Introduction: Inappropriate sinus tachycardia (IST), a clinical syndrome with distressing symptoms, is characterized by paroxysmal or persistent sinus tachycardia in the absence of any identifiable primary etiology. Sinus node modification is not first line therapy given frequent recurrence and high complication rates. While medical therapy may be effective, symptoms frequently persist. Our objective is to describe the range of arrhythmias encountered during ablation in a cohort of IST patients refractory to medical therapy and to further the understanding of the etiology and mechanism of IST. Methods: We present a retrospective review of 33 patients who underwent sinus node modification for the treatment of therapy-refractory IST. Results: Arrhythmias included IST in 33 patients (100%), atrial tachycardia or frequent premature atrial contractions in 16 patients (48%), atrial fibrillation in 7 patients (21%), typical and atypical atrial flutter in 13 (39%) and 2 patients (6%), respectively, Wolff-Parkinson-White syndrome in 3 patients (9%), AV nodal reentry tachycardia in 3 patients (9%), and ventricular tachycardia or premature ventricular contractions in 4 patients (12%). Accelerated atrioventricular junctional (AVJ) tachycardia was present in 7/33 patients (21%), was refractory to medical therapy and caused disabling symptoms in all seven patients. Patients with AVJ tachycardia required extensive ablation at multiple sites, and 3/7 patients became pacemaker dependent. Conclusion: In patients undergoing SAN modification for IST, multiple arrhythmias were encountered. Accelerated AVJ tachycardia was frequently encountered and required extensive ablation of up-regulated tissue in the AVJ to improve symptoms. Thus, the pathologic process underlying IST may not be limited to the sinus node.

We report seven patients who underwent bail out cryoballoon ablation of ventricular arrhythmias refractory to conventional endocardial radiofrequency ablation. Ablated arrhythmia substrates included right ventricular moderator band (n=2), left ventricular (LV) papillary muscle (n=2), left fascicular (n=1) and deep LV myocardial (n=2). Cryoballoon ablation was successful in 5/7 patients. Advantages of cryoballon ablation include adhesive stability on endocavitary structures and creation deep homogeneous myocardial lesionds. Newer balloon technologies designed to improve myocardial contact that incorporate high density mapping on the balloon surface may expand utility of this technology for ablation of ventricular arrhythmias.

Cardiac resynchronization therapy (CRT) is highly effective for patients with left bundle branch block (LBBB), heart failure and left ventricular (LV) systolic dysfunction. Chronic right ventricular (RV) apical pacing is associated with pacing-induced cardiomyopathy and can be associated with exertional intolerance. The goal of this study was to assess the acute hemodynamic effects of His-bundle Pacing (HBP) compared to RV apical pacing in absence of LV systolic dysfunction in patients with exertional intolerance. Our patient population consisted of 5 patients with preserved LV systolic function and complete AV block. All five patients suffered from exertional intolerance in spite of preserved LV systolic function. At the time of generator change, all patients underwent implantation of a HBP lead. The QRS duration decreased from 179±13 ms with RVP to 113±6 with HBP (p < 0.001). Compared to RVP, HBP was associated with significantly longer diastolic filling time and improved septal early diastolic myocardial relaxation velocity (E’). Four of five patients noted acutely improved exertional dyspnea. In patients with AV block, exertional intolerance and preserved LV systolic function who are treated with chronic RV apical pacing, HBP may improve acute diastolic function and symptoms of exertional intolerance when compared to RV apical pacing. Randomized controlled trials are warranted to explore the effects of conduction system pacing in this unique patient population.