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Vagal Responses to Adjustable Sutures in Strabismus Correction
Vagai Responses to Adjustable Sutures in Strabismus Correction H. Sprague Eustis, M.D., C l e m e n t C. E i s w i r t h , M.D., and D a v i d R. S m i t h , M.D.
The oculocardiac reflex is a recognized complication of ocular stimulation, precipitated most commonly by traction on the extraocular muscles. To determine the true incidence of occurrence of the oculocardiac reflex during suture adjustments, 20 patients undergoing suture adjustment were monitored for blood pressure, heart rate, and rhythm abnormalities during the suture adjustment. A control group of ten patients with strabismus were studied postoperatively for comparison. Thirteen study patients and two control patients were noted to have a vagai response (P < .001). The most common response noted was a decrease in heart rate in 15 patients. Only two patients were symptomatic during vagai response (one patient became light-headed and another had an episode of nausea and vomiting). Suture adjustment was found to be the most common triggering event in precipitating vagai responses. Surgeons performing suture adjustment in strabismus correction should be cognizant of vagai responses so that they may properly inform patients of this possibility and take steps to minimize its occurrence.
in 1975 by Jampolsky, 1 the adjust able suture method is recognized as a safe and useful adjunct in strabismus correction. By ma nipulating the position of the operated-on mus cle when the patient has awakened, strabismus DESCRIBED
Accepted for publication June 10, 1992. From the Department of Ophthalmology, Ochsner Clinic and Alton Ochsner Medical Foundation, New Orleans, Louisiana (Dr. Eustis); Gulf South Heart Insti tute, East Jefferson General Hospital, New Orleans, Louisiana (Dr. Eiswirth); and Department of Ophthal mology, University of Toronto, Hospital for Sick Chil dren, Toronto, Ontario, Canada (Dr. Smith). Reprint requests to H. Sprague Eustis, M.D., Ochsner Clinic, 1514 Jefferson Hwy., New Orleans, LA 70121.
surgeons are better able to obtain a desirable alignment. Using this technique, the reoperation rate for strabismus has been reduced to approximately 10% in even the most difficult cases. 2 The oculocardiac reflex is a well-described phenomenon precipitated by ocular stimula tion, especially traction on the extraocular mus cles. In two large series of patients undergoing strabismus correction, the intraoperative inci dence of oculocardiac reflex during traction on extraocular muscles was 56% 3 and 68%. 4 Be cause the adjustable suture technique allows the surgeon to exert marked traction on the extraocular muscles, it is not uncommon to encounter the oculocardiac reflex during suture adjustment. Isenberg and Blechman 5 in 1982 described the oculocardiac reflex during manip ulation of adjustable sutures. In 1986, Flynn 6 estimated that the incidence of the reflex occur ring during suture adjustment was probably low. In 1987, Vrabec, Preslan, and Kushner 7 supported this belief with a prospective study of 44 patients undergoing suture adjustment in strabismus correction. During suture adjust ment, two of 44 patients (4.5%) had bradycardia, defined as a decrease in heart rate of 10% below normal. In the Vrabec, Preslan, and Kushner study, 7 however, a digital pulse meter was the only means of patient monitoring; no electrocardiographic or blood pressure moni toring was performed. Therefore, the dysrhythmias and decreases in blood pressure that can occur with a vagai response would not have been detected. We conducted this study to identify the true incidence of vagai responses occurring during suture adjustment and to determine whether these responses are oculocardiac reflexes or are vasovagal in origin. We also attempted to cate gorize the responses by simultaneous blood pressure, electrocardiographic, and heart rate monitoring. We hoped to identify which steps in the suture adjustment are important in elicit ing the reflex.
©AMERICAN JOURNAL OF OPHTHALMOLOGY 114:307-310, SEPTEMBER, 1992
308
September, 1992
AMERICAN JOURNAL OF OPHTHALMOLOGY
Patients and Methods From June 1986 through January 1988, all patients undergoing suture adjustment in stra bismus correction were considered for inclu sion in the study. Patients were excluded when monitoring equipment was not available at the time of the suture adjustment. Of the 20 patients included, 18 had induction of general anesthesia and two had injection of retrobulbar or peribulbar anesthetic. The pre operative medication and the intraoperative anesthetic management varied depending on the anesthesiologist assigned to the case. In all cases, droperidol and atropine sulfate were giv en shortly before anesthetic induction. Four to six hours postoperatively, patients were trans ferred to the clinic area where the postoperative adjustment was performed. Before any manipu lation of the eye, baseline heart rate, blood pressure, and electrocardiograms were ob tained. Blood pressure readings were obtained at one-minute intervals using the Dinamap au tomated blood pressure machine (Johnson & Johnson Co., models 1846SX and 1846SX/P, Critikon, Inc., Tampa, Florida), and heart rate and rhythm were continuously assessed by the electrocardiography. Notations were made on both the rhythm strips and blood pressure read outs so that the exact cardiovascular status could be determined at any point during the adjustment procedure. The adjustment process was performed with the patient in a seated position and included placement of topical anesthetic in the eye, mus cle balance testing, placement of eyelid specu lum, advancement or recession of an extraocular muscle, removal of mucus from the conjunctival sac, and tying of the muscle su ture. All steps of the adjustment process were noted on the blood pressure and rhythm strips along with any record of patient symptoms. The control group consisted of a group of patients undergoing strabismus correction from July to November 1988. Patients were excluded from study only if the monitoring equipment was unavailable. Patients were stud ied three to four hours postoperatively by using techniques similar to those described previous ly for study patients. Control patients were, however, monitored in a supine rather than a seated position, as was done in study patients. There was no ocular manipulation. All results and information were submitted to one of us (C.C.E.) for analysis, who knew which
patients were study or control. Vagai response was defined as a 10% decrease in pulse rate below baseline or a 35-mm Hg decrease in systolic blood pressure below baseline. The vagai response was further defined as chronotropic, vasodepressor, or combined mecha nism. The maneuver precipitating the vagai response was identified, and any electrocardiographic abnormality or patient symptom was noted. Results were analyzed using chi-square anal ysis and the Wilcoxon rank sums test.
Results The demographics of the study and control groups were similar. The study group consisted of nine males and 11 females with an age range from 13 to 86 years (average age, 38.2 years). The control group consisted of five males and five females with an age range from 16 to 59 years (average age, 38.4 years). The one differ ence between the control and study groups was that three patients in the study group had heart disease for which they were being treated. In the study group, the muscle on adjustable suture varied with the patient diagnosis. Distri bution of the muscle on adjustable suture was as follows: medial rectus muscle, 11 patients; lateral rectus muscle, eight patients; inferior rectus muscle, three patients; and superior rec tus muscle, three patients. Five of the 20 pa tients in the study group had two muscles on adjustable suture, for a total of 25 muscles on adjustable suture in the study group. Thirteen of 65 study patients (65%), com pared with two of ten control patients, were noted to have vagai responses. This was highly significant by chi-square analysis (P < .001) and Wilcoxon rank sums test (P < .001). In the study group, 17 vagai responses were noted in these 13 patients. There were 15 chronotropic responses, one vasodepressor response, and one combined response. Four patients had more than one vagai response during the obser vation period. Two chronotropic responses were noted in the control group. No electrocardiographic abnormalities were noted in the control group. One patient with strabismus had a ten-beat run of supraventricular tachycardia. Another patient with strabis mus had two separate episodes of ventricular triplets during adjustment. Only two patients were symptomatic during the adjustment process. One patient became
Vol. 114, No. 3
Vagai Responses to Suture Adjustment
light-headed, yet never lost consciousness. An other patient became nauseated and vomited. The event that triggered the vagai response varied among patients. All steps of the adjust ment procedure elicited a vagai response in susceptible patients. A vagai response was caused by suture adjustment in 11 patients, a tying procedure in three patients, and placing the speculum in three patients.
Discussion The oculocardiac reflex is a well-recognized result of ocular stimulation. Although any ocu lar stimulation can result in the oculocardiac reflex, traction on the extraocular muscles is recognized as most important in eliciting this vagai response. Welhaf and Johnson 3 deter mined the incidence of the oculocardiac reflex to be 56% in 78 patients with strabismus stimu lated with intraoperative traction on the extraocular muscles. Apt, Isenberg, and Gaffney4 found a 68% response rate in 240 patients undergoing strabismus correction. The results of our study suggested that the incidence of the oculocardiac reflex when trac tion is exerted on extraocular muscles during suture adjustment in strabismus correction is similar to the incidence found in the previously mentioned studies. However, results of our study were markedly dissimilar to those of Vrabec, Preslan, and Kushner, 7 who prospectively studied 44 patients undergoing suture adjustment and found an incidence of oculocar diac reflex of only 4.5%. We propose that the discrepancy in incidence between our study and the study by Vrabec, Preslan, and Kushner 7 can be attributed to differences in methodolo gy. We used electrocardiography to monitor heart rate. Vrabec, Preslan, and Kushner 7 used a digital pulse meter, which provides a computer average of heart rate over an eight-second inter val with the heart rate monitor. We propose that the digital pulse meter is much less sensitive to bradycardic episodes of short duration com pared with electrocardiography. Whereas elec trocardiography provides a second-by-second analysis of heart rate, the digital pulse meter uses a computer program that averages eightsecond intervals. This digital pulse meter could have missed or disregarded short bradycardic episodes that would have been identified with electrocardiography. Our incidence figures were similar to those of Apt, Isenberg, and
309
Gaffney4 and Welhaf and Johnson, 3 which sup ports this claim. Other important differences between our study and that of Vrabec, Preslan, and Kushner 7 deserve mention. Vrabec, Preslan, and Kush ner 7 made adjustments on the postoperative morning, rather than four to six hours postoperatively as we did. Possibly, a patient's suscepti bility to vagai responses is greater in the imme diate postoperative period. Two of our control patients demonstrated an unexplained postop erative chronotropic response. Also, we per formed the adjustment with the patient in a seated position (rather than supine as in the study by Vrabec, Preslan, and Kushner 7 ), which might elicit a vasodepressor response. Finally, we used an eyelid speculum (not used by Vrabec, Preslan, and Kushner 7 ), which might trigger an oculocardiac reflex. This variance in methods, therefore, prevents accurate compari son of the two studies and might account, to a certain degree, for the increased incidence of oculocardiac reflexes in our study. Although the definition of the chronotropic vagai response (a 10% decrease in heart rate) was similar to the definition of oculocardiac reflex used in other studies, this definition may be too conservative. Two of our control patients demonstrated a chronotropic vagai response, one of whom had a decrease in heart rate of 32 beats per minute from baseline. Possibly, what is considered " n o r m a l " in the immediate post operative period requires redefinition. Although we suspect that most vagai re sponses represent a true oculocardiac reflex, anxiety-related vasovagal responses are also probably included. Despite proper counseling, many patients are apprehensive and fearful of strabismus correction. The stress and anxiety of the adjustment maneuver merely compound the problem. Although any type of ocular stim ulation can induce the oculocardiac reflex, it is doubtful that eyelid speculum placement or tying of the muscle sutures represents enough stimulation to result in the oculocardiac reflex. In the six patients in our study in whom these steps resulted in a vagai response, we suspect the vagai response to have been anxiety related. Unfortunately, the available data prevent accu rate differentiation between oculocardiac reflex and vasovagal responses. Vrabec, Preslan, and Kushner 7 described a similar experience. One patient had a bradycardic response with cover testing, but no response when traction was exerted on the extraocular muscles. We suspect, as do Apt and Isenberg, 8 that this response was also vasovagal.
310
September, 1992
AMERICAN JOURNAL OF OPHTHALMOLOGY
Although vagai responses occur commonly during suture adjustment, patients rarely be come symptomatic. 6 In a survey of the Ameri can Association of Pediatrie Ophthalmology and Strabismus membership, 9 the incidence of symptomatic vasovagal reflexes occurring dur ing suture adjustment was 0.28%. In our study, only one patient was symptomatic but recov ered quickly before losing consciousness. In this instance, a chronotropic oculocardiac re flex resulted in a decrease in heart rate from 110 to 80 beats per minute (27% below baseline). The patient was placed in the supine position with prompt resolution of symptoms and return of heart rate to normal range. We suggest that vagai responses are common; however, most patients (65%) will be asympto matic and symptoms will be unrecognized un less cardiac monitoring is used. The wide dis parity in incidence between symptomatic and asymptomatic vagai events can be explained. We suspect that the duration of the bradycardic or hypotensive event determines whether a pa tient becomes symptomatic. Oculocardiac re flexes of short duration do not result in a marked decrease in cerebral perfusion; there fore, the patient remains asymptomatic. Con versely, if the oculocardiac reflex is of long duration, cerebral perfusion becomes compro mised, and the patient becomes light-headed and syncopal. Unfortunately, the duration of the oculocardiac reflexes was not calculated, and therefore, the critical time period for pa tients experiencing oculocardiac reflexes to be come symptomatic is undetermined by this study. Fortunately, the oculocardiac reflex encoun tered during suture adjustment is generally a brief, self-limited event, rarely resulting in
symptoms or any other sequelae. When oculocardiac reflexes do occur, however, these episodes are disturbing to both patient and physician. Therefore, the physician who per forms the adjustment should properly inform patients of this possibility.
References 1. Jampolsky, A. L.: Strabismus reoperation tech niques. Trans. Am. Acad. Ophthalmol. Otolaryngol. 79OP.-704, 1975. 2. Wisnichi, H. J., Repka, N. X., and Guyton, D. L.: Reoperation rate in adjustable strabismus sur gery. J. Pediatr. Ophthalmol. Strabismus 25:112, 1988. 3. Welhaf, W. R., and Johnson, D. C: The oculocardiac reflex during extraocular muscle sur gery. Arch. Ophthalmol. 73:43, 1965. 4. Apt, L., Isenberg, S., and Gaffney, W. L.: The oculocardiac reflex in strabismus surgery. Am. J. Ophthalmol. 76:533, 1973. 5. Isenberg, S. ]., and Blechman, B.: Oculocardiac reflex during postoperative muscle adjustment (cor respondence). Am. J. Ophthalmol. 94:422, 1982. 6. Flynn, J. T.: The adjustable suture. A clinician's experience. Trans. New Orleans Acad. Ophthalmol. 245, 1986. 7. Vrabec, M. P., Preslan, M. W., and Kushner, B. J.: Oculocardiac reflex during manipulation of ad justable sutures after strabismus surgery. Am. J. Ophthalmol. 104:61, 1987. 8. Apt, L., and Isenberg, S. J.: Oculocardiac reflex during manipulation of adjustable sutures after stra bismus surgery (correspondence). Am. J. Ophthal mol. 104:551, 1987. 9. Eustis, H. S,: Syncopal episodes during postop erative suture adjustment in strabismus surgery. A survey. Binocular Vision 5:133, 1990.
The oculocardiac reflex is a recognized complication of ocular stimulation, precipitated most commonly by traction on the extraocular muscles. To determine the true incidence of occurrence of the oculocardiac reflex during suture adjustments, 20 patients undergoing suture adjustment were monitored for blood pressure, heart rate, and rhythm abnormalities during the suture adjustment. A control group of ten patients with strabismus were studied postoperatively for comparison. Thirteen study patients and two control patients were noted to have a vagai response (P < .001). The most common response noted was a decrease in heart rate in 15 patients. Only two patients were symptomatic during vagai response (one patient became light-headed and another had an episode of nausea and vomiting). Suture adjustment was found to be the most common triggering event in precipitating vagai responses. Surgeons performing suture adjustment in strabismus correction should be cognizant of vagai responses so that they may properly inform patients of this possibility and take steps to minimize its occurrence.
in 1975 by Jampolsky, 1 the adjust able suture method is recognized as a safe and useful adjunct in strabismus correction. By ma nipulating the position of the operated-on mus cle when the patient has awakened, strabismus DESCRIBED
Accepted for publication June 10, 1992. From the Department of Ophthalmology, Ochsner Clinic and Alton Ochsner Medical Foundation, New Orleans, Louisiana (Dr. Eustis); Gulf South Heart Insti tute, East Jefferson General Hospital, New Orleans, Louisiana (Dr. Eiswirth); and Department of Ophthal mology, University of Toronto, Hospital for Sick Chil dren, Toronto, Ontario, Canada (Dr. Smith). Reprint requests to H. Sprague Eustis, M.D., Ochsner Clinic, 1514 Jefferson Hwy., New Orleans, LA 70121.
surgeons are better able to obtain a desirable alignment. Using this technique, the reoperation rate for strabismus has been reduced to approximately 10% in even the most difficult cases. 2 The oculocardiac reflex is a well-described phenomenon precipitated by ocular stimula tion, especially traction on the extraocular mus cles. In two large series of patients undergoing strabismus correction, the intraoperative inci dence of oculocardiac reflex during traction on extraocular muscles was 56% 3 and 68%. 4 Be cause the adjustable suture technique allows the surgeon to exert marked traction on the extraocular muscles, it is not uncommon to encounter the oculocardiac reflex during suture adjustment. Isenberg and Blechman 5 in 1982 described the oculocardiac reflex during manip ulation of adjustable sutures. In 1986, Flynn 6 estimated that the incidence of the reflex occur ring during suture adjustment was probably low. In 1987, Vrabec, Preslan, and Kushner 7 supported this belief with a prospective study of 44 patients undergoing suture adjustment in strabismus correction. During suture adjust ment, two of 44 patients (4.5%) had bradycardia, defined as a decrease in heart rate of 10% below normal. In the Vrabec, Preslan, and Kushner study, 7 however, a digital pulse meter was the only means of patient monitoring; no electrocardiographic or blood pressure moni toring was performed. Therefore, the dysrhythmias and decreases in blood pressure that can occur with a vagai response would not have been detected. We conducted this study to identify the true incidence of vagai responses occurring during suture adjustment and to determine whether these responses are oculocardiac reflexes or are vasovagal in origin. We also attempted to cate gorize the responses by simultaneous blood pressure, electrocardiographic, and heart rate monitoring. We hoped to identify which steps in the suture adjustment are important in elicit ing the reflex.
©AMERICAN JOURNAL OF OPHTHALMOLOGY 114:307-310, SEPTEMBER, 1992
308
September, 1992
AMERICAN JOURNAL OF OPHTHALMOLOGY
Patients and Methods From June 1986 through January 1988, all patients undergoing suture adjustment in stra bismus correction were considered for inclu sion in the study. Patients were excluded when monitoring equipment was not available at the time of the suture adjustment. Of the 20 patients included, 18 had induction of general anesthesia and two had injection of retrobulbar or peribulbar anesthetic. The pre operative medication and the intraoperative anesthetic management varied depending on the anesthesiologist assigned to the case. In all cases, droperidol and atropine sulfate were giv en shortly before anesthetic induction. Four to six hours postoperatively, patients were trans ferred to the clinic area where the postoperative adjustment was performed. Before any manipu lation of the eye, baseline heart rate, blood pressure, and electrocardiograms were ob tained. Blood pressure readings were obtained at one-minute intervals using the Dinamap au tomated blood pressure machine (Johnson & Johnson Co., models 1846SX and 1846SX/P, Critikon, Inc., Tampa, Florida), and heart rate and rhythm were continuously assessed by the electrocardiography. Notations were made on both the rhythm strips and blood pressure read outs so that the exact cardiovascular status could be determined at any point during the adjustment procedure. The adjustment process was performed with the patient in a seated position and included placement of topical anesthetic in the eye, mus cle balance testing, placement of eyelid specu lum, advancement or recession of an extraocular muscle, removal of mucus from the conjunctival sac, and tying of the muscle su ture. All steps of the adjustment process were noted on the blood pressure and rhythm strips along with any record of patient symptoms. The control group consisted of a group of patients undergoing strabismus correction from July to November 1988. Patients were excluded from study only if the monitoring equipment was unavailable. Patients were stud ied three to four hours postoperatively by using techniques similar to those described previous ly for study patients. Control patients were, however, monitored in a supine rather than a seated position, as was done in study patients. There was no ocular manipulation. All results and information were submitted to one of us (C.C.E.) for analysis, who knew which
patients were study or control. Vagai response was defined as a 10% decrease in pulse rate below baseline or a 35-mm Hg decrease in systolic blood pressure below baseline. The vagai response was further defined as chronotropic, vasodepressor, or combined mecha nism. The maneuver precipitating the vagai response was identified, and any electrocardiographic abnormality or patient symptom was noted. Results were analyzed using chi-square anal ysis and the Wilcoxon rank sums test.
Results The demographics of the study and control groups were similar. The study group consisted of nine males and 11 females with an age range from 13 to 86 years (average age, 38.2 years). The control group consisted of five males and five females with an age range from 16 to 59 years (average age, 38.4 years). The one differ ence between the control and study groups was that three patients in the study group had heart disease for which they were being treated. In the study group, the muscle on adjustable suture varied with the patient diagnosis. Distri bution of the muscle on adjustable suture was as follows: medial rectus muscle, 11 patients; lateral rectus muscle, eight patients; inferior rectus muscle, three patients; and superior rec tus muscle, three patients. Five of the 20 pa tients in the study group had two muscles on adjustable suture, for a total of 25 muscles on adjustable suture in the study group. Thirteen of 65 study patients (65%), com pared with two of ten control patients, were noted to have vagai responses. This was highly significant by chi-square analysis (P < .001) and Wilcoxon rank sums test (P < .001). In the study group, 17 vagai responses were noted in these 13 patients. There were 15 chronotropic responses, one vasodepressor response, and one combined response. Four patients had more than one vagai response during the obser vation period. Two chronotropic responses were noted in the control group. No electrocardiographic abnormalities were noted in the control group. One patient with strabismus had a ten-beat run of supraventricular tachycardia. Another patient with strabis mus had two separate episodes of ventricular triplets during adjustment. Only two patients were symptomatic during the adjustment process. One patient became
Vol. 114, No. 3
Vagai Responses to Suture Adjustment
light-headed, yet never lost consciousness. An other patient became nauseated and vomited. The event that triggered the vagai response varied among patients. All steps of the adjust ment procedure elicited a vagai response in susceptible patients. A vagai response was caused by suture adjustment in 11 patients, a tying procedure in three patients, and placing the speculum in three patients.
Discussion The oculocardiac reflex is a well-recognized result of ocular stimulation. Although any ocu lar stimulation can result in the oculocardiac reflex, traction on the extraocular muscles is recognized as most important in eliciting this vagai response. Welhaf and Johnson 3 deter mined the incidence of the oculocardiac reflex to be 56% in 78 patients with strabismus stimu lated with intraoperative traction on the extraocular muscles. Apt, Isenberg, and Gaffney4 found a 68% response rate in 240 patients undergoing strabismus correction. The results of our study suggested that the incidence of the oculocardiac reflex when trac tion is exerted on extraocular muscles during suture adjustment in strabismus correction is similar to the incidence found in the previously mentioned studies. However, results of our study were markedly dissimilar to those of Vrabec, Preslan, and Kushner, 7 who prospectively studied 44 patients undergoing suture adjustment and found an incidence of oculocar diac reflex of only 4.5%. We propose that the discrepancy in incidence between our study and the study by Vrabec, Preslan, and Kushner 7 can be attributed to differences in methodolo gy. We used electrocardiography to monitor heart rate. Vrabec, Preslan, and Kushner 7 used a digital pulse meter, which provides a computer average of heart rate over an eight-second inter val with the heart rate monitor. We propose that the digital pulse meter is much less sensitive to bradycardic episodes of short duration com pared with electrocardiography. Whereas elec trocardiography provides a second-by-second analysis of heart rate, the digital pulse meter uses a computer program that averages eightsecond intervals. This digital pulse meter could have missed or disregarded short bradycardic episodes that would have been identified with electrocardiography. Our incidence figures were similar to those of Apt, Isenberg, and
309
Gaffney4 and Welhaf and Johnson, 3 which sup ports this claim. Other important differences between our study and that of Vrabec, Preslan, and Kushner 7 deserve mention. Vrabec, Preslan, and Kush ner 7 made adjustments on the postoperative morning, rather than four to six hours postoperatively as we did. Possibly, a patient's suscepti bility to vagai responses is greater in the imme diate postoperative period. Two of our control patients demonstrated an unexplained postop erative chronotropic response. Also, we per formed the adjustment with the patient in a seated position (rather than supine as in the study by Vrabec, Preslan, and Kushner 7 ), which might elicit a vasodepressor response. Finally, we used an eyelid speculum (not used by Vrabec, Preslan, and Kushner 7 ), which might trigger an oculocardiac reflex. This variance in methods, therefore, prevents accurate compari son of the two studies and might account, to a certain degree, for the increased incidence of oculocardiac reflexes in our study. Although the definition of the chronotropic vagai response (a 10% decrease in heart rate) was similar to the definition of oculocardiac reflex used in other studies, this definition may be too conservative. Two of our control patients demonstrated a chronotropic vagai response, one of whom had a decrease in heart rate of 32 beats per minute from baseline. Possibly, what is considered " n o r m a l " in the immediate post operative period requires redefinition. Although we suspect that most vagai re sponses represent a true oculocardiac reflex, anxiety-related vasovagal responses are also probably included. Despite proper counseling, many patients are apprehensive and fearful of strabismus correction. The stress and anxiety of the adjustment maneuver merely compound the problem. Although any type of ocular stim ulation can induce the oculocardiac reflex, it is doubtful that eyelid speculum placement or tying of the muscle sutures represents enough stimulation to result in the oculocardiac reflex. In the six patients in our study in whom these steps resulted in a vagai response, we suspect the vagai response to have been anxiety related. Unfortunately, the available data prevent accu rate differentiation between oculocardiac reflex and vasovagal responses. Vrabec, Preslan, and Kushner 7 described a similar experience. One patient had a bradycardic response with cover testing, but no response when traction was exerted on the extraocular muscles. We suspect, as do Apt and Isenberg, 8 that this response was also vasovagal.
310
September, 1992
AMERICAN JOURNAL OF OPHTHALMOLOGY
Although vagai responses occur commonly during suture adjustment, patients rarely be come symptomatic. 6 In a survey of the Ameri can Association of Pediatrie Ophthalmology and Strabismus membership, 9 the incidence of symptomatic vasovagal reflexes occurring dur ing suture adjustment was 0.28%. In our study, only one patient was symptomatic but recov ered quickly before losing consciousness. In this instance, a chronotropic oculocardiac re flex resulted in a decrease in heart rate from 110 to 80 beats per minute (27% below baseline). The patient was placed in the supine position with prompt resolution of symptoms and return of heart rate to normal range. We suggest that vagai responses are common; however, most patients (65%) will be asympto matic and symptoms will be unrecognized un less cardiac monitoring is used. The wide dis parity in incidence between symptomatic and asymptomatic vagai events can be explained. We suspect that the duration of the bradycardic or hypotensive event determines whether a pa tient becomes symptomatic. Oculocardiac re flexes of short duration do not result in a marked decrease in cerebral perfusion; there fore, the patient remains asymptomatic. Con versely, if the oculocardiac reflex is of long duration, cerebral perfusion becomes compro mised, and the patient becomes light-headed and syncopal. Unfortunately, the duration of the oculocardiac reflexes was not calculated, and therefore, the critical time period for pa tients experiencing oculocardiac reflexes to be come symptomatic is undetermined by this study. Fortunately, the oculocardiac reflex encoun tered during suture adjustment is generally a brief, self-limited event, rarely resulting in
symptoms or any other sequelae. When oculocardiac reflexes do occur, however, these episodes are disturbing to both patient and physician. Therefore, the physician who per forms the adjustment should properly inform patients of this possibility.
References 1. Jampolsky, A. L.: Strabismus reoperation tech niques. Trans. Am. Acad. Ophthalmol. Otolaryngol. 79OP.-704, 1975. 2. Wisnichi, H. J., Repka, N. X., and Guyton, D. L.: Reoperation rate in adjustable strabismus sur gery. J. Pediatr. Ophthalmol. Strabismus 25:112, 1988. 3. Welhaf, W. R., and Johnson, D. C: The oculocardiac reflex during extraocular muscle sur gery. Arch. Ophthalmol. 73:43, 1965. 4. Apt, L., Isenberg, S., and Gaffney, W. L.: The oculocardiac reflex in strabismus surgery. Am. J. Ophthalmol. 76:533, 1973. 5. Isenberg, S. ]., and Blechman, B.: Oculocardiac reflex during postoperative muscle adjustment (cor respondence). Am. J. Ophthalmol. 94:422, 1982. 6. Flynn, J. T.: The adjustable suture. A clinician's experience. Trans. New Orleans Acad. Ophthalmol. 245, 1986. 7. Vrabec, M. P., Preslan, M. W., and Kushner, B. J.: Oculocardiac reflex during manipulation of ad justable sutures after strabismus surgery. Am. J. Ophthalmol. 104:61, 1987. 8. Apt, L., and Isenberg, S. J.: Oculocardiac reflex during manipulation of adjustable sutures after stra bismus surgery (correspondence). Am. J. Ophthal mol. 104:551, 1987. 9. Eustis, H. S,: Syncopal episodes during postop erative suture adjustment in strabismus surgery. A survey. Binocular Vision 5:133, 1990.