Reoperative Repair of the Aortic Root and Ascending Aorta

Elective repair of aneurysms involving the ascending aorta and aortic root is performed with predictably low operative risk. Complex procedures such as composite valve-graft replacement or valve-sparing root reconstruction carry an expected mortality rate of less than 4%, with surprisingly few perioperative complications.^1–4 Cardiac reoperations such as coronary artery bypass grafting (CABG) and valve replacement currently carry little increase in risk above a first-time operation.^5,6 However, reoperative surgery on the ascending aorta continues to challenge cardiac surgeons. The mortality rate associated with these complex reconstructions is at least 3 times higher than it is for the initial surgery. Complications after such procedures also occur with disappointingly high frequency, leading to substantial morbidity and delayed recovery.

The earliest report on this high-risk cohort examined 59 patients undergoing 67 reoperative aortic procedures.⁷ Myocardial failure, stroke, and hemorrhage contributed heavily to morbidity and death. Surgeons with a particular interest in aortic disease have dramatically reduced the risk of these reoperations^8–13 through advances in myocardial and cerebral protection and surgical technique. Excellent long-term survival and freedom from further surgery can be anticipated for a majority of patients.¹³ This report updates our previously published results⁸ in this high-risk surgical cohort.

Patients and Methods

Our primary study on this population of patients was approved by the institutional review board of the Weill Cornell Medical College. From July 1997 through March 2011, 1,531 consecutive patients underwent reconstruction of the ascending aorta or aortic root for aortic aneurysms or dissections. Of these patients, 242 had undergone previous cardiac surgery. Patients with either native or prosthetic aortic valve endocarditis were excluded from this analysis. Patients' ages ranged from 24 to 85 years (median, 69 yr). Men comprised 174 of the 242 patients. Preoperative comorbid conditions are listed in Table I. Chronic renal insufficiency was defined as a baseline creatinine level greater than 1.5 gm/dL. The previous cardiac surgery procedures appear in Table II. The extent of aneurysmal disease, the presence of aortic dissection, and the proximity of the aorta to the sternum were evaluated in all patients preoperatively by means of computed tomographic scans of the chest and abdomen. Right- and left-sided heart catheterization was also performed in all hemodynamically stable patients. Transthoracic echocardiography was performed if left ventricular function could not be determined at the time of catheterization.

Table I. Preoperative Comorbid Conditions in 242 Patients Undergoing Reoperative Repair of the Aortic Root and Ascending Aorta

Table II. Previous Cardiac Surgery Procedures in 242 Patients Undergoing Reoperative Surgery of the Aortic Root and Ascending Aorta

Operative Techniques

General anesthesia, right-sided heart catheterization, and transesophageal echocardiography (TEE) were routinely performed after safe induction of general anesthesia. External pacing and defibrillation pads (ZOLL Medical Corporation; Chelmsford, Mass) and cerebral oxymetry monitors (Somanetics Corporation, part of Covidien; Troy, Mich) were positioned, and tubing from the cardiopulmonary bypass (CPB) circuit was brought onto the field. Either aprotinin or amicar was used in all patients.

A reoperative median sternotomy was performed in 1 of 3 ways. If preoperative computed tomography showed a clear space below the posterior sternal table, an oscillating saw was used to divide the sternum. If the plane between the posterior sternum and the heart or aorta was thought to be diminutive, the mediastinal contents were dissected away from the posterior sternal table under direct vision. The sternum was then divided sequentially with a reciprocating saw.¹⁴ If there was no space between the sternum and the aorta, femoral or axillary artery cannulation was performed, CPB was initiated, and systemic cooling to 18 °C was performed. The sternum was then opened with an oscillating saw, with the patient under profound hypothermic circulatory arrest (PHCA). In cases in which significant aortic insufficiency was present, a small anterior thoracotomy was made over the ventricular apex for the placement of a vent.

In cases wherein presternotomy PHCA was not required, dissection of the cardiac anatomy, including all bypass grafts, was completed before heparin was administered. If the patient had a pseudoaneurysm or a true aneurysm (without dissection), the ascending aorta or aortic arch was preferred as the site for arterial cannulation. In the presence of a chronic or acute type A dissection involving the arch, the femoral artery was the preferred second site for arterial cannulation. Axillary artery cannulation was rarely needed. To assist with myocardial protection, padded bulldog clamps were used to occlude patent internal mammary artery grafts. Cold-blood potassium cardioplegic solution was administered in an antegrade and retrograde fashion. When PHCA was required, the patient was cooled to a bladder temperature of 18 °C. Retrograde cerebral perfusion was delivered as previously described.¹⁴

All postoperative complications were recorded, and mortality was defined as the death of any patient in the hospital or within 30 days of the procedure.

Statistical Analysis

A retrospective, comparative statistical analysis of perioperative variables was performed using the SPSS statistical package (SPSS, owned by IBM Corporation; Somers, NY). Univariate analyses were performed with χ² analysis to determine the relationships between mortality and perioperative risk factors. The influences of these significant factors on mortality were then examined using multiple logistic regression. Parameters with a P value <0.05 were included in the model.

Results

The indications for surgery are listed in Table III. Of the 242 patients in this cohort, 113 required reconstruction of the ascending aorta at the sinotubular junction with a tube graft. The remaining 129 had reconstruction of the aortic root: 103 had composite replacement of the aortic root via the exclusion technique,⁸ 21 required a modification of the Cabrol procedure,¹⁵ and 5 underwent valve-sparing reconstruction. One hundred sixty-seven (69%) required aortic arch reconstruction.

Table III. Indications for Surgery in 242 Patients with Previous Cardiac Surgery Requiring Reoperative Repair of the Ascending Aorta and Aortic Root

The aortic valve required repair or replacement in 162 cases (67%). Fourteen additional valve procedures were necessary.

Of the 49 patients with previous CABG, 45 (92%) had patent saphenous vein grafts requiring reimplantation; 44 of the 242 patients in the cohort (18%) required new bypass grafts.

The mean time of CPB was 172 minutes (range, 63–352 min; median, 163 min), and the mean myocardial ischemic time was 98 minutes (range, 22–208 min; median, 102 min).

Blood product usage was also recorded for these procedures. The mean number of units of packed red blood cells and fresh frozen plasma needed was 1.4 units per patient (packed red blood cell range, 0–13 U; fresh frozen plasma range, 0–9 U). Approximately 3.8 units of platelets were needed for each patient (range, 0–24 U), and a mean of 0.8 units of cryoprecipitate (range, 0–20 U) were also used.

Postoperative complications are listed in Table IV. A return to the operating room for postoperative hemorrhage did not significantly increase the in-hospital mortality rate (P=0.5). One patient had a prolonged period of hypotension secondary to catastrophic bleeding upon sternal re-entry. Of the major abdominal complications, acalculous cholecystitis was treated successfully with cholecystectomy; an additional patient died secondary to gangrenous bowel. There were no deep sternal wound infections.

Table IV. Postoperative Complications in 242 Patients Undergoing Reoperative Repair of the Aortic Root and Ascending Aorta

Ten patients did not survive reoperative aortic surgery (4.1%). Age greater than 75 years (P <0.0001), CPB time longer than 4 hours, (P <0.0001), cross-clamp time longer than 150 min (P <0.0001), previous CABG (P <0.014), postoperative respiratory failure (P <0.004), and the need for a perioperative intra-aortic balloon pump (P <0.0001) predicted perioperative death by univariate analysis. Age greater than 75 years was the only risk factor (P <0.025, relative risk=12.38) to remain significant under multivariate analysis.

Discussion

Patients who require reoperations on the ascending aorta and aortic root still have a higher operative risk than do those undergoing first-time procedures. Previous studies have reported operative mortality rates ranging from 5% to 19%.^8–13 After successful reoperation, patients can expect excellent long-term results with 5- and 10-year survival rates of 80% and 60%, respectively.¹³ In addition, when the surgical approach is aggressive at reoperation, few patients will need future procedures for aortic-related problems.

Statistical analysis of previously published reports examining these high-risk procedures has identified several risk factors that contribute to poor outcome. Advanced New York Heart Association functional class, preoperative renal dysfunction and postoperative hemodialysis, advanced age, long duration of CPB, and myocardial ischemia continue to weigh heavily on perioperative morbidity and mortality rates. Technical complications can be catastrophic, and safe sternal re-entry is the first step toward a successful outcome. In the series reported by Schepens and colleagues,¹⁰ 2 of 3 patients who had re-entry problems died. Our single experience with this complication produced equally dismal results, and we do not hesitate to apply pre-entry PHCA when there is potential for this fatal event. Preoperative imaging of the chest should identify patients who are in need of this re-entry technique.

Previous coronary bypass grafts create exceptional technical challenges for surgeons performing these operations. In addition to the extended time needed for vein graft reimplantation or new bypass grafting, marginal myocardial protection, especially with a patent internal mammary artery graft, can lead to a greater incidence of ventricular failure. After a padded clamp has been placed on the patent mammary graft, retrograde cardioplegia should be started in a meticulous fashion. When extended periods of myocardial ischemia are anticipated, there should be concern for right-sided heart protection. In this setting, liberal retrograde administration of cardioplegic solution is encouraged, along with obtaining control of the internal mammary artery. For elective surgery in patients with the constellation of complex aortic disease and extensive native-vessel coronary artery disease, percutaneous coronary intervention could be considered as an alternative to surgery. For patients in need of urgent or emergent aortic surgery, a higher operative mortality rate is expected when extensive coronary disease is present.

Patients with ascending aneurysms or dissections in the setting of previous cardiac surgery present formidable surgical challenges. However, most will have excellent short- and long-term survival following these complex procedures. A successful outcome can be expected when technical mishaps are avoided. Patients older than 75 years with complex aortic disease and significant coronary artery disease are members of a particularly high-risk cohort that deserves thoughtful preoperative evaluation.