The Littmann sign: An indication of hyperkalemia

A 74yearold dialysisdependent male with a history of diabetes received annual health checkups with an electrocardiogram (ECG; ECG1550, Nihon Kohden, Tokyo, Japan) without showing any symptoms. His ECG revealed no significant changes compared with his previous electrocardiograms. However, the computer revealed his heart rate to be 218/min, twice the true heart rate of 108/ min. This result was considered as doublecounted (Figure 1A). Automated interpretation of the electrocardiogram revealed “multiple ventricular premature beats” and could not measure the P wave axis or the PR interval. The patient remained totally asymptomatic, but laboratory tests showed a serum potassium level of 6.4 mEq/L. He underwent regular dialysis without any problems. We performed the electrocardiogram again using the same ECG machine (Figure 1B), which revealed no double count of the heart rate. (The patient’s serum potassium level was 4.7 mEq/L.) Automated interpretation of the electrocardiogram showed sinus rhythm, no ventricular arrhythmia, a P wave axis of 86°, and a PR interval of 172 ms. Double counting the true heart rate is a frequently observed phenomenon in clinical settings, especially in monitor electrocardiograms.1 But in 12lead electrocardiograms, this phenomenon is not frequently observed, even with automated interpretation using ECG software. Littmann et al. reported that double counting in automated interpretation of ECG software suggested easily recognizable signs of hyperkalemia.2 In their study, 28 of the 33 patients in whom the interpretation software doublecounted the heart rate had hyperkalemia. Their automated interpretation program was limited to GEMarquette system when the rate was measured, but Tomcsányi et al. found that this “Littmann sign” could be observed in another ECG recording by a different manufacturer (Schiller).3 The exact cause of the double count has been unclear. Littmann et al. considered that a computer might recognize the T waves as being the QRS complex.2 Our results suggested that one of the P, QRS, or T waves was misinterpreted as showing premature ventricular beats. Considering previous considerations by Littmann et al. the T wave might be recognized as ventricular beats in our case. Our case is important due to two important implications. First, according to our results, we have also shown that the “Littmann sign” is possible in ECGs recorded using the Nihon Kohden, which is frequently employed in Japan. Second, we could not reveal any significant signs of hyperkalemia, such as tall peaked T waves, shortened QT intervals, or a progression of PR and QRS intervals in the first ECG.4 Double counting was considered to be the sole sign of hyperkalemia in this patient. In general, we should interpret ECGs on our own, irrespective of automated interpretation results because of frequent errors.5 However, as shown in this case, some specific automated interpretation information might help us to diagnose hyperkalemia appropriately.