On-line computerized vectorcardiography: Influence of body position, heart rate, radiographic contrast fluid and myocardial ischemia

On-line computerized vectorcardiography (cVCG) is increasingly being used for continuous monitoring of myocardial ischemia, however, little is known about factors other than ischemia causing electrocardiographic abnormalities. This paper describes how three important cVCG parameters, STC-VM, ST-VM and QRS-VD, are affected by different body positions, myocardial ischemia, contrast injection and increasing heart rate in patients with and without coronary artery disease. The main findings of the study are: contrast injection and different body positions caused major changes in QRS-VT but affected ST-VM and STC-VM to a minor degree. Increasing heart rate by atrial pacing produced substantial changes in all three parameters. Ischemia during angioplasty also produced changes in all three parameters, STC-VM being the most sensitive parameter. In conclusion: (1) STC-VM (greater than or equal to 50 mu V) is the most valuable parameter for monitoring ischemia; (2) we propose ST-VM greater than or equal to 50 mu V as criterion instead of previously used 25 mu V; (3) QRS-VD cannot be used as a single marker of ischemia, and (4) electrocardiographic changes induced by increased heart rate should be taken into account during interpretation.