If it is transient, it is termed accrochage if it persists, it is called synchronization ( 1). The mechanism of this coordination is unknown. In this patient's electrocardiogram the sinus-initiated P waves and the junction-initiated QRSs occur virtually simultaneously, and each occurs in the absolute refractory period of the other so that there are no atrial or ventricular captures. Alternatively, an accelerated or frankly tachycardic junctional or ventricular rhythm has usurped control of the ventricles, but the atria maintain their own rhythm. In many of these the sinus or atrial rhythm is too slow, and a junctional or ventricular escape rhythm has emerged. Although complete atrioventricular block is the quintessence of atrioventricular dissociation, it may occur with other arrhythmias ( Table) ( 2). The electrocardiographer must state what rhythms are dissociated and why ( 1, 2). In most cases, the P waves emerge more distinctly from the front or the back of the QRSs, i.e., Ps and QRSs are less synchronized, than is seen here.Ītrioventricular dissociation simply signifies that the atria and the ventricles have independent rhythms, either all of the time, i.e., complete dissociation, or intermittently, i.e., dissociation is incomplete due to atrial and/or ventricular captures. As is usually the case, the junctional rhythm is perfectly regular or nearly so, and slight sinus arrhythmia is responsible for the P waves being seen at the beginning or at the end of the QRSs. Thus, there is isorhythmic dissociation of an accelerated junctional rhythm from sinus rhythm. The perturbations of the QRS complexes are due to their occurring simultaneously with sinus P waves. Each of those QRSs has a notch at the beginning of the upslope of the R wave that corresponds to a small upward deflection at the beginning of the QRS in the simultaneously recorded lead V1, whereas all other V1 QRSs are pure QS complexes. At first glance no P waves are visible, but careful inspection of the lead II rhythm strip shows a notch on the downslope of all R waves except the fourth one from the beginning of the tracing and the fourth one from the end. The QRS complexes are narrow and occur regularly at a rate of 98 beats/min. In addition, nonspecific ST-T changes are present. See text for explication of the arrhythmia. Electrocardiogram recorded after the coronary angioplasty.
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