Cardiac surgery is the specialty of medicine concerning the surgical treatment of pathologies related to the heart and thoracic aorta. The spectrum of modern cardiac surgery can be understood by its history beginning at the end of the 19th century.[1][2] Since then cardiac surgery developed through the work of numerous dedicated surgeons offering more and more treatments for diverse cardiac pathology. This development is still ongoing today.[3][4]

In 1882, Billroth performed the first pericardiectomy. The first successful treatment of cardiac trauma was done by Ludwig Rehn when he operated on a cardiac stab wound in 1896 against the wide held belief that the heart is not an organ on which surgeons should operate.[5] The development of cardiopulmonary bypass[6] was necessary to reach the structures of interest and was pushed by the high mortality of the early cardiac operations like embolectomy (first completed by Trendelenburg).

Surgical revascularization is one option to relieve ischemic heart disease with complicated atherosclerosis.[7] Vineberg implanted the left internal mammary artery (LIMA) into the anterior free wall forming no direct anastomoses to the coronary vessels.[8] He has observed, in earlier experiments, that collaterals develop when ischemia is present. During the 1960s several surgeons in different locations pioneered the first coronary artery bypass grafting (CABG) operations.[9] The era of reversing coronary artery disease started with the invention of cardiac catheterization by Forssman in 1929 and injection of contrast media to visualize coronary vessels and locate stenosis by Shirey in 1962. Bypass grafting and interventional revascularisation form the 2 main possibilities to treat ischemic heart disease besides drug treatment.

Surgical treatment of valvulopathies started closed mitral commissurotomy by passing a finger or instrument through the narrow orifice of the mitral stenosis to dilate or cut it as did Cutler in 1923 for the first time. The Hufnagel cage and ball valve was the first artificial valve introduced in 1952. It was placed in the descending thoracic aorta to prohibit blood flow reversal in aortic regurgitation. In 1967 a similarly structured valve, the Edwards cage and ball valve, had been implanted 1000 times for mitral valve disease.[10] Surgical techniques improved from early, single valve procedures to 4-valve replacement in 1992. Special techniques were introduced, for example, the Ross procedure replacing the aortic valve with pulmonic valve autograft. To treat proximal aortic dissection or aneurysm, Bentall implanted an artificial aortic valve combined with ascending aortic vessel prosthesis.

In 1944, cardiac surgeons Blalock, Taussig, and Thomas first forayed into the field of congenital heart lesions, when they operated on the tetralogy of Fallot, one of the cyanotic heart lesions.[11]There are also acyanotic heart lesions such as pulmonary stenosis.[12]

Regarding cardiac arrhythmias, the Cox-Maze procedure offers surgical treatment of atrial fibrillation. The evolution of cardiac pacemakers started by applying external electrodes to stimulate the heart. Lillehei placed electrodes directly to the heart during open heart surgery. The first implanted pacemaker lasted only 8 hours. Modern aggregates offer long-lasting solutions to diverse rhythm abnormalities.[13]

In 1967, several surgical teams around the world performed the first heart transplantations: Barnard in South Africa, Shumway in Stanford (offering increased post-transplant survival by adding immunosuppressive treatment), and Kantrowitz with pediatric transplantation in New York.[14]

Some devices can supply mechanical circulatory support. Since 1963, the intra-aortic balloon pump (IABP) enhanced left ventricular function through the mechanism of counterpulsation. Open heart surgery requires a cardiopulmonary bypass (CPB) to temporarily replace the human heart and lung by an external circuit consisting of pumps and an oxygenation membrane. Artificial hearts were first applied extracorporal in 1982. Later devices allowed for implantation.

Cardiac surgery represents high operative and perioperative risk requiring professional staff and advanced equipment. Besides the diseases that require cardiac surgery, the perioperative period shows a variety of characteristic pathologies: systemic inflammatory response following CBP, myocardial stunning and low cardiac output syndrome, arrhythmias, massive transfusion requirements and multiorgan involvement with kidney injury, stroke, and respiratory distress.

With the surge of interventional and minimally invasive methods to treat cardiac pathologies, the medical fields of cardiology and cardiac surgery recently need to adapt to these changes.[15] As Lytle and Mack described in their 2005 editorial, "The times they are changing" the field of cardiac surgery is undergoing a fundamental transformation. In his presidential address, Guyton said: "if we do not embrace innovation we will become its victims." Recent developments include the upcoming of cardiac arrest centers, broader and simpler application of extracorporeal membrane oxygenation (ECMO),[16] organizational changes such as fast-track hospital stay, and interprofessional decision making by heart teams, and challenges posed by an aging patient population.[17][18][19]

The rib cage surrounds the chest organs. This allows for additional protection against environmental influences but confers a higher difficulty for surgeons to reach the structures of interest. Surrounded by the ribs laterally, the sternum anteriorly, and the thoracic spine posteriorly, 2 compartments can be divided: the bilateral pleural and the mediastinal compartment. The pleural spaces contain both wings of the lung. The mediastinum encloses many structures such as the esophagus, the trachea, the vena cava superior and inferior, thoracic arteries, the vagus nerve, azygos vein, lymphatic vessels, thymic remnant and the pericardial sac containing the heart. The confined space of the pericardial sac poses the heart at risk for tamponade physiology. This occurs hematoma compresses the heart obstructing normal cardiac blood flow.[20]

As blood flows through the 4 chambers of the heart, it passes 4 valves. Reaching the right atrium via the superior and inferior vena cava, blood passes through the tricuspid entering the right ventricle and pulmonary valve to be released into pulmonary circulation. The right heart is a low-pressure system compared to the left heart, which supplies the systemic circulation that requires more myocardial tissue to produce higher pressure. Blood is collected from the 4 pulmonary veins to enter the left atrium, passes through the mitral valve, the left ventricle, and the aortic valve into the systemic circulation.[21] The aortic root comprises the sinuses of Valsalva, the interleaflet triangles, the sinotubular junction, and the aortic valve annulus with leaflet attachment; the 3 leaflets named according to the coronary arteries right, left, and noncoronary cusp (RCC, LCC, and NCC respectively). Since the parts of the valve apparatus are interdependent, surgeons might need to address connected structures to relieve pathology.

All cardiac valves are surrounded by an annulus that poses difficulties for creating artificial grafts without leakage. To illustrate the importance of anatomy and physiology, the example of mitral valve replacement and the negative consequence of left ventricular outflow tract obstruction can be named. While the aortic valve annulus is circular, the mitral valve annulus is more crescent-shaped requiring more sophisticated prosthesis and implantation technique. This is expressed by a plentitude of artificial valve models each having advantages and disadvantages regarding anatomic, physiologic, technical, and procedural characteristics. Having a closer look on the mitral valve the annulus and the anterior and posterior valve each consisting of 3 segments (A1 to A3 and P1 to P3) and are connected to the subvalvular apparatus which consists of chordae tendineae connecting the valve leaflet to the papillary muscles.

The heart has intrinsic rhythmic activity, that can be slowed or quickened through the influence of the autonomic nervous system with sympathetic reaction leading to accelerated heart rate and parasympathetic reaction leading to decelerated heart rate. The cardiac electrical conduction is structured hierarchically and runs from the sinus node through the right atrium to the atrioventricular node, the His bundle, and via the Purkinje fibers to the ventricles. The anatomic and physiologic role of the cardiac electrical activity is important to understand its clinical implications. Following cardiac surgery, atrial fibrillation is common. The Maze procedure applies anatomical knowledge to interrupt uncontrolled atrial activity for solving atrial fibrillation. The implantation of artificial heart valves can lead to atrioventricular blocking due to proximity to the valve area.

The quality of vessel grafts is important for the outcome of CABG surgery. Surgeons can harvest a variety of vessels. Arteries are of superior, long-term durability compared to veins.[22] The quality of vessel grafts can be assessed preoperatively. Commonly used vessels include the left and right internal mammary arteries (RIMA), radial arteries and the saphenous veins (SVG). Due to vessel length, the RIMA is usually connected to the right coronary artery (RCA) and the LIMA to the left anterior descending artery (LAD). The posterior descending artery (PDA) and left circumflex artery (LCX) are commonly supplied with a venous bypass graft. Venous grafts can be used to create bypasses to smaller branches such as the diagonal branches of the LAD and marginal branches of the LCX.[23]

Indications for cardiac surgery are described in current guidelines.[24][25] Although there are differences between some recommendations general indications are same. Decision making is done in consensus with cardiologists meeting as a heart team. Prior imaging with echocardiography, computed tomography(CT) , or magnet resonance imaging (MRI) is routinely necessary.

In valvular heart disease, stenotic lesions and regurgitation can be differentiated. In general classification of valvulopathies is a 3-step approach, mild, moderate, and severe, in contrast to 4-step angiographic grading done in the catheterization laboratory. Severe valve regurgitation or stenosis requires intervention. Depending on the valve affected surgeons offer replacement or reconstruction.[26]

With the upcoming of transcatheter aortic valve replacement (TAVR) first introduced by Cribrier in 2002, the heart team decides on the surgical or interventional treatment of severe aortic stenosis.[27][28] When the opening area becomes less than 1 square centimeter, aortic stenosis is severe. The operative risk is an important consideration. People with high operative risk according to EUROScore or STS score should be treated with TAVR.[29] Lower risk scores allow for surgical aortic valve replacement (SAVR). High operative risk includes patients with porcelain aorta, liver cirrhosis child pugh B and C, previous CABG with lima, and frailty. Aortic valve endocarditis requires SAVR. The 2010 PARTNER Trial compared outcomes of TAVR and SAVR thus influencing patient selection.

Decision making in aortic regurgitation requires pathophysiologic consideration. Aortic regurgitation due to enlargement of ascending aorta requires operative treatment. Patient with symptoms due to severe aortic regurgitation also need surgery. Asymptomatic patients with decreased left ventricular ejection fraction (LVEF) or increased left ventricular residual volumes should also receive operation. (LVEF less than 50% or LVEDD greater than 70 mm or LVESD greater than 50 mm). Echocardiographic characteristics of severe aortic stenosis are vena contracta of more than 6 mm pressure half-time of less than 200 ms effective regurgitant office area of more than 30 and regurgitant volume of more than 60 ml.

Mitral stenosis is mainly caused by rheumatic heart disease which is rare in industrialized countries. Mitral regurgitation (MR) is treated depending on the etiology.[30] Primary MR describes the structural pathology of the mitral valve apparatus itself including leaflets, annulus, chords and papillary muscles. Primary MR is classified according to Carpentier. Secondary, which is functional MR, is caused by left ventricular dilatation, ischemia, and tethering. In contrast to aortic valve pathology lesion affecting the mitral valve are primarily treated with repairing techniques including Alfieri edge-to-edge, resection, annuloplasty, and neochordae. Severe MR is defined by echocardiographic criteria with vena contracta more than 7 mm, a regurgitant volume of more than 60 ml, and a regurgitant fraction of more than 50%.[31]

Multivalvular disease comprises an especially difficult decision making since studies are rare.[32] When an operation for left heart disease is considered, secondary tricuspid regurgitation can be corrected concomitantly. Criteria assess the right ventricle and the tricuspid valve to decide on the operation are not clear. Tricuspid area diameter of more than 40 mm is an indication for tricuspid valve repair when mitral valve surgery is planned.[33][34][35][36][37][38]

Cardiac surgery offers treatment for a plentitude of cardiac rhythm disturbances through the implantation of pacemakers such as dual chamber devices for atrioventricular blocks, defibrillators for ventricular arrhythmia, and cardiac synchronization therapy for advanced heart failure.

Congenital heart disease is divided into cyanotic and non-cyanotic lesions. Ventricular and atrial septal defects can be surgically closed. Special operation techniques have been developed for diseases such as Ebstein anomaly, tetralogy of Fallot, and transposition of the great vessels among others.

The most common benign tumor of the heart is an atrial myxoma. The most frequent malign cardiac tumor is a sarcoma. Secondary metastatic tumors to the heart are more frequent than primary cardiac tumors. Tumors may cause obstructive or embolic symptoms.

Pulmonary thrombendarterectomy may be necessary as a final treatment option for severe pulmonary embolism. With a certain extension of the thoracic aorta, operation of dissection and aneurysm and replacement with a vessel graft are indicated.

For the therapy of coronary artery disease (CAD), surgical revascularization can be a preferred option.[39] Decisions on management can be made by the heart team where cardiologists and cardiac surgeons meet. Decision aids are the syntax score describing the complexity of CAD to decide between treatment by CABG or percutaneous coronary intervention (PCI). Left main stem and triple vessel disease are common indications for CABG. High-risk PCI patients with increased operative risk may be treated percutaneously despite difficult stenotic lesions.

Terminal heart failure despite best medical therapy can be treated with cardiac resynchronization, implantation of assist devices or heart transplantation.[40] Resynchronization therapy is indicated in patients with a severe reduction in left ventricular function (LVEF less than 35%), symptoms described as NYHA III to IV and an electrocardiogram showing the QRS complex to be longer than 130 ms. In times of organ shortage, assist devices are becoming increasingly popular.[41][42] Studies showed comparable outcomes between these 2 treatment options.[43] The REMATCH trial showed 2-year survival advantage in patients with an assist device of 23% versus 8% with medical therapy. Slaughter and colleagues compared continuous flow assist devices to pulsatile flow LVADs. The median duration of support 1.7 years for continuous flow and 0.6 years for pulsatile flow with 88% and 79% of time spend outside hospital, respectively.[44] Timing and selection of patients for assist device implantation or heart transplantation is challenging. The INTERMACS classification and the Lietz-Mmiller destination risk score are useful tools in patient selection.

During operation preparation, risk factors and contraindications are evaluated. Since cardiac surgery is limited to advanced cardiac diseases benefits of operation as last treatment options often outweigh risks. To assess the operative risk the EuroScore risk stratification tool has been developed. There are many other risk tools such as the Parsonnet score or the Society of Thoracic Surgeons (STS) score to identify patients that are eligible for surgery.[45][46][47]

Instability of the patient may cause the operation to be postponed. In a patient with myocardial infarction planned for CABG, the time point of operation may be difficult to decide. Valve replacement in cases of endocarditis may require operating on a septic patient to control the infectious source.

Cardiac surgery requires a lot of sophisticated equipment. For diagnostic purpose, pulmonary artery catheter, thermodilution techniques, pulse contour analysis, ultrasound, among others can be used to assess cardiac performance and disease. Critical issues related to cardiac output, volume responsiveness, and tissue oxygenation should be addressed.[48]

Equipment for treatment includes pacemakers, assist devices, extracorporeal membrane oxygenation (ECMO), and CPB. The application of CPB started in the 1930s when Gibbon used an external pump circuit to maintain life in Boston. The development was interrupted due to early drawbacks. Since then, modifications have been made. Dogliotti presented a partial heart and lung machine with 1 liter per minute flow in 1951. Hypothermic technique reducing metabolic demand and injury to the heart was first used by Lewis in 1952 when closing an atrial septal defect. Lillehei came up with the idea of cross circulation. He temporarily replaced one dog's circulation by sharing it with another dogs circulation. A broader application was possible with the mechanical heart-lung machine by Kirklin who made modifications to the IBM Gibbon machine, which increased the number of survivors. The use of CPB allows for venting the heart and clearing the operating area.[49]

However, CPB comes with side effects. Exposure to the circuit elicits a systemic inflammatory response.[50] Changes to the operation technique, such as decreasing time and size of CPB, and changing the surface of the tubes have an effect. The inflammatory response to CPB appears similar to infection triggered an inflammatory reaction with increased inflammatory markers and signs of shock, but the time course is different, peaking on the first postoperative day and decreasing after that.[51] Cuthbertson described SIRS due to CPB as ebb and flow process with initial reduced metabolic activity lasting 2 to 3 days, followed by hypermetabolic phase lasting for over a week. Several solutions have been proposed such as aprotinin, heparin-coated CPB circuits, hemofiltration, leukofiltration, and off-pump coronary artery bypass (OPCAB).[52][53]

Use of CPB and assist devices requires frequent coagulation tests. Together with cases of postoperative hemorrhage, usual coagulation diagnostic such as international normalized ratio (INR) and partial thromboplastin time (PTT) and more detailed laboratory assessment, for example, rotational thrombelastography, activated clotting time (ACT) or certain coagulation factors (antithrombin III, fibrinogen, factor VII) may be necessary.[54]

Veno-venous ECMO includes an oxygenator and thus supports the respiratory system in adding oxygen and removing carbon dioxide. Veno-arterial ECMO not only allows for oxygenation and decarboxylation but also replaces cardiac output partially. Cannulation for VA-ECMO is either placed centrally in the ascending aorta at sternotomy producing antegrade flow or peripherally with cannulas placed in the external iliac artery and vein. ECMO can be used as a bridge to recovery, bridge to bridge and bridge to transplant modality.

The use of intra-aortic balloon pump has decreased since studies could not show any benefit in mortality. Initial physiologic consideration was improved diastolic coronary perfusion of the coronaries and pull effect during systole via counterpulsation of a balloon placed in the descending thoracic aorta.

In valve replacement, decision making on which prosthetic heart valve to use is necessary. Mechanical heart valves offer higher resistance to structural valve degeneration (SVD) but require lifelong anticoagulation. Mechanical heart valves are recommended for younger patients. Bioprosthetic heart valves either from porcine or pericardial tissue do not require anticoagulation but may suffer from earlier SVD and reoperation.[55] Bioprosthetic heart valves are indicated in women that wish to have children and older patients. An additional option for aortic valve replacement is Ross procedure which is a pulmonic autograft placed in aortic position.[56]