Editorial comment: “Plug‐In Hybrid”—Are we ready for this in heart valve surgery?

If we think about plug‐in hybrids, the treatment of paravalvular leaks in cardiac surgery may not be the first thing that comes to mind. Yet, there appears to be an attractive analogy between the plug in hybrid car and an interventional device that may be “plugged in” intra‐operatively to treat a paravalvular leak. Both technologies provide additional degrees of freedom to the fields, combine different technologies but may also be criticized for their increase in cost, introduction of new problems and their questionable practical need. We address this analogy based on a case series presented in this issue of the Journal of Cardiac Surgery.


| INTRODUCTION
The automobile industry has presented the combination of a combustion engine with an electric engine (hence, plug-in hybrid) as a meaningful development to meet the environmentally required need to reduce carbon dioxide emission, but still maintain the flexibility of modern mobility and avoid range anxiety. While this technical alliance may serve its purpose for specific situations, its value has been questioned for the general lack of efficiency improvement. 1 Metallic occlusive devices have been developed to percutaneously occlude vessels or intracardiac openings, such as atrial or ventricular septal defects. 2 These devices have then been adopted to address paravalvular leaks (PVL) in patients that have high operative risks. 3 The first descriptions of such techniques date back to the early 90 s. 4 To address PVL in patients undergoing conventional (mostly redo) surgery, different surgical options exist for even challenging situations.
In addition, some experts may argue that ample techniques exist to avoid leaks to occur during a primary valve replacement. Thus, the intra-operative use of an interventional occluder to "plug up a technical problem" (although helpful) may be considered unnecessary, similar to the plug-in hybrid car. So let us examine the topic closer.

| PATHOPHYSIOLOGY OF PARAVALVULAR LEAKS
PVL present at the end of a classic aortic or mitral valve replacement is an unpleasant and infrequently discussed complication. The incidences of PVL amount up to 10% in the aortic position and up to 17% in the mitral position during follow-up. [5][6][7][8][9] PVL is often asymptomatic, but if it becomes symptomatic, its management is challenging. 10 The guidelines provide a class I recommendation for surgery in patients with acceptable operative risk and a class IIa recommendation for a transcatheter approach in patients with prohibitive operative risk. 3 Mild PVL has been considered harmless until the advent of transcatheter aortic valve implantation generated large amounts of patients with mild PVL giving rise to concern regarding a potential long-term detrimental effect. 11 Inspecting the literature carefully reveals similar associations for PVL after classic surgery. 10 The occurrence of PVL after classic surgery have been associated with endocarditis (a factor, i.e., relatively independent of technical aspects) and a whole series of technical factors that may or may not be avoided during the index valve replacement. Table 1 shows a listing of these factors that have been associated with the occurrence of PVL either in the mitral or the aortic position. 5,[12][13][14][15] Let us examine them and our ability to avoid its occurrence.

| TECHNICAL CONSIDERATIONS TO AVOID PVL
It should be clear that using upledgeted sutures (mainly for the aortic position) and running sutures may carry a greater risk of cutting through potentially friable tissue. This risk can easily be avoided by using pledgeted sutures, although some surgeons may argue that in small aortic annuli, the placement of pledgets into the outflow tract may limit hemodynamic performance. 16 Supraannular placement of an aortic valve prosthesis has been described as a risk factor for PVL. 12,13 This may at first be surprising because a properly placed supra-annular prosthesis should be pushed onto the annulus during diastole, a mechanism which counteracts the development of PVL. However, this consideration brings us to the proper size and geometric placement of a prosthesis into an annulus (be it aortic or mitral). If the distances (e.g., from commissure to commissure or from P1 to P3, etc.) are not equally distributed along the prosthetic sewing ring, different forces may act at different parts of the sewing ring. Such geometric inconsistencies may have an impact on the development of PVL during follow up. They may also explain the occurrence of PVL in supraannular aortic position, specifically in the non-coronary position. It is conceivable that "more sewing ring" remains for "less native annulus" in the non-coronary part which is often the last area to be tied. The result is greater forces on the sutures being applied during tying and an increased risk of rupture or suture dehiscence, im- | 2427 be heavily criticized, may turn out to be helpful enrichments of the classic surgical armamentarium.

ACKNOWLEDGMENT
Open access funding enabled and organized by Project DEAL.

CONFLICT OF INTERESTS
Joseph Zacharias receives speaker fees from Edwards Lifesciences, Cryolife, Abbott and Medtronic. Torsten Doenst has no conflict of interest to declare.