Ventriculoatrial conduction capability and prevalence of 1:1 retrograde conduction during inducible sustained monomorphic ventricular tachycardia in 305 implantable cardioverter defibrillator recipients

Prevalence and predictors of ventriculo-atrial conduction in structurally normal hearts

BACKGROUND

The prevalence of ventriculo-atrial (VA) conduction varies from 20% to 90%, depending on the population studied (Militianu et al., 1997; Inoue et al., 1985; Kazmierczak et al., 1993; Ciemniewski et al., 1990; Hayes and Furman, 1983; Westveer et al., 1984). This wide range is mostly based on studies done in patients with implanted devices or impaired atrioventricular conduction. However, the prevalence of VA conduction in structurally normal heart has not been well documented till date.

OBJECTIVE

To study the prevalence and identify predictors of retrograde conduction via the His-Purkinje system and AV node in structurally normal hearts.

METHODS

We included 54 consecutive adults without structural heart disease who underwent electrophysiological (EP) study for various tachycardias. The basic parameters including PR, AH and HV intervals, atrioventricular Wenckebach point (AVWP) and anterograde effective refractory period (ERP) of atrioventricular node (AVNERP), were measured after ablation. The VA conduction was assessed basally and if absent, after isoprenaline. The VA Wenckebach point (VAWP) and retrograde ERP(VAERP) were recorded in patients showing VA conduction.

RESULTS

The mean age was 37.1±12.6years. Twenty five (46%) of the patients were men. VA conduction was present in 30 (55%) patients at baseline. Of the remaining 24 patients, 18 (34%) showed VA conduction after isoprenaline. Only 6 (11%) patients failed to reveal VA conduction even after adequate response to isoprenaline. Amongst all clinical and EP variables analysed, only the HV interval was shorter (p<0.01) in patients with VA conduction.

CONCLUSION

In structurally normal hearts, VA conduction was present at baseline in 55% of patients. Isoprenaline unmasked VA conduction in an additional 34% of the subjects. The HV interval was longer in patients without VA conduction.

ICD discrimination of SVT versus VT with 1:1 V-A conduction: A review of the literature

Inappropriate ICD shocks are associated with increased mortality. They also impair patients' quality of life, increase hospitalizations, and raise health-care costs. Nearly 80% of inappropriate ICD shocks are caused by supraventricular tachycardia. Here we report the case of a patient who received a single-lead dual-chamber sensing ICD for primary prevention of sudden cardiac death and experienced inappropriate ICD shocks. V-A time, electrogram morphology, and response to antitachycardia pacing suggested atrioventricular nodal reentry tachycardia, which was confirmed in an electrophysiology study. Inspired by this case, we performed a literature review to discuss mechanisms for discrimination of supraventricular tachycardia with 1:1 A:V relationship from ventricular tachycardia with 1:1 retrograde conduction.

Dual chamber arrhythmia detection in the implantable cardioverter defibrillator

INTRODUCTION

Dual chamber implantable cardioverter defibrillator (ICD) technology extended ICD therapy to more than termination of hemodynamically unstable ventricular tachyarrhythmias. It created the basis for dual chamber arrhythmia management in which dependable detection is important for treatment and prevention of both ventricular and atrial arrhythmias.

METHODS AND RESULTS

Dual chamber detection algorithms were investigated in two Medtronic dual chamber ICDs: the 7250 Jewel AF (33 patients) and the 7271 Gem DR (31 patients). Both ICDs use the same PR Logic algorithm to interpret tachycardia as ventricular tachycardia (VT), supraventricular tachycardia (SVT), or dual (VT+ SVT). The accuracy of dual chamber detection was studied in 310 of 1,367 spontaneously occurring tachycardias in which rate criterion only was not sufficient for arrhythmia diagnosis. In 78 episodes there was a double tachycardia, in 223 episodes SVT was detected in the VT or ventricular fibrillation zone, and in 9 episodes arrhythmia was detected outside the boundaries of the PR Logic functioning. In 100% of double tachycardias the VT was correctly diagnosed and received priority treatment. SVT was seen in 59 (19%) episodes diagnosed as VT. The causes of inappropriate detection were (1) algorithm failure (inability to fulfill the PR<RP condition in atrial tachyarrhythmias with 1:1 AV conduction, and far-field R wave sensing intermittently present during sinus tachycardia); (2) programming settings (atrial fibrillation/atrial flutter with ventricular rate above the SVT limit); and (3) algorithm limitations (atrial tachycardia with ventricular rate around the shortest programmable SVT limit and SVT redetection following VT therapy). Programming measures improved detection ability in 13 of 59 of inappropriately detected arrhythmias.

CONCLUSION

Dual chamber detection algorithms evaluated in a subset of diagnostically difficult arrhythmias allow safe detection of double tachycardias but require further extension and programmability to improve VT:SVT discrimination rules.

Ventriculoatrial conduction metrics for classification of ventricular tachycardia with 1:1 retrograde conduction in dual-chamber sensing implantable cardioverter defibrillators

The introduction of dual-chamber sensing in implantable cardioverter defibrillators (ICDs) has greatly reduced the incidence of false detection due to supraventricular tachycardias. The remaining arrhythmias which serve to confound classification are supraventricular tachycardias (SVTs) with 1:1 anterograde conduction and ventricular tachycardias (VT) with 1:1 retrograde conduction. An algorithm has been designed and tested (28 patients) which employs ventriculoatrial (VA) conduction measurements to separate 1:1 VTs from 1:1 SVTs. A study was conducted to assess realistic VA interval boundaries for classification of arrhythmias with 1:1 retrograde atrial conduction. Intracardiac atrial and ventricular recordings of 7 passages of VT with retrograde conduction, 12 passages of atrioventricular nodal reentrant tachycardia (AVNRT), 3 passages of atrial tachycardia (AT), 8 passages of sinus tachycardia (ST), and 2 passages of orthodromic reentrant tachycardia (ORT) were analyzed. Automated real-time atrial and ventricular waveform recognition was performed on each passage and VA intervals were measured. Separation of VT with retrograde conduction from other 1:1 supraventricular tachycardias was effected by imposing discrete VA interval boundaries. VA boundaries of 80 ms to 234 ms classified 1:1 VT with 100% sensitivity (SENS) and 80% specificity (SPEC). In addition, the lower boundary completely classified AVNRT with 100% SENS and 100% SPEC, and all passages of ST were contained above the upper boundary. These findings could be of importance in algorithms for next-generation implantable cardioverter defibrillators which include two-chamber (atrial and ventricular) sensing and two-chamber interval measurements.