THE FINE ART OF DIAGNOSIS

Melvin M. Scheinman, MD, University of California, San Francisco, San Francisco, California, USA, opened the session with a discussion on how the laboratory is used to differentiate the various types of supraventricular tachycardia (SVT). A number of newer concepts have helped in making the differential diagnosis of these different SVT types, which, along with atypical AVNRT, include atrial tachycardia, septal accessory pathway (AP), concealed nodofascicular tachycardia, and functional tachycardia. He referred the audience to two recently published articles by Veenhuyzen and colleagues that provide an excellent review of both the traditional and newer concepts of laboratory diagnosis [Pacing Clin Electrophysiol 2011; Pacing Clin Electrophysiol 2012].

Dr. Scheinman emphasized that there are pitfalls to every new concept and rule, and shared some useful tricks to differentiate the types of arrhythmias. To differentiate AVNRT from orthodromic reciprocating tachycardia (ORT) in a patient with SVT, for example, ventricular overdrive pacing (VOP) should be used to look for two things: the postpacing interval minus tachycardia cycling, and the stimulus ventriculo-atrial (VA) versus the VA during the SVT. However, this rule does not hold true in all cases and an important trick in these cases is to use entrainment with infusion to make the differential diagnosis, a novel approach used effectively by Dandamudi et al. to differentiate between ORT and AVNRT [Heart Rhythm 2010]. This study showed that atrial capture in all ORT patients occurred after the first nonfused paced QRS in all patients during VOP. In AVRNT patients, on the other hand, atrial capture occurred 2 or 3 beats after the first unfused QRS. Dr. Scheinman said that this technique is most valuable for patients who have SVT termination during VOP.

Some of the pitfalls to be aware of when using VOP during SVT, is that VOP may not distinguish the decremental AP, it does not distinguish the presence of bystander AP, and the fusion with capture may not be seen within 3 beats in the left lateral AP.

MarkMcGuire, MBBS, PhD, Royal Prince Alfred Hospital, Sydney, Australia, provided a historical review of the different theories of the mechanism of AVNRT.

Based on a review of a number of studies presented, he said that on balance the current evidence suggests a number of AVNRT mechanisms: 1) an upper common pathway of nodal tissue probably does not exist; 2) a lower common pathway of nodal tissue may exist in some patients; 3) AVN reentry can occur byway of any two atrionodal connections that have the appropriate properties of refractoriness and conduction velocity; and 4) the presence in an individual patient of one or more forms of AVNRT probably depends on the properties of the atrionodal connections.

TREATMENT OF AVNRT

Stephan Willems, MD, University Hospital Eppendorf, Hamburg, Germany, provided an update on the most recent data on radiofrequency (RF) ablation for AVNRT. He emphasized that RF ablation of the slow pathway remains the first line of treatment for most forms of AVNRT, with the most recent 2003 guidelines showing a high success rate (96%) and low recurrence rate (3% to 7%) [Blomström-Lundqvist C et al. J Am Coll Cardiol 2003].

Summarizing various results from studies that have emerged since this last guideline, Prof. Willems noted that the data over the past decade continue to show that RF ablation is associated with a high acute success rate. However, the data also show a slightly lower success rate in some patients with a variants of AVNRT, which he said highlights the need for proper diagnosis. The data also show a very low recurrence rate with long-term follow-up and that slow pathway ablation should be used. One ongoing discussion is whether slow pathway modulation is as good as slow pathway ablation, noting that the current data suggest they are comparable. Prof. Willems also emphasized that current data shows that RF ablation has achieved almost 0% AV block, even in the elderly. Overall, one of the most striking findings is the continuous decrease in AV block during the last decade (Table 1).

Isabel Deisenhofer, MD, German Heart Centre, Munich, Germany, discussed the use of cryoablation in AVNRT. Reiterating the high success and recurrence rate and safety of RF ablation for AVNRT, she said that outcomes to date with a number of cryoablation trials have shown comparable acute success rates to RF but the problem is the substantially higher recurrence rates up to −20% with cryoablation [Gupta D et al. Europace 2006].

Similarly, results from the European Multicenter Study Radiofrequency Versus Cryo in Atrioventricular Nodal Reentry Tachycardia [CYRANO; Deisenhofer I et al. Circulation 2010] that randomized 258 patients with AVNRT to RF ablation and 251 to cryoablation found that the recurrence rate with cryoablation was nearly double compared with RF (9.4% vs 4.4%; p=0.029). No differences were found between the two groups in terms of acute treatment failure or AV block. According to Prof. Deisenhofer, the significant increase in the recurrence rate accounted for the significant difference between cryoablation and RF ablation in terms of the primary endpoint of the study which was a combination of acute treatment failure, complete AV block, and freedom of AVNRT recurrence during 6 months of follow-up (12.6% vs 6.3%; p=0.018).

Results in a study of 49 pediatric patients also showed an unacceptably high rate of AVNRT recurrences, occurring in 22.4% of patients at a mean follow-up of 30.2 months after cryoablation [Reents T et al. Europace 2012].

Based on this evidence, Prof. Deisenhofer emphasized that clinicians need to balance the minimal risk of RF-induced AV block risk against the considerable risk of AVNRT recurrence with cryoablation.

Currently, she said that her clinic has switched back to using RF ablation for most patients based on the current data and outcomes.