Background: Inappropriate sinus tachycardia (IST) is characterized by heart rate (HR) increase out of proportion to stress level. Radiofrequency (RF) modification of the sinus node (SN) is an accepted treatment modality for medically refractory IST. We describe a new technique using noncontact mapping and a saline irrigated catheter for SN modification.
Methods: Seven consecutive patients with medically refractory IST were referred for ablation. Intrinsic heart rate (IHR) was calculated with complete autonomic blockade by atropine and propranolol. Isoproterenol (ISO) 1 mcg/min was initiated and increased to 10 mcg/min. Site of earliest activation was tagged at each dose of ISO once stable HR was achieved. RF ablation to target site of earliest activation at peak HR on ISO 10 mcg/min was performed. With any change in P-wave morphology, activation was reassessed and the new site of earliest activation targeted. Endpoint was a decrease in HR and change in P-wave morphology in lead III and aVF.
Results: Five of seven patients had abnormal IHR. Mean number of RF lesions was 25 (10–52). All patients had either flattening of the P wave or development of negative P waves in leads III and aVF post RF associated with a decrease in HR of ≥25% from baseline off ISO. A caudal shift of the site of early activation compared with baseline was observed. One patient who had a prior SN modification developed symptomatic intermittent junctional bradycardia and required an atrial pacemaker 2 weeks later. The other 6 patients in follow-up from 6 to 24 months had no further IST.
Conclusions: Noncontact mapping using the described technique in conjunction with the saline-cooled ablation catheter for SN modification in the treatment of IST may provide effective HR control.