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Eur J Cardiothorac Surg 2004;25:1001-1005
© 2004 Elsevier Science NL

Clinical significance of a new Q wave after cardiac surgery

Giuseppe Crescenzia, Tiziana Bovea, Federico Pappalardoa, Anna M. Scandroglioa, Giovanni Landonia*, Giacomo Alettic, Alberto Zangrilloa, Ottavio Alfierib

a Department of Cardiovascular Anesthesia, IRCCS San Raffaele Hospital of Milan, Via Olgettina, 60, 20132 Milan, Italy
b Department of Cardiac Surgery, IRCCS San Raffaele Hospital of Milan, Milan, Italy
c Department of Mathematics, University of Milan, Milan, Italy

Received 18 November 2003; received in revised form 24 February 2004; accepted 25 February 2004.

* Corresponding author. Tel.: +39-02-2643-7154/7164/4524; fax: +39-02-2643-7178/7155
e-mail: landoni.giovanni{at}hsr.it


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 References
 
Objective: The appearance of new Q waves on the electrocardiogram (ECG) after cardiac surgery has been traditionally considered a sign of major myocardial tissue damage. The aim of this study was to investigate the clinical significance of new Q waves appearing following cardiac surgery and to correlate them with the release of myocardial cell damage biomarkers. Methods: 206 consecutive patients undergoing cardiac surgery were prospectively evaluated. A 12 lead ECG was recorded and cardiac troponin I and creatinekinase subfraction MB assayed the day before surgery, on arrival at the intensive care Unit. 4 and 18 h postoperatively and every morning until the fifth postoperative day. Results: The incidence of new Q waves was 7.3%. Patients with isolated ECG findings had an uneventful postoperative course; on the contrary, when ECG changes were coupled with the release of myocardial necrosis biomarkers, patients had a complicated postoperative course. Conclusions: The association of a new Q wave and high levels of myocardial necrosis biomarkers is strongly associated with postoperative cardiac events. On the contrary, the isolated appearance of a new Q wave has no impact on the postoperative cardiac outcome.

Key Words: Myocardial infarction • Cardiac surgery • Electrocardiogram • Q wave • Troponin • Creatinekinase


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Results
 4. Discussion
 References
 
No consensus exists on the definition and incidence of perioperative myocardial infarction (PMI) after cardiac surgery. Typical electrocardiographic changes are often nonspecific and myocardial biomarkers always elevated. As Q-waves on the electrocardiogram (ECG) have been traditionally considered a sign of major myocardial tissue damage, the appearance of new Q-waves following cardiac surgery has been accepted as the most reliable criterion for PMI diagnosis [1,2]. The recent finding of a higher rate of Q-waves after coronary artery bypass surgery (CABG) than after PTCA has raised the question of whether these Q-waves represent the same entity in the two groups [3,4]. Data in the literature have often focused on coronary artery surgery, but these phenomena are also present also following valve surgery and represent a challenging dilemma.

We investigated the clinical significance and the prognostic value of new Q-waves and the elevation of cardiac biomarkers after cardiac surgery.


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Results
 4. Discussion
 References
 
This study complied with Helsinki Declaration and the research protocol was approved by the Institutional Review Board. All patients signed an informed consent. During a 2-month period (June-July 2002) we prospectively evaluated 206 consecutive patients (Table 1) undergoing cardiac surgery. Exclusion criteria were: preoperative Q-waves, preexisting or postoperative left bundle branch block, thoracotomy, and low ejection fraction (<35%). Coronary patients were 136 (79 CABG and 57 combined procedures); the remaining 70 underwent a valve operation. Cardiopulmonary bypass was conducted with an institutional custom pack including a coated membrane oxygenator, with mild hypothermia (32–33 °C). Pump flow was set at 2.4 l/min/m2. Myocardial protection was ensured by means of anterograde and retrograde cold blood cardioplegia according to Buckeberg protocol.


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  		Table 1. Preoperative characteristics of 206 patients who underwent cardiac surgery

 
A 12 lead ECG was recorded the day before surgery, at arrival at the ICU, 4 and 18 h postoperatively, and every morning until the fifth postoperative day. All ECGs were analyzed by an independent cardiologist blinded to patient identity and type of surgery. New Q waves were defined as the appearance of a Q wave >=40 ms in at least two adjacent leads; the loss of R wave amplitude in precordial leads was considered a Q wave equivalent when greater than 50%.

Blood samples were drawn at the same time as ECG recording to assay levels of cardiac Troponin I (cTnI) and Creatine Kinase subfraction MB (CK-MB). CTnI and mass CK-MB were analyzed with Dimension X Pand (Dade-Bohering diagnostics). Biochemical markers cut-off values were based on the routine criteria currently employed at our Institute (CK-MB>40 ng/ml and cTpI>11 ng/ml). Peak biomarker release was considered for analysis.

We defined a cardiac event as the occurrence of low output syndrome (CI<2 l/min/m2) secondary to ventricular dysfunction requiring high doses inotropes (>0.05 ug/kg/min) or intra-aortic balloon pumping for more than 24 h.

2.1. Statistical analysis
Data are expressed as percentages, as mean ±1 standard deviations or as median (25th–75th percentiles). A logistic regression analysis with two independent variables (Q waves+one biomarker) was performed among patients who developed cardiac events or had a benign cardiac course to evidence the capability of cardiac biomarkers and new Q waves to predict adverse cardiac events. For each marker studied, ROC curves were constructed by plotting sensitivity against (1-specificity) for cardiac events [5]. ROC curves were repeated for the combined (Q wave+one biomarker) rules. The capacity of the cardiac biomarker of predicting cardiac events (in presence or absence of a new Q wave) was calculated. All analysis were repeated for both cardiac biomarkers (cTnI, CK-MB). Data were analyzed by use of SAS software, version 8 (SAS Institute).


   3. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
4. Discussion
 References
 
In the study period we observed 15 new Q-waves (7.3% of 206 patients): these new Q-waves were found in 11 CABG patients out of 136 (8.0%) and in four valvular patients out of 70 (5.7%).

Peak enzyme levels were above our predefined cut-off values in 72 patients for cTnI and in 92 patients for CK-MB. Cardiac biomarker release is shown in Table 2 and patients outcome in Table 3.


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  		Table 2. Cardiac biomarker release in 206 patients who underwent cardiac surgery at baseline (preop), on Intensive Care Unit arrival, 4 and 18 h postoperatively and peak value (peak)

 

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  		Table 3. Outcome of 206 patients who underwent cardiac surgery

 
New Q-waves were coupled with an increase of CK-MB in 8 patients (3.9%) and of cTnI in 7 patients (3.4%).

The study population was divided therefore into four groups according to the presence or absence of new Q-waves and peak cardiac marker elevations. Each group (Figs. 1 and 2) was analyzed for postoperative cardiac events. The total number of cardiac events was 25. The concomitant presence of the study criteria defined an incidence of postoperative cardiac events of 75% with CK-MB, and of 85.7% with cTnI.



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  		Fig. 1. Q waves and Creatinekinase MB (CK-MB) (ng/ml) as predictors of postoperative cardiac events.

 


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  		Fig. 2. Q waves and troponin (cTnI) (ng/ml) as predictors of postoperative cardiac event.

 
On the contrary, the isolated appearance of a new Q-wave (n=7) had no correlation with the postoperative cardiac outcome (no cardiac event was observed in these 7 patients).

In two cases (both valvular patients) the ECG changes disappeared on the first postoperative day (transient Q-wave) and the remaining isolated new Q-waves (all 5 patients underwent CABG) were associated with an anamnestic non-Q infarction and chronic occlusion of the posterior descending artery.

The logistic regression analysis with two independent variables (Q waves+one biomarker) was performed. In the Q wave+MB model: MB (OR 1.01 C.I. 1.005–1.024 per unit P=0.003); new Q wave (OR 5.7 95% CI, 1.7–19.4 P=0.005). In the Q wave+cTnI model: cTnI (OR 1.07 95% CI, 1.03–1.12 P=0.001); new Q wave (OR 6.5 95% CI, 2.0–21.3 P=0.002).

For each biochemical marker, we performed ROC curve analyses for the prediction of cardiac events. These curves were constructed for the whole cohort of patients. For each marker, a cut-off value above which cardiac event was likely, was determined from the ROC curves (Figs. 3 and 4) through an attempt to identify the best compromise between sensitivity and specificity (MB 44 mg/ml: Sensitivity 0.77, 1-Specificity 0.34) (cTnI 10.3 mg/ml: Sensitivity 0.77, 1-Specificity 0.32). These results were very close to our prespecified cut-off level and in accordance to literature [6]. The ROC curves were repeated for the combined (Q wave+one biomarker) rules without significant increases of specificity and sensitivity: MB Sensitivity 0.76, 1-Specificity 0.32; cTnI Sensitivity 0.77, 1-Specificity 0.31. MB>44 mg/ml predicted 35% of cardiac events when in combination with a new Q wave and 8% of cardiac events when no Q wave appeared. CTnI>10.3 mg/dl predicted 38% of cardiac events in combination with a new Q wave and 9% of cardiac events when no Q wave appeared.



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  		Fig. 3. ROC curve for creatinekinase MB (CK-MB).

 


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  		Fig. 4. ROC curve for troponine I (cTnI).

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
References
 
This study confirms that the isolated presence of a new Q-wave following cardiac surgery does not necessarily signify new myocardial infarction and is not related to cardiac outcome while peak biochemical marker release coupled with a new Q wave is highly predictive for postoperative cardiac events (Fig. 1 and 2).

The European Society of Cardiology and the American College of Cardiology suggested troponin as the preferred indicator of cardiac injury, but its elevation does not define the mechanism of cardiac injury in the specific context of cardiac surgery [7]. In fact, cardiac surgery can cause myocardial cellular damage with mechanisms different from infarction: focal trauma by heart manipulation, diffuse ischemia for inadequate myocardial protection, air embolism in the coronary arteries or vein grafts, atriotomy, pericardiectomy, direct electrical cardioversion, myocardial stunning.

Nonetheless, irrespectively of the cause, a high postoperative peak of cTnI is associated with increased risk of death, death from cardiac causes, and nonfatal cardiac events within 2 years after coronary artery bypass grafting [8]; in addition cTnI concentration measured 20 h after the end of surgery is an independent predictor of in-hospital death after cardiac surgery and elevated concentrations of cTnI are associated with a cardiac cause of death and with major postoperative complications [9].

For decades the appearance of a new Q wave identified the occurrence of a new postoperative myocardial infarction [1]. Chaitman et al. analyzing data of 1340 patients included in the Coronary Artery Surgery Study, noticed a worsening of medium and long term outcome with the appearance of new Q waves [2]. These initial experiences make the clinicians identify PMI with new Q-waves.

More recent trials showed no correlation between Q-waves and poor cardiac prognosis [3,4,10,11].

Hodakowski et al. demonstrated that a postoperative Q-wave is not frequently associated to angiographic, ecocardiographic, enzymatic and clinical data of myocardial infarction [12].

In our study, patients with isolated ECG findings had an uneventful postoperative course; on the contrary, when these ECG changes were coupled with elevated peak myocardial necrosis biomarker release, patients had an impaired postoperative course requiring prolonged inotropic and/or mechanical circulatory support.

In accordance with Svedjeholm, nearly half Q-waves after cardiac surgery in our population were not related to tissue damage; in 50% of cases they were not associated to an increase of CK-MB or cTpI [6].

New Q wave was transient in two valvular cases, suggesting an etiologic role for coronary air embolism after aortic cross clamp release: their disappearance may be explained by the resolution of stunned myocardium [13–17].

The remaining cases of isolated Q-wave appeared after CABG surgery; and all these patients had an anamnestic non-Q myocardial infarction and chronic occlusion of the posterior descending artery. In these cases, according to literature, we speculate that the decreased anteroapical electrical forces before operation (secondary to ischemia) cancelled the loss of opposing forces of the infarcted inferior wall; after operation, with relief of anterior ischemia by left internal mammary artery to left anterior descending artery bypass grafting, anterior electrical forces were augmented and preexisting inferior infarction unmasked [18].

Limitation of the study: the study population is rather low with only 15 Q waves studied in a selected population of patients with EF>=35%; furthermore no transesophageal or coronary findings are reported.

In conclusion, our study confirms that nearly half new Q-waves appearing after cardiac surgery are not associated with major myocardial tissue damage and have little influence on short term outcome in a population with EF>=35%; therefore, the use of Q wave criteria alone as the gold standard for the diagnosis of postoperative myocardial infarction is questionable as myocardial stunning and Q-wave unmasking could have a predominant role in this setting. In contrast, the association of electrocardiographic alterations and augmentation of enzymatic biomarkers is strongly associated to postoperative cardiac events.


   Acknowledgments
 
We are indebted to Costantini Marco, RN, Lampugnani Mariano, RN and Costantini Adele, RN for their care provided to these patients and for the support in the data-entry.

All the Acknowledged RN are from the Cardiovascular Intensive Care Unit, IRCCS San Raffaele Hospital of Milan. Via Olgettina 60, 20132 Milan, Italy.


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 References
 

  1. Stenberg L., Wisneski J.A., Ullyot J.D., Gertz E.W. Significance of new Q waves after aortocoronary bypass surgery. Circulation 1975;52:1037-1044.[Abstract/Free Full Text]
  2. Chaitman B.R., Alderman E.L., Sheffield L.T., Tong T., Fisher L., Mock M.B., Weins R.D., Kaiser G.C., Roitman D., Berger R., Gersh B., Schaff H., Bourassa M.G., Killip T. Use of survival analysis to determine the clinical significance of new Q waves after coronary bypass surgery. Circulation 1983;67:302-309.[Abstract/Free Full Text]
  3. The Bypass Angioplasty Revascularization Investigation (BARI). Comparison of coronary bypass surgery with angioplasty in patients with multivessel disease. N Engl J Med 1996;335:217-225.[Abstract/Free Full Text]
  4. King S.B., Lembo N.J., Weintraub W.S., Kosinski A.S., Barnhart H.X., Kutner M.H. Angioplasty versus Surgery Trial (EAST). A randomized trial comparing coronary angioplasty with coronary bypass surgery. N Engl J Med 1994;331:1044-1050.[Abstract/Free Full Text]
  5. Hanley J.A., McNeil B.J. The meaning and use of the area under a receiver operator characteristic (ROC) curve. Radiology 1982;143:29-36.[Abstract/Free Full Text]
  6. Svedjeholm R., Dahlin L.G., Lundberg C., Szabo Z., Kagedal B., Nylander E., Olin C., Rutberg H. Are electrocardiographic Q-wave criteria reliable for diagnosis of perioperative myocardial infarction after coronary surgery?. Eur J Cardiothorac Surg 1998;13:655-661.
  7. Alpert J.S., Thygesen K., Antman E., Bassand J.P. Myocardial infarction redefined—a consensus document of the Joint European Society of Cardiology/American College of Cardiology Committee for the redefinition of myocardial infarction. J Am Coll Cardiol 2000;36:959-969.[Free Full Text]
  8. Fellahi J., Gué X., Richomme X., Monier E., Guillou L., Riou B. Short- and long-term prognostic value of postoperative cardiac troponin I concentration in patients undergoing coronary artery bypass grafting. Anesthesiology 2003;99(2):270-274.[CrossRef][Medline]
  9. Lasocki S., Provenchere S., Benessiano J., Vicaut E., Lecharny J.B., Desmonts J.M., Dehoux M., Philip I. Cardiac troponin I is an independent predictor of in-hospital death after adult cardiac surgery. Anesthesiology 2002(97):405-411.
  10. Jain U., Laflamme C.J., Aggarwal A., Ramsay J.G., Comunale M.E., Ghoshal S., Ngo L., Ziola K., Hollenberg M., Mangano D.T. Electrocardiographic and hemodynamic changes and their association with myocardial infarction during coronary artery bypass surgery. A multicenter study. Multicenter study of perioperative ischemia (McSPI) research group. Anesthesiology 1997;86:576-591.[CrossRef][Medline]
  11. Hamm C.W., Reimers J., Ischinger T., Rupprecht H.J., Berger J., Bleifeld W. The German angioplasty bypass surgery surgery investigation (GABI). A randomized study of coronary angioplasty compared with bypass surgery in patients with symptomatic multivessel coronary disease. N Engl J Med 1994;331:1037-1043.[Abstract/Free Full Text]
  12. Hodakowski G.T., Craver J.M., Jones E.L., King S.B., III, Guyton R.A. Clinical significance of perioperative Q-wave myocardial infarction: The emory angioplasty versus surgery trial. J Thorac CardioVasc Surg 1996;112:1447-1454.[Abstract/Free Full Text]
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