Both intracardiac electrograms and intracardiac ultrasonography have been used to target lesion delivery, with achievement of successful modification or ablation in 73 to 100 percent of patients. Sinus nodal modification is associated with a 10 to 27 percent risk of sinus node damage necessitating permanent pacing. The use of intracardiac ultrasonography targets the fastest portions of the sinus node by ablating the uppermost portion of the crista terminalis. This approach seems to require fewer radiofrequency applications than electrogram-guided approaches. It may also reduce the need for permanent pacing.
Recurrence rates are high.
Ablation to the extent that permanent pacing is required may be necessary for sustained success. Thus, patients require careful follow-up for recurrent tachycardia or progressive sinus node dysfunction. Surgical isolation of the sinus node for IST has also been followed by recurrent tachycardia at new foci. All radiofrequency applications to the sinus node region should be preceded by pacing at 10 to 20 milliamperes. If diaphragmatic stimulation is seen, damage to the ipsilateral phrenic nerve may ensue.