Retired Doc recently lamented the lack of skill in ECG interpretation among internal medicine and emergency medicine residents. Perhaps in the present era of high technology electrocardiography has become a lost art much like physical examination. J. Willis Hurst has written extensively about the reasons, and possible remedies, for the decline in skill in electrocardiography.  . He cites various weaknesses in postgraduate teaching, as well as the failure to understand basic electrophysiologic principles. Sadly, there is a lack of formal training. Learning by osmosis is not very effective.
There are a few decent web based learning resources. The best I’ve found is ECG Wave-Maven. This site is cased based, somewhat interactive, and has annotations with literature citations. Medscape’s ECG of the Week (free access after registration) is also somewhat helpful. Unfortunately, another of my favorites, the American College of Cardiology ECG of the month, has gone behind access controls.