In a crucial study in pigs, Oh and coworkers in 1992 described for the first time pressure-flow relations during retroperfusion in an experimental setting with selective pump retroperfusion of the anterior cardiac vein and venting of the left anterior descending artery to zero pressure . They recognized that the level of pressure in the coronary vein during retroperfusion is important for providing effective restoration of regional myocardial flow and function, but it could also cause vascular damage as suggested by silicone injection studies at high coronary venous pressures. There was a near linear pressure-flow relation in the anterior cardiac vein during retroperfusion, but these relations were variable in slope among animals, indicating the anatomic heterogeneity of the coronary venous system and the extent of venous interconnections, even within the same species. Therefore, the pressure-flow relation and the level of regional myocardial supply by retroper-fusion were dependent on the capacitance and compliance of the individual coronary venous system.
Early work on catheter-based percutaneous retroperfusion of coronary veins has been initiated by Meerbaum et al.  and Mohl et al. . It was focused on a nonse-lective treatment using a balloon catheter placed in the coronary sinus or the great cardiac vein. Though ECG-synchronized diastolic retroperfusion of the coronary sinus reached clinical application between 1986 and 1991[10-12], its relatively low efficacy and complex procedure limited wide-spread clinical use. As a consequence of the limited success of synchronized diastolic retroperfusion, selective suction and retroinfusion was developed in 1990  and shown to substantially improve efficacy in a study with "head to head" comparison of selective suction and retroinfusion to synchronized diastolic retroperfusion . Moreover, the concept of adjusting retroinfusion pressure to the individual coronary venous system by a pressure-regulated retroinfusion system was introduced in 1997  based on the findings of Oh and coworkers in 1992  described above. The next step forward then was to recognize that the systolic coronary venous occlusion pressure (SCVOP) of the individual coronary venous system determined before ischemia could be used to predict retroinfusion efficacy during ischemia. Therefore, pressure-regulation of retrograde flow is a prerequisite to optimize efficacy by avoiding under- or overperfusion of the ischemic myocardium.
The feasibility and efficacy of selective pressure-regulated retroinfusion of the coronary veins (Myoprotect®) has been shown in a clinical study during acute myocardial ischemia . Despite complete occlusion of the artery, preservation of 70-80% of baseline flow and regional myocardial function was possible during a 10 min up to 1 h ischemic period. More than 260 patients have been treated with the Myoprotect® system without complications and a success rate of more than 90% , allowing for prolonged arterial occlusion intervals without loss of function of the corresponding myocardial region (Figure 1).
Pressure-regulated retroinfusion has also been applied safely in patients with acute myocardial infarction as a regional drug delivery device to prevent ischemia and reperfusion injury.
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