To the Editor—Differentiation of orthodromic reciprocating tachycardia from atrioventricular nodal reentrant tachycardia

Letters to the Editor

e27

Kroll suggests that a different effect may be observed if a “tuned” waveform was used for defibrillation. A fixed 50% tilt biphasic waveform was evaluated in our study. This allows the results to be generalized better to current clinical practice since the majority of implantable cardioverterdefibrillators that are implanted either cannot be or are not programmed to use tuned waveforms. The importance of pulse width, either with impedance adjusted (i.e., tuned) or with fixed durations, to improve DFTs remains controversial.2– 4 Moreover, studies showing a benefit of alternative waveforms often identify only a subgroup with lower DFTs in post hoc analysis. Dr. Kroll also posits that in a single-coil, active can defibrillator, channeling current from the more posterior and basal RVOT might offer an advantage over the RVA. This becomes particularly relevant as the electrophysiology community moves to implant more single-coil leads, which are safer to extract in the event of lead infection or failure. If adequate DFTs are observed with RVOT implants using single-coil leads, then this could both allow for simpler lead implantations and potentially avoid the deleterious effects of RVA pacing. We agree that the effectiveness of singlecoil RVOT lead implantation needs to be validated prospectively. In this regard, the PROMISE study will be the first attempt to validate some of these issues by comparing fixed and tuned waveforms for single-coil defibrillation. Carl R. Reynolds, MD,* *From the University of Pennsylvania, Philadelphia, Pennsylvania Michael R. Gold, MD, PhD, FHRS† E-mail: [email protected]. Medical University of South Carolina, Charleston, South Carolina.

References 1.

2. 3. 4.

Reynolds CR, Nikolski V, Sturdivant JL, et al. Randomized comparison of defibrillation thresholds from the right ventricular apex and outflow tract. Heart Rhythm 2010;7:1561–1566. Shorofsky SR, Foster AH, Gold MR. Effect of waveform tilt on defibrillation thresholds in humans. J Cardiovasc Electrophysiol 1997;8:496 –501. Gold MR, Shorofsky SR. Strength duration relationship for human transvenous defibrillation. Circulation 1997;96:3517–3520. Natarajan S, Henthorn R, Burroughs J, et al. “Tuned” defibrillation waveforms outperform 50/50% tilt defibrillation waveforms: a randomized multi-center study. Pacing Clin Electrophysiol 2007;30(Suppl 1):S139 –142.

To the Editor— Differentiation of orthodromic reciprocating tachycardia from atrioventricular nodal reentrant tachycardia With great interest we read the report by Dandamudi et al1 entitled “A Novel Approach to Differentiating Orthodromic Reciprocating Tachycardia From Atrioventricular Nodal Reentrant Tachycardia,” published in Heart Rhythm. In their work, Dandamudi et al1 showed that by pacing the right ventricular (RV) apex during the tachycardia at a cycle length that was 10 to 40 ms shorter than the tachycardia cycle length, the first fully preexcited RV paced beat reset

the atrium in all cases of orthodromic reciprocating tachycardia (ORT). In the case of atrioventricular nodal reentrant tachycardia (AVNRT), the average number of fully preexcited RV beats was 3.7 ⫾ 1.1, and in no case of AVNRT was the atrium reset in less than 2 fully preexcited beats. The authors conclude: “A cut-off of at least 2 beats would yield a positive predictive value of 100% for AVNRT.” However, we recently performed an electrophysiological study in a 60-year-old man with orthodromic reciprocating tachycardia over a slightly decremental right inferoseptal accessory pathway in which the above criteria would have led to a wrong diagnosis of atypical AVNRT. The induced tachycardia was long-VA tachycardia with a cycle length of 470 to 490 ms and proximal-to-distal coronary sinus activation. The introduction of a premature ventricular beat at a time when the His bundle was refractory led to a slight prolongation of the following VA interval, implying the presence of a decremental accessory pathway as a retrograde limb of the reentry. RV pacing at a cycle length of 430 ms resulted in tachycardia reset after the fourth fully preexcited beat. According to the article by Dandamudi et al,1 this would have proven the presence of atypical AVNRT. After anatomical variations of the coronary sinus (such as diverticula) had been excluded by angiography, activation mapping during tachycardia was performed. The earliest atrial activation was registered at the inferomedial segment of the tricuspid valve (30 ms earlier than proximal coronary sinus). Radiofrequency application at this site resulted in termination of tachycardia by VA block in 3.4 seconds. During a waiting time of 45 minutes, no tachycardia was inducible in the patient. Considering this case, an exception to the criteria proposed by Dandamudi et al1 might be ORT over a decremental accessory pathway. We believe that it is very important to illustrate this exception because in our case a misdiagnosis of atypical AVNRT would have led to repeated radiofrequency application in the slow-pathway area, thus increasing the risk of inadvertent AV block. Charalampos Kriatselis, Sotirios Nedios, Mattias Roser, Jin-Hong Gerds-Li,

MD MD MD MD

German Heart Institute Berlin Berlin, Germany

Reference 1.

Dandamudi G, Mokabberi R, Assal C, et al. A novel approach to differentiating orthodromic reciprocating tachycardia from atrioventricular nodal reentrant tachycardia. Heart Rhythm 2010;7:1326 –1329.

Author Reply–To the Editor: Differentiating AV nodal reentry tachycardia from orthodromic reciprocating tachycardia Our cases series1 included patients with orthodromic reciprocating tachycardia without decremental conduction (short RP tachycardia). We did not have any patients in our series