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Multimodality cardiac imaging: From redundant information to clinical needs

Non-Invasive Imaging

Over the last decades, there has been a sustained decrease in coronary artery disease (CAD)-related mortality. From 1980 to 2000 , CAD related mortality decreased from 543 to 267 in males and from 263 to 134 in females. During the same years, noninvasive diagnostic imaging (echocardiography, nuclear, magnetic resonance imaging, cardiac computed tomography) has increased very rapidly, too. However, it is impossible to understand how much of the decrease in mortality is related to our expanded diagnostic capabilities due to technological developments in cardiac imaging.

What we know is that the cost of imaging has increased by 70% from 2000 to 2007, compared with a 15% increase in the costs of all other medical services. Overall, imaging costs increased from 6.89 billion $ in 2000 to 14.11 billion $ in 2006 (~33% is related to cardiac imaging). Interestingly, the expenditure in cardiac imaging is not uniform throughout the world but it is directly related to gross domestic product of each country. We also know that at least 18% of these tests are inappropriate and in at least a further 16% their appropriateness is uncertain. Not only are the costs an issue, but the amount of radiation and the related risk of malignancies to which we expose our patients when using computed tomography and nuclear imaging should also be taken into account.

Since continued growth in imaging is clearly unsustainable, we need to rethink the use of imaging in order to select the technique or combination of techniques that could maximize the benefits while minimizing the risks and costs for each clinical situation and hopefully, for each patient.

In patients with known or suspected CAD, imaging is mainly used to: diagnose the disease, assess its physiological extent and/or severity, stratify the risk of the patient and assess myocardial viability. Several imaging techniques are used to reach these goals (echocardiography, nuclear, magnetic resonance imaging- MRI, cardiac computed tomography- CCT). Each has its strengths and weaknesses, and what we do not know is the additive value of the new players (MRI and CCT) over the established techniques in improving the prognosis of our CAD patients.

To obtain these data, we should change our way of assessing imaging techniques from competition between techniques in diagnosing CAD, to their combination to obtain more cost-effective management strategies. That is moving from relegating them to the role of gate keeper of any single technique for coronary angiography to the more useful role of identifying high risk patients by combining different techniques. Two clinical scenarios may help to clarify: post-infarction left ventricular dysfunction and acute chest pain.

We know that among patients with heart failure and LV dysfunction due to previous myocardial infarction 54% have only scar, 19% dysfunctioning but viable myocardium, 17% ischemic myocardium, and 10% both viable and ischemic myocardium. The difficult task is to quantify, among the dysfunctioning myocardium, the extent of viable and ischemic myocardium that can be recovered by revascularization. In these patients, dobutamine echo should be the first imaging technique. If there are more than 4 LV segments that are viable the patient can safely be sent for revascularization because there is high likelihood of postoperative improvement of LV function. If there are 2 or less segments viable, other treatment options than revascularization should be considered (medical therapy or heart transplant). The most difficult decision is when there are 2 - 4 viable LV segments. In these patients, the addition of nuclear imaging (Thallium) or MRI will help distinguish patients who will benefit from revascularization from those who will not.

Patients who present at the Emergency Room with acute chest pain and non diagnostic ECG changes are a clinical dilemma. An effective strategy may be to assess their ESC risk score, then exercising them. High risk patients should be sent for coronary angiography. Low risk patients can be reassured and sent home. In intermediate risk category patients, the new CCT, which combines angiography and perfusion imaging has proven to be effective. This is because CCT angiography has been found to have a very high negative predictive value but a poor positive predictive one (sensitivity= 94%; specificity= 83%; positive predictive value= 48%; negative predictive value= 98%) that can be overcome by adding perfusion information. Using this technique, we can identify flow limiting coronary stenosis to be sent for coronary angiography, and no flow limiting stenosis that can be treated conservatively with secondary prevention strategies, and no stenosis at all, to be reassured and sent home.

These are two examples of integrated clinical use of imaging techniques to develop management strategies. However, to develop more strategies like these, we need more and new research strategies. We need Comparative Effectiveness Research encompassing broad clinical areas involving large segments of population, using transparent end-points and validation methods (ethnic, men and women) whose findings will be disseminated to patients, healthcare providers and policy makers.

To perform this type of research we need to change our hierarchy of evaluation of imaging techniques and assessing them in terms of: 

  1. Diagnostic selectivity
  2. Symptom benefit
  3. Prognostic utility
  4. Optimized test effectiveness strategy




Highlights from EuroEcho 2008

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.