Bioimpedance-derived differences in cardiac physiology during exercise stress testing in low-risk chest pain patients.
BACKGROUND
Little has been written about the utility of thoracic electrical bioimpedance (TEB)-derived cardiac physiologic variables in evaluating patients with low-risk chest pain syndromes. Noninvasive bioimpedance can monitor cardiac physiology while a patient is performing an exercise stress test. In addition, the demographics of patients with chest pain, the incidence of coronary artery disease (CAD), and the methods used for evaluation have well-documented sex differences.


OBJECTIVE
The objectives are to show that there are different cardiac physiologic responses to exercise stress test in Chest Pain Evaluation Unit patients with and without true CAD that could be used to stratify patients and that there is a sex difference in TEB results.


METHODS
Patients 18 to 65 years of age with low-risk chest pain were eligible. Patients were attached to the TEB throughout the exercise stress test procedure. Heart rate (HR) was monitored. Primary dependent variables were TEB-measured cardiac output (CO, L/min) and stroke volume (SV, ml) at peak exercise. Secondary variables were TEB-measured ejection fraction (%), end-diastolic volume (EDV, ml), ventricular ejection time (ms), and thoracic fluid index (omega) at peak exercise. Outcome variables were either proved CAD or patient sex. CAD was proved by angiography, stress scintigraphy, or stress echocardiogram. Results were compared using a Student's t test assuming equal variances, with significance considered at a P < 0.05, and 95% confidence intervals were calculated for significant results.


RESULTS
Nine patients had proved CAD, 82 patients did not. Forty-three women and 48 men were included in the study. At peak exercise, patients with CAD had a significantly smaller increase in EDV than patients without CAD (32.8 +/- 59.5 ml versus 89.3 +/- 101.8 ml) without a significant change in CO, SV, or HR. At peak exercise, women had a significantly smaller increase in CO and SV without a significant change in HR. In addition, women had a significantly smaller increase in EDV.


CONCLUSIONS
When compared with patients without CAD, patients with CAD have a significantly smaller increase in EDV and a trend toward the same effect in CO and SV. Women have significantly smaller increases CO, SV, and EDV compared with men. Because there were no differences in HR, using HR as the sole end point would miss these differences. TEB is a practical means of measuring these variables.
Weiss
Steven J
SJ
Division of Emergency Medicine, Department of Internal Medicine, School of Medicine, University of California, Davis, UC Davis Medical Center, Sacramento, CA 95817, USA. sweiss52@aol.com
Ernst
Amy A
AA
Godorov
Gary
G
Diercks
Deborah B
DB
Jergenson
Josh
J
Kirk
J Douglas
JD
D000293:Adolescent; D000328:Adult; D000368:Aged; D002303:Cardiac Output, Low / Q000503:physiopathology; D002307:Cardiography, Impedance; D002637:Chest Pain / Q000503:physiopathology*; D003324:Coronary Artery Disease / Q000175:diagnosis* / Q000503:physiopathology*; D003663:Decision Trees; D003971:Diastole / Q000502:physiology; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012737:Sex Factors; D013318:Stroke Volume / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology