Hybrid operating room concept for combined diagnostics, intervention and surgery in acute type A dissection^†

Abstract

OBJECTIVES

In acute type A dissection (AAAD), it is commonly decided to carry out immediate surgical repair without invasive diagnostics. The hybrid operating room (Hybrid OR) concept encompasses simultaneous haemodynamic control, non-invasive and invasive diagnostics and immediate surgical and/or interventional treatment. Results over a seven-year period are presented here.

METHODS

From March 2004 to March 2011, 1883 cardiological and surgical patients were treated in a Hybrid OR. Of these, 124 patients (age 60 ± 13, 64% male) diagnosed with AAAD were operated upon. External computed tomography (CT) was available for 87% (108/124) of cases and angiography in 15% (19/124). Preoperative transoesophageal echocardiography (TEE) was done in all patients and angiography in 57% (71/124). Surgery was performed without angiography in 27% (34/124), of which 14% (17/124) was due to shock. Postoperative control angiography followed in 18% (22/124) due to suspected ongoing malperfusion.

RESULTS

Preoperative angiography was performed in 71 patients, and no angiography related complications were observed during the procedure. A total of 32% (23/71) of these underwent coronary artery bypass graft (CABG)—for newly-diagnosed coronary artery disease in 21% of cases and for coronary malperfusion in 11%. Visceral/peripheral malperfusion syndromes, necessitating primary endovascular intervention, were detected in 23% (16/71). Ascending aorta replacement was performed in 100% (124/124) of patients, arch replacement in 88% (109/124) and descending aorta repair in 35% (44/124). Five postoperative endovascular interventions became necessary due to persistent malperfusion. In-hospital mortality was 13% (12/90) in patients who had undergone preoperative invasive diagnostics and 24% (8/34) in patients who had not.

CONCLUSIONS

The Hybrid OR concept enables the exact diagnosis of coronary status and downstream malperfusion sites and influences the design of surgical and/or endovascular treatment, without time delay and at negligible risk to the patient.

INTRODUCTION

A commonly accepted principle in the treatment of acute AAAD is immediate surgical proximal aortic repair, due to the high mortality rate associated with time delay [1, 2]. The patient's clinical status is often compromised by the time taken to reach a diagnosis. In order to eliminate several transports to diagnostic labs and to expedite treatment and transfer to a cardiosurgical centre, the diagnostic procedures are restricted to CT or echocardiography alone for evaluation of the main thoracic aortic disease [3]. Angiography is therefore not recommended for evaluation of the extent of dissection, particularly with regard to evaluation of malperfusion syndromes and co-existing coronary artery disease [4, 5]. However, the presence of malperfusion is associated with significantly increased mortality, with or without emergency proximal aortic repair, and patient comorbidities correlate to the risk profile of coronary artery disease, which represents an additional risk factor for perioperative myocardial infarction [6, 8-10].

Given the ever-present threat of tamponade and the desirable option of immediate life-saving surgery, a Hybrid operating room (OR) concept was initiated in order to combine invasive diagnostics, endovascular procedures and aortic surgery on the same operating table at the same time. Thus, it becomes possible to identify of potential concomitant malperfusion or co-existing coronary artery disease without lost time. This study presents our experience with the Hybrid OR concept over the last seven years.

METHODS AND PATIENTS

Hybrid operating room

The Hybrid OR was established in March 2004 and represents a combination of catheterization lab with operating table [11]. For reasons of good hygiene, the Artic C system with DynaCT (Siemens, Germany) is floor-mounted (Fig. 1). The table is placed in the middle of the room and has seven degrees of freedom, allowing angiographic imaging of the whole body, as well as tilting intraoperatively. Ample workspace is provided for anaesthesiology, to enable monitoring of haemodynamics, pulmonary, cerebral, spinal cord function and haematological/coagulation control. The heart-lung machine is behind the surgeon's back, opposite to the C-arm. Diagnostic imaging and monitored parameters are displayed on ceiling-mounted mobile monitors. An aseptic operative field is ensured by laminar airflow above the table. A control room behind lead glass allows direct viewing of the OR and is organized as a conference room with monitors for observation of the Hybrid OR procedures.

The Hybrid OR concept in acute aortic dissection

To ensure immediate diagnostics and treatment in acute AD, a 24-hour Aortic Team was set up, consisting of cardiac surgeons, cardiologists and cardiac anaesthesiologists. All patients with established or suspected diagnosis of acute aortic syndrome are admitted directly from helicopter or ambulance transport to the Hybrid OR in the presence of the Aortic Team.

After positioning the patient on the operating table, all the following procedures are carried out there according to our management algorithm (Fig. 2):

• Haemodynamic and pulmonary monitoring and preparation for surgery are carried out simultaneously.

• TEE is carried out immediately after intubation, giving information on the extent of dissection and entry/re-entry sites, pericardial effusion or tamponade, aortic valve status and the descending aortic situation. In cases of severe haemodynamic instability, e.g. tamponade, surgery starts immediately. In stable patients, angiography is performed via an 8-Fr guiding sheath in the femoral artery with surgical standby.

• Four potential malperfusion sites—coronary, cerebral, visceral and peripheral vascular branches—are studied for strategic planning.

• In case of a delay between the onset of symptoms, diagnosis and admission to Hybrid OR, severe static obstruction of the visceral and/or peripheral arteries, endovascular restoration of end-organ perfusion is aimed at prior to surgery (Fig. 3).

  

  Figure 3:

  A 67-year-old female patient admitted with AAAD complicated by tamponade and distal malperfusion. Angiography followed sternotomy, pericardial drainage (A, arrow) and temporary re-adaptation of the incision. True lumen collapse with dynamic visceral malperfusion was found (B) as well as static renal artery and peripheral malperfusion (C). The computed tomography after three months (D) demonstrated a regular perfusion after Bentall operation (BioValsalva^TM graft, Vascutek) and 2/3 arch replacement, which was performed after primary restoration of distal perfusion by two uncovered thoracoabdominal stents (XL-Stent, Jotec), stenting of the left renal artery and the right iliac artery.

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• In cases of dynamic malperfusion, the decision to carry out pre- or postoperative endovascular therapy depends on the haemodynamic condition of the patient.

• In cases of tamponade, sternotomy and staged release of pericardial tension by controlled drainage are carried out first. If the patient's condition stabilizes, angiography is performed. In patients younger than 50 years, coronary angiography is omitted except in cases of suspected myocardial ischaemia.

• In DeBakey Type I aortic dissection, a stiff guide wire is placed in the proximal descending aorta via a pigtail catheter, for potential antegrade stent grafting or frozen ‘elephant trunk’ placement through the arch.

• In selected cases, control angiography follows surgery to confirm the distal perfusion situation. In the event of ongoing malperfusion, additional endovascular interventions ensue.

Patients

From March 2004 to March 2011, a total of 1883 cardiological and surgical patients with cardiovascular disease, including acute coronary and aortic syndrome, patients for transcatheter valve intervention and hybrid cardiovascular operation, were treated in a Hybrid OR. Of these, 137 patients were admitted with acute aortic dissection involving the ascending aorta. Thirteen died preoperatively and were excluded from the study. Of these, eight were presented under cardiopulmonary resuscitation (CPR) after rupture or myocardial infarction and, in five patients, a surgical intervention was refused due to documented massive cerebral infarction and complete visceral ischaemia. One hundred and twenty-four underwent immediate surgery and were included in the study—92% (114/124) with acute type A AD, 2% (3/124) with acute type B AD with retrograde proximal extension, and 6% (7/124) with acutely exacerbated chronic type A AD. The delay time between onset of symptoms and treatment was less than 24 h in 83% (103/124) and longer than 72 h in 10% (12/124). Mean age of the patients was 60 ± 13 years; 64% (80/124) were male (Table 1). External diagnosis with CT scan was available in 87% (108/124) cases and invasive diagnostics in 15% (19/124). Angiography was performed in the Hybrid OR in 57% (71/124) of cases. This was decided for the following reasons: age being less than 50 years (6/34), cardiogenic shock (17/34) the surgeon's decision according to tamponade (5/34), previous coronary angiograms (2/34) and unavailability of the Hybrid OR (4/34). TEE was applied intraoperatively in all patients. In order to evaluate the influence of preoperative knowledge on the extent of the dissection and comorbidities, patients who underwent preoperative invasive diagnostics in the Hybrid OR or elsewhere (total 90/124) were compared to patients who had not undergone angiography (34/124).

Definitions and data analysis

In this study, malperfusion was defined as a direct association of symptoms with the extent of dissection. Clinical signs indicating cardiac malperfusion at time of admission were ST elevation or ventricular tachycardia in ECC and/or increased cardiac ischaemic markers. Paresis, aphasia, sensory loss and somnolence in the absence of sedation were used to determine cerebral malperfusion. Visceral malperfusion was suspected in cases with abdominal pain and elevated transaminases as well as lactate. Distal pulselessness with creatinkinase and myoglobin elevation indicated peripheral malperfusion. The integrated Penn classification was used for categorization of clinical status prior to surgery [12].

Data were selected prospectively from the institutional database for aortic disease and statistical analysis was performed using SPSS 19.0 software. Continuous variables are presented in mean ± standard deviation (SD) and categorical variables in percentages. The two-sided unpaired t-test and Fisher's exact test were used for comparison of continuous and categorical variables, respectively.

RESULTS

Time delay between primary diagnosis and admission to the Hybrid OR was a mean of four hours. Angiography on the surgical table was performed in 69 of 71 patients before sternotomy and in 2 of 71 after release of tamponade. Three patients underwent invasive diagnostics after percutaneous pericardial drainage. All patients requiring CPR were operated on immediately, without delay for angiography. Patients operated on without angiography were younger (P = 0.06) and more frequently presented intubated (P = 0.039) and with tamponade (P = 0.002). The ischaemic profile between patients with and without angiography was similar using the integrated Penn classification (Table 2).

Hybrid OR concept results

The incidence of co-existing coronary artery disease (CAD) was 27% (19/71) (Table 3). Three-vessel disease was documented in nine patients, two-vessel disease in two and one-vessel disease in eight. According to the severity of CAD, coronary artery bypass revascularization followed in 21% (15/71) of cases. No revascularization was performed in four patients with moderate coronary stenosis (3 one-vessel and 1 two-vessel disease).

Angiography revealed a dissection of the coronary arteries in 21% (15/71) requiring coronary bypass grafting in 11% (8/71). In seven patients, repair of the right coronary orifice was performed. Dissection of cerebral arteries was observed in 65% (46/71); of visceral arteries in 34% (24/71), renal arteries in 48% (34/71) and the limbs in 58% (41/71). Of these, cerebral malperfusion was documented in 19 of 46, visceral malperfusion in 13 of 24 and peripheral malperfusion in 16 of 41 patients, respectively. Retrograde endovascular interventions for visceral and/or peripheral malperfusion were performed in 23% (16/71). Twelve of 13 patients with visceral malperfusion underwent preoperative endovascular repair: four by fenestration, six by splitting of true lumen using uncovered stenting of the aorta and five by selective stenting of abdominal arteries. Additionally, retrograde stent grafting of the descending aorta was used for true lumen stabilization by severe collapse in two patients. Peripheral endovascular intervention was performed for restoration of static malperfusion in 7 of 16 by iliac artery stenting.

Operative procedures

Distal anastomosis was performed in all patients, by open technique, after resection of the entries: 12% at the level of the distal ascending aorta/proximal arch, 28% mid-arch and 60% at the distal arch. Additional antegrade stent grafting of the descending aorta was used in 35% of patients. Additional procedures are listed in Table 4. The rate of coronary artery bypass grafting was 27% and was performed for CAD more often in patients with preoperative angiography (P = 0.013).

Postoperative results

Immediate postsurgical control angiography was performed in 18% of cases and before hospital discharge in an additional 6%. Five patients underwent endovascular re-interventions for persisting malperfusion: two directly postoperatively and three thereafter (Table 4). Overall in-hospital mortality was 16% (20/124), comprising 13% (12/90) of patients who underwent preoperative invasive diagnostics and 24% (8/34) of patients who did not (P = 0.18) (Table 5). Low output syndrome was the most common reason for mortality (11%, 13/124) and was associated with preoperative cardiac malperfusion (P = 0.015). In addition, four patients succumbed to multi-organ failure, two to stroke and one to pneumonia. In-hospital mortality in patients with visceral malperfusion was 25% (3/12) after preoperative endovascular repair, compared with 75% (3/4) in patients without preoperative endovascular repair.

A visceral postoperative ischaemic event occurred in 7% (9/124) of patients, leading to explorative laparotomy in 4%. A peripheral postoperative ischaemic event was observed in 6% (7/124), requiring partial toe amputation in 2%. Three patients who were treated conventionally suffered new postoperative visceral or peripheral ischaemic events, but this did not occur in the Hybrid OR scenario. The incidence of new stroke (7%) and renal failure (38%) requiring temporary haemofiltration was similar in patients who had or had not undergone preoperative angiography. Renal failure requiring permanent dialysis did not occur.

DISCUSSION

Hybrid ORs are currently gaining popularity worldwide, due to the exponential growth of transcatheter aortic valve implantation procedures. In Essen, one of the first Hybrid ORs in the world was set up early in 2004, designed for close collaboration between cardiologist and cardiac surgeon. Close to 2000 procedures have been performed there in less than seven years. Besides transcatheter valve cases, complex cardiosurgical cases with immediate angiographic control and hybrid operations with simultaneous intervention have been carried out there, as well as high-risk vascular surgical/cardiological procedures using support systems. The potential of this OR concept is, that it enables fast online diagnostics, followed by immediate intervention and/or surgery, particularly for patients with suspected acute aortic syndrome.

In acute AAAD, the patient’s outcome depends on many factors. One of the most important is time, due to the dynamic disease process with a 1–3% death rate within the first 24 hours and a pre-hospital death rate of up to 25% [13, 14]. Multiple diagnostic tests delay transfer to the OR, therefore, referring institutions have been informed to send such patients quickly as possible to the Hybrid OR after primary CT or TEE diagnostics, without additional delay. This has led to a significant reduction of delay time from eight to four hours at our institution [3, 11].

The classic treatment algorithm—to operate quickly in acute AAAD to relieve impending pericardial tamponade, to close the proximal entry tear and to reinstall peripheral true lumen perfusion—can be fulfilled using the Hybrid OR. However, additional features have to be addressed: malperfusion is a serious risk factor and the association between malperfusion and surgical mortality has been demonstrated by several studies [6–8, 15]. Often, the underlying CT diagnosis is several hours old and more accurate information about the coronary, cerebral, visceral and peripheral perfusion state would be desirable.

Thus, the Essen Hybrid OR concept has been introduced. Primarily, a multidisciplinary 24-hour Aortic Team has been established, consisting of cardiac surgeon, cardiologist and cardiac anaesthesiologist. The patient's haemodynamic control after arrival, the primary TEE examination and the decision-making for additional invasive imaging or immediate surgery are managed collaboratively by this team of experts.

Coronary malperfusion can be detected clinically and by TEE and seen directly at surgery. However, our data demonstrate that coronary angiography on the Hybrid table revealed a co-existing coronary artery disease in 27% of patients. Though preoperative coronary artery evaluation in acute AD is normally not recommended, the results from the International Registry for Acute Aortic Dissection demonstrated no association between preoperative coronary angiography and mortality [4, 5, 16, 17]. Based on our experience, a quarter of our patients would be at risk of myocardial ischaemia without additional coronary artery revascularization, due to co-existing coronary artery disease. Thus we consider this additional preoperative knowledge valuable, if performed on a Hybrid OR table. Surgical standby certainly reduces the cardiologist's concerns over performing an otherwise risky, invasive examination.

Cerebral malperfusion still is a kind of blind spot for TEE investigation and surgical judgement depends mainly on the clinical picture. However, the angiographic knowledge of true lumen collapse, or even non-perfusion of carotid arteries, certainly influences surgical planning. Right axillary artery cannulation, in case of dissection of the innominate artery with its potential deleterious sequelae, can be avoided and switching to direct true lumen ascending aortic cannulation can be indicated [18].

Visceral/peripheral malperfusion is described as an infrequent but serious concomitant morbidity with a dynamic progress and the underlying CT diagnosis is often several hours old. More accurate information about the visceral and peripheral perfusion state would be desirable and this explains the increased incidence of end-organ ischaemia in our study, compared to others [19]. Primary surgical repair of the entry site at the ascending aorta/aortic arch using hypothermic extracorporeal circulation, with or without circulatory arrest, adds trauma to already ischaemic organs and the ensuing uncontrolled reperfusion usually ends in the patient's death. For this reason, Deeb and co-workers recommended preoperative evaluation, endovascular intervention and delaying surgery for primary distal reperfusion and stabilization [6, 14]. Although this concept may be beneficial in severe cases of visceral malperfusion, the preoperative mortality rate is essential and a subject of controversy [6]. The Hybrid OR concept offers two ways of possible outcomes after successful interventional restoration of visceral or peripheral perfusion: (i) immediate surgery following intervention or (ii) pericardial drainage and ICU-controlled delay with TEE probe left in place under haemodynamic monitoring [20]. Recovery from visceral and/or peripheral reperfusion injury is expected. Although the small number of patients does not allow a statistical analysis, we do observe a trend towards a better survival rate after endovascular perfusion repair prior to cardiopulmonary bypass, with a 75% survival rate in patients with endovascular perfusion repair vs a 25% survival rate in patients without endovascular perfusion repair. Besides preoperative intervention, postoperative control of the restoration of true lumen perfusion is possible with additional options for downstream stenting, if required. In our series, 4% of all patients underwent a secondary distal intervention postoperatively.

To the controversial aspects of the Hybrid OR concept belong the hygienic conditions due to the presence of a multidisciplinary team and the C-arm positioning on a prepared table for surgery as well as the substitution of contrast agent in an already critical renal perfusion. However, no sternal wound infection was observed and, to our surprise, the incidence of postoperative renal failure was similar for patients who underwent angiography and those who did not. We do explain the increased rate of temporary venovenous haemofiltration as a consequence of our internal policy of liberal and early use of haemofiltration in renal failure.

A limitation of the study is still the small number of cases, due to the inhomogeneity of the patient population with regard to the characteristics of dissection and their clinical status at presentation. Based on our experience, we decline the option of randomization with this complicated disease, in order to achieve a homogenous patient cohort. The increased number of patients undergoing surgery for tamponade without preoperative angiography is a result dating from the first years of our experience. In the intervening years, immediate sternotomy and controlled tamponade release has enabled angiographic evaluation to take place under stable haemodynamic conditions.

The Hybrid OR concept in acute aortic dissection represents the ideal environment for teamwork between surgeon, cardiologist and cardiac anaesthesiologist. We consider the required high level of experience in endovascular techniques for diagnostics and intervention in acute dissection not as a limitation to the concept but as an opportunity for enhanced perspectives in the treatment of type A, especially in critical clinical situations. The Hybrid OR concept, especially in acute aortic syndrome cases, has for the first time provided the opportunity to obtain reliable online information of the patient's condition, thus opening up a wide array of therapeutic options, which can be both applied and controlled again.

Conflict of interest: none declared.

REFERENCES

APPENDIX. CONFERENCE DISCUSSION

Dr W. Schiller(Bonn, Germany): The Essen group took the forward-looking decision to acquire a hybrid OR seven years ago. But time is going on, and today we have CT scanners in the emergency departments which have 64 lines and above, which are giving excellent 3D resolution, and we can judge at least the proximal parts of coronary arteries, as well as the extent and the location of the intimal tear, which is very important for operation planning. Formerly, we had to look into the arch and then we knew what was going on there. Now with modern CT scans, most of the time we know quite exactly where the tear is. Although in angiography you see good functional imaging, I would say the information is not as good as in a good CT scan.

So the first question is, what is your decision-making in operation planning concerning the arch in relation to your imaging and concerning your perfusion method, your cooling and the extent of replacement. And second, the common approach was first to replace the proximal aorta, replace the intimal tear to improve the perfusion of the patient, and then to look at what remains of the malperfusion syndromes. You have a high rate of malperfusion syndromes, probably due to the high rate of early admission: 83% of your patients came within the first 24 hours to your department, which is very high, and of course it's a sort of negative selection because otherwise patients with high risk die before they come to the department. You have this strategy first to treat malperfusion, you have these two groups which cannot really be compared because the smaller group is very small, and it's a group with a much higher risk. Have you seen any improvement compared to the time before you had the hybrid OR?

Dr Tsagakis: The number of patients is limited and therefore we cannot provide a statistical analysis for the pre- and post- hybrid OR era. However, due to the use of the hybrid room concept, the mortality rate did not increase. In addition, the hybrid OR concept underwent development during the years. At the beginning, patients admitted with severe instability underwent immediate surgery. Meanwhile, a tamponade is primarily released, then angiography is performed prior to cardiopulmonary bypass. Therefore, a clear patient cohort does not exist.

Regarding the first comment about the evaluation of entries using preferably intraoperative CT in contrast to angiography, I do agree that CT resolution nowadays is very good. But angiography allows differentation between dynamic and static malperfusion and the decision for immediate endovascular repair or not. In our clinic a static malperfusion is treated immediately. In dynamic malperfusion, the decision for endovascular intervention depends on the symptoms. This differentiation cannot be provided by CT. In addition, we also use intravascular ultrasound to detect the dissection of arteries and also for evaluation of entry site. Then, the second question was about the management of arch replacement?

Dr Schiller: Yes, concerning intimal tears and imaging.

Dr Tsagakis: We try to exclude any entries that we find. If we have an entry in the arch, of course, complete replacement is performed. If we have an entry in the descending aorta, we do antegrade stent-grafting.

Dr Schiller: But you have to look into the aorta, and how deep are you cooling if you don't know if you have to replace the arch or not?

Dr Tsagakis: We routinely perform hypothermic arrest at 25 degrees and recently in selected cases at 28. Then we open the arch and the anastomosis is performed in open technique. Thus the option to view into the descending aorta for additional tears with the angioscope is given.

Dr A. Bryan(Bristol, United Kingdom): Can I just press you a little bit on the concept. I think we can all sign up to this as a valuable concept. What I'd like to know is what about the timing of the angiography intervention? Because I think some of us might think that the primary surgery would correct a percentage of malperfusion syndromes and that therefore my proposal would be that the time for the investigation might be at the completion of the primary surgery rather than before the primary surgery. What would you say to that?

Dr Tsagakis: This is, of course, an important issue. We therefore try to reduce any delay in the angiographic procedure. The presence of the surgeon at the hybrid OR table is very important in order to manage the situation and to decide about the necessity or extent of angiography. In cases of endovascular repair, there is indeed a delay to surgery. In patients with just an evaluation of the coronary arteries and a simple angiography of the descending and abdominal aorta, time loss is about one hour.

Dr K. Imoto(Yokohama, Japan): I'd just like to ask about the coronary artery disease. You have many patients with coronary artery dissection with or without symptoms. So my question is, why don't you place a coronary stent at the catheterization? Because the myocardial infarction is established within almost 90 minutes after the coronary artery occlusion. We have experience with 6 patients who had coronary stent placement before operation with a successful result.

Dr Tsagakis: Regarding myocardial infarction, it does not only depend on the delay in the hybrid OR. Though the admission of the patients to the hybrid OR is very quick, a delay of 4 hours between diagnosis elsewhere and admission to the hybrid OR is a matter of fact. If we have a dissection of a coronary artery, myocardial damage has already taken place. Thus I don't think that additional angiography impairs prognosis. With regard to coronary stenting, I think that operative revascularization represents the best option for these patients. Due to coagulation disorders in many of these patients, a differentiated coagulation treatment is required intra- and postoperatively for bleeding. Thus, stenting of coronary arteries could induce thrombosis and occlusion.

Dr A. Haverich(Hannover, Germany): I want to come back to the remark of the chairman regarding the timing of angiography. I think your concept is unbelievably good and in 10 years from now probably all the aortic dissections will be done under those circumstances. I still believe that one should delay the angiography until after the aortic repair, because the control of the aortic dissection by putting a graft in will result in less perfusion or nonperfusion of the false lumen, which will correct by itself for a number of pathologies, including the coronary arteries. In your angiography group, you ended up with a revascularization rate that is much higher than in any published series and is probably not necessary. So again, it's a wonderful technique, but the timing of the angiography should probably be delayed until after the procedure, because also the risk of malperfusion in many of those cases has been controlled for by correcting the aortic pathology alone without the necessity of putting a stent more distally.

Author notes