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Letters to the Editor |
a Department of Thoracic & Cardiovascular Surgery and Vascular Medicine, Dupuytren University Hospital, Limoges, France
b EA 3174 University of Limoges, Limoges, France
c Centre d’Investigations Cliniques 9201 INSERM, Hôpital Européen Georges Pompidou, Assistance Publique des Hôpitaux de Paris, France
Received 14 December 2008; accepted 18 December 2008.
* Corresponding author. Address: Department of Thoracic & Cardiovascular Surgery and Vascular Medicine, Dupuytren University Hospital, 2, Avenue Martin Luther King, 87042, Limoges, France. Tel.: +33 555 056 371; fax: +33 555 056 384. (Email: victor.aboyans{at}unilim.fr).
Abbreviations: BP = blood pressure • CABG = coronary artery bypass graft surgery • HR = heart rate • PP = pulse pressure
Key Words: Heart rate • Pulse pressure • Coronary artery disease • Surgery • Prognosis
We thank Dr Apostolakis et al. for their regular comments in this journal. Their comments regarding our paper [1] are focused on the highly debated usefulness of beta-blockers prior to cardiac surgery [2]. The poorer prognosis of our patients with high HR could potentially be interpreted as beneficial effects of beta-blocking therapy [1]. To date, trials on beta-blocker therapy prior to coronary surgery provide conflicting results [3].
It should be stressed that our study is descriptive [1], emphasising that rest heart rate (HR) and pulse pressure (PP) are two independent predictive markers of perioperative events, which should be considered in risk scores for coronary surgery. While we adjusted our findings to the use of preoperative HR lowering medications, primarily beta-blockers, because of their evident influence on HR and to some extent on PP values, the analysis of events according to preoperative beta-blocker therapy is beyond the scope of this observational study. Such analysis would have required a randomised controlled trial, or at least a propensity score analysis. Yet, the aim and design of our study could not support such conclusions. Of note, we did not find any significant difference regarding PP distribution according to beta-blocker administration.
We consider the issue raised about ‘mean PP’ unclear.
The conditions for HR assessment are important. We measured HR systematically the day before surgery, at patient's admittance. Pulse pressure was calculated according to systolic and diastolic blood pressure (BP) values averaged from a single BP measure during the anaesthetist's outpatient visit one month prior to surgery and from two consecutive BP measures upon admission. The assessment being strictly preoperative, any interference with specific premedication can reasonably be excluded. Consequently, we consider the conditions for HR and PP measurement in this study as realistic, as usually performed in clinical routine. With the aim of using these two parameters for perioperative risk stratification, we consider that they should be measured in a steady state, long before surgery.
Defining perioperative myocardial damage during heart surgery by any cut-off for troponin-I concentration remains indeed arbitrary. In a consensus statement, it has been acknowledged that ‘the situation for patients undergoing CABG is too complex to define simple cut-off values’ [4]. Hence, the troponin-I threshold used, although rather high, is consistent with findings in the literature [5], with similar rates of clinical complications. Of note, we found similar trends when we used a lower cut-off (10 µg/l), comparable to reported results with the 20 µg/l threshold.
In conclusion, we consider evidence regarding the systematic use of beta-blockers in the setting of CABG, as well as the use of biomarkers to assess perioperative myocardial damage still insufficient to be subject to consensual guidelines. Further adequate clinical trials and meta-data analyses are required to respond to these daily clinical concerns.
References
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