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Ann Thorac Surg 1995;59:689-694
© 1995 The Society of Thoracic Surgeons
Divisions of Cardiovascular and Thoracic Surgery and Pediatric Cardiology, University of Minnesota, Minneapolis, Minnesota
Accepted for publication November 23, 1994.
| Abstract |
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| Introduction |
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One important limitation in implanting transvenous pacemakers in children, particularly in infants, is the size of their upper chest veins. A substantial number of children still receive epicardial pacemakers via thoracotomy, because their subclavian veins are too small to accept a pacemaker lead. Whenever possible, thoracotomies should be avoided at such a young age. In addition, transvenous systems have proved to be more reliable [1, 2].
The number of complications in children's pacemaker implantations has been significantly higher than in the adult population [38] regardless of the approach [911]. Pacemaker manufacturers now make short leads and thin and small pulse generators, so they can be implanted in the chest. Careful assessment of the vein size is, therefore, a must when transvenous leads are implanted. The literature on obliteration of subclavian veins in children undergoing transvenous pacemaker implant is very scarce or nonexistent [12, 13]. In our own experience, we have seen at least 4 children who had total obliteration of the subclavian vein, the innominate vein, and in 1 case of the superior vena cava after transvenous pacemaker implantation. This complication occurred without any serious obvious acute manifestation, but when the children returned to have the pacemaker replaced or an attempt was made to pass new leads, we found (after performing venography) that the vein was completely occluded, and in 1 patient with obstruction of the superior vena cava, thoracotomy intervention was necessary to remove the lead that had caused obstruction of the superior vena cava. Placement of a patch to widen the vein and maintain continuity of that vessel was necessary. Therefore, the rate of occlusion or obliteration of veins due to this type of operation is unknown.
We began looking into this problem in an attempt to come up with a sensible and objective method to decide when it was safe to implant the transvenous lead in a vein only slightly larger than the lead itself. The problem of venous thrombosis after transvenous implantation of pacemaker leads has been described in adults because this occurs suddenly and the patients usually are symptomatic. However, in children, the course is more protracted and it is not until revision or a new pacemaker implantation is attempted that the child is found to have the vein occluded.
A protocol, therefore, was developed to treat these children and is herein described. As pointed out by O'Sullivan and associates [10], the advantage of using small pulse generators in small children is lost if the pacemaker lead is excessively long and the remnant needs to be wrapped with the pulse generator, increasing the bulk of the unit, making it unsuitable for implantation in the subcutaneous tissue of the chest wall of these children.
We recently described a surgical technique conceived at the University of Minnesota [14] that provides for a safe method of implanting pulse generators in the chest to avoid complications at the pocket site, like overstretched scars or even dehiscence caused by a bulky pulse generator and lead when the incision lies over the unit.
| Material and Methods |
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The indications for pacemaker implantation were complete postsurgical heart block (9 patients) or congenital heart block (5 patients) with severe bradycardia. One hundred percent follow-up of these patients has extended from 2 months to 6 years. Eight patients required pacemaker implantation after a corrective intracardiac operation as follows: correction of transposition of great vessels, 1; aortic valve replacement, mitral valve replacement, and ventricular septal defect repair, 1; atrioventricular canal, 1; Fontan, 1; Rastelli, 1; pulmonary atresia and ventricular septal defect, 1; double-outlet right ventricle, 2; and tetralogy of Fallot, 1 (1 patient had two operations).
Protocol
Our method fulfills five conditions: (1) Doppler ultrasound assessment of all four upper chest veins (subclavian and internal jugular veins), measuring patency, diameter, and cross-sectional area; (2) use of active fixation leads in ventricle and atrium; (3) use of short leads 36 to 45 cm long; (4) anchoring of pulse generator with nonabsorbable material to muscle fascia to prevent migration; and (5) routine use of lateral approach as previously described [14] if the pulse generator was implanted in the chest.
Duplex Assessment of Veins
This examination provides important information on the diameter and cross-sectional area of the subclavian and internal jugular veins, compared with the cross-sectional area of the pacemaker leads. We then are able to estimate the amount of obstruction the leads could cause in the vessel (Fig 1
).
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In patients receiving dual-chamber systems, the atrial lead was also CPI ``sweet tip'' type.
Lead Fixation at Vein Entry Point
Because of the small size of the subclavian veins in children less than 4 years old, our preferred site of insertion is the internal jugular vein. Even in children more than 4 years old, we preferred the internal jugular vein if they had a small subclavian vein by duplex (less than 5 mm in diameter) from whichever cause. In every case of lead implantation in the jugular system, we tunneled it under the clavicle to reach the site of the pacemaker pocket in the upper part of the chest (in children more than 2 years old) or in the left flank of the abdomen (in children less than 2 years old) (Fig 2
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As soon as the lead is anchored in the cardiac chamber, the pursestring suture is tied down and cut. The lead also is secured to the fascia with a transfixation stitch.
Anchoring the Pulse Generator
To prevent migration of the pulse generator inferiorly, with the possibility of exerting traction on the transvenous lead, the pulse generator is secured with nonabsorbable material to the fascia of either the pectoralis major muscle or the abdominal muscles, depending on the site selected. Interrupted stitches with nonabsorbable material are placed between the subcutaneous fascia and the anterior fascia of the muscle, along the inferior and lateral borders of the pulse generator.
Lateral Approach
If the pulse generator is implanted in the chest, our previously described lateral approach [14] is used (see Fig 3
). Basically, an incision is made along the lateral border of the pectoralis major muscle. The dissection is carried medially and superiorly, creating a pocket in the superior quadrant of the chest over the pectoralis muscle where the pulse generator is implanted. This prevents tension, dehiscence, infection, or formation of thin wide scars over the pulse generator site.
| Results |
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Even in children 3 to 7 years old, the subclavian veins are relatively small, from 2.3 to 6 mm in diameter. Not until the child is more than 10 years old are the subclavian veins larger, from 8 to 10 mm in diameter; by the same age, the internal jugular veins are up to 18 mm in diameter. This uneven ratio (with the internal jugular veins growing larger than the subclavian veins) probably is related to the growth rate of the child's head in proportion to the arms.
Therefore, we did not consider it safe to implant single transvenous pacemaker leads into a vein with less than 19 mm2 of cross-sectional area (5 mm diameter) regardless of its location. With a double-lead implantation (for dual-chamber pacemaker systems), the two leads have a combined cross-sectional area of 6.28 mm2, so the ideal size of the vein must be at least 7 mm in diameter, equivalent to a cross-sectional area of 38 mm2 (see Table 2
). We believe that once the lead occupies close to 50% of the vein's cross-sectional area or more, the risk increases for thrombosis or vein obstruction by the lead.
These recommendations are shown in Table 2
. All our patients met these requirements. If in doubt about the size or integrity of the subclavian vein, we do not hesitate to insert the leads in the jugular system.
Therefore, all patients less than 3 years of age underwent implantation via the jugular vein. In addition, 2 of the patients in the second group (4 to 7 years) also underwent implantation in the left internal jugular veins.
Of the 14 patients followed up, lead replacement was required in 1, due to a sudden increase in the stimulation threshold. In 6 patients, we needed to replace the generator due to exhaustion of the battery, and 2 children underwent release of the lead due to obvious tension as a result of their growth.
Vein Obstruction and Site Follow-up
No thrombosis of the internal or subclavian veins due to partial obstruction of its lumen by the pacemaker leads has developed in any of our patients. In fact, ultrasound examinations routinely repeated on 5 patients showed no compromise of the vein lumen or any sign of thrombosis at any level.
No cases of pulse generator site dehiscence or migration have been observed after we implemented the lateral approach as a routine technique for children.
| Comment |
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We prefer, therefore, the direct puncture of the subclavian vein or the internal jugular vein. Using the lateral approach for implantation of the pulse generator, if the skin overlying the pacemaker pocket is too thin, it is very easy to bury the pulse generator under the pectoralis major muscle instead of under the skin with a highly satisfactory cosmetic appearance and no discomfort to the patient.
| Footnotes |
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| References |
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