J Cardiol 2004 Dec; 44（6）: 251 – 254

Entrapment of a Tined Lead by theChiari Network With Preserved
Atrial Sensing Ability in a PatientWith Atrioventricular Block : ACase Report
Takahisa

MARUYAMA, MD

Fumio

KUROGOUCHI,Abstract ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
An 82-year-old woman with 2 : 1 atrioventricular block underwent a pacemaker implantation procedure,
but a tined lead became entrapped by the Chiari network. All manipulations failed to achieve release of theelectrode, by which the atrial electrical potential could be recorded. Tines equipped near the tip of a pacemaker lead are intended to prevent dislodgment, but entrapment of the tined tip by intracardiac structures isprobable. Together with another screw-in ventricular lead, this entrapped tined lead could act as a dualchamber pacemaker in VDD mode.
─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────J Cardiol 2004 Dec ; 44（6）: 251−254

Key Words
Complications entrapment
Pacemaker, artificial tined lead
Heart defects, congenital Chiari network

INTRODUCTION
Entrapment of devices by intracardiac structures
is a rare complication of invasive cardiac examinations or interventions1−5）. The tined type of pacemaker lead may carry increased risk of this complication because of the configuration of the tip. Wetreated a patient with atrioventricular block with atined lead which became entrapped by the Chiarinetwork, but the lead was available for sensing theatrial potential in VDD mode.
CASE REPORTAn 82-year-old woman with a history of hypertension and diabetes was referred to our hospital
because of dizziness or near syncope on exercise.
Her pulse rate was 40 beats/min. Electrocardiography demonstrated 2 : 1 atrioventricular blockand right bundle branch block. Chest radiography
showed no pulmonary congestion. Transthoracic
echocardiography did not show any intracardiac

tumorous lesion, abnormality of ventricular movements, or inter-atrial shunt flow. Emergent temporary pacing was performed, and her complaint disappeared thereafter.
Implantation of a dual chamber type of permanent pacemaker was performed on the third hospitalday. A tined ventricular lead（ Medtronic, 505452 cm, Medtronic Inc.）and a tined J-shaped atrial
lead（Medtronic, 5554-45 cm）were passed throughthe left subclavian vein under local anesthesia.
During the introduction of the first lead into theright ventricle, the tip of the lead became entrappedby an intraatrial structure, which seemed to be theChiari network. All manipulations and the passageof various stylets failed to release the entrapped tip.
Another tined J-shaped lead was also entrapped
transiently, but was fortunately released soon after.
We abandoned the extraction of the entrapped first
lead, and decided to utilize that lead for atrial sensing because an intraatrial P wave potential of 0.6 to
1.2 mV could be recorded by the entrapped lead.

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長野市民病院 循環器内科 : 〒 381−8551 長野県長野市富竹 1333−1
Division of Cardiology, Nagano Municipal Hospital, Nagano
Address for correspondence : MARUYAMA T, MD, Division of Cardiology, Nagano Municipal Hospital, Tomitake 1333−1, Nagano,Nagano 381−8551 ; E-mail : maruyama@hospital.nagano.nagano.jp
Manuscript received March 4, 2004 ; revised May 27, 2004 ; accepted May 27, 2004

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Fig. 1 Postoperative chest radiographs
Anterior view（left）, and lateral view（right）showing the tip of the entrapped intraatrial lead is located posteriorly.

The tined J-shaped lead was withdrawn from thepatient, and a new screw-in lead（Medtronic,Capsurefix, 5068-52 cm）was successfully introduced for right ventricular pacing and sensing without difficulty. The dual chamber pacemaker（Medtronic, Kappa, KDR721）was operated in
VDD mode（60 to 120 pace/min）with the atrial sensitivity set to maximum（0.18 mV）.
The lateral view of the postoperative radiography
showed that the tip of the entrapped lead was situated toward the posterior wall of the right atrium（Fig. 1）. Echocardiographic examination showedthe entrapped atrial lead was thickened andappeared like a string of various sized beads, compared with the smooth appearance of the ventricularlead（Fig. 2）. On electrocardiographic monitoring,
the P-sensed ventricular pacing was prevalent,
although under-sensing of the atrium with exclusive ventricular pacing was also recorded.
Assessment of pacemaker function 1 week after theimplantation showed the intraatrial P wave potential was 0.18 to 0.25 mV in the supine position and0.30 to 0.50 mV in the sitting position.
The patient has suffered no events since discharge. Repeated assessment 5 months after
showed the intraatrial P wave potential was 0.35 to
0.50 mV in all postures. During 5 months, the total
number of paced ventricular beats was 13 million,Fig. 2 Postoperative echocardiogram in the subxyphoid view
Compared with the smooth appearance of the ventricular lead（arrowheads）, the entrapped atrial lead（arrows）
is thickened and appears like a string of beads, suggesting entanglement by a filamentous and membranousstructure.
RA ＝ right atrium ; LA ＝ left atrium ; LV ＝ left ventricle.

J Cardiol 2004 Dec; 44（6）: 251 – 254

Lead Entrapment by Chiari Network

whereas that of sensed atrial potential was eight
and a half million, suggesting that P-sensed ventricular pacing amounted to about two thirds of all ventricular paced beats.
DISCUSSION
Endocardial leads of permanent pacemakers aswell as implantable cardioverter defibrillators
include some mechanisms to prevent dislodgement,
one of which contains tines equipped near thetips6）. Tined leads may reduce the likelihood of perforation and cardiac tamponade, compared withscrew-in leads, but have the potential disadvantage
of increased probability of accidental entrapmentby intracardiac structures. Difficult procedures toextract tined leads entrapped by the rim or the chordae of the tricuspid valve have previously beenreported1,2）. Lead entrapment by the Chiari network
like the present case has not been reported,
although a diagnostic catheter and a guide wire
have been entrapped by the Chiari network3,4）.
The Chiari network, together with the eustachianvalve, is one of the congenital remnants of a membranous course in the embryo that directs oxygenated blood from the inferior vena cava across theforamen ovale. This remnant consists of a fine filamentous membrane attached to the coronarysinus7）. The Chiari network is present in 1.3% to
4% of autopsy cases and 2% of patients in transesophageal echocardiography series8）. In the present case, the observer（ the first author）of thetransthoracic echocardiography performed urgently
at patient admission did not recognize the presenceof the Chiari network. However, the following reasons led us to conclude that the structure entrapping
the lead was the Chiari network. 1）Since the atrialelectrical potential could be recorded, the tip of thelead was not located in the right ventricle but in theright atrium. 2）There was no tumorous lesion in
要the right atrium. 3）The tip of the intraatrial lead
was located posteriorly on the lateral view of the
postoperative radiograph, so the structure entrapping the lead might be attached around the inferoposterior parts of the right atrium, such as theeustachian valve, crista terminalis, or thebesianvalve. 4）Postoperative transthoracic echocardiography showed the thickened appearance of theentrapped lead, indicating a lead entangled by a filamentous or membranous structure. The patientrefused transesophageal echocardiography, whichmight have shown some more information about
the Chiari network.
The atrial electrical potential obtained from theentrapped lead was not constant, but depended on
the patient s posture. However, we supposed thatsome under-sensing of the atrial potential would
not significantly impair the exercise capacity of thiselderly patient. We could also have introduced thethird atrial lead and abandoned the entrapped lead.
However, atrial pacing was not essential because
her sinus node function was normal.
In general, the Chiari network is thought to be oflittle clinical significance, so observers of echocardiography may not pay very much attention to theChiari network on routine examinations. However,the slight possibility of entrapment of intracardiac
devices by the Chiari network during invasive
examinations or interventions must be kept inmind. The present case suggests that if the Chiari
network is recognized on echocardiography examination before the scheduled implantation of a permanent pacemaker or a cardioverter defibrillator,
the operator should be prudent in selecting the typeof leads and in manipulating their delivery. A
screw-in lead might be preferable to a tined lead insuch situations, otherwise the tined tip should not
be turned infero-posteriorly in the right atrium.

約

ペースメーカー植え込みに際しキアリ網に捕捉されたタインド型リードを心房電位の感知に利用した房室ブロックの 1 例
丸山隆久

黒河内典夫

タインド型ペースメーカーリードは，その形状ゆえに心臓内の構造物に捕捉されてしまう可能性がまれながらある．症例は労作時のめまいを主訴とする 82 歳の女性．2 : 1 の房室ブロックによる徐脈を認め，緊急一時ペーシングにより症状は消失した．永久ペースメーカー植え込み術の際に，タインド型の心室用リードが右房内でキアリ網に捕捉され抜去不可能となった．このリードから心J Cardiol 2004 Dec; 44（6）: 251 – 254

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Maruyama, Kurogouchi

房電位を検出可能であったため，これを心房センシング専用とし，新たに挿入し留置したスク
リューイン型の心室リードとともに，VDD モードでの作動とした．術後の経過は良好である．キ
アリ網の臨床的意義は一般には少ないが，術前評価においては心エコー図法でキアリ網の有無に注目すべきである．本例ではリード捕捉ののち，次善の合理的なペーシングモードを選択しえた．

J Cardiol 2004 Dec; 44（6）: 251−254

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