1 │Case presentation:
A 57 year old female patient had recently been upgraded to cardiac resynchronisation therapy (CRT) because of progression of heart failure and development of QRS prolongation to 170ms and left bundle branch block morphology. She presented 1999 at age 37 after silent anterior myocardial infarction. In 2010 left ventricular function had deteriorated and she received a prophylactic single chamber ICD. Also in 2010, she presented with SVT and underwent successful slow pathway ablation for presumed AV-nodal re-entry tachycardia.
Interrogation of her CRT device showed several episodes of tachycardia lasting seconds to minutes. Registration of one of these tachycardias is shown in figure 1a. Her device labelled this as SVT. There was 1:1 relation of atrial and ventricular depolarizations and based on this registration, both VT with 1:1 retrograde conduction or SVT with antegrade A-V connection were possible. The patient had an RA-RV delay of 170ms and an RV-LV delay of 100ms during normal sinus rhythm (figure 1b), comparable to the presenting tachycardia. In addition to the tachycardia in figure 1a, the patient exhibited tachycardias that could be correctly classified. She had VTs with a cycle length comparable to the presenting tachycardia as demonstrated in figure 2. This tachycardia starts with VA dissociation (3 fast ventricular beats without acceleration of the atrial rhythm. From the third beat of the VT there was retrograde VA conduction but during 1:1 period of the tachycardia, the delays were profoundly different with an RA-RV delay of 220ms and and RV-LV delay of 0ms. Figure 3 shows start and end of an SVT, most likely focal atrial tachycardia even though atypical (slow retrograde and fast antegrade) AV nodal re-entry tachycardia cannot complete be ruled out. During this SVT RA-RV delay was 160ms and RV-LV delay 100ms, comparable to the situation during normal sinus rhythm. Based on RV-LV timing the tachycardia from figure 1a could also be diagnosed as SVT.