P wave abnormalities in the orthogonal electrocardiogram: Correlation with ventricular overload in pulmonic and aortic valvular heart disease

J. ELECTROCAR DIOLOGY, 8 (2) 103-112, 1975

P Wave Abnormalities in the Orthogonal Electrocardiogram: Correlation with Ventricular Overload in Pulmonic and Aortic Valvular Heart Disease BY CHRISTIAN R. BROHET, M.D., CLAUS-E. LIEDTKE, PH.D., AND NAIP TUNA, M.D., PH.D.

SUMMARY The correlation between several P wave m e a s u r e m e n t s from the orthogonal electroc a r d i o g r a m ( S V E C I I I l e a d s y s t e m ) ext r a c t e d by c o m p u t e r a n a l y s i s and simple hemodynamic parameters related to ventricular dysfunction was studied in two groups of patients. Group I consisted of 32 patients with pulmonie v a l v u l a r stenosis and intact interventrieular septum. There was a significant correlation between electrocardiographic criteria of right atrial overload and the two hemodynamic parameters studied: peak pulmonic systolic pressure gradient and right ventrieular end diastolic pressure (r = 0.502, p < 0.005 and r = 0.661, p < 0.001 respectively). Groul~ II consisted of 49 patients with aortic valve disease. In this group, a significant correlation between the electrocardiographic parameters of left atrial overload and the left ventrieular end diastolic pressure could be demonstrated only by a multivariate regression analysis (r = 0.630, p < 0.005). The P wave measurements that are well correlated with the ventricular end diastolic p r e s s u r e c a n be c o n s i d e r e d as v a l u a b l e criteria for atrial enlargement secondary to a decrease of ventrieular compliance, such as seen in ventricular hypertrophy, failure or in v e n t r i c u l a r constrictive or restrictive diseases. The pathophysiologic mechanisms o f t h e i n f l u e n c e of t h e v e n t r i c u l a r overload (dysfunction) on the atrial function and the resulting P wave changes are discussed.

In recent years, there has been considerable interest in the analysis of the P wave, using the orthogonal electrocardiogram (ECG), both in normal subjects 1-5 and in patients with right and left atrial overload. 6-s Chronic diseases involving the left ventricle can lead to left a t r i a l a b n o r m a l i t i e s , 9-11 and s e v e r a l studies concerning the importance of atrial depolarization abnormalities in the detection of left ventricular disease have been reported. 12-13 There appears to be a direct influence of left ventricular dysfunction on the electrical activity of the left atrium, and several authors have shown the usefulness of the P wave analysis for assessing the degree of severity of the left ventricular disease. 14-17 The relationship between right ventricular overload and P wave abnormalities has been less extensively s t u d i e d f -s There have been no uniform approaches to the study of the relationship between the P wave and ventricular overload. Some investigators have used the conventional 12-lead ECG while others have used various orthogonal or nonorthogonal vectorcardiographic lead systems for this purpose. The types of hemodynamic parameters employed for the evaluation of ventricular overload also vary considerably. The purpose of this study is to evaluate the relationship between P wave patterns of atrial overload, as recorded by the SVEC III orthogonal lead system and analyzed by a digital computer, and simple hemodynamic parameters which are commonly used to determine the presence and degree of ventricular overload (decreased v e n t r i c u l a r compliance, whatever the cause might be: hypertrophy, dilation or failure) in clinical practice.

From the Section of Cardiology, Department of Medicine, and the Divisions of Health Computer Sciences, Department of Laboratory Medicine and Pathology, University of Minnesota. This investigation was supporte~l in part by The N a t i o n a l H e a r t and Lung I n s t i t u t e Grant HL=08527-09 and NIH Grant No. RR-267. Reprint requests to: Naip Tuna, M.D., Box 481, University Hospitals, Minneapolis, MN 55455.

Patients

MATERIAL AND METHODS A total number of 81 patients was divided into two groups: group I consisted of 32 patients with valvular pulmonic stenosis and intact interventricular septum. There were 22 males and 10 103

104

BROHET ET AL

females. The average age was 12 years (range: 5-36 years). They had various degrees of right ventricular hypertrophy as demonstrated by chest x-rays, right ventriculography, ECGs and VCGs. The average peak systolic gradient across the pulmonic valve was 56.6 mmHg and the range was between 15 and 210 mmHg. The average of the right ventricular end diastolic pressure for the group was 9.81 mmHg and the range was between 0 and 25 mmHg. Group II consisted of 49 patients with aortic valvular disease. There were 11 with pure aortic stenosis and aortic regurgitation. Forty-two were males and seven were females. The mean age was 41 years (range: 4-69 years). They had various degrees of left ventricular hypertrophy as determined by chest x-rays, left ventriculography, ECGs and VCGs. The average of the left ventricular end diastolic pressure for the group was 15.45 m m H g and the range was between 4 and 40 mmHg. No attempt was made to separate patients with left v e n t r i c u l a r systolic overload (aortic stenosis) from those with left ventricular diastolic overload (aortic insufficiency) because of the limited size of these subgroups. The basis for the selection of these patients was the availability of complete cardiac catheterization data (right heart catheterization for the group of pulmonic stenosis and right and left heart catheterization for the group of aortic valve disease) and of computer analyzed orthogonal ECGs (SVEC III system). Patients with marked electrolyte abnormalities or those on quinidine or procainamide, which are known to affect cardiac depolarization and repolarization, have been excluded. The recording t e c h n i q u e s of the SVEC IiI orthogonal ECGs have been reported previously. TM A program similar to the Pipberger's measurement program TM was used for processing the orthogonal ECGs by a Supernova digital computer. The magnitude and directions of instantaneous vectors of P wave were determined at fixed time intervals of ten milliseconds. Five vectors were taken after the P wave onset and an analogous series of five vectors were taken from the terminal part of the P wave, beginning at the end of the wave and progressing in retrograde fashion toward the beginning of the wave. Eight instantaneous vectors of the time normalized P wave, i.e. P wave divided in eight equal time segments, were also identified. M a x i m a l vectors for P, QRS and T, time integrals for 88 segments of the P wave in scalar leads X, Y and Z, the ventricular gradient and maximal spatial vector for QRS a n d T were calculated. The measurements of amplitudes and durations of P, QRS and T waves in leads X, Y and Z were also determined in a fashion similar to that reported by Draper and CoWorkers. 2 The maximal vector of P and the instantaneous vectors at fixed time intervals for P also were determined in the three plane projects: frontal, right sagittal and horizontal. The beginning and the end of P, QRS and T were determined from the digital plots of simultaneously recorded X, Y and Z leads with time marks every millisecond. In order to conform to the commonly used electrocardiographic leads, the polarity of lead Y of SVEC III was reversed while the polarity of X and

Z remained unchanged, Thus, the Y lead would look like aVF and the Z lead like V2 of the regular 12-lead ECG. The reference frame used for the angular measurements of P and QRS vectors is shown in Fig. 1. The calculations of angles were made using procedures suggested by Downs and Associates.2~ Various electrocardiographic and vectorcardiographic measurements were correlated with the h e m o d y n a m i c findings. In a few patients the hemodynamic studies and the electrocardiographic and vectorcardiographic recordings were not performed at the same time. In group I the interval between the two procedures were more than one year only in two patients; the other 30 patients had the two examinations within the same week, most of them on the same day. In group II the interval b e t w e e n t h e ECG and VCG r e c o r d i n g and catheterization studies was more than one year in seven patients; it varied between one and ten months in nine patients, and for the rest, the two procedures were performed within the same week. However, the patients with a longer interval between the hemodynamic studies and the ECG recording were clinically stable and none showed significant changes in the routine ECG tracings, cardiac fluoroscopy and chest x-rays or in clinical status during the time interval.

Hemodynamic Parameters The P wave measurements in the orthogonal ECG were correlated with several hemodynamic variables of ventricular overload recorded with the patient at rest. In group I, the peak systolic gradient across the pulmonic valve (pulmonic gradient) and the right ventricular filling pressure (right ventricular end diastolic pressure) were investigated. These hemodynamic variables were chosen on the basis of their common use in clinical practice for assessing the degree of right ventricular overload. For group II, the left ventricular filling pressure (left ventricular end diastolic pressure) was selected as being the most commonly used hemodynamic parameter of left ventricular overload. Only the most stable value, or the mean of several values when they varied slightly at different readings, was retained for the correlation study. Since our purpose was not to make a detailed analysis of the ventricular function, other more sophisticated: hemodynamic variables, such as ventricular volumes, ejection fraction, contractility indices or the changes in left ventricular function induced by exercise were not used:

Electrocardiographic Parameters Among the 200 different measurements of the P wave (which included planar, scalar and vector m e a s u r e m e n t s ) available after computer processing, only the variables listed in Table 1 were used. Some of these parameters have been chosen because of their traditional usage in routine electrovectorcardiography for the diagnosis of right atrial 6'7'21'22 or left atrial enlargement2 '7'23 Some others were e m p i r i c a l l y introduced as criteria probably useful for the delineation of P wave abnormality. Finally, there were parameters selected by a multivariate analysis used for the classification of P wave pattern; these include most

J. ELECTROCARDIOLOGY, VOL 8, NO. 2, 1975

P WAVE ABNORMALITI ES

105

TABLE 1 Selection of ECG Parameters for the Criteria of Right Atrial Overload (RAO) and Left Atrial Overload (LAO).

RAO: Nine measurements SYMBOL

....

P (POS) Y P (MAX) F P (MAX) Z P (MAX) Y P (MAX SPAT) P (3/8) Z P (POS) Z P (MAX) AZ P (MAX) EL

DESCRIPTION

Area of positive part of P wave in lead Y Magnitude of the ~aximal P vector in frontal plane Amplitude of maximal P vector in lead Z Amplitude of maximal P vector in lead Y Amplitude of maximal spatial P vector Amplitude of the 3/8th of the P wave in lead Z Area of positive part of P wave in lead Z Azimuth angle of the maximum spatial P vector Elevation angle of the maximum spatial P vector

SOURCE

G E,M G E,M G G E,G G G

LAO: Fifteen measurements SYMBOL

P (DU R) P-R int. P (POS) X P (NEG) Z P (MAX SPAT) P (NEG) AZ P (AREA) Y P (AREA) Z P (TIME) P (MAX) H P (2/4) Z P (3/4) Z P (NEG) EL P (6/8) X P (2/4) EL

DESCRIPTION

Duration of P wave P-R interval Area of positive part of P wave in lead X Area of negativepart of Pwave in lead Z Amplitude of the maximum spatial P vector Aximuth angle of negativepart of P wave Total area of P wave in lead Y Total area of P wave in lead Z Time from P onset to maximum spatial P vector Amplitude of maximum P vector in horizontal plane Area of the 2/4th of P wave in lead Z Area of the 3/4th of P wave in lead Z Elevation angle of negativepart of P wave Amplitude of 6/8th of P wave in lead X Elevation anglesof 2/4th area of P wave

SOURCE

E,M E G G,E,M G G,E G G,M G,M M M,G M,G G G,M G,M

The symbols are those used throughout the text. The sourcesare given by letters: E = parameterequivalent to the ECG criterion of P wave abnormality G = parameter "guessed" as good criterion of P wave abnormality M = parameterselected by previousmultivariate analysisfor classification of P wave patternss

of the ECG criteria recommended by Ishikawa and Co-Workers8 for the diagnosis of left atrial overload (LAO) and right atrial overload (RAO).

Statistical Analysis Initially, for each group of patients, individual correlations between the values of the hemod y n a m i c v a r i a b l e s and each of several ECG parameters were determined. Since a single ECG parameter might fail to show any relationship between the hemodynamic variable and the ECGI a multivariate analysis using a linear combination of various ECG measurements as a predictor for J. ELECTROCARDIOLOGY, VOL. 8, NO. 2, 1975

the hemodynamic variable was also performed. The linear combination of ECG measurements was considered as the independent variable and the expected ventricular filling pressure as the dependent variable. For this purpose, a step-wise multiple regression technique was used and ~ multiple correlation coefficient, i.e., a measure of the correlation between the actual pressure and the predicted pressure was computed. 24~5 Because of the importance of the sampling problem in the estimation of the multiple correlation coefficient, the number of cases as well as the number of ECG

106

BROHET ET AL

parameters were taken into consideration and proper corrections made on the assumption of sampling errors. 26

TABLE 2 Multiple RegressionAnalysis in Group I (Pulmonic Stenosis): Right Ventricular End Diastolic Pressure Predicted by Using Seven P Measurements (N=32).

RESULTS I. P U L M O N I C S T E N O S I S GROUP)

GROUP (RVO

Correlation Analysis T he correlation studies between the pulmonic systolic pressure gradient and each of nine P m e a s u r e m e n t s selected as criteria for r i g h t a t r i a l o v e r l o a d (RAO) c o n s i s t i n g of P(MAX)Z, P(MAX SPAT), P(POS)Z, P ( M A X ) Y , P ( M A X ) A Z , P ( P O S ) Y , P(%)Z, P(MAX)F and P(MAX)EL showed t h a t t he r e was significant correlation only with the first t h r e e m e a s u r e m e n t s (P(MAX)Z: r = 0.502, p < 0.005; P(MAX SPAT): r = 0.470, p < 0.01 and P(POS)Z: r = 0.421, p < 0.02). The correlations between the pulmonic systolic pressure gradient and each of the r e m a i n i n g six P m e a s u r e m e n t s were low and not significant. T he correlation studies between the right v e n t r i c u l a r end diastolic pressure and each of the following seven P m e a s u r e m e n t s (P(MAX SPAT), P(POS)Z, P(MAX)Z, P(MAX)F, P(POS)Y, P(MAX)Y and P(%)Z) showed t hat t h e r e were significant correlations with each m e a s u r e m e n t except P(%)Z (r = 0.160, p = not significant). The correlation coefficients were as follows: P(MAX SPAT): r = 0.661, p < 0 . 0 0 1 ; P ( P O S ) Z : r = 0 . 5 8 2 , p < 0. 001; P(MAX)Z: r = 0.566, p < 0.001; P(MAX)F: r = 0.478, p < 0.01; P(POS)Y: r = 0.373, p < 0.05 and P(MAX)Y: r = 0.376, p < 0.05. The correlation between the P(MAX SPAT) and the R V EDP is shown in graph form in Fig. 2A. T h e P(MAX)Z, the P(MAX SPAT) and the P(POS)Z show significant correlations with both the pulmonic systolic pressure gradient a n d t h e RVEDP. T he P(MAX)Z shows the highest correlations.

Multiple correlation coefficient r = 0.707 95% confidence interval estimate for the prediction of the average pressure 4-1.393

Rank of P variables: 1. 2. 3. 4. 5. 6. 7.

Fig. 2B shows the graphic display of the c o r r e l a t i o n b e t w e e n the predicted R V E D P using a l i near combination of the seven P m e a s u r e m e n t s and the observed RVEDP.

H. A O R T I C V A L V E D I S E A S E G R O U P (LVO GROUP)

Correlation Analysis Initially, a set of six P m e a s u r e m e n t s consisting of P(DUR), PR i n t e r v a l , P(POS)X, P(NEG)Z, P(MAX SPAT) and P(NEG)AZ was

Reference

Frame

for

Angular

FRONTAL -90 ~

Measurements

HORIZONTAL AND AZIMUTH _90 ~

u 180 ~

Multiple Regression Analysis T h e r e s u l t of t h e m u l t i p l e r e g r e s s i o n analysis is shown in Table 2. At the first step of this analysis, the most i m por t ant paramet e r was P(MAX SPAT) (r = 0.662, p <0.001) which was already identified as the best variable when individual correlations were computed. At the second step, t he next most imp o r t a n t p a r a m e t e r added was the P(MAX)F (r = 0.677, p < 0.005) which was only the fourth best p a r a m e t e r in the individual correlation study. By t a k i n g more P p a r a m e t e r s , the sign i f i c a n c e of t h e c o r r e l a t i o n g r a d u a l l y decreased because of the decrease in t he n u m b e r of degrees of freedom. At the last step, when all seven P m e a s u r e m e n t s were used, the multiple correlation coefficient was r = 0.707, a non-significant value (p < 0.1).

P (MAX SPAT) P (MAX) F P (3/8) Z P (P0S) Z P (MAX) Y P (MAX) Z P (POS) Y

u

~

L~

+Y Inferior +90 ~

+Z Anterior -I-90 ~

RIGHT SAGITTAL -90 ~

ELEVATION _90 ~

T 180 ~

Ant(~rtor

+Y Inferior +90 ~

0~

+Y Inferior +90 ~

Fig. 1. The polarity of lead Y of SVEC III is reversed while the polarity of X and Z remain unchanged. J. ELECTROCARDIOLOGY, VOL. 8, NO. 2, 1975

P WAVE ABNORMALITIES

pressure P(NEG)Z (r = 0.423, p <0.005) and P(NEG)AZ (r = 0.286, p < 0.05) while only one m e a s u r e m e n t showed significant correlation with the left ventricular end diastolic pressure (P(NEG)AZ: r = 0,363, p < 0.02).

HIGHEST CORRELATION COEFFICIENT .31

.26 ~ .22 ~ .17 E .13

.08 0

2.2 4.5

6.8

9~

11.3 13.6

L5.9

18.1 2G4 22:7

25.0

MEASURED RVEDP

LINEAR COMBINATION OF 7 MEASUREMENTS 21.2

j ~ . . ~

JJ

.

14.0

9

5

107

..................

S

A n o t h e r s e t of n i n e m e a s u r e m e n t s (P(AREA)Y, P(AREA)Z, P(TIME), P(MAX)H, P(2/4)Z, P(3/4)Z, P(NEG)EL, P(6/8)X and P(2/4)EL) which includes several criteria recommended by Ishikawa and Co-Workers s for the diagnosis of LAO, were tested for correlation with the LVEDP. Only the P(AREA)Z showed a significant correlation with the LVEDP (r = 0.358, p < 0.02). Thus, out of a total of 15 P wave m e a s u r e m e n t s investigated, only the P(NEG)AZ and the P(AREA)Z show significant correlations with the left ventricular end diastolic pressure. Three P measurements, the P(MAX SPAT), the P(DUR) and the P(NEG)Z, which are generally regarded as useful electrovectorcardiographic criteria for t h e diagnosis of LAO, were further investigated in two subgroups of patients with aortic valve disease, those with LVEDP of less t h a n 15 m m H g and those with LVEDP greater t h a n 15 mmHg. A Student's t test performed to evaluate the difference between the means of each of these P measurements for the two subgroups showed no significant differences.

Multiple Regression Analysis 6.9

s.sl

0

~

,

2.2 4.5

,

,/

6.8 9.0

,

,

. . . .

li.3 13.6 i5.9 181 20.4 22.7 25.0

MEASURED RVEDP

Fig. 2:A Group I: Pulmonic Stenosis. Correlation graph of the P measurement: P(MAX SPAT) (millivolts) having the highest correlation coefficient with the right ventricular end diastolic pressure: measured RVEDP (mmHg). B. Group I: Pulmonic Stenosis. Correlation graph between the measured right ventricular end diastolic pressure: measured RVEDP (mmHg) and the RVEDP (mmHg) predicted by using a linear combination of 7 P-measurements.

a n a l y z e d for c o r r e l a t i o n w i t h t h e m e a n pulmonary wedge pressure (as an estimate of l e f t a t r i a l p r e s s u r e 27 a n d w i t h t h e l e f t ventricular end diastolic pressure. Only two measurements showed significant correlations with the mean pulmonary wedge J. ELECTROCARDIOLOGY, VOL. 8, NO. 2, 1975

The r e s u l t of t h e m u l t i p l e r e g r e s s i o n analysis using 15 P m e a s u r e m e n t s for the prediction of LVEDP and the order of importance of the P m e a s u r e m e n t s for the prediction of LVEDP is shown in Table 3. At the first step, the most important P parameter was the P(NEG)AZ (r = 0.363, p < 0.05). At the second step, the next most significant parameter added to the regression equation was the P(3/4)Z (r = 0.43, p < 0.01). The value of the multiple correlation coefficient and its significance increased until the fifth step. At this point, with five P parameters involved in the regression equation, the multiple correlation coefficient was r = 0.630 (p < 0.005). From the 5th to the 15th step, the multiple correlation coefficient increased, b u t the significance decreased due to decreasing number of degrees of freedom and the small sample size. At the last step the correlation was no longer significant. Fig. 3A displays in graph form the individual correlation between the P(NEG)AZ and the LVEDP. Fig. 3B shows the multiple correlation between the LVEDP and the atrial ECG by a linear combination of five most significant P m e a s u r e m e n t s .

108

BROHET ET AL

TABLE 3 Multiple Regression Analysis in Group II (Aortic Valve Disease): Left Ventricular End-Diastolic Pressure Predicted by Using 15 P Measurements (N=49).

HIGHEST CORRELATION COEFFICIENT 180

i62

Multiple correlation coefficient r = 0.682 95% confidence interval estimate: +_1,823 Rank of the ? variables: 1. P (NEG) AZ 2. P (3/4) Z 3. P(2/4) Z 4. P (MAX SPAT) 5. P (DUR) 6. P (POS) X 7. P (6/8) X 8. P (TIME)

9. P (MAX) H 16. P-R int. 11. P(2/4) EL 12. P (NEG) Z 13. P (AREA) Z 14. P (NEG) EL 15. P (MAX) Y

144-

vz Q_

126

tO8

~-..~,

9O

4.0

.~.~,';~.~_.

7.2

IO.5

.,

,,, *,

o

15.8 17.O 20.5 23.6 26.8 30.I

,

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35.4 36,7 40,0

MEASURED LVEDP

DISCUSSION In order to properly interpret the findings, a brief discussion of the SVEC III lead system employed in this study is necessary. The SVEC III lead system is one of the several corrected orthogonal lead systems in use in v e c t o r c a r d i o g r a p h y 3 e It h a s 14 electrodes as compared to the more widely used F r a n k lead system which has only seven electrodes .29 Burger has studied the relationship bet w e e n v a r i o u s o r t h o g o n a l leads (Burger, SVEC III, F r a n k and McFee Parungao). He found t h a t the SVEC III, the McFee Parungao and the F r a n k lead systems m a r k e d l y resemble each other, a~ Langner, who compared the SVEC III, the Frank, the Helm and the M c F e e - J o h n s t o n o r t h o g o n a l lead systems, also concluded t h a t the SVEC III and the F r a n k lead systems were similar and interchangeable in normal individuals and in a majority of abnormal subjects. 3~ Pipberger, who has done extensive studies with both the SVEC III and the F r a n k lead systems, has concluded t h a t the two lead systems show a very close relationship in their performance in man, for all practical purposes are interchangeable for, vector directions, and the amplitude values can be easily converted using a constant. 2'32 The use of more electrodes in the SVEC III s y s t e m is a d i s a d v a n t a g e when compared with the simpler system of Frank. However, mainly because of the use of more electrodes, Pipberger has found t h a t the SVEC III system is more accurate and reliable. 32 Furthermore, the SVEC III system is not as sensitive to slight variations in the placement of electrodes, which in the F r a n k system can produce m a r k e d changes in the magnitude and direction of recorded potentials. 33-35

LINEAR COMBINATION OF 5 MEASUREMENTS 52.2 // 27.1 9 f/j/

220

.

I

j 6.7

J

/"

I~

4.0

9

." L .

7.2

9

. -

,

J

. I

n

IO.5 158

-~i

i

L

I

17.O 20.5 25.6 26.9

i

3OJ

i

_

l

53.4 56,7 40.0

MEASURED LVEDP

Fig. 3:A. Group II: Aortic valve disease. Correlation graph between left ventricular end diastolic pressure: measured LVEDP (mmHg) and the P-measurement: P(NEG)AZ (negative values of degrees) having the highest individual correlation coefficient. B: Group II: Aortic valve disease. Correlation graph between the measured left ventricular end diastolic pressure: measured LVEDP (mmHg) and the LVEDP (mmHg) predicted by using a linear combination of the "best" five P-measurements.

One of the main problems in this study concerned the choice of the ECG variables to be included in the correlation analysis. The validity for the use of some P measurements as criteria for left atrial overload was assessed by t h e correlation of these m e a s u r e m e n t s J. ELECTROCARDIOLOGY, VOL. 8, NO. 2, 1975

P WAVE ABNORMALITIES

with the mean wedge pressure, commonly accepted as a reliable estimate of the mean left atrial pressure. However, it is recognized that the accuracy of this e s t i m a t i o n d e c r e a s e s when the mean wedge pressure is markedly e l e v a t e d Y In the present correlation analysis, some of the P measurements selected in a previous study s by means of a multidimensional a n a l y s i s for classification purposes were also used. As judged by their relative position in the multiple regression equation, they appear to be useful criteria for right and left atrial overload (Tables 2 and 3). However, other P measurements selected on the basis of their resemblance to known criteria of RAO and LAO in scalar electrocardiography, as well as some s p a t i a l p a r a m e t e r s , showed e q u a l l y good r e s u l t s in t h e r e g r e s s i o n analysis. In the present study, a significant correlation between the hemodynamic parameters of ventricular overload and P wave abnormalities in the orthogonal ECG has been demonstrated for both sides of the heart. The relationship between left ventricular dysfunction and electrocardiographic changes reflecting left atrial abnormality has previously been investigated2 '1~ Most studies dealing with the influence of left ventricular dysfunction on LAO are based on relatively acute conditions: congestive h e a r t failure, m y o c a r d i a l infarction, etc. ~2'14-~7 I n t h e s e cases the relationship is usually strong. This is not the case in conditions associated with chronic left ventricular dysfunction. Morris, studying the occurrence of LAO in aortic stenosis, has shown that the relationship is relatively poor in this condition. H The only good correlation was between the aortic systolic pressure gradient and the P terminal forces in V1 (Morris Index). However, this part of his study was limited to only 15 patients. It is of i n t e r e s t t h a t this a u t h o r found a n o r m a l mean left atrial pressure in eight of these 15 patients. In our study, the average value of the mean wedge pressure for the group of aortic valve disease patients was 13.75 mmHg. Ishikawa and Co-Workers, 8 in the study of a group of patients with hypertension and aortic stenosis, found that the usual criteria used in t h e d i a g n o s i s of LAO p e r f o r m e d rather poorly and the rate of recognition of LAO was only 19%. However, the rate of recognition increased with increase in the severity of left ventricular disease. Their performance was much better in the group of patients with mitral valve disease. One explanation for these findings m a y be t h e low p r e v a l e n c e of a c t u a l left a t r i a l a b n o r m a l i t y in left v e n t r i c u l a r d i s e a s e . Another explanation would be the existence J. ELECTROCARDIOLOGY, VOL. 8, NO. 2, 1975

109

of a different pathophysiologic mechanism in the development of LAO ~'secondary" to left ventricular overload than that in ~'primary" LAO as seen in mitral stenosis. It is possible t h a t t h e same m u l t i v a r i a t e classification analysis, if performed only on a group of patients with left ventricular overload without mitral valve disease, could have led to different criteria for LAO. In the present study, in the aortic valve disease group, the multiple regression technique was necessary to establish the existence of a relationship between decreased left ventricu l a r compliance and electrocardiographic changes of left atrial abnormality. O u t of 15 P m e a s u r e m e n t s , w h e n considered individually, only two parameters, the P(NEG)AZ and the P(AREA)Z, were significantly correlated with the left ventricular e n d d i a s t o l i c p r e s s u r e . The p a r a m e t e r , P(NEG)Z, which had been found a good cri: terion for left atrial overload and which correlated with the mean pulmonary wedge pressure, was not significantly correlated with the left ventricular end diastolic pressure. In the regression analysis the P(NEG)AZ is selected, at the first step, as the best predictor of LVEDP. It is of interest that the parameter P(NEG)Z, analog to the negative terminal forces of the P wave in V1, occupies only the 12th position in the sequence of importance. H o w e v e r , t h e c o m p o n e n t s of t h e s a m e parameter, i.e. P(3/4)Z and P(2/4)Z, occupy the second and the third position respectively. These three most important predictors are consistent with the commonly accepted ECG criteria for left atrial overload: increased left terminal forces of the P wave and posterior rotation of the P vectors. The spatial measurement, P(MAX SPAT), is the fourth most important parameter while the duration of the P wave occupies the fifth position. Various mechanisms have been suggested to explain the mode of action of chronic left v e n t r i c u l a r d y s f u n c t i o n on left a t r i u m . Nolan 36 demonstrated the occurrence of some degree of mitral regurgitation with reversed diastolic mitral gradient in cases of pure aortic regurgitation, leading to atrial dilatation and hypertrophy. Stott 37 showed that in aortic stenosis a stronger presystolic left atrial c o n t r a c t i o n s e c o n d a r y to d e c r e a s e d left v e n t r i c u l a r c o m p l i a n c e could lead to t h e development of atrial hypertrophy without the elevation of m e a n left atrial pressure. Yurasov 3s showed that in the acute stage of experimentally produced aortic stenosis in rabbits, the P wave changes (left deviation of the P axis) were different than those seen in the later more chronic stages (increased P voltage).

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It can be speculated that in later and more chronic stages, such as seen ~in relatively elderly patients with chronic aortic valve disease, d i f f e r e n t pathological c h a n g e s t a k e place in the left atrial wall. These might inc l u d e i n t r a - a t r i a l c o n d u c t i o n d e f e c t s or asymmetric hypertrophy in some parts of the left a t r i u m which, in t u r n , could lead to further changes in the P wave. This could partly explain the poore r results obtained when conventional ECG criteria of LAO are used in cases of chronic left ventricular overload. In the present study there is a better correlation b e t w e e n the r i g h t . v e n t r i c u l a r overload and electrocardiographic changes indicating right atrial overload. Out of nine P measurements, three were significantly correlated with the pulmonic systolic pressure gradient and six with the r i g h t v e n t r i c u l a r end d i a s t o l i c p r e s s u r e . These results seem to indicate that the principal factor responsible for the right atrial overload is the decrease of ventricular compliance as indicated by the rise in the right ventricular filling pressure rather than the right ventricular hypertrophy itself, as estim a t e d by t h e level of p u l m o n i c s y s t o l i c gradient. The six P measurements found to be significantly correlated with the right ventricular end diastolic pressure, generally agree with the accepted criteria of right atrial overload in the orthogonal electrocardiogram. 7 Thus, the P(POS)Z and the P(MAX)Z reflect the anterior displacement of the P loop in the horizontal plane, secondary to the increased anterior P vectors.

strength of the relationship between the right ventricular end diastolic pressure and the e l e c t r o c a r d i o g r a p h i c m e a s u r e m e n t s indicating right atrial overload. Two explanations can be offered for this apparent difference between the right and the left side of the heart: The group of patients with aortic valve disease was less homogenous than the group with pulmonic stenosis, representing various pathologic conditions (aortic stenosis, insufficiency or both). This group also represented a relatively more chronic situation where various mechanisms might be involved at various stages of the disease and a few patients had somewhat longer intervals between the VCG analysis and the catheterization procedure. These m a y partly account f o r the w e a k e r correlation between the hemodynamic and the electrocardiographic data in this group. In the pulmonic stenosis group, the patients were younger and the course of the disease was r e l a t i v e l y s h o r t e r b e c a u s e corrective surgery had usually been performed shortly after the onset of symptoms. Thus, the influence of right ventricular overload on right atrial function could be detected r e l a t i v e l y early in the course of the disease.

The P(MAX)Y and the P(POS)Y are equivalent to the increased amplitude of the P wave in the frontal plane and can be related to the tall and peaked upright P wave in leads II, III and aVF of conventional ECG. The P(MAX)F can be attributed to the vertical and rightward shift of the electrical axis of P wave in the frontal plane. However, it should be emphasized that the area under the positive part of the P wave in lead Z (P(POS)Z) and the amplitude of the Z component of the m a x i m u m spatial P vector (P(MAX)Z) are better individual parameters for recognition of right atrial overload than the P(MAX)Y, i.e. the Y component of the m a x i m u m spatial P vector, which is usually thought to represent the most sensitive criterion of right atrial overload in scalar electrocardiography. Also, on the basis of these results, the spatial P measurements (P(MAX SPAT)) could c o n t r i b u t e c o n s i d e r a b l y to the diagnosis of right atrial overload. The multivariate approach confirmed the

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