To the Editor--Dynamic ECG abnormalities at the junction of QRS complex and ST segment as indicators of arrhythmia risk during acute ischemia

LETTERS TO THE EDITOR To the Editor–Dynamic ECG abnormalities at the junction of QRS complex and ST segment as indicators of arrhythmia risk during acute ischemia We read with great interest the paper by Oguro et al1 on electrical alternans induced by brief periods of myocardial ischemia. The alternating morphology of QRS complex and ST segment observed during short-lasting proximal left anterior descending artery (LAD) occlusions is indeed remarkable and invites additional discussion, as the illustrations provided by the authors may reflect different electrophysiological phenomena. Several electrocardiogram (ECG) patterns related to changing configuration of QRST complex during acute ischemia were described in previous studies and named as lambda,2 J-wave,3 or Sclarowsky-Birnbaum Grade 34 patterns. Common for all of them, it is the terminal part of the QRS complex that contributes mostly to QRS broadening, with appearance of slurring or notches at the junction of the QRS complex and the ST segment. Whether the abovementioned ECG phenomena have similar underlying mechanisms is discussible. Also, using surface ECG only, it is not clear whether these changes reflect alterations in ventricular repolarization or depolarization processes. In an experimental study on myocardial infarction induced by LAD occlusion published in Heart Rhythm last year,3 we observed nonalternating QRS-T patterns similar to those depicted as cases 1 and 2 in the study by Oguro et al; that is, steeply descending ST segment with notch or slur on the terminal part of the R wave. In our study these abnormalities, which we denoted as J-wave pattern, were associated with ventricular fibrillation occurring shortly after QRS broadening and J-wave appearance. In contrast, stable ST elevation with horizontal ST segment, similar to case 4 in the study by Oguro et al, which would also fulfill the grade 3 ischemia definition by Sclarowsky-Birnbaum, was rarely associated with malignant arrhythmias in our experiment. Our findings suggested that arrhythmia risk during acute ischemia is related to the dynamic QRS changes, such as the rapid QRS broadening and J-wave pattern appearance, rather than the absolute value of QRS duration. Future research is clearly needed to clarify the mechanisms that lead to dynamic ECG changes predominantly confined to the junction of the QRS complex and ST segment during coronary artery occlusion, as its evolution is likely to bear prognostic information in regard to arrhythmia risk. Marina M. Demidova, MD, PhD Pyotr G. Platonov, MD, PhD, FHRS 1547-5271/$-see front matter B 2016 Heart Rhythm Society. All rights reserved.

Lund University, Lund, Sweden E-mail address: [email protected].

References 1. Oguro T, Fujii M, Fuse K, Takahashi M, Fujita S, Kitazawa H, Sato M, Ikeda Y, Okabe M, Aizawa Y. Electrical alternans induced by a brief period of myocardial ischemia during percutaneous coronary intervention: the characteristic ECG morphology and relationship to mechanical alternans. Heart Rhythm 2015;12(11): 2272–2277. 2. Aizawa Y, Jastrzebski M, Ozawa T, et al. Characteristics of electrocardiographic repolarization in acute myocardial infarction complicated by ventricular fibrillation. J Electrocardiol 2012;45(3):252–259. 3. Demidova MM, Martin-Yebra A, van der Pals J, Koul S, Erlinge D, Laguna P, Martinez JP, Platonov PG. Transient and rapid QRS-widening associated with a Jwave pattern predicts impending ventricular fibrillation in experimental myocardial infarction. Heart Rhythm 2014;11(7):1195–1201. 4. Birnbaum Y, Mahaffey KW, Criger DA, et al. Grade III ischemia on presentation with acute myocardial infarction predicts rapid progression of necrosis and less myocardial salvage with thrombolysis. Cardiology 2002;97(3): 166–174.

Reply to the Editor—Regarding dynamic ECG abnormalities at the junction of QRS complex and ST segment as indicators of arrhythmia risk during acute ischemia We thank Drs Demidova and Platono for their interest in our manuscript.1 Visible electrical alternans was associated with a steep declining pattern at the junction of the QRS complex and ST segment in 4 of 5 patients. However, none of the patients with electrical alternans developed ventricular fibrillation (VF). This is likely due to the short duration of ischemia (ie, o30-second balloon occlusion). We read the article by Demidova et al2 with interest. They induced myocardial ischemia via 40-minute left anterior descending artery occlusion in animals, and observed that the transient QRS widening associated with the “J-wave” pattern was an immediate risk of VF.2 Slur or notch (¼ J wave) were considered to be responsible for QRS broadening. However, their “J-wave” pattern is somewhat different from our “lambda” pattern, which was defined as a steep declining pattern of the ST segment toward T waves.3 The “lambda” pattern was subsequently shown to be highly associated with VF during the acute phase of myocardial infarction.4 The “J-wave” pattern of Demidova et al shows no such declining pattern in the ST segment Furthermore, in the study by Demidova et al, q waves disappear when QRS becomes wider in the precordial leads (Figure 7). The widening of QRS must be partly due to new conduction block. In animal experiments,5 J-point elevation can be induced by myocardial ischemia, but conduction abnormalities are common during myocardial http://dx.doi.org/10.1016/j.hrthm.2016.01.015