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Clinical significance of epicardial pacing wire cultures
Clinical significance of epicardial pacing wire cultures Routine cultures of epicardial pacing wires removed 5 to 10 days postoperatively were obtained in 205 adults who underwent cardiac operations through median sternotomy. The study was conducted in a double-blind prospective fashion in which clinicians were unaware of culture results. With the exception of 10 out-of-town patients who were foUowed up only until the day of hospital discharge, the patients were foUowed for at least 6 weeks (195 patients) for evidence of poststernotomy wound infections. Deep wound infection rate was slightly less than 1 % in this patient population, with less than 0.5 % having had superficial wound problems. Of the 205 patients, 27 had positive epicardial pacing wires cultures, with a total of 30 microbial isolates. Of 30 isolates, 26 were consistent with local skin flora (Staphylococcus, Streptococcus, Enterococcus, and diphtheroids). Wound infection developed in none of these patients. The remaining four cultures were of either Enterobacter or Serratia. In two of these four patients deep sternal infections developed. In the remaining 178 patients whose wire cultures were negative, no deep sternal infections developed. The fact that aU clinicaUy manifested deep sternal infections were associated with positive epicardial pacing wires cultures suggests that epicardial pacing wires cultures may be useful in the treatment of high-risk patients or of those in whom deep sternal infections are suspected. (J THORAC CARDIOVASC SURG 1993;105:165-7)
J. Clifton Hastings III, MD, and Francis Robicsek, MD, Charlotte, NiC.
Deep mediastinal infections after cardiac surgery remains a rare but potentially serious and lethal problem. Infection rates vary in the literature from 0.4% to 5.0%,1 and successful management of this problem relies on early diagnosis followed by aggressive debridement and closure with muscle flaps if needed. In an attempt to identify accurately the deep mediastinal infection at an early stage, a prospective double-blind study with the use of pacing wire cultures was undertaken.
Materials and methods From July 1990 to October 1990 patients' atrial epicardial pacing wires implanted in the course of their heart operations wereculturedon postoperative days 5 to 10. Excluded from the studywerethosepatientswhose wireswouldbe removed either before postoperative day 5 or after day 10, patientswhose wires were inadvertently contaminated during the removal process, and patients whose wires would have required an inordinate From Carolinas Heart Institute, Carolinas Medical Center, and Heineman Research Laboratories, Charlotte, N.C. Received for publication June 4, 1991. Accepted for publication Feb. 17, 1992. Address for reprints: Francis Robicsek, MD, P.O. Box 32861, Charlotte, NC 28231-2861.
12/1/38386 0022-5223/93/$1.00/+ 0.10
amount of tension to pull out. In the latter situation the wires would have been cut at the skin level and left in place, but all wiresweresuccessfully removed. Fewerthan 10 patients' wires werecontaminatedin the removalprocess. The pacerwireswere removed and cultured according to the following protocol: the skin sutures holdingthe wires in place were cut; the skin was prepared with 0.2% povidone-iodine solution and dried with sterilegauze;and the wireswerepulledon insucha manner that the tips werenot contaminated. The tipsof the wireswerethen cut with sterile scissors, allowed to fall into a sterile specimen cup,and sentimmediatelyto the microbiology laboratorywhere both aerobic and anaerobic cultures were made. Fisher'sexact test was performedon 2 X 2 tables with small expected values. Also, oddsratioswith95%confidence intervals were calculated. Standard 95% confidence intervalswere calculated for individual proportions. Patientswereobserved for evidence ofsternal infection. Each wound was inspected daily for signsof infection, temperature curveswere followed, and a routine white bloodcell count was obtained beforedischarge. Patients' wounds were also inspected at postoperative weeks 2 and 6. If signs of infection were noted, the patient had further work-upfor possible deep mediastinal infection as directed by the attending physician. At no pointduring the studywerethe attending physicians notified of the wire culture results. Deep mediastinal infections were defined as those which involved the sternum and retrosternal space with positive woundcultures.Superficialinfections were defined as those in which the extent of infectiondid not extend beyond the subcutaneous tissues.
165
166
Hastings and Robicsek
Results
Of the 205 epicardial pacing wires cultures obtained, 27 were positive for microbes ( 13.2%with 95% confidence interval of 8.54% to 17.8%). Three of the positive cultures grew two separate microbial isolates. Most common of the microbial isolates was coagulase-negative Staphylococcus aureus (19 cultures) followed by enterococcus (4), a-haemolytic streptococci (two), Enterobacter aerogenes (two), Enterobacter sakazakii (one), Serratia marcescens, (one) and diphtheroids (one). Of the 205 patients followed up for signs of infection, 195 were observed for 6 weeks. Of these patients signs of sternal infection developed in three. The remaining 10 patients were from different geographic regions and were followed up by their own local physicians. No infections were reported in this group. Of the three infections, one did not and two did involve the sternum and the mediastinum. The superficial infection occurred in a 38-year-old diabetic patient with bilateral mammary artery bypass grafts. It was diagnosed in the office during a follow-up visit, and treatment consisted of local incision and drainage, dressing changes, and parenteral antibiotics followed by oral antibiotics. The patient was hospitalized for 5 days for this treatment. His epicardial pacing wires cultures had been negative for infection. Both patients with deep sternal infections had positive epicardial pacing wires cultures. One ofthese patients was a 63-year-old man who had costochondral separation caused by the harvesting of the left internal mammary artery. The infection was diagnosed 12 days postoperatively and was treated with debridement followed by flap closure 3 days later. Epicardial pacing wires cultures and later cultures obtained in the course of intraoperative debridement both grew E. aerogenes. The second infection occurred in a 61-year-old woman whose infection was diagnosed 9 days postoperatively. Her deep sternal infection was successfully treated with debridement followed by muscle flap closure. Her epicardial pacing wires cultures grew S. marcescens; however, intraoperative debridement cultures grew only {j-Iactamase-positive S. aureus. All three patients recovered from their infections and returned home in good condition. Conclusion
Because deep sternal infections may be difficult to diagnose, different signs and symptoms, and diagnostic tests, have been recommended to aid the clinician in the task of identification. The most significant presenting sign is purulent wound drainage followed by other signs such as sternal instability, widened mediastinum on chest x-ray film, severe sternal pain, and evidence of a superficial
The Journal of Thoracic and Cardiovascular Surgery
infection. Less specific signs include fever, elevated white blood cell count, diminished appetite, and general failure to thrive. Helpful diagnostic tests have included computed tomographic scans of the chest' chest x-ray films, thermograms' and nuclear scans with radioactive-labeled white blood cells," and aspiration of substernal mediastinal fluid for culture.o 6 Because the culture of the tips of the epicardial pacing wires provides a much easier access to this area with no risk and at much lower cost, this study of culturing epicardial pacing wires was undertaken. Browdie and co-workers" reported 19 epicardial pacing wires cultures in patients suspected of or having deep sternal infections," but we know of no published series with routine epicardial pacing wires cultures to screen for possible deep sternal infections. Twenty-seven epicardial pacing wires cultures were positive, with a total of 30 microbial isolates. Of the 30 microbial isolates, 26 were consistent with local skin flora. No patient in whom deep sternal infections later developed was in this group. The remaining four microbial isolates were either Enterobacter or Serratia, with both deep infections occurring in this group. No deep sternal infection developed in patients with previously negative epicardial pacing wires cultures. The lone superficial infection did not have positive epicardial pacing wires cultures. Total deep infection rate was low at 0.98%, with the superficial infection rate lower at 0.49%. Of the 27 cultures, 25 were false positives (i.e., did not develop subsequent wound infection), but the majority of these grew only skin flora, leading us to believe that errors in the culturing technique may have led to these positive cultures. In addition, one may also argue that the term false positive cannot be applied at all to epicardial pacing wire cultures. It is entirely possible that a number of deep sternal infections never required surgical exploration because the culprit organism was eliminated either by antibiotics or by the body's natural defenses." The question naturally arises as to how these observations may be applied clinically. Consideration of the relatively low rate of postoperative deep sternal infections, and the possibility of false-negative results, routine culturing of all removed pacer wires appears to be impractical. However, when the finding of zero false-negative cultures and the fact that both deep sternal infections had positive pacing wire cultures are considered, we are led to believe that epicardial pacing wire culturing may be useful in the early diagnosis of deep sternal infections and may well be used in two subgroups of patients: (I) those who are at high risk for infection (i.e., those who had to be taken back to the operating room because of bleeding, sternal separation, balloon catheter, or other assist device removal) and (2) those in whom the diagnosis is clinically suspected, to
Volume 105 Number 1
January 1993
confirm the diagnosis and/or to identify the invading organism. REFERENCES
1. Sarr MG, Gott VL, Townsend TR. Mediastinal infection after cardiac surgery. Ann Thorac Surg 1984;38:415. 2. Kay HR, Goodman LR, Teplick SK, Mundth ED. Use of computed tomography to assess mediastinal complications after median sternotomy. Ann Thorac Surg 1983;36:70612. 3. Robicsek F, Masters TN, Daugherty HK, et al. The value of thermography in the early diagnosis of postoperative sternal wound infections. Thorac Cardiovasc Surg 1984;32: 260-5.
Epicardial pacing wire cultures
I67
4. Browdie DA, Bernstein RW, Agnew R, et al. Diagnosis of poststernotomy infection: comparison of three means of assessment. Ann Thorac Surg 1991;51:290-2. 5. Culliford AT, Cunningham JN Jr, Zeff RH, Isom OW, Teiko P, Spencer FC. Sternal surgery and costochondral infections following open-heart surgery: a review of 2594 cases. J THORAC CARDIOVASC SURG 1976;72:714-26. 6. Jimenez-Martinez M, Arguero-Sanchez R, Perez-Alvarez JJ, Mina-Castaneda P. Anterior mediastinitis as a complication of median sternotomy incisions: diagnostic and surgical considerations. Surgery 1970;67:929-34. 7. Robicsek F. Letter to the Editor. Ann Thorac Surg (in press).
Boundvolumes available to subscribers Bound volumesof THEJOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY are available to subscribers (only) for the 1993 issues from the PUblisher, at a cost of $75.00 for domestic, $98.25 for Canadian, and $93.00 for international subscribers for Vol. 105 (JanuaryJune) and Vol. 106 (July-December). Shipping charges are included. Each bound volume contains a subject and author index and all advertisingis removed. Copies are shipped within 60 days after publication of the last issueof the volume. The binding is durable buckram with the JOURNAL name, volume number, and year stamped in gold on the spine. Paymentmust accompany all orders. Contact MosbyYear Book, Inc., SUbscription Services, 11830 Westline Industrial Drive, St. Louis, Missouri 63146-3318, USA; phone (800) 325-4177, ext. 4351, or (314) 453-4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.
J. Clifton Hastings III, MD, and Francis Robicsek, MD, Charlotte, NiC.
Deep mediastinal infections after cardiac surgery remains a rare but potentially serious and lethal problem. Infection rates vary in the literature from 0.4% to 5.0%,1 and successful management of this problem relies on early diagnosis followed by aggressive debridement and closure with muscle flaps if needed. In an attempt to identify accurately the deep mediastinal infection at an early stage, a prospective double-blind study with the use of pacing wire cultures was undertaken.
Materials and methods From July 1990 to October 1990 patients' atrial epicardial pacing wires implanted in the course of their heart operations wereculturedon postoperative days 5 to 10. Excluded from the studywerethosepatientswhose wireswouldbe removed either before postoperative day 5 or after day 10, patientswhose wires were inadvertently contaminated during the removal process, and patients whose wires would have required an inordinate From Carolinas Heart Institute, Carolinas Medical Center, and Heineman Research Laboratories, Charlotte, N.C. Received for publication June 4, 1991. Accepted for publication Feb. 17, 1992. Address for reprints: Francis Robicsek, MD, P.O. Box 32861, Charlotte, NC 28231-2861.
12/1/38386 0022-5223/93/$1.00/+ 0.10
amount of tension to pull out. In the latter situation the wires would have been cut at the skin level and left in place, but all wiresweresuccessfully removed. Fewerthan 10 patients' wires werecontaminatedin the removalprocess. The pacerwireswere removed and cultured according to the following protocol: the skin sutures holdingthe wires in place were cut; the skin was prepared with 0.2% povidone-iodine solution and dried with sterilegauze;and the wireswerepulledon insucha manner that the tips werenot contaminated. The tipsof the wireswerethen cut with sterile scissors, allowed to fall into a sterile specimen cup,and sentimmediatelyto the microbiology laboratorywhere both aerobic and anaerobic cultures were made. Fisher'sexact test was performedon 2 X 2 tables with small expected values. Also, oddsratioswith95%confidence intervals were calculated. Standard 95% confidence intervalswere calculated for individual proportions. Patientswereobserved for evidence ofsternal infection. Each wound was inspected daily for signsof infection, temperature curveswere followed, and a routine white bloodcell count was obtained beforedischarge. Patients' wounds were also inspected at postoperative weeks 2 and 6. If signs of infection were noted, the patient had further work-upfor possible deep mediastinal infection as directed by the attending physician. At no pointduring the studywerethe attending physicians notified of the wire culture results. Deep mediastinal infections were defined as those which involved the sternum and retrosternal space with positive woundcultures.Superficialinfections were defined as those in which the extent of infectiondid not extend beyond the subcutaneous tissues.
165
166
Hastings and Robicsek
Results
Of the 205 epicardial pacing wires cultures obtained, 27 were positive for microbes ( 13.2%with 95% confidence interval of 8.54% to 17.8%). Three of the positive cultures grew two separate microbial isolates. Most common of the microbial isolates was coagulase-negative Staphylococcus aureus (19 cultures) followed by enterococcus (4), a-haemolytic streptococci (two), Enterobacter aerogenes (two), Enterobacter sakazakii (one), Serratia marcescens, (one) and diphtheroids (one). Of the 205 patients followed up for signs of infection, 195 were observed for 6 weeks. Of these patients signs of sternal infection developed in three. The remaining 10 patients were from different geographic regions and were followed up by their own local physicians. No infections were reported in this group. Of the three infections, one did not and two did involve the sternum and the mediastinum. The superficial infection occurred in a 38-year-old diabetic patient with bilateral mammary artery bypass grafts. It was diagnosed in the office during a follow-up visit, and treatment consisted of local incision and drainage, dressing changes, and parenteral antibiotics followed by oral antibiotics. The patient was hospitalized for 5 days for this treatment. His epicardial pacing wires cultures had been negative for infection. Both patients with deep sternal infections had positive epicardial pacing wires cultures. One ofthese patients was a 63-year-old man who had costochondral separation caused by the harvesting of the left internal mammary artery. The infection was diagnosed 12 days postoperatively and was treated with debridement followed by flap closure 3 days later. Epicardial pacing wires cultures and later cultures obtained in the course of intraoperative debridement both grew E. aerogenes. The second infection occurred in a 61-year-old woman whose infection was diagnosed 9 days postoperatively. Her deep sternal infection was successfully treated with debridement followed by muscle flap closure. Her epicardial pacing wires cultures grew S. marcescens; however, intraoperative debridement cultures grew only {j-Iactamase-positive S. aureus. All three patients recovered from their infections and returned home in good condition. Conclusion
Because deep sternal infections may be difficult to diagnose, different signs and symptoms, and diagnostic tests, have been recommended to aid the clinician in the task of identification. The most significant presenting sign is purulent wound drainage followed by other signs such as sternal instability, widened mediastinum on chest x-ray film, severe sternal pain, and evidence of a superficial
The Journal of Thoracic and Cardiovascular Surgery
infection. Less specific signs include fever, elevated white blood cell count, diminished appetite, and general failure to thrive. Helpful diagnostic tests have included computed tomographic scans of the chest' chest x-ray films, thermograms' and nuclear scans with radioactive-labeled white blood cells," and aspiration of substernal mediastinal fluid for culture.o 6 Because the culture of the tips of the epicardial pacing wires provides a much easier access to this area with no risk and at much lower cost, this study of culturing epicardial pacing wires was undertaken. Browdie and co-workers" reported 19 epicardial pacing wires cultures in patients suspected of or having deep sternal infections," but we know of no published series with routine epicardial pacing wires cultures to screen for possible deep sternal infections. Twenty-seven epicardial pacing wires cultures were positive, with a total of 30 microbial isolates. Of the 30 microbial isolates, 26 were consistent with local skin flora. No patient in whom deep sternal infections later developed was in this group. The remaining four microbial isolates were either Enterobacter or Serratia, with both deep infections occurring in this group. No deep sternal infection developed in patients with previously negative epicardial pacing wires cultures. The lone superficial infection did not have positive epicardial pacing wires cultures. Total deep infection rate was low at 0.98%, with the superficial infection rate lower at 0.49%. Of the 27 cultures, 25 were false positives (i.e., did not develop subsequent wound infection), but the majority of these grew only skin flora, leading us to believe that errors in the culturing technique may have led to these positive cultures. In addition, one may also argue that the term false positive cannot be applied at all to epicardial pacing wire cultures. It is entirely possible that a number of deep sternal infections never required surgical exploration because the culprit organism was eliminated either by antibiotics or by the body's natural defenses." The question naturally arises as to how these observations may be applied clinically. Consideration of the relatively low rate of postoperative deep sternal infections, and the possibility of false-negative results, routine culturing of all removed pacer wires appears to be impractical. However, when the finding of zero false-negative cultures and the fact that both deep sternal infections had positive pacing wire cultures are considered, we are led to believe that epicardial pacing wire culturing may be useful in the early diagnosis of deep sternal infections and may well be used in two subgroups of patients: (I) those who are at high risk for infection (i.e., those who had to be taken back to the operating room because of bleeding, sternal separation, balloon catheter, or other assist device removal) and (2) those in whom the diagnosis is clinically suspected, to
Volume 105 Number 1
January 1993
confirm the diagnosis and/or to identify the invading organism. REFERENCES
1. Sarr MG, Gott VL, Townsend TR. Mediastinal infection after cardiac surgery. Ann Thorac Surg 1984;38:415. 2. Kay HR, Goodman LR, Teplick SK, Mundth ED. Use of computed tomography to assess mediastinal complications after median sternotomy. Ann Thorac Surg 1983;36:70612. 3. Robicsek F, Masters TN, Daugherty HK, et al. The value of thermography in the early diagnosis of postoperative sternal wound infections. Thorac Cardiovasc Surg 1984;32: 260-5.
Epicardial pacing wire cultures
I67
4. Browdie DA, Bernstein RW, Agnew R, et al. Diagnosis of poststernotomy infection: comparison of three means of assessment. Ann Thorac Surg 1991;51:290-2. 5. Culliford AT, Cunningham JN Jr, Zeff RH, Isom OW, Teiko P, Spencer FC. Sternal surgery and costochondral infections following open-heart surgery: a review of 2594 cases. J THORAC CARDIOVASC SURG 1976;72:714-26. 6. Jimenez-Martinez M, Arguero-Sanchez R, Perez-Alvarez JJ, Mina-Castaneda P. Anterior mediastinitis as a complication of median sternotomy incisions: diagnostic and surgical considerations. Surgery 1970;67:929-34. 7. Robicsek F. Letter to the Editor. Ann Thorac Surg (in press).
Boundvolumes available to subscribers Bound volumesof THEJOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY are available to subscribers (only) for the 1993 issues from the PUblisher, at a cost of $75.00 for domestic, $98.25 for Canadian, and $93.00 for international subscribers for Vol. 105 (JanuaryJune) and Vol. 106 (July-December). Shipping charges are included. Each bound volume contains a subject and author index and all advertisingis removed. Copies are shipped within 60 days after publication of the last issueof the volume. The binding is durable buckram with the JOURNAL name, volume number, and year stamped in gold on the spine. Paymentmust accompany all orders. Contact MosbyYear Book, Inc., SUbscription Services, 11830 Westline Industrial Drive, St. Louis, Missouri 63146-3318, USA; phone (800) 325-4177, ext. 4351, or (314) 453-4351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.