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New Q waves after coronary artery bypass surgery for angina pectoris
New Q Waves After Coronary Artery Bypass Surgery for Angina Pectoris
JAIME
ESPINOZA,
JANET
LIPSKI,
ROBERT EPHRAIM SIMON
MD
MD
LITWAK,
MD,
DONOSO, DACK,
MD,
FACC
MD,
FACC
FACC
New York, New York
Pre- and postoperative electrocardiograms were evaluated in 44 patients with angina pectoris who underwent single or multiple coronary artery bypass procedures. Two groups were identified: Group A, 37 patients with bypass procedures only, and Group B, 7 patients with bypass procedures and gdditional surgery (valve replacement in 4 and ventricular resection in 3). Preoperative electrocardiograms showed abnormal Q waves in 14 of 37 patients in Group A and in 3 of 7 patients in Group B. After coronary artery bypass, new Q waves appeared in 11 of 37 patients (30 percent) in Group A, including 1 of 9 (11 percent) with one-vessel disease on preoperative coronary arteriograms, 7 of 20 (35 percent) with two-vessel disease and 3 of 8 (37.5 percent) with three-vessel disease; new intraventricular conduction abnormalities appeared in 4 of the 37. None of the seven patients in Group B had new G waves postoperatively, but three had intraventricular conduction abnormalities. There was no correlation between new Q waves and preoperative values for left ventricular end-diastolic pressure. In Group A, new 0 waves were demonstrated in 2 of 9 patients (22 percent) with one coronary bypass procedure, 5 of 21 patients (24 percent) with two bypass procedures and 4 of 8 patients (87 percent) with three bypass procedures. The single patient who had four coronary artery bypass procedures had no new Q waves after operation. It is evident that the prevalence of new Q waves was greater in patients who had two- or three-vessel disease by coronary arteriography as well as in those who had three coronary artery bypasses. Postoperative clinical course and mortality were not affected.
Myocardial revascularization utilizing direct saphenous vein bypass graft has been used extensively, and several reports of postoperative electrocardiographic changes have appeared. Diethrich et al.’ in 1968 reported electrocardiographic changes compatible with acute myocardial infarction in 11 of 40 patients (27.5 percent) who underwent the Vineberg procedure. The reported frequency of electrocardiographic changes compatible with myocardial infarction after coronary artery bypass has ranged from approximately 8 to 35 percent.“- “) This electrocardiographic study was undertaken to assess the frequency of new Q waves after saphenous vein bypass surgery for occlusive coronary artery disease. From the Division of Cardiology, Department of Medicine, The Mount Sinai Hospital and The Mount Sinai School of Medicine of the City University of New York, New York, N. Y. Manuscript accepted July 31, 1973. Address for reprints: Simon Dack. MD, Division of Cardiology, The Mount Sinai Hospital, 1 East 100th St., New York, N. Y. 10029.
Material
and Methods
The pre- and postoperative electrocardiograms, together with preoperative coronary arteriograms and left ventriculograms, were studied in 44 patients who underwent coronary artery bypass surgery at this hospital. Five other patients who died on the day of operation were not included because postoperative 12 lead electrocardiograms were not obtained. The study group comprised 37 men and 7 women whose ages ranged from 32 to 68 years.
February 1974
The American Journal of CARDIOLOGY
Volume 33
221
Q WAVES
AFTER
CORONARY
ARTERY
BYPASS-ESPINOZA
ET AL
I
TABLE
Analysis of Preoperative
Electrocardiograms
Previous myocardial Anterior Inferior lnferolateral ST-T changes
infarction
Right bundle Normal
block
branch
* 1 had previous
myocardial
The 44 patients were classified in two groups. Group A comprised 37 patients who had single or multiple coronary artery bypass procedures only. Group B comprised seven patients who had single or multiple bypass procedures and additional surgery: valve replacement in four (two aortic and two mitral) and ventricular resection in three (for vent ricular aneurysm [2 patients] and idiopathic hypertrophic subaortic stenosis [one patient]).
in 44 Cases 17 4 12 1 20 3* 5
Results Preoperative
infarction.
TABLE II Vessel Involvement
Vessels Involved
Cases
(no.)
(no.)
Group A 1 2 3 Total
by Coronary Arteriography
Previous Myocardial Infarction
9 20 8 37
3 9 2 14
3 2 2 7
1 1 1 3
Group B 1 2 3 Tota I
New Conduction No PostAbnoroperative malities Change
New Q Waves
l(ll%) 7(35%,) 3(37%0) 11 0 0 0 0
2 1 1 4
6 12 4 22
1 1 1 3
2 1 1 4
Analysis of Pktoperative
Electrocardiograms Group A
New Q waves New conduction No change Total
abnormalities
no.
%
11 4 22 37
30 11 59 100
in 44 Cases Group B no.
%
0 3 4 7
0 43 57 100
Since S-T segment and T wave changes occur frequently after cardiac surgery and their specificity for myocardial infarction is doubtful, only the QRS complexes were analyzed during this period. The New York Heart Association’s criteria” for an abnormal Q wave were used. Preand postoperative abnormal Q waves were analyzed. Preoperative coronary arteriograms were obtained in all patients. Arterial obstruction of greater than 50 percent was considered significant, and the number of arteries involved was tabulated. Left ventricular end-diastolic pressure, determined in 38 patients, was considered abnormal if it exceeded 12 mm Hg. Postoperative electrocardiograms were ana-
lyzed by at least four of us, and new Q waves were correlated with selective coronary arteriographic data, left ventricular end-diastolic pressures and the number of arteries bypassed. 222
February
Preoperative electrocardiograms indicated previous myocardial infarction in 17 patients, 14 of 37 in Group A (38 percent) and 3 of 7 in Group B (43 percent). The infarction was located in the inferior wall in 12, the anterior wall in 4 and the inferolateral wall in 1. Right bundle branch block was present in three patients, including one with evidence of old myocardial infarction. Twenty patients had S-T segment and T wave changes only, and five had normal electrocardiographic findings (Table I). Coronary arteriograms in Group A disclosed onevessel disease in 9 patients, two-vessel disease in 20 and three-vessel disease in 8 (Table II). In Group B, one-vessel disease was present in three patients, twovessel disease in two and three-vessel disease in two. Previous myocardial infarction was present in 4 of the 12 patients with one-vessel disease (3 in Group A and 1 in Group B), 10 of the 22 patients with two-vessel disease (9 in Group A and 1 in Group B) and 3 of t,he 10 patients with three-vessel disease (2 in Group A and 1 in Group B) (Table II). Postoperative
TABLE III
1974
The American
Journal
of CARDIOLOGY
Findings
Findings
Postoperative electrocardiograms revealed abnormal new Q waves in 11 of the 37 patients in Group A (30 percent) but in none of the 7 patients in Group B. Four patients in Group A (11 percent) had new conduction abnormalities, intraventricular conduction delay (three patients) and left bundle branch block (one patient) (Table III). In Group B, three of seven patients (43 percent) manifested a new left bundle branch block. Of the 11 patients in Group A who had new Q waves, only 2 (18 percent) had electrocardiographic evidence of previous myocardial infarction. Before operation, three of these patients had three-vessel disease, seven had two-vessel disease and one had one-vessel disease (Table II). Preoperative left ventricular end-diastolic pressure data were available in 32 patients in Group A and in 6 patients in Group B (Table IV). In Group A, 23 patients had normal values and 9 had increased values (13 to 33 mm Hg). In Group B, two patients had normal values and four had abnormal values (13 to 23 mm Hg). After coro’nary artery bypass, 6 patients in Group A with previously normal left ventricular end-diastolic pressure manifested new Q waves, 2 had conduction abnormalities and 15 showed no change; of the 9 patients with abnormal 3 manifested
two patients Volume
33
left ventricular
end-diastolic
pressure,
new Q waves and 6 no change. In the in Group B with normal left ventricular
Q WAVES
end-diastolic pressure, one had a conduction abnormality and one showed no change. In the four patients with abnormal left ventricular end-diastolic pressure, two had conduction abnormalities only (Table IV). In Group A, correlation of electrocardiographic data with the number of arteries bypassed (Table V) disclosed new Q waves in 2 of 9 patients (22 percent) who had one coronary artery bypass procedure, 5 of 21 patients (24 percent) who had two bypass procedures and 4 of 6 patients (67 percent) who had three bypass procedures. The single patient with four bypass grafts manifested no electrocardiographic changes after operation. Of the 44 patients studied, 42 were discharged from the hospital and 2 died. The presence of new Q waves did not appear to affect hospital mortality rate. One patient with new Q waves postoperatively had mediastinitis and intraventricular conduction abnormality and died of sepsis. The other patient manifested a postoperative intraventricular conduction disturbance on the electrocardiogram and died with shock secondary to a bleeding disorder. Discussion The overall frequency of postoperative myocardial infarction in 12,712 patients who underwent a general surgical procedure during a 5 year period at the New York Hospital was reported to be 0.95 percent.12 In the presence of previous postoperative myocardial infarction this rate rose to 6.5 percent. Our study reveals that of 37 patients who underwent coronary artery bypass surgery alone, 11 (29.7 percent) manifested new Q waves. Transitory Q waves may be seen on the electrocardiogram under various circumstances and may not represent myocardial necrosis. Q waves were observed after shock and severe metabolic stress by Shugoll,‘a after cross-clamping of the aorta and during the initiation of extracorporeal circulation by Klein et a1.14 and during atria1 pacing by De la Fuente et al.‘” The explanations given by these investigators do not apply to our study since the new Q waves in our patients were not transitory but persisted at least until discharge from the hospital. We believe that these Q waves represent acute myocardial infarction occurring during or immediately after coronary artery bypass surgery. There have been attempts to evaluate objectively the accuracy of diagnosis of acute myocardial infarction after thoracic surgery. Although many factors may affect serum enzyme values, several reports suggest that these values correlate well with the presence or absence of myocardial infarction.l,n+re However, our patients did not have serial postoperative enzyme studies. The frequency of postoperative myocardial infarction in patients undergoing a Vineberg procedure for coronary artery disease ranges from 9 to 27.5 percent.1JsJ7~20 The reported frequency of acute myocardial infarction after coronary artery bypass surgery has varied. Dawson et a1.2 reported a rate of 22 February
AFTER
TABLE
CORONARY
ARTERY
BYPASS-ESPINOZA
ET AL.
IV
Correlation of Left Ventricular End-Diastolic Pressure (LVEDP), Previous Myocardial Infarction and Electrocardiographic
LVEDP Group A Normal Increased Group 6 Normal Increased
Changes New Conduction Abnormalities
Previous Mycardial Infarction
New Q Waves
23 9
8 4
6(26%‘0) 3(33%b)
2 0
15 6
2
0 0
0 0
1 2
1 2
Patients (no.)
4
No Change
TABLE V Pre- and Postoperative Coronary Bypass Grafts
Patients
(no.)
(no.)
Group A 1 2 3 4 Total Group 6 1 2 3 4 Total ~-
Electrocardiograms
and Number
of
Bypasses
9 21 6 1 37 3 2 2 0 7
New Q Waves
2(22%) 5(23%‘0) 4(66%b) 0 11 0 0 0 0 0
New Conduction Abnormalities
No Change
0 4 0 0 4
7 12 2 1 22
1 1 1 0 3
2 1 1 0 4
percent (30 of 134), Brewer et al.:i a rate of 20 percent (49 of 243), Sheldon et a1.4 a rate of 9 percent (9 of 100) and Hultgren et al.” a rate of 34 percent (17 of 50); the latter series represents a mixed group of saphenous vein bypass grafts, Vineberg and other revascularization procedures. More recently, Anderson et a1.e reported a 17 percent frequency (8 of 46), Kansal et a1.7 a 10 percent frequency (15 of 151) and Williams et al8 a 23 percent frequency (23 of 100). Vectorcardiographic analysis of acute myocardial infarction revealed a 6 percent prevalence (6 of 100) in the study of Friedewald et a1.9, an 8 percent prevalence (15 of 193) in that of Friedberg et al.1° and a 35 percent prevalence (6 of 17)in that of Anderson et al.” Selection of patients may be a significant factor in these differences since, in our patients with extensive disease requiring more than one bypass, acute myocardial infarction occurred more frequently than in those with less severe disease. The time that patients remained under extracorporeal circulation during operation was implicated by Brewer et al.,:’ who found that myocardial infarction occurred more frequently 1974
The American Journal of CARDIOLOGY
Volume 33
223
Q WAVES
AFTER CORONARY
ARTERY BYPASS-ESPINOZA
ET AL.
in patients who h’ad more than 120 minutes of pump time. The anoxic arrest of 10 to 15 minutes for each coronary artery anastomosed may be a significant factor in a patient with severe preexisting coronary artery disease. This was manifested in our study by a greater prevalence of new Q waves in patients with three coronary artery bypasses (67 percent) than in those with one or two bypasses (22 and 24 percent, respectively). Technical factors may also play a role in the development of myocardial infarction and should be evaluated and analyzed further. Recently a high rate of myocardial infarction after combined coronary endarterectomy and coronary artery bypass was reported,‘Jl but only one patient in our series had this procedure. Nine of our patients who had no previous electrocardiographic evidence of myocardial infarction manifested new Q waves. However, of 14 patients with electrocardiographic changes of previous myocardial
infarction, only 2 had new Q waves. New intraventricular conduction abnormalities that developed in four patients in Group A made the diagnosis of acute myocardial infarction impossible. Therefore, this change may have masked a higher frequency of new Q waves. None of the seven patients in Group B had new Q waves; however, four had new conduction abnormalities that ma/ have masked the electrocardiographic findings. Electrocardiographic changes did not correlate significantly with preoperative left ventricular end-diastolic pressure data. In conclusion, it appears that the greater the severity of coronary artery disease, the greater the prevalence of myocardial infarction after saphenous vein bypass surgery. The immediate operative mortality in our series was not affected. These electrocardiographic changes require further evaluation by longer follow-up studies, and their ultimate clinical significance should be considered in the overall evaluation of coronary artery bypass surgery.
References
1. Diethrich E, Liddlcoat J, Alessi F, et al: Serum enzyme and
2.
3. 4.
5.
6.
7.
8.
9.
10.
11.
224
electrocardiographic changes immediately following myocardial revascularization. Ann Thorac Surg 5:195-203, 1968 Dawson J, Hall R, Garcia E, et al: Myocardial infarction after coronary artery bypass surgery (abstr). Circulation 45-46: suppl ll:ll-144, 1972 Brewer D, Bilbro R, Bartel A: Myocardial infarction as a complication of coronary bypass surgery. Circulation 4758-64, 1973 Sheldon W, Favaioro R, Sones M, et al: Reconstructive coronary artery surgery. Venous autograft technique. JAMA 213: 78-82, 1970 Huitgren H, Mlyagawa M, Buck W, et al: lschemic myocardial injury during coronary artery surgery. Am Heart J 82:624-631, 1971 Anderson W, Brundage B, Cheitlin M, et al: Vectorcardiographic changes following saphenous vein bypass graft (abstr). Am J Cardiol 31:116, 1973 Kansal S, Roitman D, Sheffield T, et al: Acute myocardial injury following aortocoronary bypass surgery (abstr). Am J Cardiol 31:140, 1973 Williams D, iben A, Hurley E, et al: Myocardial infarction during coronary artery bypass surgery (abstr). Am J Cardiol 31: 164, 1973 Frledewaid V, Futral J, Kinard S, et al: Vectorcardiographic changes following saphenous vein coronary bypass surgery (abstr). Am J Cardiol 31:132, 1973 Friedberg D, Zeft H, Sliberman R, et al: Myocardial infarction following coronary surgery. Vectorcardiographic assessment (abstr). Am J Cardiol 31:132, 1973 New York Heart Association. Nomenclature and Criteria for Diagnosis. In, Diseases of the Heart and Blood Vessels. sixth edition. Boston, Little Brown, 1964, p. 57-58
February 1974
The American Journal of CARDIOLOGY
12. Topkins #, Antuslo J: Myocardial infarction and surgery, a five year study. Anesth Analg (Cleve) 43:716-720, 1964 13. Shugoll G: Transient electrocardiographic changes simulating myocardial infarction associated with shock and severe metabolic stress. Am Heart J 74:402-409, 1967 14. Klein H, Gross H, Rubin I: Transient electrocardiographic changes simulating myocardial infarction during open-heart surgery. Am Heart J 79:463-470, 1970 15. De la Fuente 0, Gambetta M, Goldbarg A, et al: The significance of transient Q waves (abstr). Circulation 45: suppl ll:ll153, 1972 16. Greenberg B, McCalilster B, Frye R, et al: Serum glutamic oxaloacetic transaminase and electrocardiographic changes after myocardial revascularization procedures in patients with coronary artery disease. Am J Cardiol 26:135-142, 1970 17. Shirey E, Proudiit W, Sones M: Serum enzyme and electrocardiographic changes after coronary artery surgery. Chest 57: 122-130, 1970 18. Haak E, Sanchez-Palacios M, Goulden D, et al: Clinical significance of electrocardiogram and enzyme changes associated with coronary artery bypass surgery (abstr). Circulation 45-46: suppl ll:ll-162, 1972 19. Dawson J, Garcia E, Hall R, et al: Serum enzymes after coronary artery bypass surgery (abstr). Circulation 45: suppl ll:li144,1972 20. Favaloro R, EHier D, Groves L, et al: Myocardial revascularization by internal mammary implant procedure. J Thorac Cardiovast Surg 54:359-368, 1967 21. Benchimoi A, Promisiofi S, Desser K, et al: Electro-vectorcardiographic changes after proximal right coronary artery venous bypass graft and distal gas endarterectomy. Am J Cardiol 30: 466-471. 1972
Volume 33
JAIME
ESPINOZA,
JANET
LIPSKI,
ROBERT EPHRAIM SIMON
MD
MD
LITWAK,
MD,
DONOSO, DACK,
MD,
FACC
MD,
FACC
FACC
New York, New York
Pre- and postoperative electrocardiograms were evaluated in 44 patients with angina pectoris who underwent single or multiple coronary artery bypass procedures. Two groups were identified: Group A, 37 patients with bypass procedures only, and Group B, 7 patients with bypass procedures and gdditional surgery (valve replacement in 4 and ventricular resection in 3). Preoperative electrocardiograms showed abnormal Q waves in 14 of 37 patients in Group A and in 3 of 7 patients in Group B. After coronary artery bypass, new Q waves appeared in 11 of 37 patients (30 percent) in Group A, including 1 of 9 (11 percent) with one-vessel disease on preoperative coronary arteriograms, 7 of 20 (35 percent) with two-vessel disease and 3 of 8 (37.5 percent) with three-vessel disease; new intraventricular conduction abnormalities appeared in 4 of the 37. None of the seven patients in Group B had new G waves postoperatively, but three had intraventricular conduction abnormalities. There was no correlation between new Q waves and preoperative values for left ventricular end-diastolic pressure. In Group A, new 0 waves were demonstrated in 2 of 9 patients (22 percent) with one coronary bypass procedure, 5 of 21 patients (24 percent) with two bypass procedures and 4 of 8 patients (87 percent) with three bypass procedures. The single patient who had four coronary artery bypass procedures had no new Q waves after operation. It is evident that the prevalence of new Q waves was greater in patients who had two- or three-vessel disease by coronary arteriography as well as in those who had three coronary artery bypasses. Postoperative clinical course and mortality were not affected.
Myocardial revascularization utilizing direct saphenous vein bypass graft has been used extensively, and several reports of postoperative electrocardiographic changes have appeared. Diethrich et al.’ in 1968 reported electrocardiographic changes compatible with acute myocardial infarction in 11 of 40 patients (27.5 percent) who underwent the Vineberg procedure. The reported frequency of electrocardiographic changes compatible with myocardial infarction after coronary artery bypass has ranged from approximately 8 to 35 percent.“- “) This electrocardiographic study was undertaken to assess the frequency of new Q waves after saphenous vein bypass surgery for occlusive coronary artery disease. From the Division of Cardiology, Department of Medicine, The Mount Sinai Hospital and The Mount Sinai School of Medicine of the City University of New York, New York, N. Y. Manuscript accepted July 31, 1973. Address for reprints: Simon Dack. MD, Division of Cardiology, The Mount Sinai Hospital, 1 East 100th St., New York, N. Y. 10029.
Material
and Methods
The pre- and postoperative electrocardiograms, together with preoperative coronary arteriograms and left ventriculograms, were studied in 44 patients who underwent coronary artery bypass surgery at this hospital. Five other patients who died on the day of operation were not included because postoperative 12 lead electrocardiograms were not obtained. The study group comprised 37 men and 7 women whose ages ranged from 32 to 68 years.
February 1974
The American Journal of CARDIOLOGY
Volume 33
221
Q WAVES
AFTER
CORONARY
ARTERY
BYPASS-ESPINOZA
ET AL
I
TABLE
Analysis of Preoperative
Electrocardiograms
Previous myocardial Anterior Inferior lnferolateral ST-T changes
infarction
Right bundle Normal
block
branch
* 1 had previous
myocardial
The 44 patients were classified in two groups. Group A comprised 37 patients who had single or multiple coronary artery bypass procedures only. Group B comprised seven patients who had single or multiple bypass procedures and additional surgery: valve replacement in four (two aortic and two mitral) and ventricular resection in three (for vent ricular aneurysm [2 patients] and idiopathic hypertrophic subaortic stenosis [one patient]).
in 44 Cases 17 4 12 1 20 3* 5
Results Preoperative
infarction.
TABLE II Vessel Involvement
Vessels Involved
Cases
(no.)
(no.)
Group A 1 2 3 Total
by Coronary Arteriography
Previous Myocardial Infarction
9 20 8 37
3 9 2 14
3 2 2 7
1 1 1 3
Group B 1 2 3 Tota I
New Conduction No PostAbnoroperative malities Change
New Q Waves
l(ll%) 7(35%,) 3(37%0) 11 0 0 0 0
2 1 1 4
6 12 4 22
1 1 1 3
2 1 1 4
Analysis of Pktoperative
Electrocardiograms Group A
New Q waves New conduction No change Total
abnormalities
no.
%
11 4 22 37
30 11 59 100
in 44 Cases Group B no.
%
0 3 4 7
0 43 57 100
Since S-T segment and T wave changes occur frequently after cardiac surgery and their specificity for myocardial infarction is doubtful, only the QRS complexes were analyzed during this period. The New York Heart Association’s criteria” for an abnormal Q wave were used. Preand postoperative abnormal Q waves were analyzed. Preoperative coronary arteriograms were obtained in all patients. Arterial obstruction of greater than 50 percent was considered significant, and the number of arteries involved was tabulated. Left ventricular end-diastolic pressure, determined in 38 patients, was considered abnormal if it exceeded 12 mm Hg. Postoperative electrocardiograms were ana-
lyzed by at least four of us, and new Q waves were correlated with selective coronary arteriographic data, left ventricular end-diastolic pressures and the number of arteries bypassed. 222
February
Preoperative electrocardiograms indicated previous myocardial infarction in 17 patients, 14 of 37 in Group A (38 percent) and 3 of 7 in Group B (43 percent). The infarction was located in the inferior wall in 12, the anterior wall in 4 and the inferolateral wall in 1. Right bundle branch block was present in three patients, including one with evidence of old myocardial infarction. Twenty patients had S-T segment and T wave changes only, and five had normal electrocardiographic findings (Table I). Coronary arteriograms in Group A disclosed onevessel disease in 9 patients, two-vessel disease in 20 and three-vessel disease in 8 (Table II). In Group B, one-vessel disease was present in three patients, twovessel disease in two and three-vessel disease in two. Previous myocardial infarction was present in 4 of the 12 patients with one-vessel disease (3 in Group A and 1 in Group B), 10 of the 22 patients with two-vessel disease (9 in Group A and 1 in Group B) and 3 of t,he 10 patients with three-vessel disease (2 in Group A and 1 in Group B) (Table II). Postoperative
TABLE III
1974
The American
Journal
of CARDIOLOGY
Findings
Findings
Postoperative electrocardiograms revealed abnormal new Q waves in 11 of the 37 patients in Group A (30 percent) but in none of the 7 patients in Group B. Four patients in Group A (11 percent) had new conduction abnormalities, intraventricular conduction delay (three patients) and left bundle branch block (one patient) (Table III). In Group B, three of seven patients (43 percent) manifested a new left bundle branch block. Of the 11 patients in Group A who had new Q waves, only 2 (18 percent) had electrocardiographic evidence of previous myocardial infarction. Before operation, three of these patients had three-vessel disease, seven had two-vessel disease and one had one-vessel disease (Table II). Preoperative left ventricular end-diastolic pressure data were available in 32 patients in Group A and in 6 patients in Group B (Table IV). In Group A, 23 patients had normal values and 9 had increased values (13 to 33 mm Hg). In Group B, two patients had normal values and four had abnormal values (13 to 23 mm Hg). After coro’nary artery bypass, 6 patients in Group A with previously normal left ventricular end-diastolic pressure manifested new Q waves, 2 had conduction abnormalities and 15 showed no change; of the 9 patients with abnormal 3 manifested
two patients Volume
33
left ventricular
end-diastolic
pressure,
new Q waves and 6 no change. In the in Group B with normal left ventricular
Q WAVES
end-diastolic pressure, one had a conduction abnormality and one showed no change. In the four patients with abnormal left ventricular end-diastolic pressure, two had conduction abnormalities only (Table IV). In Group A, correlation of electrocardiographic data with the number of arteries bypassed (Table V) disclosed new Q waves in 2 of 9 patients (22 percent) who had one coronary artery bypass procedure, 5 of 21 patients (24 percent) who had two bypass procedures and 4 of 6 patients (67 percent) who had three bypass procedures. The single patient with four bypass grafts manifested no electrocardiographic changes after operation. Of the 44 patients studied, 42 were discharged from the hospital and 2 died. The presence of new Q waves did not appear to affect hospital mortality rate. One patient with new Q waves postoperatively had mediastinitis and intraventricular conduction abnormality and died of sepsis. The other patient manifested a postoperative intraventricular conduction disturbance on the electrocardiogram and died with shock secondary to a bleeding disorder. Discussion The overall frequency of postoperative myocardial infarction in 12,712 patients who underwent a general surgical procedure during a 5 year period at the New York Hospital was reported to be 0.95 percent.12 In the presence of previous postoperative myocardial infarction this rate rose to 6.5 percent. Our study reveals that of 37 patients who underwent coronary artery bypass surgery alone, 11 (29.7 percent) manifested new Q waves. Transitory Q waves may be seen on the electrocardiogram under various circumstances and may not represent myocardial necrosis. Q waves were observed after shock and severe metabolic stress by Shugoll,‘a after cross-clamping of the aorta and during the initiation of extracorporeal circulation by Klein et a1.14 and during atria1 pacing by De la Fuente et al.‘” The explanations given by these investigators do not apply to our study since the new Q waves in our patients were not transitory but persisted at least until discharge from the hospital. We believe that these Q waves represent acute myocardial infarction occurring during or immediately after coronary artery bypass surgery. There have been attempts to evaluate objectively the accuracy of diagnosis of acute myocardial infarction after thoracic surgery. Although many factors may affect serum enzyme values, several reports suggest that these values correlate well with the presence or absence of myocardial infarction.l,n+re However, our patients did not have serial postoperative enzyme studies. The frequency of postoperative myocardial infarction in patients undergoing a Vineberg procedure for coronary artery disease ranges from 9 to 27.5 percent.1JsJ7~20 The reported frequency of acute myocardial infarction after coronary artery bypass surgery has varied. Dawson et a1.2 reported a rate of 22 February
AFTER
TABLE
CORONARY
ARTERY
BYPASS-ESPINOZA
ET AL.
IV
Correlation of Left Ventricular End-Diastolic Pressure (LVEDP), Previous Myocardial Infarction and Electrocardiographic
LVEDP Group A Normal Increased Group 6 Normal Increased
Changes New Conduction Abnormalities
Previous Mycardial Infarction
New Q Waves
23 9
8 4
6(26%‘0) 3(33%b)
2 0
15 6
2
0 0
0 0
1 2
1 2
Patients (no.)
4
No Change
TABLE V Pre- and Postoperative Coronary Bypass Grafts
Patients
(no.)
(no.)
Group A 1 2 3 4 Total Group 6 1 2 3 4 Total ~-
Electrocardiograms
and Number
of
Bypasses
9 21 6 1 37 3 2 2 0 7
New Q Waves
2(22%) 5(23%‘0) 4(66%b) 0 11 0 0 0 0 0
New Conduction Abnormalities
No Change
0 4 0 0 4
7 12 2 1 22
1 1 1 0 3
2 1 1 0 4
percent (30 of 134), Brewer et al.:i a rate of 20 percent (49 of 243), Sheldon et a1.4 a rate of 9 percent (9 of 100) and Hultgren et al.” a rate of 34 percent (17 of 50); the latter series represents a mixed group of saphenous vein bypass grafts, Vineberg and other revascularization procedures. More recently, Anderson et a1.e reported a 17 percent frequency (8 of 46), Kansal et a1.7 a 10 percent frequency (15 of 151) and Williams et al8 a 23 percent frequency (23 of 100). Vectorcardiographic analysis of acute myocardial infarction revealed a 6 percent prevalence (6 of 100) in the study of Friedewald et a1.9, an 8 percent prevalence (15 of 193) in that of Friedberg et al.1° and a 35 percent prevalence (6 of 17)in that of Anderson et al.” Selection of patients may be a significant factor in these differences since, in our patients with extensive disease requiring more than one bypass, acute myocardial infarction occurred more frequently than in those with less severe disease. The time that patients remained under extracorporeal circulation during operation was implicated by Brewer et al.,:’ who found that myocardial infarction occurred more frequently 1974
The American Journal of CARDIOLOGY
Volume 33
223
Q WAVES
AFTER CORONARY
ARTERY BYPASS-ESPINOZA
ET AL.
in patients who h’ad more than 120 minutes of pump time. The anoxic arrest of 10 to 15 minutes for each coronary artery anastomosed may be a significant factor in a patient with severe preexisting coronary artery disease. This was manifested in our study by a greater prevalence of new Q waves in patients with three coronary artery bypasses (67 percent) than in those with one or two bypasses (22 and 24 percent, respectively). Technical factors may also play a role in the development of myocardial infarction and should be evaluated and analyzed further. Recently a high rate of myocardial infarction after combined coronary endarterectomy and coronary artery bypass was reported,‘Jl but only one patient in our series had this procedure. Nine of our patients who had no previous electrocardiographic evidence of myocardial infarction manifested new Q waves. However, of 14 patients with electrocardiographic changes of previous myocardial
infarction, only 2 had new Q waves. New intraventricular conduction abnormalities that developed in four patients in Group A made the diagnosis of acute myocardial infarction impossible. Therefore, this change may have masked a higher frequency of new Q waves. None of the seven patients in Group B had new Q waves; however, four had new conduction abnormalities that ma/ have masked the electrocardiographic findings. Electrocardiographic changes did not correlate significantly with preoperative left ventricular end-diastolic pressure data. In conclusion, it appears that the greater the severity of coronary artery disease, the greater the prevalence of myocardial infarction after saphenous vein bypass surgery. The immediate operative mortality in our series was not affected. These electrocardiographic changes require further evaluation by longer follow-up studies, and their ultimate clinical significance should be considered in the overall evaluation of coronary artery bypass surgery.
References
1. Diethrich E, Liddlcoat J, Alessi F, et al: Serum enzyme and
2.
3. 4.
5.
6.
7.
8.
9.
10.
11.
224
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