137
THE USE OF M-MODE ECHOCARDIOGRAPHY I N ISCHAEMIC HEART DISEASE DwG,
GIBSON,
From Brompton Hospital, London SW3 6HP
The c h a r a c t e r i s t i c feature o f l e f t v e n t r i c u l a r involvement i n ischaemic h e a r t disease i s i t s regional d i s t r i b u t i o n due t o t h e non-uniform nature o f t h e coronary a r t e r y lesions. This r e s u l t s i n a number o f disturbances o f function, o f which the best recognized are a regional reduction i n w a l l movement during systole, aneurysm formation, popularly supposed t o be accompanied by paradoxical movement and f i n a l l y , a generalized reduction i n w a l l movement 'accompanied by an increase i n c a v i t y size, so-called ischaemic cardiomyopathy. These abnormalities a l l have i n comnon a disturbance i n t h e o v e r a l l amplitude o r d i r e c t i o n o f wall movement, and t h e i r analysis i n i n d i v i d u a l p a t i e n t s i s usually based merely on inspection o f angiograms. Another type o f i n t e r f e rence w i t h the a c t i o n o f the l e f t v e n t r i c l e may occur i n ischaemic heart d i sease, however, i n which t h e o v e r a l l amplitude and d i r e c t i o n o f wall movement are both normal, b u t i n which i t s timing i s disturbed. This i s much harder t o characterize by d i r e c t inspection o f t h e angiogram, and y e t may have e f f e c t s on l e f t v e n t r i c u l a r f u n c t i o n out o f a l l proportion t o t h e ext e n t o f myocardium involved by causing incoordinate contraction. M-mode echocardiography allows l e f t v e n t r i c u l a r endocardium t o be unequivocally ident i f i e d throughout the cardiac cycle, and i t s movement recorded w i t h a frequency response considerably superior t o t h a t o f c u r r e n t angiographic techniques so t h a t i t i s an e x c e l l e n t method f o r the analysis o f these disturbances. I n f i g u r e 1 i s shown the echocardiogram o f a p a t i e n t who developed a low output s t a t e a f t e r cardiac surgery. I t w i l l be seen t h a t though the amplitude o f septa1 movement i s reduced, as i s f r e q u e n t l y t h e case a f t e r open heart surgery, t h a t o f p o s t e r i o r w a l l movement i s normal. However, i t i s apparent from t h e m i t r a l valve echo, t h a t v i r t u a l l y a l l t h e increase i n transverse diameter t h a t occurs does so before t h e onset o f m i t r a l valve opening and therefore before the onset o f f i l l i n g . This increase i n l e f t v e n t r i c u l a r dimension thus represents no more than a change i n c a v i t y shape during theperiod o f isovolumic relaxation, and as such l i k e l y t o have cont r i b u t e d t o poor o v e r a l l l e f t v e n t r i c u l a r performance. Wall movement i n t h i s
138
Fig 1 . Echocardiogram showing left ventricular cavity and dtral valve echoes from a patient who developed a low cardiac output a f t e r surger& Mitral valve opening is delayed with respect to wall movement. p a t i e n t i s abnormal not i n terms o f i t s magnitude o r d i r e c t i o n , but i n i t s timing, and i t has been detected by considering the dimension, not i n i s o l a t i o n , but by c o r r e l a t i n g i t w i t h events r e f e r a b l e t o the f u n c t i o n o f t h e c a v i t y as a whole, here the s t a r t o f f i l l i n g . This method has proved a sens i t i v e one, and abnormalities o f isovolumic r e l a x a t i o n have been detected i n patients w i t h coronary a r t e r y disease, where they c o r r e l a t e c l o s e l y w i t h the presence of regional reduction i n wall movement seen on angiography ( 3 ) .
The onset of m i t r a l valve opening i s o n l y one o f several ways i n which the timing o f o v e r a l l l e f t v e n t r i c u l a r function can be assessed. A more versat i l e one i s t o use the l e f t v e n t r i c u l a r pressure trace t o construct pressure-dimension loops. The normal pressure-dimension loop i s approximately rectangular (Fig 2), w i t h l i t t l e change i n dimension during the upstroke and downstroke o f the pressure trace, which approximate i n timing t o the periods o f isovolumic contraction and relaxation. Conversely, during eject i o n and f i l l i n g , changes i n pressure are smaill. The rectangular configurat i o n o f the loop has functional significance i n t h a t the area o f the loop represents the actual work done per u n i t area on the c i r c u l a t i o n by myocardium i n the region studied, while the maximum work t h a t could have been done by the myocardium operating over t h e same range o f pressure and
I *Y
150.0
T
11. f
i
*.Ol 2.0
OuyTERD1
4-0
Fig 2. Pressure-dimension loop porn a normal subject
Fig 3 . Pressure-dimension loop from a patient with ischaemic heart disease
.
dimension is given by the product of the two, ia. by the area of the rectangle that just encloses the loop. The ratio of loop area to that of the rectangle thus represents the efficiency of transfer of mechanical energy generated by the myocardium to the circulation. The pressure-dimension loop from a patient with ischaemic heart disease is shown in fig 3. It is apparent that the loop is distorted, due mainly to dimension changes during the two isovolumic periods, causing a drop in the efficiency of energy transfer to less than 50%. Pressure-dimension loops can thus be used t o demonstrate incoordinate contraction, and when . abnormalities of this sort occur during the isovolumic periods they may have considerable functional significance. Unfortunately, measurement of left ventricular pressure requires cardiac catheterization. In order to detect abnormal wall movement however, it is not the absolute value o f pressure that is required but only the timing of the upstroke and the downstroke, and these latter have been shown to be very close to the corresponding events on the apexcardiogram (2.5). We have therefore explored the use of loops constructed from left ventricular dimension and apexcardiogram which have proved to be rectangular in all of more than 50 normal subjects studied. In the presence of mitral regurgitation, there is a reduction in dimension during the upstroke, and of aortic regurgitation, there is an increase in dimension during the downstroke, as would be expected from the basic haemodynamic disturbances in these conditions. In many patients with ischaemic heart disease similar abnormali-
I4U
ISCHAEMIC HEART DISEASE
I S C H I E M I C HEART DISEASE
Ps0
APEX CARDIOGRAM
LENGTHENING
CARDIOGRAM
I
-2-1
-
LENGTHENING RATE 8EC-l
-4 1
,
&&2 Fo~G~ ~ ~ ~ DIMENSION CM/SEC
n
-1
:
-,
CHANGE OOF ~ RATE DIMENSIW
~
~
~
w
&
,
~
cdstc
DlMENS ION CM
3.5
CM
0
TIME
SEC
1.0
F i g 4 . Apexcardiogram echo dimension loop
from a patient w i t h ischaemic heart disease. There i s a reduction i n dimension dur i n g the upstroke, and an increase i n dimension during the downstroke of theapexcardiogram.
5L
CM0
TIM
SEC
0.9
F i g 5 . Apexcardiogram echo dimension loop another patient trith ischaemic heart disease. The abnormalities are the reverse of those s h a m i n f i g 4 .
mrn
t i e s may also be found i n the absence o f v a l v u l a r r e g u r g i t a t i o n , examples being given i n f i g 4 and 5. I n these circumstances, a reduction i n dimension during the upstroke o f the apexcardiogram represents an abnormality o f isovolumic contraction, and during t h e downstroke, one o f e a r l y r e l a x a t i o n . Such abnormalities can a1 so be detected by s u i t a b l e analysis o f angiograms (3). (Prewi tt and Brown 1976) Using these methods, angiograms and apexcardio-
gram-echo dimension r e l a t i o n s were compared i n 50 p a t i e n t s w i t h ischaemic heart disease. I n t h i s study (Doran, T r a i l l , Gibson and Brown unpublished), both s p e c i f i c i t y and s e n s i t i v i t y o f t h e echo method were found t o be g r e a t e r
than 80 % with respect to the angiograms. The method has also been of value in detecting incoordinate contraction in patients with valvular heart disease or cardiomyopathy in the absence of coronary artery disease. It is useful in the follow-up of patients after saphenous by pass grafting, when successful surgery may be followed by a return of the .loop towards normal. Finally, it can detect postoperative left ventricular disease after valve replacement, and thus monitor the quality of myocardial preservation (4). This approach clearly does not replace left ventricular angiography and coronary arteriography as a means of studying patients with ischaemic heart disease. However, using traditional methods, the nature of the complex physiological disturbance to left ventricular function may not be apparent from delineation of a series of anatomical abnormalities, and it is in this field that the method appears to have value. It is non-invasive, so that repeated observations can be made in individual patients, and it can be performed in circumstances, such as the postoperative ward, where cardiac catheterization would not be possible. It is a simple way of detecting the presence of incoordinate contraction in patients with any type of heart disease, and of following changes due to therapy or progression of underlying pathological processes.
REFERENCES 1. UPTON, M.T., GIBSON, D.G. and BROWN, D.J.: Echocardiographic assessment o f abnormal left ventricular relaxation in man. Brit. Heart J. 38:1001, 1976.
2. GIBSON, D.G. and BROWN, D.J.: Assessment of left ventricular systolic function from simultaneous left ventricular echocardiographic and pressure measurements. Brit. Heart J. 38:8, 1976. 3. MANOLAS, J., RUTISHAUSER, W. and WIRZ, P . : Time relation between apexcardiogram and left ventricular events using simultaneous high fidelity tracings in man. Brit. Heart J. 37:1263, 1975.
4. VENCO, A., GIBSON, D.G. and BROWN, D.J.: Relation between apexcardiograms and changes in left ventricular pressure and dimension. Brit. Heart J 39: 117, 1977. 5. GIBSON, D.G., PREWITT, T.A. and BROWN, D.J.: Analysis of left ventricular wall movement during isovolumic relaxation and its relation to coronary artery disease. Brit. Heart J. 38:1010, 1976.
THE USE OF M-MODE ECHOCARDIOGRAPHY I N ISCHAEMIC HEART DISEASE DwG,
GIBSON,
From Brompton Hospital, London SW3 6HP
The c h a r a c t e r i s t i c feature o f l e f t v e n t r i c u l a r involvement i n ischaemic h e a r t disease i s i t s regional d i s t r i b u t i o n due t o t h e non-uniform nature o f t h e coronary a r t e r y lesions. This r e s u l t s i n a number o f disturbances o f function, o f which the best recognized are a regional reduction i n w a l l movement during systole, aneurysm formation, popularly supposed t o be accompanied by paradoxical movement and f i n a l l y , a generalized reduction i n w a l l movement 'accompanied by an increase i n c a v i t y size, so-called ischaemic cardiomyopathy. These abnormalities a l l have i n comnon a disturbance i n t h e o v e r a l l amplitude o r d i r e c t i o n o f wall movement, and t h e i r analysis i n i n d i v i d u a l p a t i e n t s i s usually based merely on inspection o f angiograms. Another type o f i n t e r f e rence w i t h the a c t i o n o f the l e f t v e n t r i c l e may occur i n ischaemic heart d i sease, however, i n which t h e o v e r a l l amplitude and d i r e c t i o n o f wall movement are both normal, b u t i n which i t s timing i s disturbed. This i s much harder t o characterize by d i r e c t inspection o f t h e angiogram, and y e t may have e f f e c t s on l e f t v e n t r i c u l a r f u n c t i o n out o f a l l proportion t o t h e ext e n t o f myocardium involved by causing incoordinate contraction. M-mode echocardiography allows l e f t v e n t r i c u l a r endocardium t o be unequivocally ident i f i e d throughout the cardiac cycle, and i t s movement recorded w i t h a frequency response considerably superior t o t h a t o f c u r r e n t angiographic techniques so t h a t i t i s an e x c e l l e n t method f o r the analysis o f these disturbances. I n f i g u r e 1 i s shown the echocardiogram o f a p a t i e n t who developed a low output s t a t e a f t e r cardiac surgery. I t w i l l be seen t h a t though the amplitude o f septa1 movement i s reduced, as i s f r e q u e n t l y t h e case a f t e r open heart surgery, t h a t o f p o s t e r i o r w a l l movement i s normal. However, i t i s apparent from t h e m i t r a l valve echo, t h a t v i r t u a l l y a l l t h e increase i n transverse diameter t h a t occurs does so before t h e onset o f m i t r a l valve opening and therefore before the onset o f f i l l i n g . This increase i n l e f t v e n t r i c u l a r dimension thus represents no more than a change i n c a v i t y shape during theperiod o f isovolumic relaxation, and as such l i k e l y t o have cont r i b u t e d t o poor o v e r a l l l e f t v e n t r i c u l a r performance. Wall movement i n t h i s
138
Fig 1 . Echocardiogram showing left ventricular cavity and dtral valve echoes from a patient who developed a low cardiac output a f t e r surger& Mitral valve opening is delayed with respect to wall movement. p a t i e n t i s abnormal not i n terms o f i t s magnitude o r d i r e c t i o n , but i n i t s timing, and i t has been detected by considering the dimension, not i n i s o l a t i o n , but by c o r r e l a t i n g i t w i t h events r e f e r a b l e t o the f u n c t i o n o f t h e c a v i t y as a whole, here the s t a r t o f f i l l i n g . This method has proved a sens i t i v e one, and abnormalities o f isovolumic r e l a x a t i o n have been detected i n patients w i t h coronary a r t e r y disease, where they c o r r e l a t e c l o s e l y w i t h the presence of regional reduction i n wall movement seen on angiography ( 3 ) .
The onset of m i t r a l valve opening i s o n l y one o f several ways i n which the timing o f o v e r a l l l e f t v e n t r i c u l a r function can be assessed. A more versat i l e one i s t o use the l e f t v e n t r i c u l a r pressure trace t o construct pressure-dimension loops. The normal pressure-dimension loop i s approximately rectangular (Fig 2), w i t h l i t t l e change i n dimension during the upstroke and downstroke o f the pressure trace, which approximate i n timing t o the periods o f isovolumic contraction and relaxation. Conversely, during eject i o n and f i l l i n g , changes i n pressure are smaill. The rectangular configurat i o n o f the loop has functional significance i n t h a t the area o f the loop represents the actual work done per u n i t area on the c i r c u l a t i o n by myocardium i n the region studied, while the maximum work t h a t could have been done by the myocardium operating over t h e same range o f pressure and
I *Y
150.0
T
11. f
i
*.Ol 2.0
OuyTERD1
4-0
Fig 2. Pressure-dimension loop porn a normal subject
Fig 3 . Pressure-dimension loop from a patient with ischaemic heart disease
.
dimension is given by the product of the two, ia. by the area of the rectangle that just encloses the loop. The ratio of loop area to that of the rectangle thus represents the efficiency of transfer of mechanical energy generated by the myocardium to the circulation. The pressure-dimension loop from a patient with ischaemic heart disease is shown in fig 3. It is apparent that the loop is distorted, due mainly to dimension changes during the two isovolumic periods, causing a drop in the efficiency of energy transfer to less than 50%. Pressure-dimension loops can thus be used t o demonstrate incoordinate contraction, and when . abnormalities of this sort occur during the isovolumic periods they may have considerable functional significance. Unfortunately, measurement of left ventricular pressure requires cardiac catheterization. In order to detect abnormal wall movement however, it is not the absolute value o f pressure that is required but only the timing of the upstroke and the downstroke, and these latter have been shown to be very close to the corresponding events on the apexcardiogram (2.5). We have therefore explored the use of loops constructed from left ventricular dimension and apexcardiogram which have proved to be rectangular in all of more than 50 normal subjects studied. In the presence of mitral regurgitation, there is a reduction in dimension during the upstroke, and of aortic regurgitation, there is an increase in dimension during the downstroke, as would be expected from the basic haemodynamic disturbances in these conditions. In many patients with ischaemic heart disease similar abnormali-
I4U
ISCHAEMIC HEART DISEASE
I S C H I E M I C HEART DISEASE
Ps0
APEX CARDIOGRAM
LENGTHENING
CARDIOGRAM
I
-2-1
-
LENGTHENING RATE 8EC-l
-4 1
,
&&2 Fo~G~ ~ ~ ~ DIMENSION CM/SEC
n
-1
:
-,
CHANGE OOF ~ RATE DIMENSIW
~
~
~
w
&
,
~
cdstc
DlMENS ION CM
3.5
CM
0
TIME
SEC
1.0
F i g 4 . Apexcardiogram echo dimension loop
from a patient w i t h ischaemic heart disease. There i s a reduction i n dimension dur i n g the upstroke, and an increase i n dimension during the downstroke of theapexcardiogram.
5L
CM0
TIM
SEC
0.9
F i g 5 . Apexcardiogram echo dimension loop another patient trith ischaemic heart disease. The abnormalities are the reverse of those s h a m i n f i g 4 .
mrn
t i e s may also be found i n the absence o f v a l v u l a r r e g u r g i t a t i o n , examples being given i n f i g 4 and 5. I n these circumstances, a reduction i n dimension during the upstroke o f the apexcardiogram represents an abnormality o f isovolumic contraction, and during t h e downstroke, one o f e a r l y r e l a x a t i o n . Such abnormalities can a1 so be detected by s u i t a b l e analysis o f angiograms (3). (Prewi tt and Brown 1976) Using these methods, angiograms and apexcardio-
gram-echo dimension r e l a t i o n s were compared i n 50 p a t i e n t s w i t h ischaemic heart disease. I n t h i s study (Doran, T r a i l l , Gibson and Brown unpublished), both s p e c i f i c i t y and s e n s i t i v i t y o f t h e echo method were found t o be g r e a t e r
than 80 % with respect to the angiograms. The method has also been of value in detecting incoordinate contraction in patients with valvular heart disease or cardiomyopathy in the absence of coronary artery disease. It is useful in the follow-up of patients after saphenous by pass grafting, when successful surgery may be followed by a return of the .loop towards normal. Finally, it can detect postoperative left ventricular disease after valve replacement, and thus monitor the quality of myocardial preservation (4). This approach clearly does not replace left ventricular angiography and coronary arteriography as a means of studying patients with ischaemic heart disease. However, using traditional methods, the nature of the complex physiological disturbance to left ventricular function may not be apparent from delineation of a series of anatomical abnormalities, and it is in this field that the method appears to have value. It is non-invasive, so that repeated observations can be made in individual patients, and it can be performed in circumstances, such as the postoperative ward, where cardiac catheterization would not be possible. It is a simple way of detecting the presence of incoordinate contraction in patients with any type of heart disease, and of following changes due to therapy or progression of underlying pathological processes.
REFERENCES 1. UPTON, M.T., GIBSON, D.G. and BROWN, D.J.: Echocardiographic assessment o f abnormal left ventricular relaxation in man. Brit. Heart J. 38:1001, 1976.
2. GIBSON, D.G. and BROWN, D.J.: Assessment of left ventricular systolic function from simultaneous left ventricular echocardiographic and pressure measurements. Brit. Heart J. 38:8, 1976. 3. MANOLAS, J., RUTISHAUSER, W. and WIRZ, P . : Time relation between apexcardiogram and left ventricular events using simultaneous high fidelity tracings in man. Brit. Heart J. 37:1263, 1975.
4. VENCO, A., GIBSON, D.G. and BROWN, D.J.: Relation between apexcardiograms and changes in left ventricular pressure and dimension. Brit. Heart J 39: 117, 1977. 5. GIBSON, D.G., PREWITT, T.A. and BROWN, D.J.: Analysis of left ventricular wall movement during isovolumic relaxation and its relation to coronary artery disease. Brit. Heart J. 38:1010, 1976.
