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Department of Anesthesiology and Reanimation; Adnan Menderes University; Aydin, Turkey; drseldasen{at}yahoo.com
In Response:
Both Hagerty (1) and Fujiwara (2) are critical regarding our use of Bazett’s formula in the QT interval analysis in preeclamptic patients (3). An important aspect not receiving proper attention is "where to" measure the QT interval (4). The only official guideline on this matter is the Committee for Proprietary Medicinal Products (cpm.P) Points to consider (5) that recommend centralized manual measurement of three consecutive sinus rhythm complexes in only 1 lead (typically limb lead II). Today, the measuring context for which the cpm.P guidelines had been written has completely changed and virtually all core laboratories use computer systems and deal with digital ECG. However, because of the absence of new guidelines, the ECG interval measurement in the majority of studies is still being carried out with the "three consecutive beats from lead II approach." No data are available on the comparison between the global QT measurement on median beats and the single lead-based measurement (4).
We performed our study in 25 severely preeclamptic pregnant women who were admitted to Maternity and Women’s Health Teaching Hospital between 1999 and 2001. The control group comprised of 25 healthy pregnant women. We did not have Holter ECG monitoring for the measurement of QT interval when we performed our study. Rather, the standard ECG lead II was continuously recorded and printed at a paper speed of 50 mm/s and an amplification of 0.1 mV/mm before and at 5, 10, 20, 30, 60, and 120 min after initiation of the spinal anesthesia. The heart rate adjusted QT (QTc) interval was calculated according to the formula of Bazett in our study.
Recently, there are several studies in literature on the effects of different drugs and situation on corrected QT interval (QTc with calculated Bazett’s formula) without Holter ECG recording (6–8).
On the other hand the potential advantages of implementing digital ECG algorithms are now being considered (9). An important opportunity offered by digital ECGs is the possibility to perform measurements on the so-called representative beats, often simply referred to as median beats, generally available as part of the digital ECG source file. The concept of representative beats is well known in academic research for many years (10), but it has been only recently considered as a viable alternative to generate reliable and reproducible interval measurements on ECG from clinical trials that may even have advantages over the traditional cpm. P-recommended approach (11).
Finally, we agree that the Holter monitoring might strengthen our results and have begun a new study investigating the effects of spinal anesthesia on QT interval with the use of Holter ECG monitoring in preeclamptic patients.
REFERENCES
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  J. M. Murkin, D. Bainbridge, and R. Novick Adequacy of Brain Oxygen Saturation for Goal-Directed Therapy Anesth. Analg., August 1, 2007; 105(2): 538 - 539. [Full Text] [PDF]
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