Computer interpretation of pediatric frank vectorcardiograms in the evaluation of congenital heart disease

The evaluation of a new computer program for analysis and interpretation of pediatric Frank vectorcardiograms is reported. The program includes extensive age- and sex-dependent criteria based on tables of limits for numerous vectorcardiographic parameters. In 728 catheterized patients, the diagnostic performance for type A statements was tested against independent and objective evidence obtained from hemodynamic and angiographic data. The overall diagnostic accuracy ranged from 75 to 89% without difference between children < 2 years of age and those >- 2 years of age. Sensitivities and specificities of the various diagnoses did not differ much between the 2 age groups. In the younger children, the accuracy of a positive diagnosis of left ventricular hypertrophy, right ventricular hypertrophy, and biventricular hypertrophy was 20, 15, and 32% higher, respectively, than in the older children. The accuracy of the diagnosis “normal” was 28% lower in the younger children. These differences were explained by the higher proportion of pathologic findings in the younger children: 93% versus 74% in the older children.Given the strict methods of the evaluation, the diagnostic accuracy of this pediatric program was considered clinically satisfactory. Program performance appears to be dependent not on patient age but on prevalence of abnormalities in the population analyzed. Further improvement can be expected by making the criteria more adaptable to the composition of the population.     

Computer analysis of vectorcardiograms in myocardial infarction with special reference to polar vector and planarity of the QRS and T loops.

Spatial characteristics of the QRS and T loops in 110 patients with old myocardial infarction were analysed in comparison with 221 normal subjects. Measured were (1) QRS and T polar vectors, (2) initial 20- and 30-msec segmental QRS polar vectors, and (3) length, width, thickness, and ratios of width/length and thickness/length of the QRS and T loops in edgewise and broadside projections. Broadside and edgewise projections were obtained by transformation of the reference frame of the Frank lead system to a patient's own frame based on the polar vector. The recognition rates of abnormality in the QRS and T polar vectors were 66% and 60% of a total of 110 patients with myocardial infarction. The initial 30 msec segmental QRS polar vector showed the highest recognition rate of abnormality in myocardial infarction, i.e., 87% in anterior myocardial infarction, 100% in extensive anterior myocardial infarction and 78% in inferior myocardial infarction. The initial segmental QRS polar vector was abnormally deviated posteriorly and superiorly in inferior myocardial infarction. In anterior myocardial infarction, the initial segmental polar vector was directed inferiorly in more than 50% of the cases, while the vector in normal subjects was located superiorly and to the left. The QRS loop of anterior myocardial infarction was significantly smaller in the width and width/length ratio and significantly larger in the thickness and thickness/length ratio than those of the normal. Poor planarity of the QRS loop was one of the characteristics of myocardial infarction, especially of extensive anterior myocardial infarction. The T loop of myocardial infarction was significantly larger in the width/length ratio than that of the normal. More than 50% of the cases with anterior myocardial infarction showed abnormally wide T loops. The polar vector was a useful index to characterize the spatial orientation and sense of rotation of the spatial loop. In addition, the initial segmental QRS polar vector represented the mild localized abnormalities of the spatial loop. The loop configuration in space was characterized in edgewise and broadside projections.     

Computer analysis of exercise-induced changes in QRS duration in patients with angina pectoris and in normal subjects

Exercise-induced changes in QRS duration were assessed in 25 normal subjects and in 17 patients with stable ischemic heart disease. None had bundle branch block or were taking medications, and all patients had angina pectoris induced during the test. QRS duration and ST60 amplitude were measured by computer during rest while standing, at a heart rate of 100 to 110 bpm during exercise, at peak heart rate for the angina patients (mean of 127 bpm), and at the corresponding matched heart rate and peak heart rate for the normals (mean of 174 bpm). As heart rate increased, the patients showed significant ST60 depression. In normal subjects, the QRS duration tended to increase initially but at the matched heart rate level and at peak heart rate it decreased significantly compared to rest (p less than 0.01). The QRS duration in the angina patients increased significantly at the heart rate level of 100 to 110 bpm (p less than 0.05). Of the eight patients who reached a peak heart rate above 127 bpm, six (75%) during that period further increased QRS duration compared to three (12%) of the 25 normal subjects (p less than 0.001). We conclude that a consistent increase in QRS duration during exercise, although subtle, may be a marker of ischemia and consequently a potential diagnostic tool.     

QRS component of the spatial vectorcardiogram and of the spatial magnitude and velocity electrocardiograms of the normal dog

The ventricular activation process (QRS) of forty healthy dogs was studied by means of vectorcardiograms using Wilson's equilateraltetrahedral reference system, scalar electrocardiograms, and by constructing spatial magnitude electrocardiograms and spatial velocity electrocardiograms. These data were correlated with anatomic cross sections through corresponding planes of the frozen animal. An attempt was made to correlate the electrical activity, as measured by electrodes placed on the body surface, with the ventricular activation process.

The typical QRSsÊ loop was roughly heartshaped, and was almost coplanar with the median sagittal plane. Good correlation existed between the actual circumferential thoracic leads and the derived scalar electrocardiograms. Apparent variations between the actual electrocardiogram and those derived from the QRSsÊ loops in the horizontal plane projection were explained on the basis of spatial orientation of the exploring electrode.

The electrical activity of the dog's heart has been presented in three divisions based on time and the areas of the ventricles activated. Activation of the interventricular septum from left-to-right constitutes the 6 milliseconds vector which is directed cephalad, ventrad and slightly dextrad. The spatial magnitude electrocardiogram of the QRS complex reaches its first peak during this period, while the spatial velocity electrocardiogram of the QRS complex reaches its first peak and following dip. Simultaneous activation of the apex and free wall of the left ventricle constitutes the 22 milliseconds vector which is directed caudad with little ventral and sinistral orientation. The spatial magnitude electrocardiogram reaches its second and maximal peak during this period, while the spatial velocity electrocardiogram reaches its second peak, a brief dip and its third and maximal peak.

Activation of the basilar areas of both ventricles and the interventricular septum constitutes the 32 milliseconds vector which is directed cephalad and dorsad, with slight dextral orientation. The spatial magnitude electrocardiogram reaches its third and minimal peak during this period, while the spatial velocity electrocardiogram continues to decline.     

A simple method for analysis of vectorcardiograms

Vectorcardiographic loops can be evaluated with the help of transparent overlays depicting normal ranges for the magnitude and orientation of various P, QRS and T vectors in each of the three conventional planes. By appropriate positioning of such overlays over vectorcardiographic loops it is possible to determine in a matter of seconds whether or not the magnitude and/or orientation of various vectors are within normal limits.