The 12-lead ECG in the figure was obtained from a previously healthy middle-aged woman who presented with back pain over the previous month. Does her ECG provide any clue to the etiology of her symptoms? Can you explain why the QRS complex in lead aVR shows global positivity (i.e., positive P wave, QRS complex, and T wave)?
The ECG in the figure provides no clue to the etiology of this patient’s symptoms. The reason the P wave, QRS complex, and T wave are all positive in aVR is that instead of the usual 12-lead format (to which interpreters in the United States are accustomed), the Cabrera format has been used instead.
The 12-lead ECGs that are recorded in the United States typically display simultaneous recording of four sets of three leads (leads I, II, III; aVR, aVL, aVF; V1, 2, 3; and V4, 5, 6). One or more long lead rhythm strips are typically displayed immediately below the 12-lead. In contrast, note that a simultaneously recorded long lead rhythm strip for each of the 12 leads is displayed in the figure and that the vertical sequence used for the limb leads is markedly different from the usual format. That is, rather than lead I, the first lead displayed is lead aVL.
Note also that a minus sign appears before the designation aVR. This is because the polarity of lead aVR is reversed when using the Cabrera format. As a result, the mirror image picture (i.e., global positivity rather than negativity) is displayed for aVR (within the blue rectangle in the figure).
With ever expanding utilization of the Internet for international medical correspondence, it is increasingly important for medical providers to recognize ECG formats used elsewhere in the world. The Cabrera format has been in general use in Sweden since 1977. It is also used in a number of other countries. Although unlikely to displace the non-sequential standard format used in the United States, the Cabrera format offers the advantage of a more logical, equally spaced (30 degrees apart) sequential lead organization (see insert in the top right corner of the figure). Once accustomed to this format, determination of axis, frontal plane ST-T wave vector calculation, and serial ECG comparisons are all facilitated.
As to interpretation of the ECG in the figure, the rhythm is sinus, left axis deviation is present, and there are nonspecific ST-T wave changes but nothing that looks to be acute. These findings are unrelated to this patient’s back pain.
NOTE: Please see http://tinyurl.com/KG-Blog-114 for additional information on the Cabrera format.
