Electrocardiographic T-wave amplitude as a non-invasive index of sympathetic myocardial activity: possible confounding effects of parasympathetic influence

A noninvasive, psychophysiologic measurement paradigm was used to examine the effects of autonomic activity on electrocardiographic T-wave amplitude and heart rate. Sympathetic nervous system activity was manipulated by having subjects perform a difficult mental arithmetic task. Parasympathetic influences were inferred by measuring respiratory sinus arrhythmia. Preliminary results suggest that both heart rate and T-wave amplitude were influenced by both sympathetic and parasympathetic input. Data for T-wave amplitude draw into question recent claims concerning the specificity of this measure as a noninvasive index of sympathetic myocardial influences.