There are clearly visible P-waves in most of the leads (Fig. 1). The P-waves are negative in leads DII, DIII and aVF. Hence, this is not a sinus rhythm. All the P-waves have the same morphology, constant PP interval at a rate of 210 beats per minute (bpm), with an isoelectric baseline between them. Therefore, the underlying rhythm is unifocal atrial tachycardia .
Lead DII shows 12 P-waves, but some of these waves are barely discernible because they are superimposed on the QRS-T complexes (Fig. 2). In the first part of the strip there are P-waves alternately conducted and non-conducted to the ventricles, characterising a 2:1 AV conduction. In the middle half of the strip there is a longer RR interval where only the ninth P-wave conducts to the ventricles, while the seventh, eighth and tenth P-waves are blocked, realising a 4:1 AV conduction. So, the atrial tachycardia presents an alternating 2:1 and 4:1 AV conduction. The long RR interval is less than twice the short RR intervals and the PR intervals progressively lengthen until a pause with 3 non-conducted P-waves occurs. These elements are consistent with alternating Wenckebach periodicity, a rare phenomenon characterised by a block in two levels of the atrioventricular node; one proximally, giving rise to a 2:1 block and one distally, responsible for the Wenckebach periodicity that explains the progressive PR lengthening until the non-conducted P-wave . Alternating Wenckebach periodicity is encountered primarily in atrial tachyarrhythmias; the most frequent block level is the atrioventricular node, but it has been described in almost every level of the conduction pathways, including accessory ones .
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Het Netherlands Heart Journal wordt uitgegeven in samenwerking met de Nederlandse Vereniging voor Cardiologie en de Nederlandse Hartstichting. Het tijdschrift is Engelstalig en wordt gratis beschikbaa ...