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A 72-year-old woman with sick sinus syndrome (SSS), who had frequent paroxysmal atrial fibrillations (PAfs) and normal cardiac function, was admitted to our hospital due to syncope. PAfs frequently occurred during the first week after DDD pacemaker implantation (PMI), with closed loop stimulation (CLS) rate-adaptive mode off, but were completely suppressed during the second week, with CLS on, and had been well-controlled over three years thereafter. However, PAfs occasionally occurred under intense sympathetic activity during 6 months after PMI as well, and were effectively terminated by disopyramide which had anticholinergic effect. Thus, the development and maintenance of PAf were thought to be associated with destabilized cardiac autonomic activities, that is, sympathetic and parasympathetic dominance, respectively. Additionally, heart rate variability analyses after implementation of CLS revealed the restoration of sympathetic and parasympathetic components. Accordingly, CLS mode was considered to play a critical role in preventing PAf by reflecting autonomic activity in heart rhythm in this SSS patient.

T-wave changes are thought to be associated with the repolarization phase of myocardial action potential. Although it has been known that persistent T-wave change is associated with the heart disease or the prognosis, the sensitivity and the specificity are not necessarily satisfactory for clinical therapeutic strategy. Recent basic studies have shown that, in some kinds of pathological states, transient repolarization changes of myocardial action potential were associated with life-threatening arrhythmia. Also clinical studies are being conducted to elucidate the clinical implication of transient T-wave changes on electrocardiography (ECG) in such an arrhythmia. Transient repolarization or T-wave change is thought to occur because of environmental or neurohumoral factors, circadian variation, stretching of myocardium or other triggers in daily life, resulting in fatal arrhythmia. Such fatal arrhythmias are thought to occur under restricted conditions even in the patients with serious heart disease. It is important to clarify and utilize the transient T-wave change directly associated with the fatal arrhythmia on a clinical basis. In this article, we first assess the mechanisms of transient repolarization or T-wave changes on ECG concerning fatal arrhythmia, and afterwards refer to possible attempts at clinical evaluation and application.