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Abnormal exercise electrocardiogram in an asymptomatic person
International
Journal
of Cardiology
44 (1994) 97-99
Commentary
Abnormal exercise electrocardiogram asymptomatic person
in an
S.R. Underwood National
Heart and Lung Institute,
(Received
8 March
1993; revision
Juneja and Wasir [1] remind us that exercise electrocardiography should not be used to screen for coronary artery disease in individuals at low risk of the disease. Despite this, we continue to see asymptomatic subjects with an ‘abnormal’ exercise electrocardiogram, and the problem is more common when there is a financial incentive to offer such screening. Although the asymptomatic patient with severe coronary artery disease is a reality, it is easy not to set the potential benefit to this individual against the harm inflicted by further investigations such as myocardial perfusion scintigraphy and coronary arteriography on many other subjects. It therefore behoves those who perform exercise electrocardiography in low-risk subjects to have a plan of further management and we should welcome the discussion provoked by this article. An important aspect of minimising the damage is to interpret the exercise electrocardiogram strictly and to maximise specificity, even if this is at the expense of sensitivity. A large proportion of low risk subjects who are judged to have an abnormal ST segment response to exercise and who are referred for further investigation have a down-sloping PQ segment and an upsloping ST segment. This suggests that the perceived abnormality is the 0 1994 Elsevier Science Ireland Ol67-5273/94/$07.00 SSDl 0167-5273(93)01952-T
Dovehouse St. London, S W3 6L Y, UK
accepted
26 August
1993)
result of baseline variation arising from atria1 repolarisation [2]. If the abnormal ST segment is required to be planar or down-sloping, it is likely that many false positives and hence the need for further investigations could be avoided. Perhaps the most interesting point for discussion is the inclusion of fluoroscopy in the proposed algorithm. Any technique that can demonstrate abnormalities of the arterial wall is of interest because of the possibility of detecting disease at an early stage, before obstruction to coronary flow produces symptoms. Other techniques that might be considered include magneticresonance imaging [3] and intravascular ultrasound [4], although the latter could not be considered a screening test. Coronary calcification seen on tine fluoroscopy is a frequent companion of advanced coronary artery disease. Ultrafast Xray computed tomography has confirmed this Iinding and has shown an increasing incidence of calcification in asymptomatic subjects with age [5]. A relationship between coronary calcification and future cardiac events has not however been demonstrated. Until the significance of an abnormal finding is clarified therefore, it seems premature to include screening for coronary calcification in the algorithm presented, and it is difficult to
Ltd. All rights reserved.
S. R
98
lJndrrwood/ ht. J. Cardiol. 44 ( 1994) 97-99
I
1 High risk
Not high risk
Fig. I. Clinical algorithm
for the management
of the asymptomatic
justify coronary arteriography because of calcification alone [6]. The role of myocardial-perfusion imaging also deserves comment. It is important to distinguish the diagnosis of obstructive coronary artery disease from an assessment of risk once the diagnosis is made. In diagnostic terms, perfusion imaging is more sensitive and specific than electrocardiography, although the specificity in particular varies between centres. The discussion of Juneja and Wasir assumes a very low specificity of 60%, but many centres are able to apply myocardial-perfusion scintigraphy more accurately. The mean sensitivity and specificity in a review of 33 studies involving 3258 patients were 84% and 87%, respectively [7], and this much higher specificity alters the thrust of the argument significantly. Perhaps the important point is that the cause of ‘false positives’ in perfusion imaging and electrocardiography differ, and it is unlikely that a patient without coronary artery disease will
and low risk patient with an abnormal
exercise electrocardiogram.
have abnormalities on both studies. A large number of patients can therefore be reassured that they do not have obstructive coronary artery disease following normal perfusion imaging and this is most commonly where the train of investigation can end. Beyond simple diagnosis, the strength of perfusion imaging is that it is the best way of determining the risk of future cardiac events, more powerful than electrocardiography and at least equal to coronary arteriography [8]. Thus, irrespective of the anatomy of the coronary arteries, it is possible to tell patients with normal myocardial perfusion that they are at low risk of events and that no further investigation is required. Conversely, the patient at high risk should have coronary arteriography in order to guide potential intervention. The importance of prognosis in asymptomatic patients is obvious, since reducing the risk of future cardiac events could be the only justification for treatment, whether medical or mechanical.
S.R.
Underwood/Inr.
J. Cardiol.
44 (1994)
97-99
Patients with abnormal but low-risk scans should not need arteriography because there is little to gain from intervention, but follow-up and preventive medical therapy would be reasonable. In a small number, the perfusion scan may not be conclusive and coronary arteriography may be considered. Even then, intervention would be of uncertain benefit because any perfusion defect must be small. Arteriography could therefore be avoided unless a guarantee of normal coronary anatomy was required for reassurance of the patient, the physician, an insurance company, or an employer. Finally, the optimism over the future role of positron emission tomography (PET) requires qualification, because it is based mainly on the cost-effectiveness of PET as analysed by Gould et al. [9]. The analysis assumes a very high specificity for PET and a low specificity for thallium, but, using more realistic figures and using the true cost of thallium imaging rather than the market price, the conclusions of this analysis can be reversed. It is likely that concentrating resources on optimal use of single-photon myocardial-perfusion imaging rather than the widespread establishment of PET facilities would be more cost-effective. I propose an alternative algorithm for the management of the asymptomatic patient who has
99
unwisely had an abnormal exercise electrocardiogram (Fig. l), recognising that an algorithm can only act as a guide and that management will differ in individual patients and with the availability and expertise of imaging techniques. Juneja R. Wasir HS. Abnormal exercise electrocardiogram in an asymptomatic person - what next? Int J Cardiol 1900; 1994; 43: I-9. Gettes LS, Sapin P. Concerning falsely negative and falsely positive electrocardiographic responses to exercise [editorial]. Br Heart J 19Y3; 70: 205-207. Mohiaddin RH. Longmore DB. Functional aspects of cardiovascular magnetic resonance imaging. Techniques and application. Circulation 1993; 88: 264-28 I. Nishimura RA. Reeder GS. Intravascular ultrasound research technique or clinical tool. Circulation 1992: 86: 322-324. Editorial. Ultrafast CT for coronary calcification. Lancet 1991; 337: 1449-1450. American Heart Association. Potential value of ultrafast computed tomography to screen for coronary artery disease. Circulation 1993; 87: 2071. Kotler TS. Diamond GA. Exercise thallium-201 scintigraphy in the diagnosis and prognosis of coronary artery disease. Ann Intern Med 1990; 113: 684-702. Brown KA. Prognostic value of thallium-201 myocardial perfusion imaging. A diagnostic tool comes of age. Circulation 1991; 83: 363-381. Gould KL, Goldstein RA. Mullani NA. Economic analysis of clinical positron emission tomography of the heart with rubidium-82. J Nucl Med 1989; 30: 707-717.
Journal
of Cardiology
44 (1994) 97-99
Commentary
Abnormal exercise electrocardiogram asymptomatic person
in an
S.R. Underwood National
Heart and Lung Institute,
(Received
8 March
1993; revision
Juneja and Wasir [1] remind us that exercise electrocardiography should not be used to screen for coronary artery disease in individuals at low risk of the disease. Despite this, we continue to see asymptomatic subjects with an ‘abnormal’ exercise electrocardiogram, and the problem is more common when there is a financial incentive to offer such screening. Although the asymptomatic patient with severe coronary artery disease is a reality, it is easy not to set the potential benefit to this individual against the harm inflicted by further investigations such as myocardial perfusion scintigraphy and coronary arteriography on many other subjects. It therefore behoves those who perform exercise electrocardiography in low-risk subjects to have a plan of further management and we should welcome the discussion provoked by this article. An important aspect of minimising the damage is to interpret the exercise electrocardiogram strictly and to maximise specificity, even if this is at the expense of sensitivity. A large proportion of low risk subjects who are judged to have an abnormal ST segment response to exercise and who are referred for further investigation have a down-sloping PQ segment and an upsloping ST segment. This suggests that the perceived abnormality is the 0 1994 Elsevier Science Ireland Ol67-5273/94/$07.00 SSDl 0167-5273(93)01952-T
Dovehouse St. London, S W3 6L Y, UK
accepted
26 August
1993)
result of baseline variation arising from atria1 repolarisation [2]. If the abnormal ST segment is required to be planar or down-sloping, it is likely that many false positives and hence the need for further investigations could be avoided. Perhaps the most interesting point for discussion is the inclusion of fluoroscopy in the proposed algorithm. Any technique that can demonstrate abnormalities of the arterial wall is of interest because of the possibility of detecting disease at an early stage, before obstruction to coronary flow produces symptoms. Other techniques that might be considered include magneticresonance imaging [3] and intravascular ultrasound [4], although the latter could not be considered a screening test. Coronary calcification seen on tine fluoroscopy is a frequent companion of advanced coronary artery disease. Ultrafast Xray computed tomography has confirmed this Iinding and has shown an increasing incidence of calcification in asymptomatic subjects with age [5]. A relationship between coronary calcification and future cardiac events has not however been demonstrated. Until the significance of an abnormal finding is clarified therefore, it seems premature to include screening for coronary calcification in the algorithm presented, and it is difficult to
Ltd. All rights reserved.
S. R
98
lJndrrwood/ ht. J. Cardiol. 44 ( 1994) 97-99
I
1 High risk
Not high risk
Fig. I. Clinical algorithm
for the management
of the asymptomatic
justify coronary arteriography because of calcification alone [6]. The role of myocardial-perfusion imaging also deserves comment. It is important to distinguish the diagnosis of obstructive coronary artery disease from an assessment of risk once the diagnosis is made. In diagnostic terms, perfusion imaging is more sensitive and specific than electrocardiography, although the specificity in particular varies between centres. The discussion of Juneja and Wasir assumes a very low specificity of 60%, but many centres are able to apply myocardial-perfusion scintigraphy more accurately. The mean sensitivity and specificity in a review of 33 studies involving 3258 patients were 84% and 87%, respectively [7], and this much higher specificity alters the thrust of the argument significantly. Perhaps the important point is that the cause of ‘false positives’ in perfusion imaging and electrocardiography differ, and it is unlikely that a patient without coronary artery disease will
and low risk patient with an abnormal
exercise electrocardiogram.
have abnormalities on both studies. A large number of patients can therefore be reassured that they do not have obstructive coronary artery disease following normal perfusion imaging and this is most commonly where the train of investigation can end. Beyond simple diagnosis, the strength of perfusion imaging is that it is the best way of determining the risk of future cardiac events, more powerful than electrocardiography and at least equal to coronary arteriography [8]. Thus, irrespective of the anatomy of the coronary arteries, it is possible to tell patients with normal myocardial perfusion that they are at low risk of events and that no further investigation is required. Conversely, the patient at high risk should have coronary arteriography in order to guide potential intervention. The importance of prognosis in asymptomatic patients is obvious, since reducing the risk of future cardiac events could be the only justification for treatment, whether medical or mechanical.
S.R.
Underwood/Inr.
J. Cardiol.
44 (1994)
97-99
Patients with abnormal but low-risk scans should not need arteriography because there is little to gain from intervention, but follow-up and preventive medical therapy would be reasonable. In a small number, the perfusion scan may not be conclusive and coronary arteriography may be considered. Even then, intervention would be of uncertain benefit because any perfusion defect must be small. Arteriography could therefore be avoided unless a guarantee of normal coronary anatomy was required for reassurance of the patient, the physician, an insurance company, or an employer. Finally, the optimism over the future role of positron emission tomography (PET) requires qualification, because it is based mainly on the cost-effectiveness of PET as analysed by Gould et al. [9]. The analysis assumes a very high specificity for PET and a low specificity for thallium, but, using more realistic figures and using the true cost of thallium imaging rather than the market price, the conclusions of this analysis can be reversed. It is likely that concentrating resources on optimal use of single-photon myocardial-perfusion imaging rather than the widespread establishment of PET facilities would be more cost-effective. I propose an alternative algorithm for the management of the asymptomatic patient who has
99
unwisely had an abnormal exercise electrocardiogram (Fig. l), recognising that an algorithm can only act as a guide and that management will differ in individual patients and with the availability and expertise of imaging techniques. Juneja R. Wasir HS. Abnormal exercise electrocardiogram in an asymptomatic person - what next? Int J Cardiol 1900; 1994; 43: I-9. Gettes LS, Sapin P. Concerning falsely negative and falsely positive electrocardiographic responses to exercise [editorial]. Br Heart J 19Y3; 70: 205-207. Mohiaddin RH. Longmore DB. Functional aspects of cardiovascular magnetic resonance imaging. Techniques and application. Circulation 1993; 88: 264-28 I. Nishimura RA. Reeder GS. Intravascular ultrasound research technique or clinical tool. Circulation 1992: 86: 322-324. Editorial. Ultrafast CT for coronary calcification. Lancet 1991; 337: 1449-1450. American Heart Association. Potential value of ultrafast computed tomography to screen for coronary artery disease. Circulation 1993; 87: 2071. Kotler TS. Diamond GA. Exercise thallium-201 scintigraphy in the diagnosis and prognosis of coronary artery disease. Ann Intern Med 1990; 113: 684-702. Brown KA. Prognostic value of thallium-201 myocardial perfusion imaging. A diagnostic tool comes of age. Circulation 1991; 83: 363-381. Gould KL, Goldstein RA. Mullani NA. Economic analysis of clinical positron emission tomography of the heart with rubidium-82. J Nucl Med 1989; 30: 707-717.