## 2 Patients and Methods
### Surgical Technique  
The right mini-thoracotomy approach, perfusion strategies and aortic clamping techniques adopted at our institution have been described previously [7; 8; 9; 10; 11; 12]. Briefly, a double lumen endotracheal tube was positioned to allow single left lung ventilation. All patients underwent operation through a right anterolateral mini-thoracotomy in the fourth inter-costal space. A soft-tissue retractor was used to expose the surgical port. No rib resection was performed in any of the patients. To improve the vision, an endoscope was inserted in an accessory port created below the working port, which also served for carbon dioxide insufflation to saturate the chest and minimize the hazards of air trapping and systemic embolism. An additional sixth intercostal space port was created for pump suction. After full heparinization, cardiopulmonary bypass was established with the patient cooled to  
Figure 2: Cardiac computed tomography-based measurements of MAC using DICOM “OsiriX MD” viewer. (**A**) Calcium thickness measurement simulating a surgical short axis view. (**B**) Calcium distribution along the perimeter of the annulus. (**C**) Trigone involvement (arrows) and internal area of the annulus. (**D**) Leaflet involvement (arrows). 28-32 \({}^{\circ}\)C, depending on the anticipated complexity of the operation. Arterial perfusion was routinely gained with a peripheral femoral or axillary cannulation, while venous drainage was obtained via double femoral and percutaneous jugular cannulation. Axillary cannulation was indicated to provide antegrade systemic perfusion in the case of severe atherosclerotic burden [9]. Aortic clamping strategies adopted during the study period were the endoaortic clamping occlusion and the trans-thoracic clamp. In the endoaortic clamping setting, aortic occlusion and cardioplegia delivery were gained with a balloon catheter inserted through the sidearm of a 21-23F femoral arterial cannula (Intraclude\({}^{\circledR}\), Edwards Lifesciences, Irvine, CA, USA). In the trans-thoracic clamping setting the clamp was addressed towards the ascending aorta through the first intercostal space with a Chitwood clamp or through the main port with a Cygnet\({}^{\circledR}\) flexible clamp. Cardioplegia was delivered through a 7F cardioplegia needle (CalMed Technologies, Santa Inez, CA, USA) placed into the proximal ascending aorta. Antegrade myocardial protection was provided with St. Thomas (Plegisol\({}^{\circledR}\), Hospira Inc., Lake Forest, IL, USA) or, more commonly, Custodiol (Bretschneider histidine, tryptophan, ketoglutate solution, Kohler Chemie, Bensheim, Germany) cold crystalloid cardioplegia [12]. No additional topical cooling, nor retrograde cardioplegia through the coronary sinus, were used on any patient. Superior and inferior vena cava snaring was obtained by placing tourniquets around the vessels or by placing endovascular balloons (7F, 65 cm) (Meditech Boston Scientific Corporation, Natick, MA, USA) to provide a temporary mini right atriotomy to drain the cardioplegic solution and in patients requiring associated right atrial procedures. The MV was exposed through a standard left atriotomy, parallel and posterior to the interatrial septum with minimal dissection of the interatrial groove. The extension of the calcification bar, leaflet involvement and the chances of valve repair were assessed. In case of valve replacement, the anterior leaflet was resected, while the posterior leaflet and corresponding chord were left intact whenever possible to minimize the hazards of fragilization of the atriventricular junction. In general, the least possible debridement was undertaken, primarily aimed to remove only protruding calcium which might interfere with the proper seating of the prosthesis. Nevertheless, a variable extension of posterior leaflet resection, possibly leaving in place the basal chordrae, was unavoidable in some cases.