CASE REPORT

Editor: Dr. Jassim al-Suwaidi*

ST- segment Elevation During Stress Test in Left Main Coronary Artery Stenosis

Dr Ayman Elmenyar, MBBch

 Introduction
 Case presentation
 Discussion
 ST elevation during ETT
 Table 1. ST-elevation During Exercise Test
 Table 2. ST-elevation During Exercise Test on Normal Resting ECG
 Conclusion
 References
 Islamic tile

Introduction

Left main coronary artery (LMCA) stenosis is associated with poor long-term prognosis without surgery (1-3). Patients with LMCA stenosis cannot be detected on the basis of their clinical presentation alone, which may not be different from those with milder coronary artery disease (CAD), hence additional investigations are needed (4-6). Exercise treadmill test may suggest the presence of such lesion and other serious CAD by giving a high index of suspicion (6-9.)

Case presentation

A 48-year-old Indian male patient presented to the cardiology outpatient clinic with atypical chest pain of a few day’s duration. Apart from a family history of CAD, he had no other risk factors such as smoking, diabetes or hypertension. Physical examination was not remarkable. He was referred for exercise treadmill test. On the day of ETT, the patient was stable, his BP 130/80, pulse 70/min. and resting ECG was normal (Figure 1). At the end of stage 1, he felt tired and developed mild chest pain with ST-elevation in V2 – V4 (Figure 2). The test was

Fig. 1. see text

Fig. 2. see textt

stopped and the patient was given sublingual Nitroglycerin with relief of chest pain and resolution of ST-elevation within one minute. However, almost immediately, he developed ST depression in leads II, III, AVF, V5 and V6 (Figure 3), which lasted for 5 minutes followed by complete normalization of the ECG (figure 4). He was admitted to the coronary care unit (CCU). Anti-ischemic therapy with aspirin, betablocker and nitrate was initiated, including subcutaneous Enoxaparin. Cardiac enzymes were normal and Troponin T-test was negative; serum cholesterol was 4.8 and triglyceride was 2.0. Echocardiogram revealed left ventricular ejection fraction of 58% with hypokinesia of the apex and inferolateral wall. A coronary angiogram revealed 80% left main coronary artery stenosis with total occlusion of the left anterior descending coronary artery, 80% lesion in the circumflex, and 60% distal RCA lesion (fig 5). The patient underwent urgent coronary artery bypass graft (CABG). Postoperative recovery was uneventful.

Discussion

Exercise treadmill test (ETT) has been used to identify patients with coronary artery disease (CAD) as well as predict its severity and the urgency for intervention (5,10,11). Patients with

Fig. 3. see text

Fig. 4. see text

3-vessel disease with significant LMCA stenosis have a 60% 4-year survival compared to a 70% 4-year survival in those without LMCA disease (12). Good exercise performance indicates a better prognosis in patients with LMCA and/or 3-vessel disease than those with similar lesions but have poor exercise performance (11,13). Most of the patients with LMCA stenosis have extensive disease elsewhere in their coronary artery tree as well (14). It is not surprising that patients with left main and 3-vessel disease have similar exercise performance but the difference in prognosis reflects the difference in mortality associated with a chance event such as plaque rupture with thrombus formation when it occurs in the left main coronary artery rather than elsewhere. The clinical and noninvasive indicators of LMCA stenosis such as crescendo angina, transient ST-depression with pain, simultaneous anterior and inferior ST-T changes during pain and fluoroscopic calcification of LMCA are well recognized but still have a low sensitivity and low predictive value to be of diagnostic value (15). During ETT, patients with LMCA disease tend to show an earlier onset, longer duration and more widespread ST-depression than those with 3-vessel disease. However, there is no single variable that helps to distinguish LMCA from 3-vessel CAD or to predict the presence of LMCA stenosis. The predictive accuracy of ETT findings can be increased to 74% if more than one of the following variables are recognized (5): development of downsloping ST depression, ST-depression >2mm, onset of ST changes in stage 1, persistence of ST-changes beyond 3 minutes, appearance of ST-changes in at least 3 ECG leads or exertional ST-elevation (9,17). Thomson and Keleman (16) found that 33% of their patients with exercise-induced hypotension had at least 75% stenosis of LMCA. Goldschlager et al (7) reported also that the duration of exercise-induced ischemia is extended longer in the recovery period in patients with LMCA stenosis. Stone et al observed that the presence of coexistent RCA disease exerted a major adverse effect on ETT performance in patients with LMCA disease and these patients had higher incidence of ventricular arrhythmia, exertional hypotension, and exertional ST elevation more than those with normal RCA (18).

ST elevation during ETT

ST elevation during ETT is not a common finding and it is important to differentiate elevation occurring over or adjacent to Q waves from elevation in non-Q areas. Candell et al, reported that in patients without previous infarction and with exercise-induced ST-elevation, very severe perfusion defects were detected when the radionuclide has been injected during the crisis of Thalium stress test (19). ST elevation during ETT on normal resting ECG represents severe transmural ischemia (table1) (9,17,20) it is very arrythmogenic and more accurate in localizing the affected vessel than ST depression (table 2) (21, 22).

Table 1. ST-elevation During Exercise Test

Table 2. ST-elevation During Exercise Test on Normal Resting ECG

Fig. 5. Coronary angiogram. White arrows indicate severe lesions in LMCA, LAD, and circumflex.

ST-elevation in non-Q areas is a very rare event. It occurs in 0.1%-0.5% of cases (23-24). During ETT, ST-elevation occurring purely during exercise indicates more severe lesions than when it occurs in the recovery period (25). ST elevation on normal ECG may occur in patients with variant angina during ETT (26). On the other hand, ST elevation in the presence of Q-waves represents wall motion abnormalities, left ventricular aneurysm, or residual viable myocardium within an infarct (27,28). In the CASS study, ST elevation during both exercise and recovery phase showed a significant reduction in coronary event-free survival and it was also noted that exercise-induced ST elevation when tested 2 weeks after uncomplicated myocardial infarction indicated higher morbidity and mortality (29-31). Our patient had normal resting ECG and no major risk factors apart from his family history. The pretest probability of CAD was low. The grossly abnormal ECG changes during ETT were rather surprising. The early development of chest pain in stage 1 with accompanying ST-elevation in leads V2-V4 indicated tight proximal left system stenosis whereas the subsequent development of ST-depression in the inferolateral leads suggested concomitant significant lesions in the RCA and circumflex arteries. The ST depression was not due to reciprocal change since it occurred after resolution of ST-elevation. Coronary angiography confirmed the pathology highly suspected from the results of the ETT.

Conclusion

Exercise testing might give a high index of suspicion for the presence of LMCA before angiography. ST elevation during ETT in the absence of prior infarction should be taken seriously as a clue to the presence of LMCA stenosis or its equivalent.

References

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