 2, for indications of ischemia, injury, MI (active, old, new etc) we look at a 12 lead as this allows us to see WHERE in the heart the problem is.
If I were you I would focus on the rhythms first then try to figure out the 12 lead. I am surprised you are doing 12 lead as it is pretty complicated. Do you have to diagnose where an MI is occurring or just know some basics of why we use 12 leads? Basically a 12 lead allows you to look at the heart from different angles. Since we are looking at conduction of electricity through the heart we expect to see certain patterns. Injured or dead heart muscle does not conduct the electricity the same way and will result in ECG changes. The lead(s) these changes show up on tell us where the injury is.
In the clinical setting we use the 12 lead along with pt's report of chest pain and results of labwork (cardiac enzymes) to help diagnose an MI vs angina when pt presents with chest pain. When a pt presents with chest pain we draw cardiac enzymes (CKMB, troponin) q 6 hr x 3 sets and do an ECG. When there is active heart muscle damage, enzymes are released from the heart tissue and show up in the blood (thus these enzymes are often called cardiac markers). If the enzymes come back positive (especially troponin as it is specific to the heart vs CKMB which is released by skeletal muscle as well), the person is dx with an MI. Problem is, these enzymes take time to show up in the blood (hence the need to have 3 negative sets to rule out an MI). Since we don't want the person sitting around having an MI while we wait for the enzymes to elevate, we can do an ECG and look for any changes. Q waves would indicate an OLD MI while T wave inversion, ST elevation or depression indicate active injury. For all of these WHAT LEAD it shows up in on the 12 lead tells you what part of the heart is being damaged and thus which coronary artery is the probable culprit.
Off the top of my head I cannot remember them all, but here is an idea. If you see changes (Q waves, ST elevation etc) in leads II, III and aVF you know it is an inferior issue. Changes in V1-V4 means anterior problem. A Q means an old MI of unknown date in this area, ST elevation means an active MI in this area and the pt goes to the cath lab where they can see what is causing the problem and fix it (balloon, stent, consult with Cardiothoracic surgery for a bypass!!).
Hope this helps,