br Conflict of interest br Introduction br Case report

Conflict of interest
Introduction
Case report A 5-year-old boy was admitted for treatment of atrial flutter after correction of pulmonary atresia with ventricular septal defect. The patient had undergone total correction of cardiac disease at 4 years and 2 months of age after previous bilateral unifocalization for major aortopulmonary collateral arteries, Blalock–Taussig shunt creation, and Brock operation were performed. Atrial flutter occurred after total correction of cardiac defects in the patient at the age of 5 years. Atrial flutter was successfully terminated by overdrive pacing, but occurred again immediately. Recurrence of atrial flutter after overdrive pacing was considered to be caused by sick sinus syndrome. Use of a myocardial lead was initially considered to treat the sick sinus syndrome. However, it would have been difficult to attach a myocardial lead at the optimal location in the right atrium for AAI pacing, due to previous thoracotomies and cardiac surgery. A screw-in type pacemaker lead Medtronic 4568-53cm (Medtronic Inc. Minneapolis, MN, USA) was inserted from a cephalic vein by cutdown and attached to the free wall of the right atrium. To allow for growth, an excess loop was left in the right atrium (Fig. 1). Medtronic THERA™ (Medtronic Inc.) was implanted under the major pectoral muscle. The patient\'s body weight, height, and surface area at the time of operation were 14.3kg, 101cm, and 0.63m2, respectively. After 16 years, the patient\'s body weight, height, and surface area were 47.2kg, 169.0cm, and 1.52m2, respectively. Because of body growth, the endocardial lead was stretched, causing a gradual increase in the radius of the endocardial loop. The round shape of the endocardial lead from the superior vena cava (SVC) to the left subclavian vein changed to a straight shape with the stretching. At the first pacemaker implantation, the voltage of the intrinsic P wave, pacing threshold, and lead impedance were 1.4–2.0mV, 1V at 0.4ms, and 441Ω, respectively. The pacing threshold gradually increased and the voltage of the intrinsic P wave decreased during the follow-up period. At the last generator exchange, the voltage of the intrinsic P wave, pacing threshold, and lead impedance were 0.6mV, 7.0V at 0.5ms, and 562Ω, respectively (Table 1). At the last pacemaker clinic, the pacing mode, voltage of intrinsic P wave, generator output, and lead impedance were AAI, 1.3–1.4mV, 7.5V at 1.0ms, and 575Ω, respectively. Venous occlusion at the Pirfenidone cost side is one of the disadvantages of transvenous implantation in children. Because we had not previously inserted a new lead from the subclavian vein, we had not checked whether the patient\'s left subclavian vein, brachiocephalic vein, or superior vena cava were occluded using a venogram or venous echo. However, dilatation of superficial veins on the anterior chest as collateral circulations for the occluded veins has not been observed. Moreover, the patient has never experienced swelling or pain in the upper extremities due to venous occlusions. During the follow-up period, no adverse phenomena, such as exit block, sensing failure, or lead floating, were observed except for a gradual increase in pacing threshold. However, the cause of the increasing capture threshold seems to be an inflammatory reaction at the electrode-myocardial interface. Increasing pacing threshold is not a phenomenon exclusive to small children, but is also observed in adult patients.
Discussion The advantages of intravenous pacemaker lead implantation are: access to pacing sites that myocardial leads cannot be attached to, such as the intra-arterial septum; lower frequency of exit block [1]; better pacing threshold at the atrium and ventricle; and better sensing capability of intrinsic P waves [2], compared with myocardial leads. However, this approach for small children requires the consideration of growth, an appropriate entry site to avoid venous obstruction, and selection of a lead that is unlikely to detach during growth. Furman and Young [3] reported using an excess loop of endocardial lead to allow for patient growth. Gheissari et al. [4] reported that an excess loop of 10mm per year was needed to allow for patient growth. Because it seems unlikely that 2 endocardial leads can be inserted into the vein without venous occlusion, many authors consider that atrioventicular synchronous pacing for small children is not useful in the treatment of atrioventicular block. Thus, in almost all reports on transvenous pacemaker lead implantations, the authors describe single chamber pacemaker implantation for VVI pacing. To perform atrial pacing as in our patient, the estimated length of excess loop left in the right atrium to allow for patient growth must not exceed the length for right ventricular apical pacing. Thus, the length of excess loop that should be left in the right atrium is as long as the length for right ventricular pacing. However, all of the excess loop estimated for right ventricular pacing cannot always be left in the right atrium. To resolve this problem, Strojanov et al. [5] suggested that the part of the lead that could not be left in the right atrium can be left in the pacemaker pocket, and that the lead should be fixed to the subcutaneous tissue with a slowly absorbable ligature with the expectation of spontaneous lead migration as the child grows.