Cardiac and neurologic complications identify risks for mortality for both men and women undergoing coronary artery bypass graft surgery.

BACKGROUND: Despite a number of studies showing that women and men respond to coronary artery bypass graft surgery differently, it is not known whether variables associated with mortality are the same for women and men. The purpose of this study was to identify variables independently associated with mortality for women undergoing coronary artery bypass graft surgery. METHODS: Single-institutional data were prospectively collected from 5,113 patients (1,558 or 30.5% women) undergoing coronary artery bypass graft surgery. The database was reviewed for patient characteristics and operative outcomes based on sex. Complications evaluated included low cardiac output syndrome (cardiac index < 2.0 l x min(-1) x m(-2) for > 8 h, regardless of treatment), stroke (new permanent global or focal motor deficits), Q-wave myocardial infarction, postoperative atrial fibrillation, and operative mortality. RESULTS: Women were older than men, and they were more likely to have preexisting hypertension, diabetes, and a history of stroke. Operative mortality for women was higher than for men (3.5% vs. 2.5%, P < 0.05). Compared with men, women were more likely to experience a postoperative myocardial infarction, stroke, and low cardiac output syndrome. When performing analysis on data from both sexes separately, low cardiac output syndrome, new stroke, myocardial infarction, and duration of cardiopulmonary bypass were independently associated with mortality for women and men both. Patient age was not independently associated with risk for mortality for women, but it was for men. However, when the authors combined both sexes in the logistic regression analysis, the age-sex interaction was not significant (P = 0.266), indicating that there was insufficient evidence to assert that age has a different effect on mortality for men and women. CONCLUSIONS: These data confirm that women have higher perioperative mortality after coronary artery bypass graft surgery compared with men. A higher frequency of cardiac and neurologic complications seem to account to a large extent for the higher operative mortality for women. Factors independently associated with perioperative mortality are generally similar for women and men.

Atrial fibrillation after coronary artery bypass graft surgery is unrelated to cardiac abnormalities detected by transesophageal echocardiography.

UNLABELLED: Atrial fibrillation is a common complication of coronary artery bypass graft (CABG) surgery that is associated with adverse patient outcomes. We evaluated whether preexisting abnormalities of cardiac structure or function detected with transesophageal echocardiography (TEE) are prevalent in patients later developing atrial fibrillation after CABG surgery. TEE imaging was performed after induction of general anesthesia, but before primary CABG surgery, in 62 consecutive patients without cardiac valvular disease or preexisting atrial fibrillation. Measurements included left atrial diameter, left ventricular wall thickness, left ventricular end-systolic and end-diastolic dimensions and fractional area change. Pulsed-wave Doppler measurements of pulmonary venous and trans-mitral blood flow velocity were obtained. Continuous monitoring with telemetry electrocardiography for the development of atrial fibrillation was performed. Eighteen patients (29%) developed postoperative atrial fibrillation. There were no significant differences in left atrial or left ventricular TEE variables or pulsed-wave Doppler pulmonary venous flow measurements between patients with and without postoperative atrial fibrillation. After adjusting for age and duration of aortic cross-clamping, there were no differences in the transmitral Doppler diastolic filling variables between these same groups. These data suggest that atrial fibrillation commonly occurs after CABG surgery in the absence of atrial enlargement or Doppler-derived cardiac functional abnormalities. The data imply that the use of TEE immediately before surgery would be an insensitive means for routine identification of patients susceptible to this arrhythmia. IMPLICATIONS: Transesophageal echocardiography performed immediately before coronary artery bypass graft (CABG) surgery is not useful for prediction of susceptibility to develop atrial fibrillation postoperatively. Postoperative atrial fibrillation commonly occurs after CABG surgery in the absence of preoperative atrial enlargement or Doppler derived functional abnormalities.

Sex differences in neurological outcomes and mortality after cardiac surgery: a society of thoracic surgery national database report.

BACKGROUND: The purpose of this study was to evaluate whether women undergoing cardiac surgery are more likely to suffer neurological complications than men and whether these complications could explain, at least in part, their higher perioperative mortality. METHODS AND RESULTS: The Society of Thoracic Surgery National Cardiac Surgery Database was examined for the years 1996 and 1997 to determine the frequency of new neurological events (stroke, transient ischemic attack, or coma) occurring after cardiac surgery. We reviewed clinical information on 416 347 patients (32% women) for whom complete neurological outcome data were available. New neurological events after surgery were higher for women than for men (3.8% versus 2.4%, P=0.001). For the whole group, the 30-day mortality was higher for women than for men (5.7% versus 3.5%, P=0.001), and among those patients who suffered a perioperative neurological event, mortality was also significantly higher for women than men (32% versus 28%, P=0.001). After adjustment for other risk factors (eg, age, history of hypertension and/or diabetes, duration of cardiopulmonary bypass, and other comorbid conditions) by multivariable logistic regression, female sex was independently associated with significantly higher risk of suffering new neurological events after cardiac surgery (OR 1.21, 95% CI 1.14 to 1.28, P=0.001). CONCLUSIONS: Women undergoing cardiac surgery are more likely than men to suffer new perioperative neurological events, and they have higher 30-day mortality when these complications occur. The higher incidence of perioperative neurological complications in women cannot be explained by currently known risk factors.

Estrogen increases hyperemic microvascular blood flow velocity in postmenopausal women.

BACKGROUND: Epidemiologic studies suggest that estrogen replacement therapy (ERT) is protective against vascular disease. ERT confers this benefit by lowering lipid levels and improving arterial function. However, its effect on the microvasculature in vivo is unknown. Thus the purposes of this study were to evaluate effect of estrogen status on the hyperemic response of the microvasculature in vivo in postmenopausal women and to compare the hyperemic response of the microvasculature in postmenopausal women taking ERT with that of premenopausal women. METHODS: We measured forearm microvasculature flow velocity by using a laser Doppler in a cross section of 64 healthy premenopausal and postmenopausal women 23 to 72 years old. Microvasculature blood flow velocity was measured at baseline. throughout 2 minutes of ischemia, and immediately after the ischemic period was terminated (i.e., during the peak hyperemic response). RESULTS: The peak of the hyperemic flow velocity (PHFV) in the postmenopausal women who were taking long-term ERT at usual doses was greater than that of postmenopausal women who were not currently taking ERT (p < .0001). Moreover, the PHFV of postmenopausal women taking ERT was similar to that of premenopausal women. Multivariate regression analysis showed estrogen status and baseline flow velocity to be independent predictors of PHFV. CONCLUSIONS: Current, long-term ERT at usual replacement doses is associated with improved microvascular responses in postmenopausal women, which may explain some of its beneficial vascular effects.

Atherosclerosis of the ascending aorta is an independent predictor of long-term neurologic events and mortality.

OBJECTIVES: This study was undertaken to determine whether atherosclerosis of the ascending aorta is a predictor of long-term neurologic events and mortality. BACKGROUND: Atherosclerosis of the thoracic aorta has been recently considered a significant predictor of neurologic events and peripheral embolism, but not of long-term mortality. METHODS: Long-term follow-up (a total of 5,859 person-years) was conducted of 1,957 consecutive patients > or =50 years old who underwent cardiac surgery. Atherosclerosis of the ascending aorta was assessed intraoperatively (epiaortic ultrasound) and patients were divided into four groups according to severity (normal, mild, moderate or severe). Carotid artery disease was evaluated (carotid ultrasound) in 1,467 (75%) patients. Cox proportional-hazards regression analysis was performed to assess the independent effect of predictors on neurologic events and mortality. RESULTS: A total of 491 events occurred in 472 patients (neurologic events 92, all-cause mortality 399). Independent predictors of long-term neurologic events were: hypertension (p = 0.009), ascending aorta atherosclerosis (p = 0.011) and diabetes mellitus (p = 0.015). The independent predictors of mortality were advanced age (p < 0.0001), left ventricular dysfunction (p < 0.0001), ascending aorta atherosclerosis (p < 0.0001), hypertension (p = 0.0001) and diabetes mellitus (p = 0.0002). There was >1.5-fold increase in the incidence of both neurologic events and mortality as the severity of atherosclerosis increased from normal-mild to moderate, and a greater than threefold increase in the incidence of both as the severity of atherosclerosis increased from normal-mild to severe. CONCLUSIONS: Atherosclerosis of the ascending aorta is an independent predictor of long-term neurologic events and mortality. These results provide additional evidence that in addition to being a direct cause of cerebral atheroembolism, an atherosclerotic ascending aorta may be a marker of generalized atherosclerosis and thus of increased morbidity and mortality.

Atherosclerosis of the ascending aorta is a predictor of renal dysfunction after cardiac operations.

OBJECTIVES: Renal dysfunction occurring after cardiac operations has been attributed to various factors, but the importance of an atherosclerotic thoracic aorta has not been previously evaluated. The purpose of this study was to identify predictors of postoperative renal dysfunction (50% or more increase from preoperative values) and to evaluate the importance of atherosclerosis of the ascending aorta as a predictor of this complication. METHODS: Nine hundred seventy-eight consecutive patients, 50 years of age and older with normal preoperative renal function (serum creatinine level of 1.5 mg/dL or less), who were scheduled to undergo cardiac surgery were prospectively evaluated. Atherosclerosis of the ascending aorta was assessed during the operation (with epiaortic ultrasound), and patients were divided into 3 groups according to its severity (normal-to-mild, moderate, and severe). RESULTS: Univariate predictors of renal dysfunction at postoperative day 1 were atherosclerosis of the ascending aorta (P <. 045) and postoperative low cardiac output (P =.05); at postoperative day 6 they were atherosclerosis of the ascending aorta (P <.0001), postoperative low cardiac output (P <.0001), advanced age (P =.001), decreased preoperative left ventricular function (P =.01), and female gender (P =.03). Multivariate analysis showed that atherosclerosis of the ascending aorta (odds ratio, 3.06; P =.04) was the only independent predictor of postoperative renal dysfunction at day 1 and that postoperative low cardiac output (odds ratio, 4.83; P <.0001), atherosclerosis of the ascending aorta (odds ratio, 2.13; P =.0006), and preoperative left ventricular dysfunction (odds ratio, 1.48; P =.028) were independent predictors of postoperative renal dysfunction at day 6. CONCLUSIONS: An atherosclerotic ascending aorta is an important predictor of postoperative renal dysfunction, possibly because atheroembolism to the kidneys occurs in the perioperative period (ie, during surgical manipulation of an atherosclerotic aorta) or because the diseased aorta may be a marker of widespread atherosclerotic disease that may predispose to perioperative renal dysfunction.

Reversal of hypocalcemia and decreased afterload in sepsis. Effect on myocardial systolic and diastolic function.

Sepsis is a major cause of death in intensive care units. Clinically, sepsis induces a number of physiologic and metabolic abnormalities, including decreased myocardial contractility and decreased plasma ionized calcium. There is debate about the proper therapy of hypocalcemia in sepsis because calcium administration may worsen cell function by causing intracellular Ca2+ overload. We investigated the effect of Ca2+ administration on myocardial systolic and diastolic function in an extensively utilized rat model of sepsis, i.e., the cecal ligation and puncture model (CLP). Approximately 24 h after CLP or sham surgery, rats were anesthetized and myocardial function assessed in vivo by a left ventricular Millar catheter and simultaneous two-dimensional guided M-mode echocardiography. Septic rats had a 28% decrease in peak left ventricular developed pressure, a 30% decrease in +dP/ dt, and a 23% decrease in -dP/dt (p < 0.05). Plasma ionized Ca2+ was decreased in septic compared with that in sham rats: 4.9 +/- 0.9 and 5.6 +/- 0.01 mg/dl, respectively (p < 0.05). CaCl2 improved both systolic and diastolic function and there was no evidence of adverse effects of Ca2+ even at supraphysiologic levels. Surprisingly, correction of decreased afterload in septic rats, using the pure alpha-agonist phenylephrine, caused normalization of all indices of cardiac contractility, indicating that the presumed decrease in cardiac function was due entirely to an effect of the decreased afterload to "unload" the left ventricle. We conclude that Ca2+ administration is not detrimental to cardiac function in the rat CLP model. Although the rat CLP model is widely utilized and reproduces many of the clinical hallmarks of sepsis, it does not cause intrinsic myocardial depression and, therefore, it may not be an appropriate model to investigate the clinical cardiac dysfunction that occurs in patients with sepsis.

Detection of coronary stenoses on source and projection images using three-dimensional MR angiography with retrospective respiratory gating: preliminary experience.

OBJECTIVE: Our objective was to study the ability of three-dimensional MR angiography with retrospective respiratory gating to reveal stenoses in proximal coronary arteries on source and projection images. CONCLUSION: Proximal coronary artery stenoses can be identified using three-dimensional MR angiography with retrospective respiratory gating, both with projection images and on source images alone. Reasons for missed lesions included collateral vessels and retrograde flow distal to complete occlusion and volume averaging of vessels with adjacent structures. Causes of false-positive interpretations included small foci of decreased signal intensity distal to complete occlusion, partial volume effects on individual partitions, and regions of distal vessels leaving the imaging plane.

Transesophageal echocardiographic and clinical features of aortic intramural hematoma.

OBJECTIVE: This study sought to determine the transesophageal echocardiographic features and natural history of patients with aortic intramural hematoma. METHODS: The transesophageal echocardiograms of all patients who had symptoms indicative of aortic dissection over 6 years were reviewed. Measurements were made of the involved aortic segment in the study patients, and follow-up was obtained. RESULTS: In patients with aortic intramural hematoma, the wall thickness of the involved segment was significantly greater for descending segments than ascending segments (ascending aorta 7 +/- 2 mm, descending aorta 15 +/- 6 mm, p = 0.0016). In each case, the crescent-shaped intramural hematoma involved one wall predominantly, leading to compression of the aortic lumen. The findings of echolucent areas and displaced intimal calcium were found in the majority of patients. Four of eight patients with intramural hematoma of the ascending aorta were treated medically and four were treated surgically. The 30-day mortality was 50% in the medically treated patients and 0% in the surgically treated group. Four of 11 patients with isolated intramural hematoma of the descending aorta were treated medically and seven were treated surgically. All medically treated and 86% of surgically treated patients were alive at 30 days. CONCLUSIONS: Aortic intramural hematoma has distinct and identifiable transesophageal echocardiographic features. These data support those of previous studies documenting high morbidity and mortality in patients with aortic intramural hematoma.

Previous coronary artery bypass grafting is not a risk factor for aortic valve replacement.

BACKGROUND: The risk of aortic valve replacement (AVR) after previous coronary artery bypass grafting (CABG) is controversial. Its magnitude influences the threshold for recommending this procedure and has been cited in arguments regarding the optimal management of mild aortic stenosis at primary CABG. We therefore reviewed our experience with reoperative AVR +/- CABG and the primary combined procedure. METHODS: Between January 1, 1985, and June 30, 1996, 427 patients underwent primary AVR+CABG, and 52 underwent AVR +/- CABG after prior CABG. Demographics, operative characteristics, and operative results were compared between groups. Data for all patients were pooled and analyzed collectively for risk factors influencing mortality. RESULTS: The extent of native coronary artery disease and the incidence of prior myocardial infarction and stroke were greater in the reoperative group. Aortic cross-clamp and cardiopulmonary bypass times were slightly shorter, and fewer distal anastomoses were performed in the reoperative group. Operative mortality (primary group, 6.3% versus reoperative group, 7.4%) and morbidity were similar. Stepwise multivariate logistic regression analysis identified age, perioperative myocardial infarction, intraaortic balloon support, ventricular arrhythmia, perioperative stroke, and development of renal failure or acute respiratory distress syndrome, but not reoperative status, as predictors of mortality. CONCLUSIONS: The risk of AVR after previous CABG is similar to that for primary AVR+CABG. Valve replacement should, therefore, be pursued despite prior CABG when hemodynamically significant aortic stenosis develops. Furthermore, a circumspect approach to "prophylactic" AVR for mild aortic stenosis at primary CABG seems warranted.

Postextrasystolic left ventricular isovolumic pressure decay is not monoexponential.

OBJECTIVE: The relationship between the left ventricular (LV) relaxation time constant and early diastolic filling is not fully defined. This study provides additional evidence that LV isovolumic pressure fall in the normal intact heart in response to certain interventions is not adequately described by a model of monoexponential decay and that its relationship to filling is complex. METHODS AND RESULTS: To gain further insight into the relationship between LV relaxation and early rapid filling we measured LV isovolumic relaxation rate, peak early filling velocity (E), LV volumes, and transmitral pressures at baseline and in the first postextrasystolic beat after a short-coupled extrasystole in 9 anesthetized dogs. Postextrasystolic isovolumic relaxation rate was slowed as measured by 3 commonly used time constants, while E was increased 32%. LV contractility and peak pressure were also increased, while LV end-systolic volume was decreased. LV minimum pressure was deceased, while the early diastolic transmitral pressure gradient was increased. Although all relaxation time constants measured over the entire isovolumic relaxation phase indicated slowed relaxation, direct measurement of isovolumic relaxation time indicated no change in relaxation rate. Calculation of the time constants and direct measurement of isovolumic relaxation time during early isovolumic pressure decay indicated slowed postextrasystolic pressure decay rate compared with baseline, while calculation of time constants and direct measurement of isovolumic relaxation time during late isovolumic relaxation indicated augmented postextrasystolic pressure decay rate versus baseline. CONCLUSIONS: This non-exponential behavior of LV isovolumic pressure decay in postextrasystolic beats after short-coupled extrasystoles provides further evidence that the relationship that exists between ventricular relaxation and early filling is not simple. The results are interpreted in terms of current theoretical formulations that attribute control of myocardial relaxation to the interaction between inactivation-dependent and load-dependent mechanisms.

The role of transthoracic echocardiography in the management of patients seen in an outpatient cardiology clinic.

Transthoracic two-dimensional (2D) Doppler echocardiography may provide new or additional information in patients, but it is often not known whether the results alter the treatment plan. We investigated whether results of clinically indicated 2D echocardiography were different from the physician's clinical examination or led to changes in management in 200 consecutive outpatients seen in a university-based clinic. A questionnaire was completed by the physician regarding physical findings and treatment plan before 2D echocardiography was performed. After results were known, the physician was asked to report any differences compared with clinical examination or changes in patient management. Most patients (83%) were studied to evaluate left ventricular (LV) or valvular function. 2D echocardiography confirmed clinical assessment in 182 patients (one inadequate 2D echocardiogram) and disclosed a new diagnosis in 17. 2D echocardiography provided additional information, not expected from clinical assessment or history, in 94 patients. Clinical assessment, compared with 2D echocardiography, was concordant in 154 (77%) of 199 patients with regard to LV systolic function but in only 22 (50%) of 44 with valve disease. Alterations in management based on results of 2D echocardiography were instituted in 73 patients (36%), most often manifested by changes in pharmacologic therapy (n = 45; 62%). Results of 2D echocardiography obviated the need for further cardiac evaluation, surgery, or procedures in 30 patients, avoiding additional patient charges of $125,754.00. In contrast, results of 2D echocardiography led to the need for further evaluation, surgery, or procedures in 32 patients, resulting in additional patient charges of $70,860.00. In conclusion, 2D echocardiography provides new or additional information that results in changes in management strategy in one third of patients, and 2D echocardiography offers relative cost savings by avoiding additional procedures.

Intraoperative transesophageal echocardiography and epiaortic ultrasound for assessment of atherosclerosis of the thoracic aorta.

OBJECTIVES: This study sought to determine the role of transesophageal echocardiography (TEE) and epiaortic ultrasound in the detection of atherosclerosis of the ascending aorta in patients undergoing cardiac surgery. BACKGROUND: Atherosclerosis of the ascending aorta is a major risk factor for perioperative stroke and systemic embolism in patients undergoing cardiac surgery. METHODS: Forty-four patients underwent prospective evaluation of the ascending aorta with two ultrasound techniques-epiaortic ultrasound and biplane TEE-and by palpation. The severity of atherosclerosis was graded on a four-point scale as normal, mild, moderate or severe. RESULTS: A comparison of results with biplane TEE and those with epiaortic ultrasound yielded a kappa value of 0.12 (95% confidence interval 0 to 0.25), indicating poor correlation between the two. Compared with epiaortic ultrasound, biplane TEE significantly underestimated the severity of ascending aortic atherosclerosis, and this underestimation was more marked in the distal ascending aorta (p < 0.0001). When compared with epiaortic ultrasound and biplane TEE, palpation of the ascending aorta significantly underestimated the presence and severity of atherosclerosis (p < 0.0001 for both). CONCLUSIONS: Epiaortic ultrasound is more accurate than TEE for identification of atherosclerosis of the ascending aorta, but both ultrasound techniques are superior to palpation. Epiaortic ultrasound and TEE provide complementary information regarding thoracic aortic atherosclerosis. Modification of surgical technique on the basis of results of intraoperative epiaortic ultrasound and TEE in elderly patients undergoing cardiac procedures may prevent atheroembolic complications.

Echocardiography in the evaluation of patients with syncope.

OBJECTIVE: Echocardiography is frequently used as a screening test for cardiac disease in patients with syncope despite the lack of published data describing its utility in this regard. The goal of the study was to examine the frequency with which echocardiography was used in the evaluation of patients admitted to one medical center because of syncope and to examine the diagnostic information, over and above that provided by the initial history, physical examination, and electrocardiography, contributed by the echocardiogram. DESIGN: A retrospective review was performed of all patients admitted to the study institution because of syncope over a seven-month period. SETTING: University teaching hospital in an urban setting of 2.5 million population. PATIENTS/PARTICIPANTS: One hundred twenty-eight patients were identified: 47 men and 81 women (average age 67 +/- 17 years). Patients for whom syncope was of a known cause, those with near-syncope or vertigo, those with clinically obvious seizure, or those referred for electrophysiologic testing were excluded, leaving 128 patients for analysis. Details from the admission history, physical examination, and electrocardiography for each patient were recorded. The results of all other diagnostic tests ordered to evaluate syncope were recorded along with any consultations obtained. The cause of syncope was assigned by examining all physicians' notes and test results and with the use of previously published diagnostic criteria as guidelines. MEASUREMENTS AND MAIN RESULTS: Ninety percent of the patients underwent cardiac testing other than routine electrocardiography and continuous telemetry monitoring while in the hospital. An echocardiogram was obtained for 64% of the patients and did not reveal an unsuspected cause for syncope in any case. The echocardiogram was normal for 52% of the patients undergoing the test. Echocardiograms of patients with syncope and no clinical evidence of heart disease by history, physical examination, or electrocardiography either were normal (63%) or provided no useful additional information for arriving at a diagnosis (37%). Nearly half (46%) of the patients undergoing echocardiography fit this clinical profile. Among the patients for whom cardiac disease was suspected after history, physical examination, or electrocardiography, the echocardiogram confirmed the suspected diagnosis for 48% and served to rule out a suspected diagnosis for the remaining 52%. In no instance did echocardiography provide an unsuspected cause for syncope. The history, physical examination, and initial electrocardiography provided sufficient information to permit a diagnosis to be made for 37 of the 48 patients (77%) for whom a cause of syncope was ultimately determined. CONCLUSION: Echocardiography was frequently used in the evaluation of patients admitted to the hospital because of syncope of unclear cause. For patients without suspected cardiac disease after history, physical examination, and electrocardiography, the echocardiogram did not appear to provide additional useful information, suggesting that syncope alone may not be an indication for echocardiography. For patients with suspected heart disease, echocardiography served to confirm or refute the suspicious in equal proportions. These data provide an objective basis to prospectively define the optimal role of echocardiography in the evaluation of patients with syncope.

Right ventricular dysfunction in low output syndrome after cardiac operations: assessment by transesophageal echocardiography.

BACKGROUND: Low output syndrome after cardiac operations is associated with high morbidity and mortality rates. The contribution of right ventricular dysfunction to this syndrome has not been fully characterized. The purpose of this study was to evaluate the utility of transesophageal echocardiography to identify the frequency and the in-hospital mortality from right ventricular dysfunction in patients with this syndrome. METHODS: Seventy-five consecutive patients undergoing transesophageal echocardiography for low output syndrome early after cardiac operations were evaluated. The findings from transesophageal echocardiography were correlated with the type of surgical procedure, cross-clamp time, right heart hemodynamics, and coronary angiography. RESULTS: Right ventricular systolic dysfunction occurred in 36 patients (42%); in 17 patients it was isolated and in 19 patients it occurred in combination with left ventricular dysfunction. Postoperative right ventricular dysfunction was not uniformly associated with important right coronary artery disease or with prolonged ischemic time during cardiopulmonary bypass. Hemodynamic data were not useful to distinguish the group with postoperative right ventricular dysfunction. Patients with right ventricular dysfunction had a high (44%) in-hospital mortality rate. CONCLUSIONS: Right ventricular dysfunction occurs frequently in patients with low output syndrome after cardiac operations and is associated with a high in-hospital mortality rate. Better understanding of the mechanisms causing postoperative right ventricular dysfunction may provide insight for preventing this complication.