POSITIVE PREDICTIVE VALUE OF EXERCISE TOLERANCE TEST IN PATIENTS; TAKING ANGIOGRAPHIC FINDINGS AS GOLD STANDARD.
Keywords: Coronary artery disease, Coronary angiography, Exercise tolerance test, Positive predictive value.
Exercise is a physiologic stress that helps the physicians to clarify the presence or absence of cardiovascular disease which may be obscure at rest. Although it is sensitive, its specificity is affected by several parameters, such as some metabolic conditions, some structural heart diseases, and some baseline electrocardiogram abnormalities. Currently, the relationship between coronary dominance and accuracy of EET is not examined1. The exercise treadmill test (ETT) assesses for exercise induced myocardial ischemia and is commonly the first-line investigation in troponin-negative chest pain suspected of having coronary artery disease2. Typical angina was defined as "the presence of substernal chest pain or discomfort that was provoked by exertion or emotional stress and was relieved by rest and/or nitroglycerin3."
Ischemia was induced by stress testing in 14% of 231 patients with typical angina, 11% of 2140 patients with atypical chest pain, and 16% of 153 patients with no chest pain at presentation. Thus, patients with typical angina were not significantly more likely than those with no or atypical chest pain to have inducible myocardial ischemia3. While ETT is widely available, its limitations are its moderate sensitivity and specificity. Abnormal ETTs that are falsely positive lead to unnecessary invasive coronary angiography4. One study reported that positive predictive value of ETT was 77.9% in patients with typical chest pain undergoing angiography for positive ETT5. Another study also showed that positive predictive value of ETT was 77% in patients with typical chest pain undergoing angiography for positive ETT6. While another study showed high positive predictive value of ETT i.e. 85.1% in patients with typical chest pain undergoing angiography for positive ETT7.
The rationale of this study is to find the frequency of positive predictive value of ETT in young adults taking angiographic findings as gold standard. Literature has showed that in patients with positive ETT, positive predictive value is high. But varied data has been retrieved from literature. Moreover, there is little local data found in the literatureand we are unable to recommend the screening of coronary artery disease on the basis of ETT instead of going for angiography. Coronary angiography is expensive, requires intervention and expertise to diagnose coronary artery disease. So we want to conduct this study to get the evidence to apply results of this study in local setting and implement ETT as first line diagnostic tool for detection of coronary artery disease instead of going for coronary angiography directly.
MATERIAL AND METHODS
This descriptive cross-sectional study was conducted at out patient department and coronary care units ofArmed Forces Institute of Cardiology and National Institute of Heart Diseases, Rawalpindi from January 2018 till June 2018. Patients between the ages of 35-75 years of both gender presenting with positive ETT undergoing angiography were included in the study using consecutive sampling. Patients with previous MI, PCI or CABG, smokers with >5 pack years and alcohol drinkers were excluded from the study. Patients fulfilling selection criteria were enrolled through OPD after the informed consent. Demographic details, diabetes history (BSR>186mg/dl) and duration of typical chest pain were noted. Then all the patients were admitted in wards and underwent coronary angiography. Angiographic findings were noted and labelled positive with vessel disease present.
Positive ETT was defined as point that is 80ms from the J point (depression of 0.1 mV (1mm) or more and/or an ST-segment slope within the range of +- 1mV/s in 3 consecutive beats) in patients with typical chest pain (for >30minutes on rest). Angiographic findings was labelled if there was >50% stenosis in any coronary artery. Positive predictive valuewas labeled if there was >50% stenosis in at least one coronary artery (SVD, DVD or TVD) on coronary angiography already diagnosed as positive on ETTAll the data was entered and analysed using SPSS version 21.
Table: Showing demographic and clinical details of patients.
Age(mean +-S.D)###40.3 +- 15.6 years
Family History of CAD###25(17.8%)
Body Mass Index
Duration of Chest Pain###6.2 +- 0.5 months
(mean +- S.D)
Type of Typical Chest Pain
Total 140 patients were included for the study. There were 85 (60.7%) male patients and 55 (39.2%) females. Mean age of the patients was 40.3 +- 15.6 years. 44 (31.4%) patients were diabetic, 53 (37.8%) overweight/obese and 25 (17.8%) patients had family history of CAD. Mean duration of typical chest was reported to be 6.2 +- 0.5 months. All the patients were ETT positive and then underwent angiography as summarized in table. Out of all the EET positive patients, 29 (27.6%) patients had single vessel disease, 31 (29.5%) double vessel disease and 60 (57.1%) patients had triple vessel disease on angiography as shown in figure.
Positive Predictive Value, PPV = True Positives
True Positives + False Positives
Positive Predictive Value, PPV = 29+31+60
Positive Predictive Value, PPV = 75
Positive predictive value of ETT was found to be 75.
Exercise tolerance test has played a central role in the diagnostic workup of CAD for almost a century8. But because of the limited sensitivity and specificity of the test, other expensive investigations are being increasingly used in our country9. The ETT is still the least costly of all other non-invasive tests currently available. The diagnostic accuracy of the treadmill test can be improved by identifying the factors which can cause false positive test results. In this study six months data of patients undergoing ETT for chest pain diagnosis followed by coronary angiography if test result turned out to be positive has been presented. The current study showed a higher percentage of true positive results among patients 105 (75%). This finding is consistent with other studies which showed high sensitivity of this test10.
Many investigators have attempted to improve the diagnostic accuracy of treadmill testing in women by creating new variables such as ST/Heart rate slope, computer generated algorithms and gender specific guidelines for interpretation11-13. Other investigators have suggested that initial testing strategies should be stress imaging rather than treadmill testing10,12. But the Duke Treadmill Score improves the diagnostic accuracy of ETT14. It was noticed that changes in the resting ECG like ST-segment depression or T wave inversion also affect the test result. William et al have shown in their study that the specificity of the ETT decreases with resting ST-segment depression (48 +- 12% versus 84 +- 3%)15, because of inclusion of more false positive test results sever systemic hypertension may interferewith the subendocardial perfusion and may lead to ST-segment depression even in the absence of atherosclerosis, thus resulting in false positive test results15.
In the current study chest pain was observedmore frequently in the true positive group and asymptom limited. Exercise induced chest discomfort without associated ECG changes maybe the only signal that obstructive coronary arterydisease is present16. Early onset of angina is animportant parameter of adverse prognosis. Strongly positive ETT was more commonlynoted in the true positive group, this has been reported byother studies as well17. Fletcher et al have reported thatthe patients who have strongly positive ETT showadverse prognosis and a multi vessel coronary arterydisease18. In patients with single vessel disease in our study, the sensitivity was of ETT is 27.6%, whereas it is 57.1% in patients with triple vessel CAD. It was also observed that the most frequent coronary artery involved was LAD followed by RCA and than LCX. This has been reported previously by other investigators as well1,6,12. Our study had few limitations, i.e., the study population was very small.
As coronary angiography is an invasive procedure and the patients who were not symptomatic should not be urged to go for the angiography.
Our study results showed that exercise tolerance test has high positive predictive value. Thus ETT is recommended for the screening of coronary artery disease instead of going for angiography as coronary angiography is expensive procedure while ETT requires little intervention and expertise to diagnose coronary artery disease.
CONFLICT OF INTEREST
This study has no conflict of interest to be declared by any author.
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|Publication:||Pakistan Armed Forces Medical Journal|
|Date:||Feb 28, 2019|
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