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SUMMARY

Introduction: Perioperative myocardial infarction is a relatively frequent complication after cardiac surgery. Objective: The aim of this study was to determine the association between several preoperative and operative variables in cardiac surgery with the presence of perioperative myocardial infarction. Methods: We conducted a retrospective, cross-sectional study between January 2008 and December 2010, which included 948 patients (701 men (74 %), mean age 62.3±8.8, 82 with perioperative myocardial infarction) of 1306 patients undergoing open heart surgery. Results: Chronic renal failure (26.6 % vs 3.6 %, p=0.003), previous myocardial infarction (41.5 % vs 21.5 %, p=0.029), aortic cross-clamp time (120±59 vs 91.6±42 minutes, p=0.009), cardiopulmonary bypass time (161±63 vs 123±54 minutes, p=0.044) and intra-aortic balloon pump insertion (25.6 % vs 8.4 %, p=0.026), showed a significant association with the presence of perioperative myocardial infarction. ICU stay (5.3±5.1 vs 2.6±1.7 hours, p=0.000), time of mechanical ventilation (52.8±76.2 vs 22.9±19.6 hours, p=0.009) and in-hospital mortality (22 % vs 7.6 %, p=0.037) were significantly greater in these group. Conclusions: Chronic renal failure, previous myocardial infarction, aortic cross-clamp time, cardiopulmonary bypass time and intra-aortic balloon pump insertion showed a significant association with the presence of perioperative myocardial infarction, with a significant increase in ICU stay, time of mechanical ventilation and in-hospital mortality in this group.

Key words:Perioperative myocardial infarction. Cardiac surgery. In-hospital mortality.

Rev Fed Arg Cardiol. 2012; 41(2): 103-108

Introduction
Some authors have reported perioperative myocardial infarction (PMI) as a relatively frequent complication after cardiac surgery. Its frequency ranges between 0% and 29.2% with an average of 3.2%, mostly in patients with prior revascularization surgery (6.5% vs. 2.7%) [1].

Risk factors associated to ischemia are multiple and could be related to preoperative, intraoperative, or postoperative conditions. Among the most relevant ones, we have identified the need of emergency surgery, the time of aortic clamping above 100 minutes, infarction in the previous week and prior revascularization [2], prolonged operative times, extracorporeal circulation time above 180 minutes, reintervention, and revascularization combined with another cardiac surgery [3]. Also, preoperative concentrations in plasma of Troponin I have been described as predictor of adverse cardiac events and in-hospital mortality [4].

Early mortality after PMI is within the range of 3.5% to 25% [5] and is greater in patients with marked increase in troponins [4]. PMI also affects survival in the long term [6]. All of these factors determine the need to know the variables that are most related to this complication in our field, to thus provide a more timely management, whether as prevention or as cure, which constituted the essential goal of this investigation.

Methods
A retrospective study with a transversal design was conducted in the cardiovascular surgery service in the “Hermanos Ameijeiras” Hospital, where 948 patients were included; from them, 82 had PMI, from a total of 1306 patients that were intervened in cardiovascular surgery during the term between January 2008, to December 2010. From them, 468 were coronary patients, 480 had valve disease, and 67 had underwent mixed surgery. Those with congenital diseases (n=40), with cardiac operations of another kind (n=183) and other non-cardiac operations (n=68) were not included in our study group. There were 67 patients excluded for not presenting all the variables being studied in the database. The study was carried out according to the guidelines proposed in the Declaration of Helsinki and was approved by the Committee on Ethics of our institution.

Preoperative variables were included (age, gender, personal history of smoking, hypertension, dyslipidemia, diabetes mellitus, chronic renal failure [CRF], peripheral arterial disease, chronic obstructive pulmonary disease, prior acute myocardial infarction, body mass index, prior surgery, prior percutaneous coronary intervention, hemoglobin, creatinine, left ventricular ejection fraction (LVEF), and preoperative clinical situation) and operative variables also (type of surgery, character of the procedure, type of revascularization, surgical time, aortic clamping time, modality of the procedure, time of extracorporeal circulation [ECC] and use of intra-aortic ballooncounterpulsation [IABCP]).
PMI was defined according to the presence of two or more of the following criteria:

• Enzymatic: CK-MB increase of more than 5 times the normal upper limit in the first 72 hours of the postoperative period or a total value above 125 U/L.
• Electrocardiographic: development of new Q waves in the electrocardiogram, defined as significant if they are above 0.04 ms, in two or more leads, or reduction of R waves voltage ≥25% in at least two leads.
• Echocardiographic: severe alterations of myocardial contractility in the same area as the electrocardiographic alterations or akinesia or hypokinesia in comparison to the preoperative echocardiogram.

Techniques and procedures
The necessary information was obtained from the department of statistics, clinical histories, surgical reports and the intensive care unit of cardiovascular surgery.

Statistical analysis
The distribution and association of the general characteristics of the patients being studied was determined, expressing the categorical variables in absolute numbers and percentage and continuous variables in average values and standard deviation, also applying the Chi2 test for the univariate analysis of categorical variables and the Student-t test for the univariate analysis of continuous variables, taking a confidence interval of 95% for a significant association if p<0.05. The Odds Ratio was also estimated for each of the analyzed variables with a confidence interval of 95%. The processing was carried out by the SPSS 13.0 statistical package for Windows.

Results
From the 948 patients included, the general characteristics of whom are presented in Table 1, 82 presented PMI as a complication in the postoperative period. Approximately a fourth of the patients presented some significant preoperative risk factors that predispose to the presence of PMI, such as LVEF <50% and history of prior surgery or percutaneous coronary intervention. A minority of the patients showed history of peripheral arterial disease, CRF, and chronic obstructive pulmonary disease, in that order. The surgical procedures that predominated were valve replacement and myocardial revascularization. Only a tenth of the patients were unstable or with an urgent need of cardiac surgery.

- Preoperative variables and their association to PMI
The history of prior infarction and CRF were the only factors that showed a significant association with this postoperative complication. The Odds Ratio that showed a highest probability of association with this event was the one corresponding to CRF. The rest of the variables had a probability of association with PMI near the unit. Besides, there was a non-significant increase in the presence of hypertension, history of chronic obstructive pulmonary disease and prior percutaneous coronary intervention in the patients with PMI (Table 2).

-Variables related to the surgical procedure and its association with PMI
The aortic clamping time and the ECC time were significantly higher in the patients with PMI in comparison to those that did not present this complication. Moreover, the use of IABCP was three times greater in the patients with PMI, a significant increase in comparison to those that did not present this event. The rest of the variables did not show any significant association (Table 3).

There was a significant increase in the stay in the intensive care unit in the group of patients that presented PMI in comparison to those that did not present this complication (5.3±5.1 vs. 2.6±1.7, p=0.000, respectively) (Figure 1).

The patients with PMI presented a significant increase in the time required for mechanical ventilation in comparison to those that did not present PMI (52.8±76.2 vs. 22.9±19.6 hours, p=0.009, respectively).

Finally, there was a significant increase of mortality (three times greater) in the group of patients that presented PMI in comparison to those that did not present this entity (22% vs. 7.2%, p=0.037, respectively) (Figure 2).

Discussion
- Preoperative variables and their association to PMI
In our study, besides the history of prior infarction, CRF was the factor that showed a greater association with the risk of PMI. There was a slight increase in the history of prior surgery in the group of patients with PMI, but it was not significant.

Greaves et al also found a significant increase in the incidence of PMI in those patients with history of infarction in the week prior to the operation [2]. On the other hand, in a study of 447 patients referred for myocardial revascularization surgery, Landesberg et al, reported a 23.3% of patients with previous history in those that died due to PMI and 38.5% of patients with renal dysfunction, with a significant association with mortality (p=0.044) [7].

In this sense, Durmaz et al reported an interesting study that included 44 patients without preoperative dialysis, but with levels of creatinine greater than 2.5 mg/dl. The patients that underwent prophylactic preoperative dialysis had a hospital mortality of 4.8% in comparison to 30.4% in the control group (p=0.048). Besides, the last group presented 33 postoperative complications, from which the most common were acute renal failure, PMI and excessive bleeding, with a morbidity of 55.2% [8].

In a study with 872 patients who underwent major vascular surgery, it was proven that mortality in individuals with serum creatinine greater than 2 mg/dl (OR for perioperative mortality=5.2) associated to adverse cardiovascular events such as PMI [9].

Different associated preoperative variables have been pointed out with a greater incidence of PMI as advanced age, smoking, diabetes, decreased body mass index, chronic obstructive pulmonary disease, peripheral arterial disease, and decreased LVEF [2]. In our investigation we did not find a significant association between each of these preoperative variables and PMI.

- Variables related to the surgical procedure and their association with PMI
In our study, the time of arrest induced, the use of IABCP and the time of ECC were the variables that showed a significant association with the presence of PMI.

Greaves et al identified the time of aortic clamping greater than 100 minutes as an independent factor associated to an increase in PMI [2]. Chaitman et al also found, besides an ECC time greater than 180 minutes, an aortic clamping greater than 100 minutes as factors associated to a higher incidence of PMI [10]. In a study of 164 patients who underwent elective cardiac surgery, Díaz-Arrieta et al reported that the patients that presented PMI had terms significantly higher of aortic clamping and ECC in comparison to those that did not present this complication (69±33 vs. 43±28 minutes, p<0.005 and 115±51 vs. 89±40, p<0.003 respectively) [11].

There are multiple causes that lead to ischemia during ECC, so the objectives in the management of myocardial impairment are preventing or minimizing the duration of the exposition to the factors that cause and provide myocardial protection during ischemia induced iatrogenically. With the aortic clamping, there is a deprivation of the coronary flow, so the measures that maximize the production of high energy phosphates minimizing their use and the accumulation of intracellular calcium during ischemia and reperfusion are effective in delaying and preventing the development of ischemic contracture and myocardial necrosis [5].

About this issue, currently there is a great controversy about whether open heart surgery can reduce mortality and the rates of stroke, PMI or revascularization when compared to conventional surgery with ECC. Although some benefits from open heart surgery related to the improvement in mortality and the decrease in postoperative complications, among them PMI, have been reported [12], most investigations have pointed out that there are no differences about it, and that even surgery without ECC yields more harmful effects than beneficial ones in this regard [13,14].

It is interesting to point out that in our study, there were no significant differences either, between surgery with or without ECC in regard to PMI.

The use of IABCP also showed a significant increase in the group of patients with PMI. Undoubtedly, this was an expected result, since the main indication of this device is low cardiac output and postoperative cardiogenic shock in the presence of ischemia, increasing coronary perfusion and minute volume without increasing the cardiac output [15].

Finally, about the type of surgery conducted, PMI is a severe complication that may appear after any cardiac surgery and not just myocardial revascularization. Most studies in regard to this issue have been carried out in patients who underwent coronary surgery, with those made on patients with valve surgery being scant, even when the main cause of early morbi-mortality of conventional valve surgery is perioperative cardiogenic shock that may be caused by ischemia, stunning or acute myocardial infarction [15]. Although no significant differences were proven regarding the type of surgery, in our study a third of the patients that presented PMI were referred only to valve replacement surgery.

Conclusions
Chronic renal failure, history of myocardial infarction, time of induced arrest and extracorporeal circulation show a significant association with perioperative myocardial infarction in cardiac surgery, with a significant increase in the stay in the intensive care unit, time of mechanical ventilation and mortality in this group.

BIBLIOGRAFIA

1. Nalysnyk L, Farhbach K, Reynolds MW, et al. Adverse events in coronary artery bypass grafts (CABG) trials: a systematic review and analysis Heart 2003; 89: 767-772.
2. Greaves SC, Rutherford JD, Aranki SF, et al. Current incidences and determinants of perioperative myocardial infarction in coronary artery surgery. Am Heart J 1996; 132: 572-578.
3.  Yau TM. Predictor’s operative risk for coronary bypass operations in patients with left ventricular dysfunction. J Thorac Surg 2005; 79: 837-845.
4. Thielman M, Massoudy, Jaeger BR, et al. Emergency revascularization with percutaneous coronary intervention, reoperation or conservative treatment in patients with acute perioperative graft failure following coronary artery bypass surgery. Eur J Cardiothorac Surg 2006; 30: 117-125.
5. Kikura M, Oikawa F, Yamamoto K, et al. Myocardial infarction and cerebrovascular accident following non-cardiac surgery: differences in postoperative temporal distribution and risk factors. J Thromb Haemost 2008; 6: 742-748.
6. McFalls EO, Ward HB, Santilli S, et al. The influence of perioperative myocardial infarction on long-term prognosis following elective vascular surgery. Chest 1998; 113: 681-686.
7.  Landesberg G. The pathophysiology of perioperative myocardial infarction: facts and perspectives. J Cardiothorac Vasc Anesth 2003; 17: 90-100.
8.  Durmaz I, Yagdi T, Calkavur T, et al. Prophylactic dialyses in patients with renal dysfunction undergoing on-pump coronary artery bypass surgery. Ann Torach Surg 2003; 75: 859-864.
9.  Kertai MD, Boersma E, Bax JJ, et al. Comparison between serum creatinine and creatinine clearance for the prediction of perioperative mortality in patients undergoing major vascular surgery. Clin Nephrol 2003; 59: 17-23.
10.  Chaitman BR, Alderman EL, Sheffield LT, et al. Use of survival analysis to determine the clinical significance of new Q waves after coronary bypass surgery. Circulation 1983; 67 (2): 302-309.
11.  Díaz-Arrieta G, Rincón-Salas JJ, Reyes-Sánchez ME, et al. Diagnóstico de infarto miocárdico perioperatorio dentro de las primeras 72 horas posteriores a la cirugía cardiaca. Arch Cardiol Mex 2009; 79: 189-196.
12.  Puskas JD, Thourani VH, Kilgo P, et al. Off-Pump coronary artery bypass disproportionately benefits high-risk patients. Ann Thorac Surg 2009; 88: 1142-1147.
13.  Shroyer AL, Grover FL, Hattler B, et al. On-pump versus off-pump coronary artery bypass surgery. N Engl J Med 2009; 361: 1827-1837.
14.  Karu I, Tahepold E, Sulling TA, et al. Off-pump coronary surgery causes inmediate release of myocardial damage markers. Asian Cardiovasc Thorac Ann 2009; 17: 494-499.
15.  Ponce G, Romero J, Hernández G, et al. El infarto sin onda Q en cirugía cardiaca valvular convencional. Diagnóstico mediante la troponina I cardiaca. Rev Esp Cardiol 2001; 54: 1175-1182.

Publication: June 2012