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Ann Thorac Surg 2000;69:1455-1458
© 2000 The Society of Thoracic Surgeons

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Original articles: Cardiovascular

Anterior intercostal nerve damage after coronary artery bypass graft surgery with use of internal thoracic artery graft

^a Comprehensive Pain Program, Toronto General and Toronto Western Hospitals, Toronto, Ontario, Canada
^b Playfair Neuroscience Unit, Toronto General and Toronto Western Hospitals, Toronto, Ontario, Canada
^c Division of Cardiovascular Surgery, Toronto General and Toronto Western Hospitals, Toronto, Ontario, Canada
^d University of Toronto Centre for the Study of Pain, Toronto, Ontario, Canada

Address reprint requests to Dr Mailis, Comprehensive Pain Program, Toronto Western Hospital, University Health Network, 4BFell-174, 399 Bathurst St, Toronto, ON, Canada M5T 2S8
e-mail: angela.mailis{at}uhn.on.ca

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. The prevalence of intercostal nerve damage associated with coronary artery bypass graft–internal thoracic (mammary) artery surgery is unknown.

Methods. A total of 37 consecutive patients with coronary artery bypass graft surgery (all with left internal thoracic artery graft) who were attending a cardiac-related exercise program underwent a thorough examination. Nerve damage was considered to be "definite" in the presence of two consistent and well-demarcated sensory abnormalities over the anterior chest wall within the T1 to T6 anterior intercostal nerve territory, and was considered "possible" in the presence of one such abnormality.

Results. Definite nerve damage was detected in 73% of the subjects, and possible nerve damage was found in another 11% at the site of internal thoracic artery harvesting. Protracted postoperative pain or unpleasant sensations, usually subsiding by 4 months, were reported by recollection by 81% of the subjects. Overall, the prevalence of persistent pain in those with definite nerve damage 5 to 28 months after surgery was 15%.

Conclusions. Intercostal nerve damage seems to occur in three-quarters of all patients undergoing coronary artery bypass graft–internal thoracic artery surgery. A significant minority may continue to experience bothersome chronic chest wall pain.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
The internal thoracic (mammary) artery (ITA) has been established since the mid-1970s as the arterial graft of choice, particularly for bypass of the left anterior descending artery in patients requiring coronary artery bypass graft (CABG) surgery [1–3]. Both early and late patency rates are superior to those obtained with saphenous vein grafts (SVG), which are subject to late occlusion due to arteriosclerosis. The superior long-term patency of ITA grafts is reflected in improved long-term survival, a decrease in the rate of reoperation, and improvement in reoperation-free survival and cardiac morbidity [1–3].

We initially reported a neuropathic pain syndrome associated with CABG-ITA surgery several years ago [4]. The syndrome was originally called "internal mammary artery syndrome" and is included under this name in the 1994 version of the International Association for the Study of Pain (IASP) classification of chronic pain syndromes [5]. However, we have adopted the term "internal thoracic artery" (ITA) instead of "mammary" to refer to the current study and to others reported in the literature, as this term currently seems to be prevalent. In the original study we described 11 patients after unilateral or bilateral ITA bypass surgery who presented to our pain clinic with significant chest wall pain and a cluster of symptoms and signs, as follows: (1) numbness to pinprick in a well-circumscribed area defined by the sternum medially and the nipple line laterally, and in the distribution of the anterior intercostal nerves between the levels of T1 to T2 and of T5 to T6; (2) severe tenderness on palpation of the manubrium of the sternum, the costosternal junctions, or the anterior rib cage, close to or beneath the area of cutaneous sensory abnormalities; (3) allodynia to light touch (touch-evoked pain) or to hair movement across the area of numbness; and (4) constant pain (usually burning), as well as shooting pains on the side of ITA graft harvesting.

We postulated that these patients had suffered injury to the anterior intercostal nerves during the harvesting of the ITA grafts. The patients in the original study represented a biased sample, as they were referred to a tertiary care pain center after numerous cardiologic investigations for elucidation of their ongoing significant chest wall pain. We were therefore unable to ascertain the true prevalence and morbidity caused by this procedure. The current study investigates the prevalence and symptom characteristics of anterior intercostal nerve damage in an unbiased sample of CABG-ITA graft patients.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
After approval was obtained from the Ethics Committee for Research on Human Subjects, 37 subjects participated in the study. The subjects were recruited consecutively from the Cardiac Rehabilitation Program of the Toronto Western Hospital. An examiner attended a number of cardiac-related fitness classes and asked all post–CABG-ITA patients who were present to participate in the study by answering short, specific questions and undergoing a brief physical examination. All patients who were asked to participate in the study agreed to do so.

Data were collected regarding age, sex, and surgical procedure, as well as the onset and duration of symptoms (if any). The patients were asked specific questions regarding protracted chest pain or other bothersome chest sensations, both postoperatively and during the interview/examination. A verbal pain scale was used by the subjects to indicate pain intensity in the past and during the examination (0 = no pain at all, 10 = the worst possible pain). Physical examination focused on detection of gross sensory abnormalities over the sternotomy incision and the anterior chest wall bilaterally, with the use of a brush for light touch testing, a pinwheel for pinprick testing, and a cold roller for examination of cold perception. Tenderness to gentle manual pressure over the sternum and across the sternotomy scar, costosternal junctions T1 to T6, and ribs T1 to T6 was also documented. The findings were marked with washable markers of different colors over each patient’s chest wall and were transferred onto transparencies for the permanent records. "Definite" nerve damage was diagnosed when consistent and well-defined areas of significant abnormality to at least two cutaneous sensory testing modalities (light touch, pinprick, or cold) were detected on the anterior chest wall in the distribution of the anterior intercostal nerves in dermatomes T1 to T6. "Possible" nerve damage was diagnosed in the presence of a consistent sensory abnormality to only one cutaneous testing modality. Although tenderness over specific ribs and costosternal junctions was noted, its sole presence was not considered indicative of nerve damage. The lateralization, extent and severity of the abnormalities were noted.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
A total of 37 consecutive patients (all with CABG–ITA graft surgery) were seen, on average, 15 months postsurgery. As it so happened, all patients in the particular exercise classes attended by the investigators were male.

A total of 19 patients (51%) reported, by recollection, protracted postoperative pain that was different from angina and were able to give a pain rating (mean 4.9, range 1 to 10). Another 11 patients (30%) reported protracted unpleasant sensations postoperatively that they were not able to rate. In the group of 37 patients, 6 continued to have ongoing spontaneous pain during the physical examination (mean 4.5, range 3 to 10). One of these patients was seen 5 weeks postsurgery. The other 5 subjects who reported ongoing pain during the examination were seen, on average, 12.4 months (range, 5 to 28 months) postsurgery. The remaining 31 subjects who currently reported no spontaneous pain were examined 16.9 months after surgery (range, 2 to 68 months). In regard to protracted postoperative pain (according to the subjects’ recollection), we separated the postoperative ratings of the 5 subjects who continued to suffer from pain at least 5 months after the procedure from those of the subjects who recalled substantial and lengthy pain after surgery but had no pain during the study (n = 13). The subject with ongoing pain examined 5 weeks postsurgery was excluded from these measurements. The 5 current pain sufferers had given much higher pain scores after surgery (mean, 8.5; range, 5 to 10), whereas the other 13 patients who were free of pain during this study had indicated much lower postoperative pain ratings (mean, 3.5; range, 1 to 8). Overall, most patients recalled that pain or unpleasant sensations cleared up within several weeks to 4 months.

Evidence of "definite" anterior intercostal nerve damage confined exclusively to the left chest wall (the site of ITA harvesting) was detected in 27 patients (73%), all of whom recalled protracted postoperative pain or unpleasant sensations. Of the 5 patients with persistent pain 5 to 28 months after surgery, 4 had definite evidence of ND. The fifth patient recalled protracted postoperative allodynia (touch-evoked pain), but was found to have only localized rib tenderness over the left first rib and the right second rib during the examination. Based on our strict criteria for definite or possible ND, he was classified in the "non–nerve damage" group. Another 4 patients (11%) had "possible" nerve damage (3 of the latter also recalled protracted pain or unpleasant sensations in the past) and 6 had "no" ND. Costosternal tenderness was detected in 12 of the 27 (44%) of the patients in the "definite" nerve damage group. Overall, the prevalence of persistent chest wall pain at the site of ITA harvesting 5 to 28 months after surgery in subjects with "definite" nerve damage was 15% (4 of 27 patients).

The sensory abnormalities in all patients with nerve damage consisted of reduced sensation (hypoesthesia) to one or more cutaneous testing modalities in 75% of the patients, and mixed or hyperesthetic abnormalities in the remaining patients. In this study, only one subject with ongoing pain 7 months after surgery had considerable allodynia (touch-evoked pain). The word "sharp" was the most frequently cited pain descriptor, whereas the bothersome early sensations were most often described as "unpleasant numbness." The descriptor "burning" was rarely reported in this study population, in contrast to frequent use of this term by the patients in our original study [4].

In summary, although only a minority of nerve damage patients (15%) had ongoing spontaneous pain during the examination 5 to 28 months after CABG-ITA, other forms of pain or discomfort were found that were evoked by various stimuli (touch, pinprick, or pressure) in the majority of patients. The data are summarized in Table 1. An illustrative example of sensory abnormalities associated with intercostal nerve damage is shown in Figure 1.

View larger version (119K): [in this window] [in a new window]   Fig 1. Male study patient, with few complaints of spontaneous pain. A, costosternal junction tenderness on gentle finger pressure outside the area of sensory abnormalities; B, pinprick hyperalgesia; and C, touch-evoked pain (allodynia).

	Comment

Top Abstract Introduction Patients and methods Results Comment References

Interestingly, the majority of CABG-ITA patients also reported protracted pain or unpleasant sensations in the postoperative period. Five of those patients continued to have significant pain 5 to 28 months after the surgery, 4 of whom had persistent evidence of nerve damage. Although the data regarding postoperative pain should not be regarded as completely accurate (as such data depend solely on patient recollection), it is worth noting that those patients who recalled the highest mean postoperative pain ratings continued to have substantial pain during this study.

The CABG-ITA procedure as a source of protracted postoperative pain and chronic chest pain has received little attention in the literature, although we previously described the syndrome in detail [4]. In 1991 Eng and Wells [6] reported a series of 178 patients who were followed-up for at least 1 year after coronary artery bypass graft–left internal thoracic artery surgery (CABG-LITA). Of the patients in whom the LITA was used, 70% experienced prolonged chest wound pain after discharge compared with 51.7% of CABG-SVG. Furthermore, 23% of coronary artery bypass graft–left internal thoracic artery surgery patients experienced chronic left-sided chest wall pain as compared with 4.5% of CABG-SVG surgery patients. In 1995 Moore [7] commented on gender differences between men and women with regard to recovery symptoms after CABG surgery, and noted that women complained of "numbness and discomfort in their breasts" during the first 3 weeks of recovery. However, in this small series of 20 men and 20 women, there were no details about the percentage of CABG surgeries using ITA graft. Rowe and King [8] collected data by means of mailed questionnaires and telephone interviews for 54 women after CABG surgery. At 12 months after surgery, 47% of the women with ITA graft (20 of 43) and 18% of those without ITA graft (2 of 11) reported chest wall discomfort, but the difference was not statistically significant. At 18 months postsurgery, however, 61% of the women with ITA graft (27 of 44) and none of those without continued to report chest wall discomfort, which was statistically quite significant. In general, the women were able to discriminate between chest wall discomfort and angina. A large study was recently reported, as well [9], in which questionnaires were mailed to 504 patients who underwent CABG surgery during 1995 to 1996. The return response rate was 76%. Of the 386 responders, 57% reported chest wall pain that was different from angina, and were considered to be suffering from post-CABG pain syndrome. Of the patients with this syndrome, 66% reported moderate to severe pain, 30% regular analgesic consumption, and 28% significant interference with daily activities. In addition, 78 patients were subjected to physical examination documenting pinprick (mechanical) and thermal hypoesthesia over the left chest wall, providing evidence for nerve damage. None of these findings were reported in patients with thoracotomy for valve replacement or age-matched healthy individuals. Unfortunately, the study provided no details regarding the length of time elapsed after surgery (and therefore one cannot ascertain the prevalence of chronic pain), the number of patients in control groups, or the possible differences between male and female patients.

We believe that our study sample is representative of the general male population fit enough to take part in a cardiac-related rehabilitation program after bypass surgery. Therefore, the present study provides data regarding both the prevalence and clinical characteristics of intercostal nerve damage after CABG-ITA. We notice, however, that there are two important differences between the patients in our original study [4] and the patients in our current study group: (1) The original CABG-ITA study patients suffered from serious pain and therefore sought advice from a tertiary care pain center, whereas the current subjects did not seek specialized care; and (2) the patients in the original study had overwhelming evidence of allodynia, in contrast to the current study group, in whom allodynia was infrequent and rather mild. It might be a reasonable hypothesis that patients with significant allodynia would be the ones who would also experience significant chronic pain and seek specialized advice. Because severe allodynia was present in only 1 patient in the current study, one must assume that either this type of pain occurs infrequently or that patients with severe allodynia may not be fit to participate in a vigorous cardiac-related rehabilitation program. Based on the current study we cannot ascertain the overall prevalence of persistent, disabling pain in patients undergoing CABG-ITA, nor extrapolate our data to female patients submitted to the same operation.

We believe that in the present study we accurately detected persistent nerve damage in at least 7 of 10 patients in the CABG-ITA population. Despite the lack of a control group in our study, the degree of iatrogenically induced nerve damage in the CABG-ITA group appears to be astounding. Notwithstanding this, the use of ITA grafts has risen dramatically since the mid 1980s. Based on the cardiovascular database at our own institution, we know that of the 1,613 CABG surgeries that were performed in 1997, the left ITA graft was used in 1,469 cases (91%) and the right ITA graft was used in 59 (3.6%). Overall, 95% of all CABG procedures performed in our institution in 1997 used IMA grafting, compared with 84% of all CABG procedures performed in Ontario in 1995 [10]. In Ontario in 1994-1995, a total of 6,554 CABG procedures were performed, which reflects a rate of 80/100,000 persons more than 20 years of age [11]. In New York State in 1992, a total of 16,028 procedures were performed [12]. Therefore, given the annual rate of CABG surgeries along with 70% incidence of nerve damage at minimum, these procedures are potentially responsible for nerve damage in more than 1,000 patients per year in our institution alone, more than 3,500 patients in Ontario, and tens of thousands of patients in the USA. Even if pain (related to nerve damage) may affect only 15% of the patients, it is almost certain that a number of patients who suffer from chronic noncardiac pain may undergo unnecessary cardiac-related investigations.

In conclusion, future research should focus on clarifying the incidence of nerve damage in CABG-ITA versus other median sternotomy groups. If indeed CABG-ITA proves to have a much higher incidence of ND, then modifications of the thoracic artery harvesting technique may be needed. Such modifications must be simple to learn and avoid addition of significant operative time in an effort to prevent/reduce nerve damage in patients with CABG surgery.

	Acknowledgments

 
The authors thank Mr Chris Boulias for his assistance in collecting some of the data.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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