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Ann Thorac Surg 1997;63:998-1002
© 1997 The Society of Thoracic Surgeons
Departments of Neurology, Cardiothoracic Surgery, and Cardiothoracic Anesthesia, Cornell University Medical College, New York, New York
Accepted for publication October 23, 1996.
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Abstract |
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 TopFootnotes Abstract IntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Methods. We monitored 82 patients during coronary artery bypass grafting with this technique and related the numbers of emboli to the outcomes and length of hospital stay.
Results. We detected cerebral emboli in all patients. Patients with stroke (n = 4; 4.9%) had a mean of 449 emboli, as compared with 169 emboli in patients without stroke (n = 78) (p = 0.005). Patients with major cardiac complications (n = 7) had a mean of 392 emboli, as compared with 163 in patients without such complications (n = 75) (p = 0.003). The mean hospital stay of survivors was 8.6 days in patients with fewer than 100 emboli (n = 40), 13.5 days in patients with 101 to 300 emboli (n = 23), 16.3 days in those with 301 to 500 emboli (n = 16), and 55.8 days in patients with more than 500 emboli (n = 6) (p = 0.0007). This relation was unchanged when patients with complications were excluded. The correlation between embolization and outcome was independent of the extent of aortic atheroma or age.
Conclusions. Emboli detected during coronary artery bypass grafting are significantly related to major cardiac and neurologic complications and affect length of stay in all patients, even in the absence of such specific complications.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Coronary artery bypass grafting is an effective and durable treatment for patients with multivessel coronary artery disease. Improvements in surgical and anesthetic techniques have led to a steady decline in overall operative mortality and cardiac morbidity in the last decade. However, as the number of elderly patients undergoing bypass grafting has risen, neurologic complications have become the leading cause of morbidity in this group of patients [1, 2]. The etiology of this dysfunction is multifactorial and includes hypoperfusion [3], altered autoregulation, and embolization [4–7]. The advent of transcranial Doppler ultrasonography (TCD) has enabled emboli to be detected intraoperatively in the cerebral circulation in most patients [7–9]. Two recent studies have attempted to determine the neurologic impairment resulting from such embolization [9, 10].
Stroke, the most convincing evidence of neurologic dysfunction, occurs in approximately 4.7% to 5.2% of patients perioperatively [11, 12]. Data for a large number of patients are therefore required to establish, with any certainty, a relationship between embolization and stroke alone. Cardiac complications, on the other hand, are more common, occurring in over a quarter of patients [13–15]. Embolization can thus be related to cardiac outcome using the data from a smaller number of patients. The duration of hospitalization, the current "gold standard" for assessing short-term outcome in an increasingly cost-conscious environment, is readily available for all patients, and of indisputable importance.
In this study, we analyzed the cardiac complications and length of hospital stay (LOS), in addition to stroke, which is the standard outcome parameter, to establish convincingly the relationship between cerebral embolization and clinical outcome.
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Material and Methods |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Anesthesia
Morphine and lorazepam or midazolam served as premedication, and thiopental, fentanyl, and pancuronium were used for induction. Anesthesia before and after bypass grafting was maintained with additional boluses of fentanyl and midazolam, as per a standardized protocol.
Cardiopulmonary Bypass
We used membrane oxygenators in conjunction with nonpulsatile centrifugal pumps. A 40-µm blood filter (Ultipor; Pall Biomedical) was incorporated into the arterial perfusion line. Bypass was initiated at flows of 2.4 L•min-1•m-2 at normothermic body temperatures and reduced to 1.6 L•min-1•m-2 at 28°C. We regulated the systemic blood pressure pharmacologically to maintain mean arterial pressures of between 50 and 80 mm Hg. We routinely used gravity venting at the aortic root but not ventricular venting. Surgical and anesthetic staff were blinded to the TCD findings during the operative procedure.
Standard Transesophageal Echocardiography
We performed biplanar and monoplanar transesophageal echocardiography on 70 patients after the induction of general anesthesia and endotracheal intubation and again at the end of the surgical procedure. A 5-MHz transesophageal echocardiography probe (Acuson) and an Acuson 128 XP system were used. All studies were recorded on standard VHS videotape and subsequently interpreted. We assessed the severity of ascending, arch, and descending aortic atheromas individually and graded each segment as follows: grade I, normal to mild intimal thickening; grade II, severe intimal thickening; grade III, atheroma protruding less than 5 mm into the lumen; grade IV, atheroma protruding 5 mm or more into the lumen; and grade V, atheroma with a mobile component. The mean aortic grade was defined as the mean of the three segments.
Intraoperative Transcranial Doppler Ultrasound Monitoring
We continuously monitored the middle cerebral artery of 82 patients from before aortic cannulation to after bypass discontinuation using a 2-MHz pulsed-wave TCD probe (Medasonics-CDS) placed on the patient's temple and adjusted to a depth of 4.5 to 6.0 cm. Embolic signals (ES) were defined as high-amplitude (greater than flow velocity), unidirectional, transient signals lasting less than 0.1 second and associated with a characteristic chirping sound. Data were stored on disks and subsequently reviewed and manually counted by a single examiner blinded to the neurologic outcome. The number of aggregate ES was concurrently recorded by an automated counter. This number was only used when flurries of embolization made manual counting impossible. We recorded the timing of all major intraoperative events and numbers of ES occurring within 4 minutes of aortic cannulation, at the inception and termination of bypass, at aortic clamping, at clamp release, and at decannulation.
Neurologic Assessment
Forty-four patients were examined by a neurologist blinded to the TCD data. These patients were examined preoperatively, in the immediate postoperative period, and before discharge. Neurologic evaluation of the remaining 38 patients consisted of chart review only. Stroke was defined as as the occurrence of a focal deficit persisting for more than 24 hours.
Cardiac Evaluation
All cardiac complications were determined during hospitalization and documented by the responsible cardiologist or intensive care anesthesiologist, then entered into a database system. Patient charts and the database were subsequently reviewed. Complications were graded as minor (sustained supraventricular arrhythmia) or major (ventricular arrhythmia requiring therapy, myocardial infarction, cardiogenic shock, failure to come off bypass, or the need for placement of an intraaortic balloon pump).
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Results |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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).
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Thirty-four patients (41.5%) suffered cardiac complications, the most common of which were supraventricular arrhythmias, including atrial flutter or fibrillation (n = 29) and supraventricular tachycardia (n = 4). Major cardiac complications occurred in 7 patients, with ventricular tachycardia or fibrillation occurring in 5, cardiopulmonary arrest in 1, myocardial infarction in 1, and cardiogenic shock with failure to come off bypass in 1. Three of these 7 patients had both major and minor cardiac complications.
The mean number of ES among the 34 patients with any cardiac complication in whom complete TCD data were available was not significantly different from that in patients without cardiac complications (226 versus 153; p = 0.1). Overall cardiac complication rates were 35% in patients with fewer than 100 ES, 42% in patients with 101 to 300 ES, 50% in patients with 301 to 500 ES, and 62% in patients with more than 500 ES (p = not significant). Similarly, minor cardiac complication rates were 27% in patients with fewer than 100 ES, 41% in patients with 101 to 300 ES, 40% in patients with 301 to 500 ES, and 25% in patients with more than 500 ES (p = not significant).
The mean number of ES among the 7 patients with major cardiac complications was 392, as compared with 163 in the remaining 75 patients (p = 0.003). Patients with major cardiac complications had larger numbers of emboli than patients with either minor (p = 0.04) or no (p = 0.01) cardiac complications (one-way analysis of variance) (Table 1). However, there were no significant differences between patients with minor and no cardiac complications (p = 0.8). Major cardiac complication rates were 4.3% in 69 patients with fewer than 400 emboli, as compared with 30.7% in 13 patients with more than 400 emboli (p = 0.0015). The 2 patients with the largest numbers of ES died, with 1 failing to come off bypass (818 ES) and the other suffering multiple strokes (947 ES). Age did not differ significantly between the patients with and without major cardiac complications (71 versus 65 years; p = 0.17).
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. The mean LOS was 8.6 ± 2.7 days in patients with fewer than 100 ES, 13.5 ± 6.9 days in patients with 101 to 300 ES, 16.3 ± 4.8 days in patients with 301 to 500 ES, and 55.8 ± 9.7 days in patients with more than 500 ES (p = 0.0007). Results were similar when patients with major cardiac or neurologic complications were excluded.
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Comment |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Using TCD, emboli have previously been detected intraoperatively in the middle cerebral artery of most patients undergoing cardiac operations [7–9], and their occurrence has been related to specific operative events [6–8]. Several recent prospective studies have established the clinical relevance of such embolization. Clark and associates [9] found neurologic complications in only 2 of 83 (2.4%) patients with fewer than 30 emboli detected by TCD but in 7 of 20 (35%) patients with more than 60 emboli. Furthermore, they found cardiac complication and mortality rates of 0.9% and 4.7%, respectively, in patients with fewer than 30 emboli, as compared with rates of 20% and 15%, respectively, in patients with more than 60 emboli. Similarly, Pugsley and colleagues [10] found a cognitive deficit 8 weeks postoperatively in 43% of 100 patients with more than 1,000 emboli but in only 8.6% of those with fewer than 200 emboli. In accordance with the findings from these studies, we found three times the number of emboli in patients with stroke as compared with the number in those without stroke.
The relationship noted between the number of intracranial emboli detected and serious cardiac complications in this series indicates that coronary embolization may also be clinically important. Coronary embolization has previously been documented to occur in relation to a variety of invasive cardiac procedures, including coronary artery bypass grafting [16–23]. Unlike cerebral embolization, however, the incidence of coronary embolization during cardiac operations is still unknown, because currently available echocardiographic techniques are not capable of sufficient resolution to visualize emboli within the lumen of coronary arteries and emboli are only rarely seen by the naked eye [17, 21].
The effects of particulate coronary embolization on the myocardium were established in an autopsy study of 32 patients dying after coronary angioplasty [17]. Thrombotic or atheromatous emboli were present in 26 of the 32 (81%) patients in this study, as compared with only 1 of the 39 control patients. Emboli were present in 26 of the 29 (90%) patients with infarct extension or new infarct but in none of the 3 without, and in 21 of the 22 (95%) patients with new electrocardiographic changes, as compared with only 5 of the 10 (50%) patients without such changes. Furthermore, 82% of the emboli were confined to the branches of the artery operated on.
The consequences of coronary embolization during coronary atherectomy have also been studied in vivo [19]. In this study, clinical distal embolization occurred in 33 of 111 (30%) patients but only 12 (10%) of these emboli were visible angiographically. Myocardial infarction, mortality, and emergency bypass operation rates did not differ between patients with and without embolization, but the LOS was significantly higher in those with emboli (3.9 versus 2.4 days).
In our study, we found the LOS, which is, perhaps the most sensitive index of short-term surgical success, to be related to the numbers of emboli detected. The duration of hospitalization clearly reflects major cardiac and neurologic complications, in addition to other variables not specifically addressed or even defined.
In patients undergoing coronary artery bypass grafting, there is a tremendous variation in the mean numbers of emboli reported by different authors, ranging from 36 [9] to 326 [24]. These differences are no longer attributable to the use of membrane oxygenators and arterial filters, however, because these are now used routinely, but they may be related to differences in the anesthetic agents [25], degree of hypothermia, cardioplegia [24], clamping techniques [8], and TCD monitoring techniques used, all of which can markedly affect the numbers of emboli that form. The distribution of emboli, on the other hand, is remarkably similar in all studies, being heavily skewed toward small numbers of emboli [9, 10, 24]. Sixty-five percent of patients in our study and over half of those in previous studies had fewer than 200 emboli [10, 24], with only a small fraction of patients having more than 500 emboli.
Neurologic complications are related to the severity of the aortic atheroma as well as to numbers of emboli, despite the fact that the severity of the aortic atheroma and the number of emboli are not significantly related to each other. The obvious relationship between the extent of aortic atheroma and the numbers of atheromatous emboli is most likely obscured by the large numbers of gaseous emboli that form and the inadequacy of transesophageal echocardiography in visualizing the ascending segment.
The body of evidence linking embolization to clinical outcome and procedural cost is growing. This has prompted considerable debate regarding the feasibility of using pharmacologic cerebral protection during bypass procedures, which may only be justifiable in high-risk groups such as those with large numbers of emboli. In the interim, anesthetic and surgical techniques are slowly being modified in an attempt to reduce the numbers of emboli that form. In doing so, and assuming a causal relationship between embolization and outcome, both the complication rates and duration of hospitalization may be reduced.
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Acknowledgments |
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Footnotes |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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