QRS Vector Loop Research Articles

Comparison of Sum Absolute QRST Integral, and Temporal Variability in Depolarization and Repolarization, Measured by Dynamic Vectorcardiography Approach, in Healthy Men and Women

BackgroundRecently we showed the predictive value of sum absolute QRST integral (SAI QRST) and repolarization lability for risk stratification of sudden cardiac death (SCD) in heart failure patients. The goal of this study was to compare SAI QRST and metrics of depolarization and repolarization variability in healthy men and women.MethodsOrthogonal ECGs were recorded at rest for 10 minutes in 160 healthy men and women (mean age 39.6±14.6, 80 men). Mean spatial TT′ angle, and normalized variances of T loop area, of spatial T vector amplitude, of QT interval and Tpeak-Tend area were measured for assessment of repolarization lability. Normalized variances of spatial QRS vector and QRS loop area characterized variability of depolarization. In addition, variability indices (VI) were calculated to adjust for normalized heart rate variance. SAI QRST was measured as the averaged arithmetic sum of areas under the QRST curve.ResultsMen were characterized by shorter QTc (430.3±21.7 vs. 444.7±22.2 ms; P<0.0001) and larger SAI QRST (282.1±66.7 vs.204.9±58.5 mV*ms; P<0.0001). Repolarization lability negatively correlated with spatial T vector amplitude. Adjusted by normalized heart rate variance, QT variability index was significantly higher in women than in men (−1.54±0.38 vs. −1.70±0.33; P = 0.017). However, in multivariate logistic regression after adjustment for body surface area, QTc, and spatial T vector amplitude, healthy men had 1.5–3 fold higher probability of having larger repolarization lability, as compared to healthy women (T vector amplitude variability index odds ratio 3.88(95%CI 1.4–11.1; P = 0.012).ConclusionsHealthy men more likely than women have larger repolarization lability.

Modeling vectorcardiograms based on left ventricle papillary muscle position

Background Vectorcardiographic QRS loops illustrate the electrical activation of the left ventricle (LV) in 3-dimensional space; however, the individual variability in these loops is not well understood. The left bundle-branch fan distributes the initial activation to the LV and has been shown to distribute its fascicles between the LV papillary muscles. Computer models of LV activation using papillary muscle as the initial electrical activation points accurately predict QRS duration and frontal plane axis. Methods Twelve healthy adults received standard 12-lead electrocardiograms and 1.5-T cardiac magnetic resonance imaging. A software developed by ECG-TECH Corp (Huntington Station, NY) generated 3-dimensional QRS vector loops for each subject. Short- and long-axis papillary muscle positions were measured for each subject using cardiac magnetic resonance images. A theoretical plane equidistant from the endocardial origins of each papillary muscle was constructed. Vectors perpendicular to the QRS vector loop and the theoretical plane termed the plane identifier were used for comparison. Spearman rank correlation was used to compare the azimuth and elevation of the plane identifiers of the QRS vector loop and the theoretical plane. Results No correlation was found between the azimuth or elevation of the theoretical plane and the QRS vector loops with Spearman rank correlation coefficients of ρ = 0.11 ( P = .71) and ρ = 0.22 ( P = .49), respectively. Subgroup analysis by QRS vector loop morphology (planar vs nonplanar, narrow vs wide) also demonstrated no correlation. Conclusions Modeling the activation of the LV based on papillary muscle position alone may be overly simplistic. Better understanding of what other factors contribute to individual variation in LV activation will help develop a more useful theoretical model.

Comparative studies on the wide frequency band electrocardiogram and vectorcardiogram in pigeon and mouse

Wide frequency band ECG and vectorcardiogram in anesthetized pigeon and mouse were studied from the standpoint of comparison. The key results were as follows: in pigeon, the direction of the main QRS was inverted in leads II, III and aVF, and upright in lead aVR, which was contrary to that in mouse. The T wave was upright in leads II, III and aVF, but inverted in lead aVR in pigeon, which was the same as that in mouse. In pigeon, there was a large notch on the upstroke of the S wave in lead II without exception, but there was no such notch in the corresponding lead in mouse. The QRS vector loop in the frontal plane lay between −90 and −180° in pigeon, while that of mouse lay between 0 and 90°. The relative power of high frequency range (80–1000 Hz) of the QRS in lead II was approximately 15% in pigeon, but 55% in mouse. The direction of the main QRS was contrary in pigeon and mouse because the subepicardial muscles were depolarized before the subendocardial muscles in pigeon, but the latter were depolarized before the former in mouse. The direction of the T waves was the same in both pigeon and mouse because subepicardial muscles were all repolarized before subendocardial muscles.

Vectorcardiography is Superior to Conventional ECG for Detection of Myocardial Injury after Coronary Surgery

Objective - The reliability of conventional scalar ECG for diagnosis of perioperative myocardial infarction (PMI) in cardiac surgery has been questioned. For the diagnosis of myocardial infarction in general vectorcardiography (VCG) is superior to ECG. Therefore, the usefulness of conventional VCG and computerized analysis of spatial VCG changes for diagnosis of PMI were studied. Design - VCG registrations were obtained from 218 patients undergoing coronary surgery. The spatial QRS vector loop area of each VCG registration was calculated and the loop area before surgery compared with the loop area after surgery. Conventional VCG criteria for myocardial infarction and set values for loop area reduction were related to sustained elevation of plasma troponin-T and clinical course. Results - Both conventional VCG criteria and spatial changes translated better than Q-waves on scalar ECG into elevation of biochemical markers of myocardial injury and impaired clinical course. Conclusion - VCG appears superior to conventional ECG as regards detection of myocardial injury in coronary surgery. Computerized programs have facilitated the registration and the interpretation of VCG and this methodology deserves further evaluation in cardiac surgery.

Normal limits of the derived vectorcardiogram in Caucasians

The derived vectorcardiogram (dVCG) can be obtained from three orthogonal leads X, Y, Z, which are synthesized from the conventional 12-lead ECG by one of a number of mathematical techniques. The application of the dVCG in routine cardiological practice has the advantage of not requiring extra recording electrode other than those used for the conventional 12 electrocardiographic leads, and offers the simultaneous availability of additional dVCG diagnostic information. In this study, the dVCGs were obtained using the inverse Dower method from 1555 apparently healthy Caucasian individuals (884 men and 671 women) and were analysed to determine the age and sex dependent normal ranges of vector measurements in a Caucasian population. The vectorcardiographic parameters measured included the directions of inscription of the QRS vector loops, the magnitude of initial 20 and 30 ms QRS vectors and the direction of the initial 20 ms QRS vector. The maximal spatial QRS vector magnitude, as well as the maximal QRS and T vector magnitudes in the frontal, horizontal, and right sagittal planes, were observed to decrease significantly with advancing age in both sexes (P < 0.001) and were significantly larger in men in all age groups (P < 0.001). The observations from the current study illustrate the significant age and sex dependent differences in the normal ranges of dVCG parameters. These are of potential importance for diagnostic applications.

Quantitative electrocardiography and vectorcardiography in postnatally developing rats

The aim of this study was to provide quantitative descriptions of developmental changes of the cardiac electrical activity of rats as background information useful for assessing abnormal development, for example, in spontaneously hypertensive rats. The data are based on the findings of serial examinations of 11 animals, slightly anesthetized by ether, on whom Frank-ECGs were recorded on days 6, 14, 21, 30, 38, and 53 of life. Typical features of the electrocardiograms during the physiologic development are P waves consisting of one positive deflection in all three leads (x, y, and z); and PQ intervals decreasing between days 6 and 14, whereas the heart rate increases during this period. QRS vector loops and the maximum spatial vector ( R ) shift to the left, whereas the amplitudes of R first increase but decrease with later age. The shape of the QRS magnitude curves is described, the peaks of which occur later during QRS in relation to increasing age. QRS intervals are considerably shorter than in the adult even at day 53. At this age rats have attained the adult configuration of the QRS loop. From day 30 onward, QRS frequency merges with the T wave. It is concluded that the ontogenetic development of the major electrical forces of the rat heart shows peculiarities compared to those seen with the development of other mammalian species. The most probable morphologic and functional postnatal adjustments are discussed with reference to the causes of the developmental electrocardiographic changes.

Diagnostic implications of figure-of-eight and clockwise QRS loop rotation on the horizontal vectorcardiogram in chronic aortic valve disease

In chronic aortic valve disease the left ventricular (LV) volumes, mass and ejection fraction (EF), as well as selected Frank ECG measurements of patients with a normal counterclockwise rotation (Type A) of the horizontal QRS vector loop are compared with those of patients showing an abnormal figure-of-eight or clockwise configuration (Type B) to investigate whether the different QRS patterns reflect ventriculographic alterations or depends on a conduction delay. In aortic stenosis (AS,n = 21) and combined AS and aortic insufficiency (AS + AI,n = 23) the Type B vectorcardiograms (VCGs) correlate with significantly increased LV end-diastolic volumes (p. .01, .01, respectively) and depressed EF (p .07, .009, respectively). In pure AI (n = 39) LV volumes, mass and EF do not differ between the Type A and Type B patterns. As compared to Type B VCGs of AS (n = 6), the LV end-diastolic volume index is clearly higher in Type A VCGs of pure AI (n = 21)(p .028). The only ECG change which is significant at the p .01 level in each group is the increase of the R peak time in lead X in the Type B VCGs. This can be related to greater volume and mass only in AS and AS+ AI, but is not substantiated by equivalent ventriculographic alterations in pure AI. The findings indicate that Type B VCGs are very likely caused by a left ventricular conduction delay since they cannot be strictly correlated with increases in LV volume and mass alone.

ＷＰＷ症候群のベクトル心電図 初期ＱＲＳベクトルの方向とＱＲＳ環，Ｔ環

WPW症候群47例 (典型例35例, 非典型例12例) の水平面初期QRSベクトルを1～V型の5型, 前額面初期QRSベクトルをa～e型の5型に分類し, この分類と水平面, 前額面QRS環およびT環の形状, 位置との関係を調べた。その結果, 水平面初期QRSベクトルの方向と水平面QRS環の位置との間には一定の関係がみられ, この関係に合わない症例は他の異常の合併が考えられ, また非典型例は典型例に比べQRS環の位置形状は正常伝導の影響を受けていることが認められた。また典型例では二次性T環変化の場合, QRS環と反対の方向にT環があり, それに合致しない場合は一次性T環変化が加わっている可能性があり, また非典型例では正常T環の影響を受けていることが考えられた。なお心電図V1のQRS波の形と水平面初期QRSベクトルの分類とは一定の関係がみられない場合があった。

The relationship between exercise-induced R wave amplitude changes and QRS vector loops

The mechanism for R wave amplitude changes during exercise testing is controversial. To investigate this, we recorded vectorcardiograms (VCG) during supine rest and bicycle exercise in 13 normals and 33 patients with coronary heart disease. In all normals, and in those CHD patients with an exercise-induced decrease in R wave amplitude, there was a posterior shift of the QRS vector loop in the transverse plane. In the CHD patients with an increase or no change in R wave amplitude, there was an anterior shift of the QRS vector loop. Though spatial vector length decreased with exercise and correlated with R wave changes, there was a better correlation between changes in the maximal QRS vector angle and R wave amplitude. The etiology of R wave changes during exercise appears to be mainly due to shifts in QRS vector loops, but the reason for these shifts is unknown.

Body Surface and Intracardiac Recordings in a Patient with Wolff-Parkinson-White Syndrome (type A) with Complete Infra-His Bundle Block

Electrocardiograms, vectorcardiograms and His bundle electrograms were recorded in a patient with Wolff-Parkinson-White syndrome (type A) who developed complete infra-Hisian block and advanced A-V block in the Kent bundle. The atrial impulses reaching the ventricles exclusively through the Kent bundle produced QRS complexes and vector loops showing diffuse (leftward initial and rightward pre-terminal) delays and slurrings. These abnormalities were not due to Wolff-Parkinson-White type A coexisting with right bundle branch block, but reflected the activation sequence characteristic of arrival of excitation; spontaneous impulse formation; or electrical stimulation, at the postero-superior wall of the left ventricle. Intracardiac recordings were a complement to body surface recordings in the study of Wolff-Parkinson-White syndrome complicated by A-V conduction disturbances.

Criteria for electrocardiographic differentiation of right ventricular hypertrophy from true posterior myocardial infarction

Electrocardiograms recorded from patients with true posterior myocardial infarction show an abnormal anterior shift in the QRS forces. Differentiation of these records from those of right ventricular hypertrophy has been recognized as a difficult problem for a long time. An attempt was made to establish criteria for separating electrocardiograms of posterior myocardial infarction from those of right ventricular hypertrophy exhibiting a similar pattern. Frank lead electrocardiograms obtained from 81 patients with posterior myocardial infarction were compared with electrocardiograms recorded from 71 patients with right ventricular hypertrophy. With two measurements that can be easily obtained, 70 percent of the posterior myocardial infarction records were classified correctly with 15 percent of the right ventricular hypertrophy records being misclassified. A set of three measurements for right ventricular hypertrophy correctly identified 55 percent of cases of right ventricular hypertrophy; however, 13 percent of the posterior myocardial infarction records were misclassified as right ventricular hypertrophy. With seven measurements obtained on the basis of multivariate analysis, 78 percent of the posterior myocardial infarction and 79 percent of right ventricular hypertrophy cases were correctly classified. These measurements were found to be useful in classifying records that could not be categorized by hand measurements. Classification procedures were also tested in 23 autopsy cases with results equal to or slightly better than those obtained in clinical samples. Several measurements on the QRS vector loop previously considered useful in the differentiation of right ventricular hypertrophy from posterior myocardial infarction gave disappointing results when tested in our samples.

Common (single) ventricle with normally related great vessels.

A rare form of common ventricle with normally related great vessels and normal tricuspid and mitral valves should be considered in the differential diagnosis of cardiac anomalies presenting with cyanosis. Fourteen cases of this type of common ventricle were studied; in seven the diagnosis was made at necropsy and in seven it was based on angiographic evidence. That the common ventricle was morphologically a left ventricle was determined in the seven necropsy cases, and angiocardiographic examination confirmed the finding in the others. Continuity of the aortic valve and the mitral valve was observed in all the necropsy cases and in five of the clinical cases. Cyanosis had been observed clinically in 13 of the 14 cases, and pulmonary stenosis was present in four necropsy and three clinical cases. Electrocardiograms showed left axis deviation in nine of the 13 cases studied. Vectorcardiographic findings, though variable and available in only seven cases, tended to show a narrow horizontal plane QRS vector loop in patients with restricted pulmonary blood flow and a wide loop in those with increased pulmonary flow. The clinical, laboratory, and pathologic findings are reported and the differential diagnosis and the profile of the condition are considered.

Genesis of electrocardiographic and vectorcardiographic QRS patterns in left bundle branch block--by means of simulation of ventricular propagation process and computational QRS reconstruction

In order to elucidate the propagation process of ventricular activation in left bundle branch block (LBBB) and its resultant QRS patterns observed on the body surface, a number of experimental studies have been made. However, the site and the mechanism of block still remain a matter of debate among these reports. It is also under question whether the results obtained from animal experiments can be applied to explanation for the genesis of naturally developed LBBB within human ventricles. The purpose of this paper is to discuss the mechanism of LBBB observed with human subjects. Namely, the ventricular propagation process of excitation was simulated in a model of the human ventricles which was constructed using the human heart as a basis and stored in a computer. A variety of speculative for LBBB was provided to the model before the simulated propagation took place. The body surface QRS patterns were computational reconstructions based on these simulated ventricular propagation processes. The obtained QRS pat-terns were then compared with those of clinical cases of LBBB. Moreover QRS vector loop were obtained and they were examined correspondence with the obtained QRS patterns. Methods: 1. Simulation and QRS reconstruction By means of digital computer simulation, a number of propagation processes in excitation of the ventricles with LBBB were obtained. The scalar QRS patterns for the thus acquired propagation processes were obtained by the above means in the conventional twelve leads and X, Y and Z leads of Frank system. QRS vector loops of Frank system were plotted by hand from the scalar QRS patterns. within human ventricles. In order to provide the ventricular model with a mechanism of LBBB, the following five kinds of different assumptions (1-a, 1-b, 2, 3 and 4) were utilized respectively. In all of these five assumptions, a lesion was assumed on the left bundle branch running on the upper portion of the ventricular septum. For the remaining parts of the ventricle, a block of the excitation spread was provided to the model according to one of the following five assumptions. Each of these assumptions was pursued on the bases of various interpretation of LBBB advocated in the previous reports on animal experiments.

The electrocardiogram and vectorcardiogram in tricuspid atresia. Correlation with pathologic anatomy

The electrocardiographic and vectorcardiographic findings of 29 patients with tricuspid atresia were related to the coexistent cardiac abnormalities and the status of pulmonary blood flow. Certain electrovectorcardiographic features were found to permit distinction between those patients with tricuspid atresia who had diminished pulmonary blood flow and those who had increased flow. Lead V 6 of patients with tricuspid atresia, subpulmonary stenosis and diminished pulmonary blood flow generally revealed shallow Q waves and small R waves. The vectorcardiograms of these patients revealed narrow QRS vector loops in each plane and were posteriorly related. Among the patients with tricuspid atresia without subpulmonary stenosis or with coexistent transposition of the great vessels, tall R waves, frequently in association with deep Q waves, were present in lead V 6. Likewise, the QRS vector loops in each plane encompassed a large area. Most patients had left axis deviation, as anticipated. A normal axis, when present, was usually related to coexistent transposition of the great vessels. The patients with subpulmonary stenosis had right atrial enlargement in infancy but left atrial enlargement when older; those without pulmonary stenosis frequently had left or combined atrial enlargement even in infancy. The origin of the left axis deviation in these patients is uncertain. Histologic studies of the myocardium failed to reveal abnormalities that might explain the alteration.

The vectorcardiogram in complete transposition of the great arteries: Correlation with anatomic and hemodynamic findings and calculated left ventricular mass

The Frank vectorcardiograms of 28 patients with complete transposition were reviewed. It was found that the direction of inscription of the horizontal plane loop was a reliable predictor of left ventricular pressure in these patients. Patients with intact ventricular septum and a left ventricular peak systolic pressure of less than one-half systemic were found to have clockwise horizontal plane QRS vector loops directed predominatly to the right and anterior. Patients with systemic pressure in the left ventricle as a result of a large ventricular septal defect, or in one case severe pulmonary stenosis with intact ventricular septum, were found to have counterclockwise or figure-of-eight horizontal plane loops. Therefore, a clockwise horizontal plane loop is good evidence that left ventricular pressure is low and that the patient does not have an associated large ventricular septal defect, severe pulmonary stenosis, or severe pulmonary vascular disease. In patients with counterclockwise or figure-of-eight horizontal plane loops (systemic pressure in the left ventricle) the vectorcardiogram was not helpful in separating patients with large pulmonary flow from those with decreased pulmonary flow secondary to severe pulmonary stenosis, a pulmonary artery band, or severe pulmonary vascular disease.

Tricuspid atresia with increased pulmonary blood flow. An analysis of 13 cases.

The pathologic and clinical findings in 13 cases of tricuspid atresia and increased pulmonary blood flow encountered in UCLA Medical Center were reviewed. In seven, the great vessels were normally related (group I), and in six, the great vessels were transposed (group II). In all group II cases, aortic arch anomalies were encountered, a finding not duly emphasized in previous reports. Comparison of the two groups revealed significant clinical and laboratory differences. Group II patients typically presented with severe congestive heart failure and expired within the first 2 months of life. Group I patients usually presented with mild congestive heart failure which responded to therapy. Five of the latter demonstrated progressive change from increased to decreased pulmonary blood flow during their clinical course and eventually required palliative shunt procedures, four prior to the age of 2 years and one at 5 years of age. While the electrocardiogram demonstrated right atrial enlargement and left ventricular hypertrophy in both groups, the mean frontal plane axis was between –15° and –100° in group I and –75° and +75° in group II. QRS vector loops tended to be superiorly oriented in group I and inferiorly oriented in group II. Because the natural history and prognosis in these two groups differ significantly, diagnostic efforts should include determination of the relationship of the great vessels. When transposition of the great vessels is demonstrated, aortography should be performed because of the high incidence of aortic arch anomalies.

Observer variation in measurement of QRS vector loops

Summary Maximum vectors, half-area vectors, and width of QRS loops in frontal, sagittal and horizontal planes (Frank System) of one hundred healthy subjects were independently measured by two observers. Overall correlations between measurements by the two observers were high. There was a significant correlation between the half-area QRS vector and the maximum QRS vector. The standard deviation of the differences in measurements between the two observers was relatively small for the maximum QRS vector, but large for the magnitude and orientation of the half-area vector and for the width of the QRS loop. It is concluded that reliability of measurement of the half-area vector and QRS loop width is so poor that their diagnostic value is limited, but that for the maximum QRS vector is acceptable.

Effect of Treatment on Survival in Hypertension

Electrocardiograms, vectorcardiograms and His bundle electrograms were recorded in a patient with Wolff-Parkinson-White syndrome (type A) who developed complete infra-Hisian block and advanced A-V block in the Kent bundle. The atrial impulses reaching the ventricles exclusively through the Kent bundle produced QRS complexes and vector loops showing diffuse (leftward initial and rightward pre-terminal) delays and slurrings. These abnormalities were not due to Wolff-Parkinson-White type A coexisting with right bundle branch block, but reflected the activation sequence characteristic of arrival of excitation; spontaneous impulse formation; or electrical stimulation, at the postero-superior wall of the left ventricle. Intracardiac recordings were a complement to body surface recordings in the study of Wolff-Parkinson-White syndrome complicated by A-V conduction disturbances.

Varying vectorcardiographic patterns in anomalous left coronary artery arising from pulmonary artery

Five patients with LCPA (anomalous origin of the left coronary artery from the pulmonary artery) were studied. Three of them underwent ligation of the anomalous vessel (Group I), whereas 2 had undergone pericardial phenolization some years previously (Group II). In the preoperative vectorcardiograms, morphologic configuration of the QRS vector loop in the horizontal plane was found to be variable. Clockwise inscription was found to be related to a very extensive infarction of the left ventricle. Counterclockwise inscription, on the other hand, was found in a patient with a more localized area of infarction which showed quick regression after ligation of LCPA. The patient with a loop inscribed partly counterclockwise and partly clockwise appeared to fall into an intermediate position with respect to area of infarction. It is suggested that this spectrum of morphologic configuration may serve to indicate the severity of infarction and the general outlook. Time vector analysis was found to provide useful information. After ligation of LCPA in one patient, changes indicative of regression of infarction appeared: widening of the QRS loop to the left and anteriorly in the horizontal plane and leftward shift of the mean axis in the frontal plane. Evidence of intraventricular conduction defect with features suggestive of periinfarction block was seen. On the electrocardiogram the features of interest were abnormal QRS transition in the precordial leads, varying distribution of abnormal Q waves, and slurring of QRS complexes with or without widening. Vectorcardiographic analyses were found to be useful in evaluating the severity and extent of infarction and as a guide to its regression after surgery.

Electrocardiographic changes in atrial septal defects: Ostium secundum defect versus ostium primum (endocardial cushion) defect

The electrocardiographic changes in 100 patients with ostium secundum type, and 33 patients with ostium primum type, of atrial septal defect have been described, and the difference between the electrocardiograms of these two groups has been emphasized. The most reliable single electrocardiographic change that has been found to be of greatest diagnostic value in all atrial septal defects is the presence of an rsR′ (with a QRS duration of less than 0.11 second) in Lead V 1. This pattern was present in 65 per cent of the secundum defects and 44 per cent of the ostium primum defects. The R′ is a manifestation of the rightward and anteriorly directed terminal QRS vector. We call this rsR′ pattern “right ventricular outflow tract hypertrophy” and believe that it is actually due to right ventricular dilatation, especially dilatation and/or hypertrophy in the region of the right ventricular outflow tract, rather than to any interruption of conduction in the right bundle branch. An Rs or qR pattern in Lead V 1 was present in 23 per cent of the secundum and 28 per cent of the ostium primum defects. “Complete” right bundle branch block was present in 5 per cent of the patients with secundum, and 15 per cent of the patients with ostium primum, defects. The mean QRS axis and the rotation of the QRS vector loop are of cardinal importance in differentiating the secundum from the primum defect. True right axis deviation (mean QRS axis or vector more than +100° rightward) was present in 81 per cent of the secundum defects and in none of the primum defects. The mean QRS axis fell between +50° and 180° in all 100 cases of secundum defect. The QRS vector loop was clockwise and below the isoelectric line (0–180°) in all 100 cases of secundum defect. Left axis deviation (mean QRS axis or vector more leftward than −30°) was present in 82 per cent of the ostium primum defects and in none of the secundum defects. The mean QRS axis fell between 0° and −100° in 90 per cent of the primum defects. The QRS vector loop rotated counterclockwise and was above the isoelectric line (0–180°) in all 27 of the patients with ostium primum defect who had true left axis deviation. The terminal QRS vector fell between +120° and −150° in 91 per cent of the secundum defects, and between −60° and −140° in 91 per cent of the ostium primum defects. The height of the P waves suggested right atrial enlargement in 25 per cent of the secundum defects and in 18 per cent of the primum defects. The P-R interval was prolonged in 6 per cent of the secundum and 18 per cent of the primum defects. Attempted hemodynamic correlation with the electrocardiogram failed to add any useful information to this study or to studies already described by other authors. 6,7,11,12 Following surgical closure of the secundum defect the R′ begins to decrease within 2 months, and usually decreases significantly within 4 months. There is often a normal rSr′ or rS in Lead V 1 within 1 year after closure. If regression does not occur, then there is cause for doubt as to the complete closure of the defect, or the presence of irreversible pulmonary vascular changes may be suspected.