Noninvasive Evaluation of Coronary Heart Disease. Present State and New Horizons.
Prof. R. Rienmuller
Interdisciplinary Cardiac Imaging Center, University of Graz, Austria.
(Радиология в медицинской диагностике [современные технологии] 2003: 77-79)

Prevention, early recognition, staging and selection of the optimal therapy in coronary heart disease is still the most exciting challenge in cardiac.

Today, coronary heart disease "is defined as manifestation of atherosclerosis in the coronary arteries. As the disease is a multifactorial process leading to myocardial ischemia it may appear as angina pectoris, myocardial infarction, cardiac dysrhythmia, sudden death or cardiac insufficiency" (J. Meyer; 1996). The inadequate coronary blood flow results in changes of the biochemical, electrical and mechanical function of the cardiac structures.

Current methods used in the evaluation of coronary heart disease.
Coronary angiography is still regarded as a gold standard in the evaluation of coronary atherosclerosis. The method however is lacking the desirable amount of sensitivity and specificity needed for early recognition of atherosclerotic plaques and for quantification of the hemodynamic effectiveness of these lesions. Recent studies demonstrate that intravasal ultrasound is superior in identifying and staging of atherosclerotic plaques. Catheterisation is used for ventriculography and/or for measuring hemodynamic and pressure data and to measure functional determinants as preload, afterload and contractility.

For the evaluation of myocardial ischemia exercise tests using ECG, echocardiography or radiommclide methods (SPECT) are used. However these methods are also lacking the necessary sensitivity and specificity and possibility to measure myocardial blood flow in absolute numbers. PET seems to be more sensitive than SPECT enabling to measure myocardial blood flow in absolute numbers.

Present questions for non-invasive evaluation of coronary heart disease (without acute coronary syndrom)
- Does the patient have coronary atherosclerosis?
- If positive: What is the stage of coronary atherosclerosis?
- Is this coronary atherosclerosis of haemodynamic effect?
- Does the patient have myocardial ischemia? (infarction?)
- If positive: What are the physiological and pathophysiological compensatory mechanisms to prevent myocardial damage?
- If positive: What are the mechanisms to keep the heart in the present function?
- If positive: How effective is the collateral coronary circulation?
- How big is the individual coronary reserve?

To answer these questions we developed the "Graz One-Stop-Shop Approach" which consists of:
1. Native single slice scan, 100ms exposure time to identify and to measure the extent of coronary calcification.
2. Multi slice scan, 50 ms exposure time and intravenous contrast agent application to measure myocardial blood flow.
3. Multi slice scan, 50 ms exposure time and intravenous contrast agent application to measure functional determinants as enddiastolic and endsystolic volumes, ejection fraction, left ventricular muscle mass and global and regional wall thickness changes over the cardiac cycles.
4. Single slice scan, 100ms exposure time and intravenous contrast agent application to evaluate the morphological state of the proximal 4-6cm of the subepicardial coronary arteries.

Using EBT with the "Graz One-Stop-Shop Approach" the above mentioned questions may be answered non-invasively on a routine daily basis in 30min by radiation dose below lO mSv and approximately 220ccm of non-ionic contrast agent.
Based on more than 2000 cardiac EBT studies using the above mentioned protocol it is possible like in an "One-Stop-Shop" to assess the extent of coronary atherosclerosis as Coronary Calcium Score (first part of the definition of coronary heart disease) to evaluate the degree, location and number of stenotic lesions in the proximal 5-6cm of the coronary arteries, to determine the severity of coronary heart disease by measuring the global and regional myocardial blood flow ( second part of the definition of coronary heart disease ) and to measure the functional left ventricular parameters giving the information if they are still in normal range or changed either as a sequel of the coronary heart disease or as a compensatory mechanism to keep myocardial blood flow as adequate as possible with respect to the balance of oxygen supply and demand.

Present experience using Multislice and Multidector CT and MR systems in patients without acute coronary syndrom:
The new advanced multidetector CT technology is coming very close to EBT technology in the evaluation of coronary calcification soft plaques and coronary arteries showing encouraging results.

Similar to EBT a new "Graz One-Stop-Shop Approach" for MR studies of the heart in patients without acute coronary syndrome was developed in our "Interdisciplinary Cardiac Imaging Center". In contrast to EBT using MR this approach is more time consuming and it requires more patients cooperation to image the coronary arteries. The evaluation of the functional-parameters is possible with higher degree of accuracy than by EBT because of the higher contrast resolution of MR. There are encouraging results and approaches to evaluate myocardial perfusion after intravenous contrast agent applications. The continuous progress in MR technology is very promising that in the near future MR will be used in clinical routine in patients with known or suspected coronary heart disease. Especially there are very interesting results in blood flow measurements not only in the great cardiac vessels but also intraventriculary and in the proximal coronary arteries. These flow measurements will increase our understanding of the determinants of myocardial blood flow and perfusion.

New horizon.
Does it mean all relevant questions of coronary heart disease are going to be answered today and in the very next future by the described methods?

The answer is simply: no.

Additionally to the acute coronary syndrome there are many open questions in coronary heart disease and we have to go to learn and to expand our understanding of the disease with respect to ethiology, epidemiology, course but especially in the mechanism of the disease and its functional controlling when we really plan to improve our diagnostic and therapeutic approach.
Therefore we have to study intensively the mechanism of intracavitary and intravascular flow, pulmonary, blood and myocardial cell gas exchange, myocardial metabolism and include molecular biology and genetic and computer science.

Although the heart and the lung represent two different organs, each has it's own specific function, both organs are characterized by closed functional interaction and therefore it is for clinical as well as for experimental purposes necessary and important to consider and to evaluate both of them simultaneously.

The final goal, the new horizon, in cardiac radiology presents a project of "anatomical and functional 3D visualisation" of the heart and the lungs, which will allow to study and to evaluate cardiac morphology, function, myocardial perfusion, global and regional pulmonary ventilation, pulmonary blood flow and its distribution during breathing in vitro and in experimental models.
For this, no question about, ambitious task there will be an increased need for interdisciplinary collaborations of all interested and involved in the heart and lungs and their pathology to reduce the morbidity and mortality and to increase the effectiveness of the medical care of our patients.