Dr. Michael Johannes Zellweger,
In this session, the speakers provided overviews summarizing the value of cardiac magnetic resonance (J. Schwitter; Lausanne, CH), nuclear techniques (S R Underwood; London, GB), echocardiography (L A Pierard; Liege, BE) and cardiac computed tomography (P J De Feyter; Rotterdam, NL) with respect to outcome.
Outcome – what might that mean in the context of cardiac imaging? It may mean:
These considerations lead to the conclusion that technical, diagnostic, and prognostic variables influence outcome. In addition, imaging is rather a decision-making tool to select treatment strategies, to choose therapeutic options that may improve patient outcome and that may turn out to be cost-effective.
In the setting of coronary artery disease (CAD) it is well recognized that a normal cardiac imaging test in general is consistent with a very good prognosis. These patients have an excellent outcome without the need of further testing and invasive therapy. However, it is important to take into account that CAD is a dynamic disease and every examination has its “warranty period”. For the nuclear methods it is up to two years, for a normal CT-angiogram it lies between four and seven years. All discussed imaging modalities have a high sensitivity and negative predictive value in the evaluation of CAD and therefore are well suited to avoid false negative tests and further unnecessary procedures.
In patients with evidence of CAD there is no prospective randomized data regarding cardiac imaging based on therapeutic approaches. However, the FAME trial has shown that routine measurement of FFR in patients with multivessel CAD who are undergoing PCI with drug-eluting stents significantly reduced the rate of the composite end point of death, nonfatal myocardial infarction, and repeat revascularization at 1 year (Tonino PA et al). Since FFR has been validated by non-invasive modalities (mainly nuclear) one may expect that an imaging guided strategy could improve outcome similarly – but this still has to be confirmed by prospective randomized trials.
The often cited observational studies by Hachamovitch et al. have shown that patients with high but reversible risk are effectively risk stratified by nuclear. Patients with <10% myocardium ischemic may not benefit from revascularization. In contrast, patients with >10% myocardium ischemic probably will benefit. In an observational series, a more aggressive intervention strategy that included direct cardiac catheterization in stable angina patients not only lead to higher diagnostic costs but also contributed to greater rates of coronary intervention and composite costs of care. At all levels of pretest clinical risk, the costs of initial and subsequent follow-up care were substantially less when a selective, provocative ischemia-driven catheterization strategy was employed using nuclear imaging. The observed lower cost of care with noninvasive stress imaging was due to a reduction in resource use for patients with a normal test result. The diagnostic yield for cardiac catheterization was enriched for populations with stress-induced myocardial ischemia, reflecting a higher pretest and posttest probability of significant coronary heart disease (Shaw LJ et al.).
The value of viability testing has been questioned after publication of the STICH trial. The presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and left ventricular dysfunction, but this relationship was not significant after adjustment for other baseline variables (Bonow RA et al.). To adequately interpret these results it is important to look at the viability definitions used in that trial. It might have been interesting to use either CMR or PET for viability assessment in that trial.
In addition to ischemia and viability testing, CMR imaging can characterize occult myocardial scar consistent with MI in (diabetic) patients without clinical evidence of MI. This imaging finding demonstrated strong association with MACE and mortality hazards that was incremental to clinical, ECG, and left ventricular function combined (Kwong RY et al). These findings could lead to more adequate diagnostic and therapeutic approaches in patients with evidence of before unrecognized scar.
Echocardiography has multiple self evident strengths that demonstrate its utility to improve outcome (e.g. diagnosis of tamponade with subsequent pericardiocentesis, diagnosis of aortic stenosis with subsequent (interventional) valve replacement etc.). In the preventive setting (Multicentre Aneurysm Screening Study (MASS)) 27147 men were successfully screened by ultrasound, and 1333 aneurysms were detected. There were 65 aneurysm-related deaths (absolute risk 0.19%) in the invited group, and 113 (0.33%) in the control group (risk reduction 42%, 95% CI 22-58; p=0.0002), with a 53% reduction (95% CI 30-64) in those who attended screening. 30-day mortality was 6% (24 of 414) after elective surgery for an aneurysm, and 37% (30 of 81) after emergency surgery (Ashton HA et al.).
Recently, the Coronary CT Angiography Evaluation for Clinical Outcomes: An International Multicenter Registry (CONFIRM) data has been published. This registry evaluation looked at 23 854 patients without known CAD (Min JK et al.). Non-obstructive and obstructive CAD by CCTA were associated with higher rates of mortality, with risk profiles differing for age and sex. The absence of CAD was associated with a very favourable prognosis underscoring the reliability of the negative predictive value of coronary CT in a very large patient population. Importantly, also patients with non-obstructive disease had a worse prognosis than patients without CAD. However, there is still no evidence if aggressive preventive therapy in these patients improves their prognosis.
Outcome is a complex topic resulting in the following points which have to be overcome in outcome research: in general, large patient populations are needed to demonstrate significant differences between patient groups. Results can be achieved only after years of follow-up implicating that outcome research needs big financial support. All the presented imaging modalities have their strengths and weaknesses and may be used in a complimentary way if needed.
Controversial issues: does imaging improve outcome?
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