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The ISCHEMIA study was carried out based on the hypothesis that patients with moderate or severe ischemia would have a higher risk of cardiovascular events and, therefore, would benefit from an invasive therapeutic strategy. Patients with moderate or severe ischemia were randomized to initially invasive treatment, with coronary angiography and surgical revascularization or angioplasty, and to a conservative strategy, with optimization of drug treatment. Most patients underwent coronary angiotomography (CT angiography) of the coronary arteries before randomization to exclude a left main coronary artery lesion greater than 50%.
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The initial results showed no statistical difference in the two types of treatment in this population of patients with chronic coronary atherosclerotic disease (CAD). A new analysis of these patients was then performed to assess whether the severity of CAD and/or ischemia was associated with the risk of mortality, acute myocardial infarction (AMI) or other cardiovascular outcomes. In addition, the presence of heterogeneity of the treatment effect in the participants was evaluated, based on the severity of CAD by CTA or ischemia induced in the stress test.
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Study method and population involved
Patients were those who made up the cohort of the ISCHEMIA study. Stress tests were myocardial scintigraphy, stress echocardiogram (stress echo), cardiac resonance with stress or exercise test, and ischemia was graded as severe, moderate, mild or absent. Coronary CT angiography was performed by 76% of patients, the reason for not performing it was, in most cases, the existence of recent coronary evaluation (up to one year before) or renal dysfunction, with
clearence less than 60 ml/min.
The primary outcome was all-cause mortality and the secondary outcomes were AMI; cardiovascular death or AMI; cardiovascular mortality, AMI, hospitalization for unstable angina,
heart failure or resuscitated cardiopulmonary arrest.
The association of outcomes with each degree of ischemia and for each type of exam separately, as well as the association of the extension and severity of CAD with the outcomes. The severity of CAD was assessed by evaluating the score Modified Duke prognosis, percentage of stenosis diameter and stenosis site. An analysis was also performed to assess whether there was a difference in event rates in relation to treatment strategies, according to the degrees of ischemia and severity of CAD.
Of the ISCHEMIA patients, 5,015 (99%) had tests with severity of ischemia available and scintigraphy was the most used test. Coronary CTA was available for analysis in 2,475 (48%) patients. The time taken to analyze the outcomes was 4 years.
More extensive ischemia was correlated with more severe CAD and patients with these characteristics they were more likely to be men. Patients who had an available CTA were more often men, with hypertension, and had more ischemia assessments by stress echo or exercise testing compared to the group with no CTA available.
Greater severity of ischemia was not associated with a higher occurrence of events in 4 years, with maintenance of this result in the evaluation of each type of examination alone.
On the other hand, the assessment of CAD by CTA showed an association between its severity and all-cause mortality. More severe CAD was also associated with a higher occurrence of AMI, both spontaneous and periprocedural, and cardiovascular mortality. There was no association with hospitalization for HF or unstable angina. Stenosis greater than or equal to 70% in the proximal anterior descending artery (LAD) was not associated with a higher occurrence of all-cause mortality, AMI or cardiovascular mortality.
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Patients in the conservative group had low rate of coronary angiography and revascularization, regardless of the degree of ischemia and severity of CAD. At 4 years, this rate was 12.4% in patients with moderately severe CAD, one-vessel, and 23.5% in patients with three-vessel or two-vessel CAD including proximal ADA. In the initial invasive strategy group, surgical revascularization was performed in 2.2% and 32.7% respectively.
Relatively on medication, patients with more severe CAD and more extensive ischemia received more high potency statin, beta blockers and long-acting nitrates, and fewer inhibitors of the renin angiotensin system, compared to the group with less severe ischemia.
Regarding the types of treatment, there was no difference in the outcomes when evaluating the degrees of ischemia and severity of CAD in relation to the conservative and invasive treatment groups, but the power The statistical analysis for this subgroup analysis was limited.
In patients with a Duke score of 6 (the most severe CAD), the occurrence of all-cause mortality was 7.7% in both groups. The occurrence of AMI was 9.2% in the invasive treatment group and 13.4% in the conservative group and the secondary outcome of AMI or cardiovascular death was 11.6% and 17.9%, respectively. All these results were not statistically different. These results were similar when considering only patients with moderate or severe ischemia and number of affected arteries.
When performing the analysis with Cox regression, which adjusts for several covariates, the confidence interval favored invasive treatment in the subgroup of patients with Duke 6 score in relation to AMI (difference -6.8%; 95%CI -12.4% a -1.3%), cardiovascular mortality or AMI (difference -8.7%; 95%CI -14.8% to -2.4%), cardiovascular mortality, AMI, hospitalization for unstable angina, heart failure or resuscitated cardiorespiratory arrest (difference -7.6%; 95%CI -14.0% to -1.1%). However, there was no adjustment for multiple comparisons.
This association occurred independently of the degree of ischemia and other clinical predictors. In the evaluation of the 659 patients with the most severe disease, there was no difference in terms of mortality, but mortality or AMI was lower in the group treated invasively. Despite these findings, there are some limitations, such as the fact that only half of the patients have CTA available and we cannot reach a definitive conclusion.
There was no benefit in overall mortality in any subgroup based on ischemia or CAD severity. There was a lower cardiovascular mortality rate or AMI in the invasive treatment subgroup with anatomically more severe CAD (three-vessel or two-vessel disease with proximal ADA), at the expense of less occurrence of AMI, but without making adjustments for multiple comparisons .
It is possible that the risk attributed to the extent and severity of CAD, modified Duke score measure, reflects only atherosclerotic burden and that drug treatment reduces the risk of plaque destabilization and occurrence of events, regardless of whether or not there is significant flow obstruction, which may justify there being no difference in outcomes between the groups.
In this study, CTA was better than ischemic assessment for risk prediction. However, in practice, the two tests are complementary, since CTA identifies plaques, but it does not give us the certainty that they are the cause of symptoms and, on the other hand, stress tests can show ischemia in patients without obstructive disease.
This study is limited by the short follow-up time and the ISCHEMIA trial is still following the patients and will bring us more data in the future. In addition, the statistical power for analyzing the subgroups was small and half of the patients had no CTA available.
In this study, there was an association of CAD severity, assessed by coronary CTA, with the occurrence of cardiovascular events, which was not confirmed for findings of ischemia in non-invasive tests . The invasive treatment strategy had no benefit in reducing the risk in 4 years, and it is possible to opt for clinical treatment or revascularization for patients with this profile. In practice, we still follow the recommendation of guidelines
current that suggest revascularization when there are large ischemic areas.
Author: 
Cardiology Editor at the PEBMED Portal ⦁ Graduated in Medicine from the Paulista School of Medicine, Federal University of São Paulo (UNIFESP) ⦁ Residency in Clinical Medicine at UNIFESP ⦁ Residency in Cardiology at the Heart Institute (InCor) at Hospital das Clínicas from the Faculty of Medicine of the University of São Paulo (USP) ⦁ Currently working in the areas of intensive care, outpatient cardiology, nursing and medical education.
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