Prediction of hemodynamic data in atrial septal defects of secundum type from simple and combined vectorcardiographic data

A search for simple and combined VCG data which could optimally predict right ventricular systolic pressure (RVSP) or shunt size was made in 50 patients with atrial septal defects of the secundum type. VCG was recorded by means of the axial lead system and a multiple regression computer program was applied. Fifty-four VCG data, age, sex, and systolic blood pressure were tested as independent predictors.Seventeen VCG data were significantly correlated with RVSP and six with flow. The best individual variable was the simple maximal negative deflection in Lead X (r = 0.64, p < 0.001). The correlations with flow were poorer, but of theoretical interest. Distinctive differences in the VCG-RVSP relationships were found in atrial septal defects compared with those in pulmonary stenosis, indicating that the increased flow sensitizes the right ventricle to the effect of pressure.Through multiple regression analysis, an equation based on four vectorcardiographic variables was derived. This equation improved the RVSP-VCG correlations significantly (p < 0.05, r = 0.80). The study confirms that vectorcardiogram is a reasonably reliable method for estimating RVSP in patients with atrial septal defects and that the use of combined VCG data may improve the method considerably.     

Assessment of left ventricular hypertrophy by ECG and VCG in patients with inferior and posterior myocardial infarction. A comparison with echocardiographic data

Electrocardiographic (ECG) and vectorcardiographic (VCG) QRS voltage criteria have been analyzed in 26 patients with inferior and 17 with posterior myocardial infarction (MI) in comparison with left ventricular (LV) mass and global and regional wall motion as assessed by M-mode and two-dimensional (2D) echocardiography. Transverse plane QRS maximal vector correlated significantly with LV mass in patients with both inferior and posterior MI (r = 0.65 and 0.87, respectively, p less than 0.01). A transverse plane QRS maximal vector greater than 1.5 mV correctly recognized 12 of 15 (80%) and 9 of 12 (75%) patients with respectively inferior and posterior MI and LV mass greater than 221 gm. Of the ECG measurements, S V1-2 + R V5-6 correlated moderately with LV mass in patients with inferior MI (r = 0.47), and R V1-2 + R V5-6 correlated moderately with LV mass in those with posterior MI (r = 0.67). ECG and VCG QRS voltage data did not correlate with global and regional LV function as assessed by M-mode and 2D echocardiography. We conclude that: ECG and VCG QRS voltage parameters can be utilized for assessing non-invasively LV enlargement in patients with postero-inferior MI; ECG and VCG QRS voltage parameters should be utilized with caution for analyzing LV function or MI size in postero-inferior MI.     

Prediction of pulmonary arterial pressures from electrovectorcardiographic data in pediatric patients with rheumatic mitral valve disease.

The Frank vectorcardiogram (VCG) and the electrocardiogram (ECG) were used to predict pulmonary arterial pressures in 30 pediatric patients with rheumatic mitral valve disease. The patients' ages ranged from eight to 14 1/2 years. Eleven were male and 19 were female. Sixteen had mitral stenosis, eight had mitral regurgitation and six had mitral stenosis and regurgitation. Mean pulmonary arterial wedge pressure ranged from 5-32 mmHg. All patients underwent complete catheterization and angiocardiographic study. None had significant gradient across the right ventricular outflow tract. Right maximum spatial vector (Rmsv) was calculated using Frank VCG.R in V1 and S in V5 of ECG were also measured. Rmsv, RV1, and SV5 were correlated with pulmonary arterial pressures (systolic, diastolic and mean). Pulmonary artery systolic pressure and Rmsv bear the best correlation (r=0.773). The correlation coefficient for pulmonary artery diastolic pressure and Rmsv was 0.698. Rmsv as calculated from Frank VCG is useful in prediction of pulmonary arterial pressures (systolic and diastolic) in pediatric patients with rheumatic mitral valve disease.     

Assessment of right ventricular overload in patients with chronic pulmonary disease by 12-lead electrocardiography, vectorcardiography, and body surface electrocardiographic mapping

Twenty-eight patients with chronic pulmonary diseases were examined with standard 12-lead electrocardiogram (ECG), vectorcardiogram (VCG), and body surface ECG mapping (MAP). The electrocardiographic findings were compared with results of 99 mTc radionuclide right ventriculography or T1-201 myocardial scintigraphy. In a stepwise multiple regression analysis between the electrocardiographic parameters and right ventricular ejection fraction, only the amplitude of the negative P wave in V2 (r = 0.69), the posterior force of P loop in VCG (r = 0.71), and the size of -2SD area at 50 msec QRS potential departure map (r = 0.55) were selected as the parameters in standard ECG, VCG, and MAP, respectively. On the radionuclide ventriculography and myocardial scintigraphy, 14 patients were judged to have right ventricular overload. The criteria by VCG, and MAP had better sensitivity and specificity for right ventricle overload than those by 12-lead ECG. VCG criteria of Chou et al had sensitivity of 93% and specificity of 71%. MAP criteria, departure index of F3 or F4 less than or equal to -2, had sensitivity of 86% and specificity of 79%. The electrocardiographic findings by standard 12-lead ECG, VCG and body surface ECG mapping are useful parameters for the noninvasive detection of right ventricular overload in patients with chronic pulmonary diseases.     

QRS向量环估测室间隔缺损肺动脉压

观察５０例单纯性室间隔缺损（ＶＳＤ）患儿心电向量图（ＶＣＧ）的ＱＲＳ向量环改变与肺动脉压力的关系。结果显示水平面ＱＲＳ环运行方向、ＱＲＳ最大向量振幅、最大前向力、终末右向力、最大前向力与最大后向力比值及终末右向力与最大左向力比值等指标在肺动脉压正常组与肺动脉高压组间有显著性差异，并与肺动脉平均压显著正相关，利用逐步回归方法建立估测肺动脉平均压的回归方程，Ｙ＝－０．９８＋１．４３Ｘ１＋１．１４Ｘ２＋     

Vectorcardiogram synthesized from a 12-lead ECG: Superiority of the inverse Dower matrix

Vectorcardiographic (VCG) criteria for the diagnosis of, for example, myocardial infarction and right ventricular hypertrophy, are superior to the corresponding 12-lead ECG criteria. Contour and rotation of the QRS loops are important parts of these VCG criteria that have no direct counterpart in the 12-lead ECG. Therefore, attempts have been made to synthesize VCGs from 12-lead ECGs for diagnostic purposes. Visual comparison of QRS loops from the Frank VCG and three different synthesized VCGs was made by three independent observers to determine which method produces the most Frank-like QRS loops. The inverse transformation matrix of Dower proved to be the best method of synthesis. Normal limits for some clinically important measurements in VCG interpretation were calculated for this synthesis method and the Frank VCG.     

The vectorcardiographic quantitation of pulmonary hypertension in mitral stenosis

Hemodynamic data and vectorcardiographic (VCG) parameters were correlated in ninety-nine patients with mitral stenosis in order to quantitate the severity of pulmonary hypertension. Using spherical coordinate representation of VCG parameters as independent variables, multi-parameter regression equations were derived for estimating mean pulmonary artery pressure (PAm) and total pulmonary vascular resistance (TPR). The regression equations of this group of ninety-nine patients performed well when the patients were divided into specific subgroups based on horizontal plane morphology. The correlation co-efficients between estimated and measured values ranged from 0.71 to 0.81 for PAm and 0.68 to 0.80 for TPR. These regression equations were used to predict the PAm and TPR in a second set of 11 patients. The correlation co-efficients between the measured and predicted values for this group were 0.54 for PAm and 0.64 for TPR.     

Predictability of electrocardiographic and vectorcardiographic criteria in pulmonary arterial hypertension caused by chronic bronchopneumopathies]

The Authors have verified in a group of 38 patients with chronic obstructive pulmonary disease (COPD) and suspected pulmonary arterial hypertension (PAH) of precapillary origin the possibility to forsee the pressure within the lesser circulation starting from some electrocardiographic and vectorcardiograhic criteria. The vectorcardiographic analysis has not been shown to be more reliable than the traditional ECG as far as the identification of an eventual PAH is concerned. The matching of both scalar and vectorial criteria has significantly increased the efficiency of the estimate, i.e. the possibility to foresee the right ventricular systolic pressure (RVSP) and the mean pulmonary arterial pressure (PAP), but the same efficiency has remained at unsatisfactory level (S = +/- 10,30 Torr as far as the PAP is concerned. With regard to the value of the various scalar and vectorial criteria or parameters, among the electrocardiographic criteria the most reliable has been the inversion of the T wave in the right precordial leads. This sign, however, did not often appear in the present series (18% of the cases). As to the VCG the analysis made by the Authors stresses as the most reliable criterion the direction of QRS loop rotation on the horizontal plane and the magnitude of the maximum rightward spatial vector. These two elements, among other things, escape detection on the traditional electrocardiographic investigation. The above mentioned conclusions, obviously, only apply to the PAH secondary to COPD, in which particular noncardiac (lung hyperinflation, lowering of the diaphgram, etc.) and cardiac (associated left ventricular hypertrophy) factors contribute to limit the diagnostic value of both the ECG and the VCG.     

Comparison of the classification ability of the electrocardiogram and vectorcardiogram

Controversy exists over the classification ability of the standard 12-lead electrocardiogram (EGG) and the vectorcardiogram (VCG). In this study the diagnostic information content and classification performance of the ECG and VCG were examined using multivariate statistical techniques and a large validated data base of 3,266 cases. Logistic classification models were developed to differentiate between 7 diagnostic entities: normal (n = 538), left (n = 557), right (n = 323) and biventricular (n = 437) hypertrophy, and anterior (n = 390), inferior (n = 657) and combined (n = 364) myocardial infarction. The models were obtained from a learning sample (n = 2,446) using an optimal set of computer derived ECG and VCG measurements. They were subsequently applied to a test sample (n = 820). In the learning sample, the discrimination models resulted in a total correct classification rate of 69.6% for the ECG and 69.4% for the VCG. The total accuracy rate was slightly lower in the test set: 66.3% for the ECG and 67.1% for the VCG. The combined use of the best ECG and VCG variables did not increase total diagnostic accuracy. When cases with biventricular hypertrophy and combined infarction were deleted, accuracy rates of more than 80% were achieved for both lead systems. Differences in the classification rates for the subgroups were not statistically significant. Thus, the conventional 12-lead ECG is as good as the VCG for the differential diagnosis of 7 main entities, provided identical procedures are used in the design of the classifiers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diagnostic value of electrocardiogram and vectorcardiogram in postinfarction ventricular asynergy

The ability of ECG-VCG to predict the severity of postinfarction LV asynergy was evaluated in 152 patients with previous myocardial infarction who underwent left cineventriculography in the right anterior oblique view. Various ECG and VCG signs were examined in order to predict the existence of severe asynergy in general (dyskinesia or akinesia or severe hypokinesia) and of dyskinesia in particular. In patients with inferior myocardial infarction (Group A) persistent ST segment elevation was the only specific ECG sign (100%) of severe asynergy; it had a poor sensitivity (6.2%). Four frontal VCG signs (presence of terminal bite, y- greater than 0.18 mV, maximum early superior vector along x axis = MESV greater than or equal to 1.3 mV, duration of initial superior forces = DISF greater than 50 msec) increased the sensitivity of the ECG-VCG method to 75.8% while maintaining a 100% specificity. Regarding the diagnosis of dyskinesia, only the ECG sign of persistent ST segment elevation and the VCG sign of y- greater than or equal to 0.3 mV had a 100% specificity. The sensitivity of the ECG-VCG method was 33.3% (16.6% ECG and 16.6% VCG). In patients with anterior myocardial infarction (Group B), concerning the diagnosis of severe asynergy, the ECG signs of sigma ST greater than 3 mm in anterior leads; pathologic Q wave in four or more anterior leads (including D1 and aVL); and the presence of LAH or LAH + RBBB, had a 100% specificity and a good sensitivity (60.5%). The VCG sign of a narrow horizontal QRS loop increased the sensitivity of the ECG-VCG method to 71% while maintaining a 100% specificity. As for the diagnosis of dyskinesia, the ECG signs with a 100% specificity were sigma ST greater than or equal to 5 mm in anterior leads, a pathologic Q wave in more than five anterior leads (including I and a VL) and RBBB + LAH; these variables had a sensitivity of 48.3%. The VCG sign of a narrow horizontal QRS loop increased the sensitivity of the ECG-VCG method to 79.3% while maintaining a 100% specificity. In patients with inferior plus anterior myocardial infarction (Group A + B) the signs mentioned above for each group were evaluated, confirming a 100% specificity. Regarding the diagnosis of severe asynergy, the ECG signs had a sensitivity of 61.3%, while VCG increased the sensitivity of the ECG-VCG method to 90.3%.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electrocardiography to define clinical status in primary pulmonary hypertension and pulmonary arterial hypertension secondary to collagen vascular disease

STUDY OBJECTIVES: To determine the utility of the ECG for predicting clinical status in adults with primary pulmonary hypertension (PPH) or pulmonary arterial hypertension (PAH) secondary to collagen vascular disease. DESIGN: Retrospective study. SETTING: Outpatient clinic in a tertiary referral center. PATIENTS: Adult outpatients with PPH or PAH secondary to collagen vascular disease who underwent electrocardiography within 30 days of undergoing right-heart catheterization, echocardiography, and 6-min walk testing. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: The following measurements were recorded from each ECG: P-wave amplitude in lead II; mean frontal QRS axis; QRS duration; R-wave and S-wave deflections in leads I and V6; and the T-wave configurations in the precordial leads. These ECG variables were correlated with hemodynamic variables, RV size, and exercise capacity. Of the 61 patients included in this study, 56 (92%) were women. Eight of 61 patients (13%) had normal findings on ECGs. There was no significant difference in the demographics or hemodynamics when comparing groups with normal vs abnormal ECGs. All ECG parameters had no more than moderate correlation with hemodynamic variables, ventricular size measured by echocardiogram, and exercise capacity as measured by a 6-min walk. The best correlation was between mean the frontal QRS axis and cardiac index (r = -0.46). CONCLUSIONS: The ECG is an inadequate screening tool to rule out the presence of clinically relevant pulmonary hypertension, either primary or secondary to collagen vascular disease. The mean frontal QRS axis correlated best with the severity of hemodynamic impairment.     

Assessment of echocardiographic left atrial enlargement in patients with atrial fibrillation. An electrovectorcardiographic study.

Standard 12 lead electrocardiograms (ECG) and timed Frank vectorcardiograms (VCG) were recorded in 53 subjects with atrial fibrillation. Thirty-eight patients had echocardiographically documented left atrial enlargement (greater than 4.0 cm) and 15 patients had normal atrial dimensions. The magnitude of the largest "f" wave component during an average cycle length was measured in lead V1 of the ECG and the horizontal plane VCG running loop. Relative sensitivies for detection of left atrial enlargement were: VCG, 25/38 (66%) and ECG 10/38 (26%). An enlarged left atrial internal dimension was diagnosed by the VCG alone in 21 of the 38 subjects (55%). In the group of 15 patients with normal echocardiographic left atrial internal dimensions the prevalence of ECG false positive diagnosis for enlarged left atrial size was 6% in contrast with 0% for the VCG. It is concluded that: 1) the timed Frank VCG is superior to the ECG for the detection of echocardiographically demonstrable left atrial enlargement; 2) the timed VCG and ECG represent complementary techniques for identifying patients with abnormally large left atria; and 3) large fibrillatory waves are rarely observed on the ECG or VCG when the left atrial internal dimension is echographically normal.     

Vectorcardiography Risk Stratifies Emergency Department Chest Pain Patients with Left Ventricular Hypertrophy on the Initial 12‐Lead ECG

Background: Vectorcardiographic (VCG) measurements of ST‐vector magnitude (VM) and QRS‐vector difference (VD) have been demonstrated to be independent predictors of adverse outcome (AO) and acute myocardial infarction (AMI) in emergency department (ED) chest pain patients with absence of bundle branch block or left ventricular hypertrophy (LVH) on the initial 12‐lead electrocardiogram (ECG). The prognostic value of ST‐VM and QRS‐VD in ED chest pain patients with LVH on the initial 12‐lead ECG has not been previously investigated. Methods: A prospective observational study was performed in 196 consecutive ED chest pain patients with suspected AMI and presence of voltage criteria for LVH on initial ECG who underwent continuous VCG monitoring during the initial evaluation. The optimal baseline ST‐VM value and 2‐hour QRS‐VD value were defined as the most accurate value on the receiver operator characteristic curve (value with lowest false‐negative and false‐positive rate). Thirty‐day AO was defined as AMI, percutaneous coronary intervention, coronary artery bypass grafting (CABG), or cardiac death occurring within 30 days of initial ED visit. Results: Fourteen patients (7.1%) were diagnosed as 24‐hour AMI and 28 patients (14.3%) experienced 30‐day AO. The optimal cut‐off value for predicting 30‐day AO was >124 μV for ST‐VM and >21.7 μV for QRS‐VD. Patients with either a positive ST‐VM or a positive QRS‐VD had 8.8 times increased odds of AMI (95% confidence interval, CI, 1.9–40.3; P = 0.003); 4.3 times increased odds of 30‐day PTCA/CABG (95% CI 1.3–13.8; P = 0.019); and 3.8 times increased odds of 30‐day AO (95% CI 1.6–9.3; P = 0.003). Conclusions: Baseline ST‐VM and 2‐hour QRS‐VD risk stratifies ED chest pain patients with LVH voltage criteria on the initial 12‐lead ECG.     

The effect of acute pulmonary artery obstruction on the dog electrocardiogram

Acute pulmonary artery obstruction was induced in 10 dogs by inflating a balloon at the end of a double lumen catheter introduced into the pulmonary artery. The ECG was recorded by means of the axial lead system. Significant and generally uniform changes in QRS, T, and ST segments were observed in all dogs when the obstruction reached a level which elevated the right ventricular systolic pressure to above 40 mm. Hg. The most important changes were a counterclockwise rotation of the total QRS loop in the horizontal plane, a large reduction of Lead Z amplitude, and a superior rightward shift of the ST and maximal T vectors. The changes appeared within a few beats after balloon inflation, were stable during constant obstruction, and disappeared rapidly when the balloon was deflated.A close relationship was observed between the degree of ECG changes and the degree of pulmonary artery obstruction. The type of changes observed corresponded well with those described in man with acute pulmonary embolism.     

Comparison of optimal scalar electrocardiographic,orthogonal electrocardiographic and vectorcardiographic criteria for diagnosing inferior and anterior myocardial infarction

A scalar electrocardiogram (ECG), orthogonal ECG and vectorcardiogram (VCG) were recorded in 46 normal persons, 38 patients with inferior myocardial infarction (MI) and 22 patients with anterior MI proved at cardiac catheterization. The diagnostic information provided by the scalar ECG, orthogonal ECG and VCG was quantitatively analyzed and the optimal criteria for diagnosing inferior and anterior MI exhibited by each method were identified. The optimal scalar electrocardlographic, orthogonal electrocardiographic and vectorcardiographic criteria, respectively, are: For inferior MI: initial superior duration in lead aVF >30 ms (sensitivity 63%, specificity 100%), superior/inferior amplitude ratio in lead Y ≥0.2 (sensitivity 63%, specificity 96%), initial superior duration >29 ms or initial superior distance >0.4 mV in the frontal plane loop (sensitivity 68%, specificity 100%). For anterior MI: initial anterior duration in lead V₂ <20 ms or initial anterior duration in lead V₃ < 25 ms (sensitivity 91%, specificity 100%), anterior/posterior duration ratio in lead Z <0.3 (sensitivity 73%, specificity 98%), initial anterior duration <15 ms in the transverse plane loop (sensitivity 64%, specificity 98%). There were no significant differences among the performances of the optimal scalar ECG, orthogonal ECG and the VCG for diagnosing inferior MI. However, the performance of the optimal scalar ECG was superior to that of the optimal orthogonal ECG and the optimal VCG for diagnosing anterior MI (chi-square = 5.20, p <0.02 and chi-square = 7.14, p >0.01, respectively).     

Polarcardiographic study of inferior myocardial infarction: Global projection of heart vector

The sensitivity of electrocardiographic, vectorcardiographic and polarcardiographic criteria for inferior myocardial infarction was studied. ECG and Frank system VCG were recorded in 50 normal cases and 40 cases of inferior myocardial infarction, whose acute phase was documented by typical electrocardiographic and serum enzymatic changes. The records were made from one month to 16 years after acute attacks. Polarcardiograms were obtained by a specially-designed analogue computer from X, Y and Z signals of the VCG, and recorded at a paper speed of 1000 mm/sec by Mingograph. The polarcardiographic tracings were measured at every 5 msec after onset of the QRS wave, and plotted on the Aitoff's equal-area projection. In normal cases, the QRS vectors plotted on Aitoff's projection passed through the narrow area between 15 to 35 msec after the QRS onset.Electrocardiographic diagnosis of myocardial infarction was correctly made in 22 cases (55%), and by VCG the sensitivity was improved to 32 cases (80%). Polarcardiographic diagnosis was made in 33 cases (82.5%). Global plots of heart vector on Aitoff's projection were a useful display to visualize the sequential changes of heart vector. In inferior myocardial infarction, the QRS vector passed through the more superior portion to normal, and the diagnosis was accurately made in 33 cases (82.5%).     

Echocardiographic left atrial enlargement. Comparison of vectorcardiogram and electrocardiogram for detection

Standard electrocardiograms (ECG) and Frank vectorcardiograms (VCG) were obtained in 43 consecutive patients in sinus rhythm who had echocardiographic evidence of left atrial enlargement (left atrial internal dimension greater than 4.0 cm; x +/- 1SD = 4.7 +/- 0.5 cm). High gain VCG P loop measurements for the study group were: maximal posterior magnitude, 0.11 +/- 0.03 mv; duration, 106 +/- 14 msec and ratio of maximal posterior to maximal anterior P vector magnitudes, 3.2 +/- 1.4. Thirty of 43 (70%) patients with echocardiographic determined left atrial enlargement had VCGs diagnostic of that condition. Utilizing New York Heart Association criteria for left atrial enlargement, 17 of 43 patients (40%) had ECGs which were diagnostic. Fifteen of 43 (35%) subjects manifested both ECG and VCG criteria for left atrial enlargement and only two patients had diagnostic ECGs and normal VCGs. It is concluded that analysis of high gain VCG P loops provides a 30% higher yield for the diagnosis of echocardiographically determined left atrial enlargement when compared with P wave examination on the standard ECG.     

起源于右室流出道间隔部特发性室性早搏心电图及心电向量图研究

目的：探讨经射频消融证实的起源于右室流出道间隔部的特发性室性早搏（室早）的心电图特征及心电向量图特征。方法采用 CARDIO-View 心电工作站收集并分析14例经射频消融术证实为右室流出道间隔部特发性室早患者的12导联心电图及 Frank 导联心电向量图参数。结果起源于右室流出道间隔部的特发性室早呈类左束支阻滞图形。12导联心电图胸导联移行指数≥0的有12例（85．7％）,V2导联 R 波时限指数＜50％的14例（100％）, V2导联 R／S 波振幅指数＜30％的有13例（92．9％）,SV2／RV3指数＞1．5的有12例（85．7％）。心电向量图特征为：QRS 环运行方向在 F 面呈 CW 和 CCW 的各有5例（35．7％）,H 面呈 CCW的有10例（71．4％）,S 面均呈 CW（100％）;起始0．04 s,QRS 环振幅逐渐增大,QRS 环方位大部分指向左前下;0．01～0．04 s 向左向量逐渐增加,向前向量逐渐减少;QRS 环最大向量及大部分面积位于左下后。结论心电图对起源于右室流出道间隔部的室早定位诊断具有较高的准确率。起源于右室流出道间隔部的室早有典型的心电向量特征。     

Hemodynamic correlates of vectorcardiographic QRS loops in pure mitral stenosis

The hemodynamic correlates of the vectorcardiographic types of right ventricular hypertrophy (RVH) according to Chou and Helm and those with normal QRS loop in the horizontal plane of Frank system were analyzed in 100 patients with pure mitral stenosis. All underwent right and left heart catheterization. Additionally, coronary arteriography was done on 16 whose ages were above 40. Type A RVH was associated with the most severe hemodynamic alterations with markedly elevated total pulmonary vascular resistance (TPVR), mean pulmonary artery pressure (MPAP), peak right ventricular pressure (RRVP) and the smallest mitral valve area (MVA). The severity of these parameters were to a lesser degree obtainable in type C but with no significant difference from type A (p greater than 0.05). However, types A and C were clearly separated from type B and normal QRS loop (p less than 0.05). Type B RVH and normal QRS loop showed milder hemodynamic changes and were not significantly different (p greater than 0.05). Our results indicate that in pure mitral stenosis the development of RVH is from a normal loop into type B, C and A reflecting an increasing severity of hemodynamic changes which affect the right ventricle. This order of development is different from the traditional view.