Missing from this page is the effect of wrong filter settings on the ECG. A higher value for the low frequency cutoff can simulate ST-elevation on the ECG. On the other hand a lower setting of the higher frequency setting can elimate pacemaker stimulus and decrease R wave signals.
Reference: García-Niebla J, Llontop-García P, Valle-Racero JI, Serra-Autonell G, Batchvarov VN, de Luna AB. Technical mistakes during the acquisition of the electrocardiogram. Ann Noninvasive Electrocardiol. 2009 Okt;14(4):389-403. (http://www.ncbi.nlm.nih.gov/pubmed/19804517)