Two ventricular tachycardias with cycle length and QRS alternans: insights into the mechanism from mapping and ablation of the tachycardias

An intriguing case of regular RR and QRS alternans during idiopathic left posterior fascicle ventricular tachycardia

This study represents a case of idiopathic left posterior fascicle ventricular tachycardia (LPF-VT), which is intriguing due to regular alternation of short-long RR intervals and QRS morphology. Transthoracic echocardiogram analysis did not detect any structural heart disease. A baseline electrophysiological study was performed. Intracardiac recording during tachycardia showed V-A dissociation, confirming the final diagnosis of idiopathic LPF-VT. No regularity in the monomorphic VT was recorded. Previous relevant studies suggested that a single focus with two exits in distal branches of the left posterior fascicle or two different foci localized in the Purkinje-myocardial network of the left posterior fascicle can clarify the mechanisms. Our team proposed an additional explanation that combines the physiological refractory period with the Ashman phenomenon in individual reentrant LPF-VT circuit.

QRS alternans due to localized intraventricular block during ventricular tachycardia in Uhl's anomaly: a case report

Background

Uhl's anomaly is a rare congenital heart disease characterized by 'Paper-like thinning of the right ventricular (RV) wall'. Since most patients with Uhl's anomaly die in infancy or childhood, the adult cases of this disorder have been limitedly reported and there were no past report describing this anomaly with ventricular tachycardia (VT), in which catheter ablation was successfully performed.

Case summary

We report the case of a 43-year-old man with a suggested Uhl's anomaly and VT. He underwent a catheter ablation of the recurrent VT. An electrophysiological study showed the VT (cycle length = 460 ms) with a right bundle branch block pattern and inferior axis represented QRS alternans. Concealed entrainment by pacing from the anterior right ventricle (RV) suggested the mechanism of this VT was re-entry and the QRS alternans was simultaneously reproduced during the pacing. Furthermore, the intracardiac electrograms exhibiting local conduction blocks were documented on the RV free wall near the apex. The electrograms seen in a 2:1 ratio were coincident with slurs in the initial QRS on the 12-lead electrocardiogram. Since the anterior RV wall was considered to be a part of the VT circuit, a linear ablation in that area was performed resulting in VT termination.

Discussion

The local conduction blocks near the RV apex were related to the mechanism of the QRS alternans during the VT in this case. That might be based on the variations in the myocardium lying in the RV, which is the specific feature of Uhl's anomaly.

Alternans of the Ventricular Electrogram in Patients with an Implanted Cardioverter-Defibrillator

BACKGROUND

The occurrence and significance of alternans of the ventricular electrogram (VEGM) in patients with an implanted cardioverter-defibrillator (ICD) has been rarely reported.

OBJECTIVES AND METHODS

This report describes our observations of VEGM alternans documented in nine patients with an ICD (seven new cases and two previously published cases for comparison).

RESULTS

We found seven new cases of near-field VEGM alternans and added two of our previously reported examples. Catecholaminergic polymorphic ventricular tachycardia (CPVT) was diagnosed in one patient based on ICD recordings. Alternans occurred during ventricular tachycardia (VT) in eight patients. A fast sinus tachycardia could not be ruled out in one patient. Stable cycle length alternans was found in five patients. QRS alternans of the left ventricular (LV) electrogram (EGM) was recorded in all five patients who had a device for cardiac resynchronization therapy capable of sensing by the LV channel. These five cases exhibited corresponding alternans of the right ventricular (RV) EGM in three cases, none in one patient, and a questionable recording in another. Alternans of the far-field (FF) VEGM occurred simultaneously with RV EGM alternans in all four patients whose device provided an FF tracing.

CONCLUSION

Ventricular alternans may be more common than realized in ICD patients with VT. The correlation of VEGM alternans with the surface electrocardiogram remains unknown. Although QRS alternans itself as an electrical pattern is generally benign, its cause may not be, as illustrated in our patient with CPVT. Furthermore, associated cycle length alternans or undersensing of the smaller alternans component may complicate ICD therapy.

Undersensing by an ICD due to alternans of the ventricular electrogram

Alternans of the ventricular electrogram (VEGM) during ventricular tachycardia (VT) is a rare cause of ventricular undersensing by an implantable cardioverter-defibrillator (ICD). This report describes a patient with a St. Jude ICD who exhibited sustained monomorphic VT associated with surface QRS alternans, alternating cycle lengths, alternans of the VEGM causing intermittent undersensing of the smaller component, and intermittent 2:1 counting of ventricular intervals during 1:1 sensing in response to the ICD detection algorithm. VEGM undersensing was corrected noninvasively simply by programming the threshold start from 62.5% to 50% which increased the sensitivity based on the amplitude of the VEGM. This maneuver did not affect the satisfactory and stable defibrillation threshold.