Fractional river reserve

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The fractional flow reserve is an index that describes the condition of the epicardial coronary vessels ( coronary vessels ). For this purpose, the pressures in the arteries in front of and behind a constriction are measured as part of a cardiac catheter examination (intra-coronary pressure measurement) . From the quotient between these two pressures it can be concluded whether an intervention on this constriction, for example through a stent implantation , is necessary.

background

coronary heart desease

The coronary heart disease sets in the western world one of the most common diseases with fatal outcome. In addition to pharmacological treatment and bypass surgery is invasive, catheter-guided stent implantation with approximately 375,000 procedures per year, the most commonly performed method of treatment in the Federal Republic of Germany.

Before the treatment of coronary heart disease, the detection of reversible ischemia (insufficient blood flow) plays a special role: stenoses (constrictions), which cause ischemia of the myocardium but remain untreated, represent a 12 times higher risk for the patient, in the next 12 Months to suffer or die from a heart attack. It is therefore of great interest to treat the stenosis causing ischemia and to minimize the risk to the patient for such an event. The treatment of stenoses by stent implantation which do not cause ischemia are of no benefit to the patient. It can even lead to a higher event rate in the course than with a non-invasively treated stenosis. The purely pharmacological treatment strategy for coronary sclerosis seems to be of advantage here.

physiology

In contrast to the skeletal muscles , the heart exhausts the oxygen almost completely, even under resting conditions. During exercise (for example, during exercise) it can only achieve its increased oxygen demand by increasing the blood flow. The increase in this flow, from the resting flow to the maximum flow , is called the coronary flow reserve (CFR). In a healthy person, the flow of rest can be increased 5-fold and even more. Everyone has an individual CFR, which has a normal range between 3 and 7. The flow regulation takes place through the microcirculation vessels, which adapt their cross-section to the respective load conditions, and by changing their resistance (widening = small resistance, narrowing = large resistance), the blood flow is increased or decreased.

Maximum blood flow to the heart is only achieved when the vessels of the microcirculation reduce their flow resistance to the maximum, that is, when they expand their cross-section as much as possible. If this state is reached, one speaks of maximum hyperemia .

The ability of these microcirculation vessels to change their resistance can be partially disturbed (rheological disorders, diabetes, age, etc.) or even completely destroyed (after a heart attack, etc.). When determining the CFR (e.g. using Doppler wire), the measured value only provides an indication of the overall condition of the arterial pathway of the heart, but does not allow any differentiation to be made about the condition of the epicardial pathways and the microcirculation vessels. There is also no clear limit value for pathological CFR. Depending on the literature, a limit value of 1.5–2.5 for the idle flow is given. The unequivocal determination of the CFR is also not always possible, since the flow at rest often cannot be determined unequivocally. However, the physiological condition of the epicardial vessels is of great interest for therapeutic planning, as it makes a decision on invasive therapy (e.g. stent implantation) much easier.

Fractional river reserve FFRmyo

The FFRmyo is an index that describes the condition of the epicardial coronary vessels (coronary vessels). The pressure conditions in a coronary vessel are identical in each segment of this vessel if the blood flow is not impaired. A measured pressure at the beginning of the vessel (Pa) always corresponds to the pressure in the distal (distant) vessel segment (Pd), regardless of the length or cross-section of the coronary artery. This applies both under resting flow and under maximum hyperemia.

The determination of the FFRmyo is basically only carried out under maximally hyperemic conditions, since there is a linear relationship between pressure and flow only under maximal blood flow to the heart muscle. If the quotient is formed from the measured values ​​Pd and Pa, the FFRmyo in a healthy vessel always corresponds to the maximum value 1 ( ).

In the presence of a stenosis, the pressure decreases distally (behind) the stenosis with maximum hyperemia. So is . A decrease in the FFRmyo below the value 1 is not only dependent on the diameter of the stenosis, its length and condition: the size of the myocardium supplied by the artery and the pathophysiological state of the associated microcirculation have a special influence. If the resistance of the microcirculation is high with maximum hyperemia and the supply area is small, it is possible that even a high-grade stenosis has little or no effect on the blood flow.

If the FFRmyo is greater than 0.80, there is no epicardial myocardial ischemia. In this case, invasive treatment of the vessel (e.g. by implanting a stent) is unlikely to be of benefit to the patient, but may even be disadvantageous. A value below 0.75 means that there is a reduction in the flow in this vessel compared to the maximum possible flow by more than 25%. A value below 0.75 clearly indicates the presence of a hemodynamically relevant stenosis. Here the patient can benefit from invasive therapy (stent implantation; bypass surgery; etc.).

The sensitivity of the FFRmyo is 88%, the specificity 100%. The FFRmyo is one of the most accurate methods of detecting the pathophysiological condition of the epicardial vessels.

commitment

The FFRmyo is not yet part of the standard for cardiac catheter examinations in Germany. Only about every 180th cardiac catheter examination is supported by the FFRmyo. This has partly to do with the difficult situation of reimbursement by the cost carriers (health insurance companies), which will change from 2010 onwards. Today, the majority of the decision whether or not to intervene in the coronary arteries is made on the basis of angiography. The consistent use of the FFRmyo leads to a postponement of such a treatment strategy. An assessment of the pathophysiology solely through the use of imaging methods is not possible without any doubt, as numerous studies show. From a coronary physiological point of view, this leads, on the one hand, to over-treatment of stenoses (> 50%) with stents (since they are assessed incorrectly angiographically positive), and on the other hand, patients are withheld from useful, invasive treatment (since their stenoses (∅ <50%) are angiographically incorrectly negative can be assessed). Under-treatment of stenoses that cause ischemia is associated with an increased MACE rate (Major Adverse Cardiac Event). For a sustainable treatment strategy, it is therefore of great advantage to prove that the stenosis actually also causes ischemia of the myocardium.

Studies

Individual evidence

  1. ↑ a b Iskander: Risk assessment using single-photon emission computed tomographic technetium-99m sestamibi imaging Sherif Iskander, and Ami E. Iskandrian J. Am. Coll. Cardiol. 1998; 32; 57-62
  2. ↑ a b DEFER: Pijls NH, van Schaardenburgh P, Manoharan G, et al. (May 2007). Percutaneous coronary intervention of functionally nonsignificant stenosis: 5-year follow-up of the DEFER Study J. Am. Coll. Cardiol. 49 (21): 2105-11. doi : 10.1016 / j.jacc.2007.01.087 . PMID 17531660 .
  3. ↑ a b c d Tonino PA, De Bruyne B, Pijls NH, et al. : Fractional flow reserve versus angiography for guiding percutaneous coronary intervention . In: N. Engl. J. Med. . 360, No. 3, January 2009, pp. 213-24. doi : 10.1056 / NEJMoa0807611 . PMID 19144937 .

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