Effects of isoproterenol in facilitating induction of slow-fast atrioventricular nodal reentrant tachycardia

The role of the autonomic nervous system in cardiac arrhythmias: The neuro-cardiac axis, more foe than friend?

The autonomic nervous system (ANS) with its two limbs, the sympathetic (SNS) and parasympathetic nervous system (PSNS), plays a critical role in the modulation of cardiac arrhythmogenesis. It can be both pro- and/or anti-arrhythmic at both the atrial and ventricular level of the myocardium. Intricate mechanisms, different for specific cardiac arrhythmias, are involved in this modulatory process. More data are available for the arrhythmogenic effects of the SNS, which, when overactive, can trigger atrial and/or ventricular "adrenergic" arrhythmias in susceptible individuals (e.g. in patients with paroxysmal atrial fibrillation-PAF, ventricular pre-excitation, specific channelopathies, ischemic heart disease or cardiomyopathies), while it can also negate the protective anti-arrhythmic drug effects. However, there is also evidence that PSNS overactivity may be responsible for triggering "vagotonic" arrhythmias (e.g. PAF, Brugada syndrome, idiopathic ventricular fibrillation). Thus, a fine balance is necessary to attain in these two limbs of the ANS in order to maintain eurhythmia, which is a difficult task to accomplish. Over the years, in addition to classical drug therapies, where beta-blockers prevail, several ANS-modulating interventions have been developed aiming at prevention and management of arrhythmias. Among them, techniques of cardiac sympathetic denervation, renal denervation, vagal stimulation, ganglionated plexi ablation and the newer experimental method of optogenetics have been employed. However, in many arrhythmogenic diseases, ANS modulation is still an investigative tool. Initial data are encouraging; however, further studies are needed to explore the efficacy of such interventions. These issues are herein reviewed and old and recent literature data are discussed, tabulated and pictorially illustrated.

Identification of potential candidate genes and pathways in atrioventricular nodal reentry tachycardia by whole-exome sequencing

Background

Atrioventricular nodal reentry tachycardia (AVNRT) is the most common manifestation of paroxysmal supraventricular tachycardia (PSVT). Increasing data have indicated familial clustering and participation of genetic factors in AVNRT, and no pathogenic genes related to AVNRT have been reported.

Methods

Whole‐exome sequencing (WES) was performed in 82 patients with AVNRT and 100 controls. Reference genes, genome‐wide association analysis, gene‐based collapsing, and pathway enrichment analysis were performed. A protein‐protein interaction (PPI) network was then established; WES database in the UK Biobank and one only genetic study of AVNRT in Denmark were used for external data validation.

Results

Among 95 reference genes, 126 rare variants in 48 genes were identified in the cases (minor allele frequency < 0.001). Gene‐based collapsing analysis and pathway enrichment analysis revealed six functional pathways related to AVNRT as with neuronal system/neurotransmitter release cycles and ion channel/cardiac conduction among the top 30 enriched pathways, and then 36 candidate pathogenic genes were selected. By combining with PPI analysis, 10 candidate genes were identified, including RYR2, NOS1, SCN1A, CFTR, EPHB4, ROBO1, PRKAG2, MMP2, ASPH, and ABCC8. From the UK Biobank database, 18 genes from candidate genes including SCN1A, PRKAG2, NOS1, and CFTR had rare variants in arrhythmias, and the rare variants in PIK3CB, GAD2, and HIP1R were in patients with PSVT. Moreover, one rare variant of RYR2 (c.4652A > G, p.Asn1551Ser) in our study was also detected in the Danish study. Considering the gene functional roles and external data validation, the most likely candidate genes were SCN1A, PRKAG2, RYR2, CFTR, NOS1, PIK3CB, GAD2, and HIP1R.

Conclusion

The preliminary results first revealed potential candidate genes such as SCN1A, PRKAG2, RYR2, CFTR, NOS1, PIK3CB, GAD2, and HIP1R, and the pathways mediated by these genes, including neuronal system/neurotransmitter release cycles or ion channels/cardiac conduction, might be involved in AVNRT.

Orthodromic atrioventricular reentrant tachycardia using a concealed isoproterenol-sensitive accessory pathway

Learning objective

Cost-reduction strategy for isoproterenol use in radiofrequency catheter ablation procedures

PURPOSE

A cost-reduction strategy for isoproterenol use in radiofrequency catheter ablation procedures was evaluated.

SUMMARY

A medication-use evaluation at a 454-bed tertiary medical center revealed that the cardiac catheterization laboratory was the highest user of isoproterenol. Isoproterenol was removed from all AcuDose-Rx machines Omnicell, Mountain View, CA, and compounding was performed by pharmacy personnel. It was initially provided to the cardiac catheterization laboratory as an 8-µg/mL concentration in 20-mL 0.9% sodium chloride injection syringes with a 24-hour beyond-use date. This resulted in an initial cost savings but with an unacceptably high rate of wastage. Isoproterenol was then compounded as a 4-µg/mL concentration in 30 mL 5% dextrose in water syringes with a 9-day beyond-use date after a thorough literature search supported longer stability with this admixture. After 12 months of our current process, isoproterenol use during radio frequency catheter ablations (RFCAs) in the cardiac catheterization laboratory was reduced by 85%, decreasing the number of ampules used from 11.15 to 1.66 per week.

CONCLUSION

A pharmacy-initiated process to mitigate an extraordinary increase in isoproterenol acquisition cost resulted in a reduction in usage in a tertiary care community hospital. Isoproterenol usage was reduced 85% after two different interventions were implemented, which is estimated to save $1,839 per procedure.

Differentiation of atrioventricular nodal reentrant tachycardia from orthodromic reciprocating tachycardia by the resetting response to ventricular extrastimuli: comparison to response to continuous ventricular pacing

BACKGROUND

The usefulness of ventricular entrainment to differentiate AV nodal reentrant tachycardia (AVNRT) from orthodromic reciprocating tachycardia (ORT) by substracting the corrected postpacing interval (cPPI) from the tachycardia cycle length (TCL) or the ventriculoatrial interval during stimulation (SA) from that during tachycardia (VA) have been widely validated. However, some tachycardias are interrupted by pacing trains but may not be so by ventricular extrastimuli resulting in resetting.

OBJECTIVES

To validate prospectively the diagnostic yield of cPPI-TCL and SA-VA measurements after resetting and to determine the proportion of AVNRT and ORT that can be entrained and/or reset from the right ventricular apex (RVA).

METHODS

223 consecutive patients with inducible AVNRT or ORT underwent pacing trains and single extrastimulus (also double extrastimuli if singles did not reset tachycardia) at the RVA. We calculated cPPI-TCL and SA-VA during entrainment and resetting.

RESULTS

Entrainment could not be achieved in 15.2% of tachycardias because of consistent tachycardia interruption by pacing; resetting was observed in 99.5%. Values of cPPI-TCL and SA-VA > 110 milliseconds after resetting identified AVNRT as accurately as after entrainment. Values for cPPI-TCL/ SA-VA were: sensitivity: 98/100%; specificity: 96/98%; positive predictive value: 98/99%; negative predictive value: 98/100%.

CONCLUSIONS

Determinations of cPPI-TCL and SA-VA after resetting with single or double RVA extrastimuli are useful maneuvers to differentiate AVNRT from ORT and can be used for nearly every inducible AVNRT or ORT, even if they are interrupted by ventricular trains.

Atrioventricular nodal reentrant tachycardia with multiple discontinuities in the atrioventricular node conduction curve: immediate success rates of radiofrequency ablation and long-term clinical follow-up results as compared to patients with single or no AH-jumps

BACKGROUND

Some patients with atrioventricular nodal reentrant tachycardia (AVNRT) demonstrate multiple discontinuities (AH jump) in their antegrade AV node conduction curves. We evaluated and compared the immediate success rates, procedure-related complications, long-term clinical follow-up results and recurrence rates after slow pathway ablation in patients with multiple versus single or no AH jumps.

METHODS

The study group consists of 278 consecutive patients (mean age 36.6 +/- 15.7) who underwent ablation for typical AVNRT, divided into three categories according to the number of AH jumps (>/=50 ms) before ablation: Group-1 consisted of 63 patients (23%) with continuous AV node function curves; Group-2 of 183 patients (66%) with a single jump and Group-3 of 32 (12%) patients showing more than one AH jumps.

RESULTS

Age was significantly higher in Group-3 as compared to Group-1 (43 +/- 18 years vs. 34 +/- 16 years, p = 0.020). The electrophysiological features of AVNRT did not differ among groups. Before ablation, the maximum AH interval was significantly longer in Group-3 as compared to Groups-1 and -2 ( p < 0.001 for both). AV node antegrade ERP was significantly shorter in Group-3 than in Group-2, both before and after ablation ( p < 0.050 for both). AV node Wenckebach cycle length (WCL) was shorter in Group-3 as compared to both Groups-1 and -2, before and after ablation ( p < 0.050 for all). AV node WCL was prolonged significantly in all groups after ablation ( p < 0.001 for all). Residual dual pathways were present in 37 of 278 patients (13%) after ablation and were significantly more frequent in Group-3 than Group-2 (31% vs. 15%, p = 0.023).

CONCLUSIONS

Patients with multiple AH jumps are older and more often have residual dual atrioventricular nodal pathway physiology after successful ablation but these features do not affect the immediate and long-term success rates of slow pathway ablation as compared to patients with single or no AH jumps.

Effects of continuous enhanced vagal tone on dual atrioventricular node and accessory pathways

BACKGROUND

The aim of this study was to test the electrophysiological effects of continuous enhanced vagal tone on dual atrioventricular (AV) nodal and accessory pathways.

METHODS AND RESULTS

This study included 10 patients with typical, slow-fast AV nodal reentrant tachycardia (AVNRT) and 10 patients with AV reciprocating tachycardia. Electrophysiological data were measured before and during continuous vagal enhancement by using phenylephrine infusion (0.6 to 1.5 microg/kg per min). For patients with AVNRT, during phenylephrine infusion, 1:1 conduction times over the anterograde fast and slow and retrograde fast pathways were prolonged (453+/-64 to 662+/-120 ms, P<0.001; 379+/-53 to 443+/-95 ms, P<0.05; 405+/-112 to 442+/-118 ms, P<0.05). The effective refractory period and functional refractory period of the anterograde fast pathway were prolonged with phenylephrine (394+/-73 to 544+/-128 ms, P<0.001; 454+/-60 to 596+/-118 ms, P<0.001). In contrast, the effective refractory period and functional refractory period of the anterograde slow and retrograde fast were not significantly changed. No significant change was observed in the conduction or refractoriness of the accessory pathways in patients with AV reciprocating tachycardia nor in atrial or ventricular refractoriness.

CONCLUSIONS

Enhanced vagal tone produces disparate effects on the refractoriness of the slow and fast AV nodal conduction pathways, with the anterograde fast pathway being the most sensitive. These changes are conducive to induction of AVNRT with a premature atrial complex and may explain in part the relatively common occurrence of AVNRT during sleep or other periods of presumed increased parasympathetic tone.

Differential effects of atropine and isoproterenol on inducibility of atrioventricular nodal reentrant tachycardia

BACKGROUND

Radiofrequency ablation of the "slow pathway" in atrioventricular nodal reentrant tachycardia (AVNRT) relies on tachycardia non-inducibility after ablation as success criterion. However, AVNRT is frequently non-inducible at baseline. Thus, autonomic enhancement using either atropine or isoproterenol is frequently used for arrhythmia induction before ablation.

METHODS

80 patients (57 women, 23 men, age 50+/-14 years) undergoing slow pathway ablation for recurrent AVNRT were randomized to receive either 0.01 mg/kg atropine or 0.5-1.0 microg/kg/min isoproterenol before ablation after baseline assessment of AV conduction. The effects of either drug on ante- and retrograde conduction was assessed by measuring sinus cycle length, PR and AH interval, antegrade and retrograde Wenckebach cycle length (WBCL), antegrade effective refractory period (ERP) of slow and fast pathway and maximal stimulus-to-H interval during slow and fast pathway conduction.

RESULTS

Inducibility of AVNRT at baseline was not different between patients randomized to atropine (73%) and isoproterenol (58%) but was reduced after atropine (45%) compared to isoproterenol (93%, P<0.001). Of the 28 patients non-inducible at baseline isoproterenol rendered AVNRT inducible in 21, atropine in 4 patients. Dual AV nodal pathway physiology was present in 88% before and 50% after atropine compared to 83% before and 73% after isoproterenol. Whereas both drugs exerted similar effects on ante- and retrograde fast pathway conduction maximal SH interval during slow pathway conduction was significantly shorter after isoproterenol (300+/-48 ms vs. 374+/-113 ms, P=0.012).

CONCLUSION

Isoproterenol yields higher AVNRT inducibility than atropine in patients non-inducible at baseline. This may be caused by a more pronounced effect on antegrade slow pathway conduction.

The effects of isoproterenol on the cardiac conduction system: site-specific dose dependence

INTRODUCTION

Isoproterenol is used to assess and facilitate AV nodal conduction, and thus potentiate the induction of supraventricular arrhythmias. It is commonly administered in increasing doses until a predetermined decrease in sinus cycle length, usually 20% to 30%, occurs. This regimen may result in undesirable side effects. We have observed that effects of isoproterenol on the AV node may occur prior to achieving the target sinus cycle length. The purpose of this study was to determine whether the sinus and AV nodes have equal sensitivity to isoproterenol.

METHODS AND RESULTS

Thirty-eight consecutive patients, who underwent electrophysiologic evaluation for a variety of indications, were given incremental doses of isoproterenol at 0.007, 0.014, 0.021, and 0.028 microgram/kg per minute. Sinus cycle length and AV node function were assessed at baseline and after 5 minutes at each dose. The percent change from baseline in AV node function was compared with the change in sinus cycle length at each dose interval. Significantly greater decreases were observed in the anterograde and retrograde AV nodal Wenckebach cycle length (P < 0.0001) than in the sinus cycle length at the lowest isoproterenol dose (0.007 microgram/kg per min). These differences were not apparent at higher doses. A sustained supraventricular tachycardia was inducible in 15 of 38 patients in the presence of isoproterenol, of which 40% occurred at the lowest dose.

CONCLUSIONS

The AV node is more sensitive than the sinus node to the effects of isoproterenol. Lower doses of isoproterenol than those commonly used may often facilitate the induction of a supraventricular tachyarrhythmia, thus reducing side effects.

Electrophysiologic characteristics and radiofrequency catheter ablation of fast-slow form atrioventricular nodal reentrant tachycardia

This study demonstrates that the fast-slow form of atrioventricular nodal reentrant tachycardia is usually catecholamine-sensitive and its electrophysiologic characteristics are significantly different from those of the slow-fast form. However, radiofrequency catheter ablation is a safe and effective treatment for patients with the fast-slow form of atrioventricular nodal reentrant tachycardia.