On-Line Computerized Vectorcardiography: Influence of Body Position, Heart Rate, Radiographic Contrast Fluid and Myocardial Ischemia

Abstract

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-VD 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 ( > 50 µV) is the most valuable parameter for monitoring ischemia; (2) we propose ST-VM > 50 µV as criterion instead of previously used 25 µV; (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.

Vectorcardiographic ST deviations related to increased heart rate in the absence of ischemia in an experimental pig model

“…The converse is unlikely, that ST-VM can change with no alteration in STC-VM. The HR-related STC-VM increases correspond to previously published clinical observations in exercise testing of coronary care patients in which higher STC-VM were observed in relation to higher HRs [3,4], although ischemia in those settings was not directly assessed by a reliable second method. Also, the response of STC-VM has not been previously studied in response to graded and controlled HR increases.…”

“…Adjustment of ST-segment changes in the standard 12-lead ECG during exercise testing was proposed already more than 20 years ago to enhance the discrimination between myocardial ischemia and physiological ST changes during conditions of increased HR [17]. Although similar speculation about VCG ST analysis and HR relations has been published [3,4], this is the first study to measure the course of VCG ST events during a course of graded HR increase with simultaneous metabolic local assessment of myocardium.…”

“…Vectorcardiography is one electrocardiographic method that can be used in diagnostic situations to detect myocardial ischemia and infarction. The ST segment is affected by heart rate (HR), and at higher HRs, ST changes are thought to be less specific for ischemia than at lower HRs [3,4]. This negatively affects the sensitivity and specificity of ST analysis for identification of ischemia when higher HRs are present.…”

Prognostic Role of On-Line Vectorcardiography as Regards Repeat Revascularization after Successful Coronary Angioplasty

“…Our impression is that contrast injection only affected ST-VM and STC-VM to a minor degree. This is supported by the study of Jensen et al [17]. All VCG recordings were analyzed by one independent observer who was blinded to clinical data and endpoints.…”

ST changes and temporal relation to the J point during heart rate increase and myocardial ischemia

“…Some of the presumed difficulties in serial ST analysis may have to do with body position in awake patients. 18,19 Clinical implications of these findings probably need to be limited to the resting coronary care unit patient where ECG and body position are monitored.…”