Digital echocardiography in myocardial infarction

Harvey Feigenbaum Distinguished ProJessor UJMedicine, Indiana University School of Medicine, Krannert Insritute of Cardiology, Indianupolis, USA

Abstract: Probably the most under-ntilised application of echocardiography is in patients wirh coronary artery disease (CAD). This under-utilisation is striking since echocardiography can be very valuable in evaluating the natural history and therapy of CAD. One reason why echocardiography is not being utilised to its fullest is because of the reliance on videotape to record and display echocardiograrns. This medium is time consuming and inconvenient for clinicians to review studies, it is not ideal for detecting subtle wall motion abnormalities, and videotape is impractical for comparing serial studies. Recording and storing echocardiograms on a digital medium overcomes these difficulties. Digital cine loops of single cardiac cycles provide great versatility. Mulriple views or studies can be displayed simultaneously, subtle changes in wall motion are more easily detected and different views, or serial studies, can be readily compared. Such images can be displayed on computers on rhe ward or in the coronary care unit (CCU) and be available 24 hours a day, seven days a week at the convenience of the clinician. One does not need to find a recording on a two hour videotape, which may be in the ultrasound instrument, and one can view the exam in 30 sec instead of 5 to 10 min. Regional and global left ventricular function is one of the most important manifestations of CAD. With new therapeutic efforts at restoring myocardial function and limiting infarct expansion, assessing L V function is more imporrant than ever. Digital echocardiography is an extremely practical and convenient way for clinicians to obtain this information. (Ausr NZ J Med 1992; 22: 521-526.) K e y words: Digital echocardiography, myocardial injarction.

INTRODUCTION robably the most under-utilised application of echocardiography is in patients with coronary artery disease (CAD). The current consensus among cardiologists in Australia and New Zealand is that no more than 25% of patients in the coronary care unit ( c c u ) warrant an echocardiogram. This under-utilisation is striking since echocardiOgraPhYcan be very effective in evaluating patients with myocardial infarction (MI).

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ECHOCARDIOGRAPHY IN PATIENTS WITH MI There are multiple reasons why echocardiography can lie so useful in these patients. First, two-

dimensional echocardiography obtains multiple tomographic views of the heart, especially the left ventricle (LV).' Figure 1 demonstrates four common two-dimensional echocardiographic views. These views include the parasternal short-axes (SAX) and long-axes (LAX) and the apical two and four chambers views. T h e LAX, two-chamber (2 CH) and four-chamber (4 CH) views are essentially longitudinal tomographic slices of the heart running from base to apex. The SAX view is orthogonal to the other three. Figure 1 shows the relationship of the four views and how the longitudinal views relate with the SAX and divide it into six segments. In many ways a recording of these four views gives a three-dimensional appreciation of the LV.

Reprint requesrs to: Dr Harvey Feigenbaum, Indiana University School of Medicine, Krannert Institute of Cardiology, Indianapolis, USA. DIGITAI. ECHOCARDIOGRAPHY IN MYOCARDIAL. INFARCTION

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- Axis LX I

Long- A x i s

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Four Chamber

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LAD ( P R O X )

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away from the left ventricular cavity). In the LAX view the mid and distal septum is abnormal. The proximal septum continues to thicken and contracts towards the left ventricular cavity. This examination indicates that the LAD is obstructed, however, the first septal perforator is still receiving blood since the proximal septum contracts normally. The SAX again confirms that the LAD is not providing sufficient blood for the muscle supplied by it to contract normally. The opposing walls, the inferiorposterior and posterior-lateral, are moving correctly. Figure 3 shows an apical 4 CH view of the same patient as in Figure 2. Again, the distal LAD regional distribution is failing to move properly. In addition, in diastole one can see that the proximal interventricular septum has full thickness, but the distal septum and apex are very thin because the wall is carr red.^,^ This type of observation is crucial because there is no prospect that this thin, scarred akinetic muscle will ever contract, even with reperfusion. There is a major clinical need to detect irreversibly damaged muscle. The echocardiographic diagnosis of scar is extremely reliable in making this diagnosis.

Figure I : Diagram illustrating the interrelationship of four commonly used two-dimensional echocardiographic views a n d t h e areas of coronary artery perfusion. 2 C = 2-chambers; 4C = 4-chambers; L A D = Iefi anterior descending; L A D prox = proximal left anterior descending; LCX = left circumflex artery; L X = long-axis; PDA = posterior descending artery; RCA = right coronary artery. (From: Feigenbaum 11. Echocardiography, fourth edition. Philadelphia, PA: Lea and Febiger, 1986.)

COMPLICATIONS OF MI Every known complication of M I can be detected with echocardiography. In many ways the patient, whose echocardiogram is shown in Figures 2 and 3, has marked scarring and dilatation of the distal

Second, two-dimensional echocardiography can predict coronary anatomy by examining regional segments on the two-dimensional echocardiogram.'-3 The left anterior descending artery (Figure 1, LAD) always lies between the anterior free walls of the left and right ventricles. T h e posterior descending artery (PDA) is opposite and lies in the groove between the posterior free walls of the right and lefi ventricles. T h e muscle straddling those two arteries is perfused by those vessels. T h e left circumflex (LCX) supplies the lateral and posterior walls. I n the parasternal LAX the anterior septum is always perfused by the LAD and the proximal septum is the muscle supplied by the first septal perforator. Each view provides information as to which artery may or may not be perfusing the myocardium properly. Figure 2 demonstrates a two-dimensional echocardiogram of a patient with CAD and an obstruction in the mid LAD. In the LAX and SAX systolic frames one can appreciate which segments are moving normally (arrowheads towards the left ventricular cavity), and abnormally (arrowheads

Figure 2: LAX and SAX views of a patient with an old anterior MI. 'The distal anterior septum is akinetic (reversed arrowheads). T h e remainder of the myocardium contracts normally (arrowheads pointing towards the cavity). (From: Feigenbaum H. Echourdiography, 4th eCi, Philadelphia, PA: Lea and Febiger, 1986.)

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segmental RV wall motion abnormalities. Pericardial effision is also an easily detected complication. The echocardiographic diagnosis of complications of M I is fairly well recognised and probably represents the 25% of patients with M I who have echocardiograms in the C C U in Australia and New Zealand. However, probably the most important current use of echocardiography in cardiology is not as well recognised. The major advance in the therapy of acute M I is reperfusion of the occluded artery. Although the emphasis thus far has been merely to open the artery, either with thrombolytic drugs or angioplasty, a primary objective should be to restore or minimise the amount of myocardial damage. Figure 4 demonstrates another patient with an obstruction of the LAD. In this case the obstruction is acute and the patient had an acute MI. On 1 March 1984 the interventricular septum did not move; it was the same thickness both in diastole and systole. The entire septum was involved which would indicate an obstruction in the LAD proximal

Figure 3: Apical 4 CH view of the same patient as seen in Figure 2. The apical half of the left ventricle is dilated and the apical septum is thin and non-functioning (reversed arrowheads). There is stagnant blood within the apex, exhibited by a cloud of echoes within the ventricular cavity. (From: Feigenbaum H. Echocardiography, 4th ed. Philadelphia, PA: Lea and Febiger, 1986.)

septum and apex which constitutes an aneurysm.6 The stagnant blood is noted as a cloud of echoes within the cavity of the apical two thirds of the ventricle and is a precursor to mural thrombi. Such clots are readily seen on two-dimensional echocardiography.' Every type of aneurysm, including pseudoaneurysm; is also detectable with echocardiography. Complications, such as mitral regurgitation' and ventricular septal defect," are easily diagnosed with spectral or colour flow Doppler. Right ventricular infarction can be identified by a dilated right ventricle (RV) with DIGITAL ECHOCARDIOGRAPHY IN MYOCARDIAL INFARCTION

Figure 4: LAX two-dimensional echocardiograms of a patient who had coronary angioplasty of the LAD within two hours following acute MI. Immediately following the angioplasty, the interventricular septum (S) was akinetic and failed to thicken (S, SYST). Four days later the septal motion returned to normal. In systole, the septum (S) moves (arrowheads) and thickens (arrows) normally. (From: Feigenbaum H . Echocardiography, 4th ed. Philadelphia, PA: Lea and Febiger, 1986.) Aust NZ J Med 1992; 22

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to the first septal perforator. In addition, the acuteness of this obstruction is indicated by the fact that septal thickness is still normal in diastole and is not thin as seen in Figure 3. The patient was taken to the cardiac catheterisation laboratory, and angioplasty was used to open the LAD. Four days later septal motion returned to normal. There was thickening of the septum from diastole to systole.

LEFT VENTRICULAR FUNCTION The ability to monitor left ventricular function after coronary reperfusion should be one of the major uses of echocardiography in patients with acute MI.II-IS Echocardiography is particularly well suited for this assessment because of its ability to examine regional left ventricular function. In addition, the restoration of wall function is variable. The ability of echocardiography to examine the patient at any time, in the emergency room, the CCU, or office, is vital in determining how much muscle returns. Stunned myocardium is a well recognised phenomenon. Stunning can vary from hours to weeks. Only a technique such as echocardiography has the versatility to make such a determination. Echocardiography is not only indicated for detecting complications and for following reperfusion. Virtually every patient with an acute MI would benefit by knowing where, how much, and It is also how severe is the myocardial important to know the state of the myocardium not involved with this infarction. Is the muscle appropriately hyperkinetic? Is there a previously unsuspected infarction? Is there underlying hypertrophy? Is the LV dilated? In addition, a baseline echocardiogram is valuable because infarct expansion can frequently occur and possibly can be prevented. If a new ischaemic event occurs, it is important to know if left ventricular function is deteriorating. It must be remembered that the state of the LV is the most important determinant of symptoms and prognosis.

DIGITAL ECHOCARDIOGRAPHY The use of echocardiography to follow the natural history and the efficacy of therapy in patients with acute M I is not new. As noted in Figure 4 at Indiana University this practice has been in place since 1984. The question is why is this technique so popular at our institution and is still not widely performed in most other hospitals? One reason why echocardiography is not being utilised fully is because of the reliance on videotape to record and display echocardiograms. This medium is time consuming and inconvenient for referring clinicians to review studies. It is not ideal for detecting subtle wall motion abnormalities Aust KZ J Med 1992; 22 524

and is impractical for comparing serial studies. With videotape a given examination is one of many of a two hour tape. Searching a tape for a study in question is time consuming. Each examination may take five to 15 minutes to review. Furthermore, it is impossible to examine two different echocardiograms simultaneously. One must review a videotape and remember the individual segments and then compare them mentally with another study on a second tape. This approach is so impractical that it is virtually never done. As a result, serial echocardiograms are compared by visualising the current study and comparing it with the previous echocardiographic report. One would not utilise such an approach with any other technique. When comparing electrocardiograms, cineangiograms, or chest films, one will always look at the actual examinations. We should do the same with echocardiography. One of the main reasons why echocardiography is so popular in examining patients with CAD at Indiana University is that we record the echocardiograms digitally as well as using videotape. Although videotape is still a useful medium for recording a vast amount of echocardiographic information, the digital examination is convenient to show to referring physicians for a quick review of the echocardiogram and to compare multiple studies and for the analysis of subtle wall motion abnormalities. Digital echocardiography requires frame grabbers to digitise the images and display them in a cine loop.22 Figure 5 illustrates a standard twodimensional echocardiograph with a frame grabber system mounted on the top. T h e strip chart recorder has been removed, and the tape recorder, which normally is on top of the instrument, is in the space previously occupied by the strip chart recorder. Although the digital views are obtained sequentially, they can be displayed simultaneously. Figure 6 demonstrates a quad screen digital echocardiogram of a common four view examination - the LCX, SAX, 4C and 2C echocardiograms. All four views can be reviewed simultaneously which enhances the ability to assess wall motion and compare one view with another. In addition, these views can be compared with similar studies made on a different day. U p to four examinations can be compared in this fashion. Thus, subtle changes in wall motion can be seen which would be impossible with videotape. Another advantage of digital echocardiography is that the images can be displayed on a computer terminal almost anywhere in the hospital. Figure 7 demonstrates this in the C C U a t University Hospital. This terminal is connected to a computer network where the echocardiograms reside inDIGITAL ECHOCARDIO(;R.APHY IS .21YOCAKl)lrlL INFAKCTION

Figitre 7: Computer terminal in the C C U whereby physicians are able to review echocardiograms at any time of the day or night. (From: Feigenbuum H. Echocardiography, 5rh ed. Philadelphia, PA: Lea and Febiger, in press.)

Figure 5: Standard echocardiograph with a frame grabber device mounted on the top. (From Feigenbaum H . Echocurdiogruphy, 5th ed. Philadelphia, PA. Lea and Febiger, in press.)

Figure 6: Digitally acquired four echocardiographic views displayed as a quad screen. LX = longaxis; SX =short axis; 4 C =four chamber; 2C =two chamber; 1.V = left ventricle; A 0 = aorta; LA = left arrium; RV =right ventricle; RA = right atrium. (From: Feigenbaum 11. Echocardiography, 51h ed. Philadelphia, PA: Lea and Febiger, iii press.)

.definitely. Thus, any physician can review echocardiograms of an individual 24 hours a day, DIGITAL ECHOCARDIOGRAPHY IN MYOCARDIAI. INFARCTION

seven days a week. The current echocardiogram and any previous echocardiograms can be seen at any given time. Such a technique makes echocardiography convenient and practical for daily use. It is actually easier to see an echocardiogram than to find the patient's electrocardiograms or chest films. The echocardiographic reports are also in the computer system and are readily available for the clinicians. Packaging of any product or service is important. The total reliance of echocardiography on videotape has disadvantages for conveying echocardiographic data to the clinician. Computer technology has made echocardiographic information one of the most accessible pieces of data. Since the echocardiograph can go to the bedside and the examination can be performed at any time, the information should also be available under the same circumstances. One should not have to wait for a formal report, which may come days after the actual examination. The clinician should be able to look at the. echocardiogram. Frequently he or she may detect something that the echocardiographer may have missed because of lack of clinical information. In this way, by allowing the clinician to view the echocardiograms, the digital approach provides quality control. T h e clinician should be able to see any abnormality and appreciate its presence or absence. If the study is of such poor quality that the clinician cannot see the abnormality mentioned in a report, then he or she should not believe the report. Furthermore, by looking at the examination, clinicians may detect abnormalities that may have 525 Aust NZ J M e d 1992; 22

been missed by the echocardiographer. For all of these reasons digital echocardiography is becoming increasingly important in this diagnostic modality. It has become a major factor in communicating with referring physicians, in handling echocardiographic information and in managing patients with acute

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