Electrocardiographic Observations in Bradycardia and Tachycardia-Dependent Atrioventricular Block

Wide‐QRS‐Complex Tachycardia with a Negative Concordance Pattern in the Precordial Leads: Are the ECG Criteria Always Reliable?

“…Although many electrocardiographic algorithms have been developed, aiming to efficiently differentiate SVTs from VTs, unusual morphology of QRS due to aberrant conduction in SVTs can be misleading, challenging the diagnostic accuracy of these algorithms. In our case, the occurrence of aberrancy after the onset of tachycardia without any detectable alteration in the cycle length of the tachycardia, could be attributed not to the classical Ashman phenomenon, but to the unusual fatigue phenomenon in the His‐Purkinje system, which has been shown to occur in specific atrial rates and could result in the functional LBBB that was observed 4 …”

An Elderly Woman with AV Block in Sinus Rhythm and Conducted Atrial Tachycardia

“…Our case demonstrates bradycardia dependent block below the His that is in the presence of only minimal conduction system disease (i.e., incomplete right bundle branch block and left anterior hemiblock). This form of AV block is unusual, but has been previously described in a baseline sinus rhythm, 2 as well as during an upright tilt 3 and following premature beats 4 . Bradycardia‐dependent block may be responsible for instances of paroxysmal AV block, where AV conduction is abruptly and persistently blocked despite otherwise normal intracardiac conduction intervals 5…”

Paroxysmal atrioventricular block precipitated by an atrial premature beat. What is the mechanism?

“…In this situation there is a relatively narrow range of rates between the critical heart rates for the development phase 3 and phase 4 blocks where normal conduction can occur [5,6].…”