The relation of QRS amplitude to the frontal QRS axis and the heart-electrode distance

Spatial R wave amplitude changes during exercise: relation with left ventricular ischemia and function

Thirty patients who exhibited increased and 65 patients decreased spatial R wave amplitude during exercise testing were compared for left ventricular function and ischemic variables. Spatial R wave amplitude was derived from the three-dimensional Frank X, Y, Z leads using computerized methods. All patients had stable coronary artery disease and they were classified into two groups: one that attained a higher (n = 48) and one a lower (n = 47) median value of maximal heart rate during exercise (161 beats/min). Within these two groups, patients with increasing or decreasing spatial R wave amplitude during exercise were analyzed for differences in oxygen consumption, exercise-induced changes in spatial R wave amplitude, ST segment depression laterally (ST60, lead X), ST displacement spatially, left ventricular ejection fraction at rest, change in left ventricular ejection fraction with exercise and thallium-201 ischemia during exercise. Significant differences were demonstrated only in exercise-induced spatial R wave amplitude changes (p less than 0.0001). There was no significant correlation between exercise-induced change in heart rate and change in spatial R wave amplitude in either the group with increasing or the group with decreasing spatial R wave amplitude. It is concluded that changes in spatial R wave amplitude during exercise are not related to ischemic electrocardiographic or thallium-201 imaging changes or to left ventricular ejection fraction determined at rest or during exercise.

Magnetocardiograms of patients with left ventricular overloading recorded with a second-derivative SQUID gradiometer

Magnetocardiograms (MCGs) were recorded by means of a second-derivative SQUID (superconducting quantum interference device) magnetometer in 60 normal subjects and 95 patients with left ventricular overloading to determine the clinical value of the MCG. In patients with left ventricular overloading, the Q or S wave was increased in the upper anterior part of the thorax, and the R wave was increased in the left lower part of the thorax, indicating increased leftward force due to left ventricular overloading. For detection of left ventricular hypertrophy or dilatation from echocardiographic measurements, the sensitivity and specificity of the MCG were similar to those of the standard ECG, or slightly better. In patients with left ventricular systolic overloading, the Q wave was decreased in the lower anterior part of the thorax, indicating a decreased septal vector. Inversion of the T wave was seen more frequently in the MCGs than in the ECGs of patients with left ventricular overloading, suggesting that the MCG is useful for detecting early abnormalities of repolarization. These results suggest that the MCG may provide information that is difficult to obtain from the standard 12-lead ECG.

Automated precordial mapping for S-T segment analysis: variability in serial mappings of normal subjects and patients with stable S-T elevation

An automated method of precordial mapping using a modified Caceres U.S. Public Health Service Electrocardiogram Diagnosing Program has been developed. The S-T segment elevation was measured in three successive complexes and averaged for each of the 35 precordial leads. The onset of the S-T segment (J point) was accurately located in over 99 percent of instances. The time required to sample the 35 leads averaged 8 1/2 minutes with subsequent data analysis requiring an additional 7 minutes. The S-T segment variability between serial mappings done over a 1 to 2 hour period was determined in normal subjects and patients with stable S-T elevation. The average S-T segment elevation/35 leads in normal subjects was 1.28 mv (range 0.41 to 2.14) and the between-mapping variability was +/- 0.25 mv at the 95 percent confidence level. The average S-T segment elevation/35 leads in the patients was 4.01 mv (range 1.35 to 7.28) mv. The between-mapping variability was +/- 0.29 mv (95 percent confidence level), and was not statistically different from the variability in normal subjects (P less than 0.05).