Symptomatic Sinus Node Dysfunction in Children Without Structural Heart Disease

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Symptomatic

Sinus

Node

Dysfunction

in

Children

Without

Structural

Heart

Disease

Steven

M. Yabek,

MD,

Terrence

Dillon,

MD,

William

Berman,

Jr,

MD,

and

Colleen

J. Niland,

RN

From the Department of Pediatrics, University of New Mexico, School of Medicine,

Albuquerque

ABSTRACT. Symptomatic sinus node dysfunction rarely

occurs in children with structurally normal hearts. Three children with syncope and bradycardia are described.

Noninvasive and invasive testing revealed isolated sinus

node dysfunction and normal cardiac anatomy.

Electro-physiologic evaluation showed abnormalities of sinus

node automaticity and sinoatrial conduction. All three

patients were treated with permanent ventricular

pace-makers and have remained asymptomatic. Sinus node dysfunction should be considered in the differential

di-agnosis whenever a child is seen with unexplained

dim-ness or syncope. Pediatrics 69:590-593, 1982; sinus node,

bradycardia, syncope.

Sinus node dysfunction (SND) in children occurs most frequently following the surgical correction of

congenital

heart

defects.’

When

symptomatic,

these children frequently require treatment with permanent pacemakers. Recently, SND has also

been reported in children and adolescents without

structural heart disease.” As these latter patients are rarely symptomatic, specific treatment has

gen-erally not been required. In this report, we describe

the clinical and electrophysiologic data from three

children with symptomatic SND and normal car-diac anatomy.

CASE REPORTS

Case 1

A 10-year-old boy in previously good health failed to awake from sleep and was unresponsive to deep pain. Heart rate was reported by the parents as being “less than 30 per minute.” On admission to the hospital, the child was awake but disoriented. Examination revealed a

Received for publication March 16, 1981; accepted July 10,1981. Reprint requests to (S.M.Y.) Department of Pediatrics, Umver-sity ofNew Mexico SchoolofMedicine, Albuquerque, NM 87131. PEDIATRICS (ISSN 0031 4005). Copyright © 1982 by the American Academy of Pediatrics

slow and irregular heart rate. Blood pressure was 80/60

mm Hg. There were no cardiac murmurs. ECG revealed

inappropriate sinus bradycardia for age and nonspecific T wave abnormalities (Fig 1). There were multiple, pre-mature atrial extrasystoles accompanied by prolongation of the PR interval and ventricular aberration. There was

no clinical or laboratory evidence of an inflammatory or infectious myocardial process. Intravenous atropine (0.25 mg) failed to increase the resting heart rate. Twelve hour

ambulatory monitoring revealed heart rates of

predomi-nantly 31 to 50 beats per minute. It also showed marked

PR interval variation with frequent periods of 1#{176} atrio-ventricular (A-V) block (PR interval greater than 200

msec) and occasional blocked P waves.

Case 2

A 16-year-old boy was referred for evaluation because of a syncopal episode, bradycardia, and dizziness associ-ated with exercise. Physical examination revealed a rest-ing heart rate of 40 beats per minute. Blood pressure was normal. There was a left ventricular lift palpated at the cardiac apex and a soft, grade 1/6 ejection murmur was heard over the pulmomc valve. ECG revealed sinus

bradycardia but was otherwise normal. A chest roentgen-ogram showed slight cardiomegaly. On submaximal

up-right exercise, heart rate increased to only 56 beats per minute. Twenty-four-hour ambulatory monitoring in the hospital showed persistent sinus bradycardia Heart rate while awake dropped to 38 beats per minute and was occasionally associated with dizziness (Fig. 2).

Case 3

A previously healthy 4-year-old boy was found

uncon-scious at home. Paramedical personnel reported a heart rate of 60 beats per minute and “seizure-like” activity. The past history included episodes of inappropriate

leth-argy and stupor, which abated spontaneously and were

never investigated. On arrival at the hospital, the child was awake but stuporous. Heart rate was 65 beats per minute and irregular. The remainder of the physical

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ARTICLES 591

Fig 1. ECG leads 1, 2, and 3 (25 mm/sec) from patient 1 showing sinus bradycardia and abnormal T wave

mor-phology. Premature atnal beat with ventricular aberra-tion is seen in lead 1.

,

HThrHH

Fig 2. Simultaneously recorded leads (25 mm/sec)

ob-tamed during 24-hour ambulatory monitoring of patient

2. Tracings show marked sinus bradycardia.

B

Fig 3. ECG rhythm strips (25 mm/sec) from patient 3.

Inappropriate sinus bradycardia for a 4-year-old child (A)

and episode of spontaneous sinus arrest with junctional escape rhythm beginning after the second sinus beat (B)

are shown.

junctional escape rhythm (Fig 3). Findings on a chest

roentgenogram were normal. The results of all other laboratory studies, including EEG, were normal.

Twenty-four-hour ambulatory monitoring showed repeated

epi-sodes of inappropriate bradycardia and periods of sinus

arrest.

Electrophysiologic Methods

Electrophysiologic studies were performed in the postabsorptive state during diagnostic cardiac

cath-eterization as previously described.7 Informed con-sent was obtained from each patient’s parents.

Pa-tients were sedated with meperidine hydrochloride

(1 mg/kg) and dropendol (0.04 mg/kg) adminis-tered intramuscularly one hour before study. Elec-trophysiologic studies were conducted before an-giography. A quadrapolar electrode catheter was inserted percutaneously into the right femoral vein and positioned at either the superior vena cava-right atrial junction for studies ofsinus node

func-tion or across the tricuspid valve for recording a His

.

it:

bundle

electrogram.

Methods

for measuring

intra-. atrial, A-V nodal, and His-Purkinje conduction

:i times using the His bundle electrogram and normal

tt. values during childhood have been described

pre-viously.79

Sinus node automaticity was evaluated following multiple periods of rapid atnal pacing from the high right atrium. Pacing was accomplished using an isolated pulse generator (Medtronic 5325) that de-livered impulses of 2-msec duration and 2 to 4 mamp. Impulses were delivered over the distal two electrodes of the catheter and the proximal two

electrodes were used to record a high right atnal

electrogram. At the termination of pacing, sinus node recovery time was measured from the last paced P wave to the onset of the first spontaneous occurring P wave of sinus origin.’0 The maximum

sinus node recovery time was used to calculate the corrected sinus node recovery time by subtracting the mean prepacing sinus cycle length. In children

with normal sinus node automaticity, corrected

sinus node recovery time should not exceed 275 msec.4

Sinoatrial conduction time (SACT) was deter-mined to assess the integrity of impulse conduction from the sinus node to the surrounding right atrium. It was measured following the introduction of sin-gle, premature atnal stimuli following every eighth normal sinus beat as described previously in chil-dren.4” If the atnal extrastimuli resulted in reset-ting of the sinus rhythm, SACT was calculated by subtracting the prestimulus sinus cycle length from the stimulus-induced reset cycle. Multiple reset re-sponses were used to determine the mean SACT. This interval represents both retrograde and anter-ograde conduction of an impulse through the pen-nodal tissues surrounding the sinus node. In chil-then with normal sinoatnal conduction, SACT should not exceed 210 msec.4”

RESULTS

Although patient 1 was disoriented on arrival at the hospital, all patients had normal neurological

examinations. Familial history of a neuromuscular disorder was not present in any case.

Each patient underwent cardiac catheterization and evaluation of sinus node function and cardiac

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TABLE. Electrophysiologic Data (msec) During Sinus

Rhythm from Three Children with Sinus Node

Dysfunc-tion

Case No. A-V Conducting Intervals CSNRT SACT

P-A A-H H-V

1 20 90 35 1,570 270

2 20 70 40 520 SNEB

3 15 75 30 620 125

S Abbreviations used are: A-V, atrioventricular, P-A,

in-traatrial interval A-H, A-V node interval; H-V, His-Pur-kinje interval; CSNRT, corrected sinus node recovery

time, SACT, sinoatrial conduction time; SNEB, sinus

node entrance block.

conduction. Data from the latter studies are shown in the Table. All three patients had anatomically and hemodynamically normal hearts. Each patient

had

normal intra-atrial

A-V

nodal, and

His-Pur-kinje conducting intervals during sinus rhythm. In

patient 1, atrial pacing at a rate just slightly greater than the intrinsic sinus rate resulted in repetitive

Mobitz type

I

(Wenckebach) block. Because of this, a second electrode catheter was introduced and

positioned across the tricuspid valve so that a His

bundle electrogram could be recorded during atrial pacing. This showed that the A-V node was the site for the pacing-induced heart block. In patients 2 and 3, atrial pacing failed to unmask any evidence for abnormal cardiac conduction.

Each patient demonstrated electrophysiologic

ev-idence for sinus node dysfunction. The maximum corrected sinus node recovery time following atrial pacing was prolonged in all three patients.

Addi-tionally, patients 1 and 2 demonstrated evidence for

abnormal sinoatrial conduction. SACT was

pro-longed in patient 1 (270 msec) and could not be calculated in patient 2 as no reset responses could

be induced following even very early atrial extra-stimuli. This latter phenomenon indicated a failure

of

premature atrial impulses to penetrate the sinus

node

and

implied

sinoatrial entrance block.

In each case, intravenous atropine (0.01 mg/kg) during catheterization failed to increase signif-icantly the abnormally low resting heart rate.

During the initial hospitalization, each child re-ceived a permanent ventricular demand pacemaker.

All three patients have remained totally

asympto-matic since leaving the hospital.

DISCUSSION

Although SND in children and adolescents most

frequently results from cardiac surgery,

sympto-matic SND in the absence of organic heart disease

is being recognized with increasing frequency. Scott

et a!5 described six boys with dizzy spells, syncope, chest pain during exercise, and palpitations. In each case, structural cardiac disease was absent and ECG

suggested SND by demonstrating inappropriate bradycardia, periods of sinus arrest, or sinus node

exit block. Because of repeated syncope, two

chil-dren required treatment with ventricular pace-makers. Nordenberg and associates reported symp-tomatic SND in two sisters with structurally normal

hearts. Both had syncope and one child eventually required a permanent pacemaker. Unfortunately,

the diagnosis of SND in the above eight cases was

made solely on the basis of surface ECG tracings

and was not confirmed by electrophysiologic eval-uation. James et al’2 reported the sudden death of two healthy, athletic boys during strenous activity. At necropsy, the sinus node arteries in both children were narrowed from intimal proliferation and

me-dial hyperplasia and there were areas of nodal

fi-brosis and perinodal hemorrhage. ECGs were not

recorded in either patient before death, but it was concluded that death resulted, at least in part, from

disordered sinus node function.

The above cases document that symptomatic SND can occur in children with otherwise normal

hearts. Our three cases are unique in that

electro-physiologic evaluation proved that the presenting symptomatology and ECG findings were indeed due to disorders of sinus node automaticity and

sino-atrial conduction.

Of

additional

interest

is the large

number

of boys

among the reported children with symptomatic SND. The significance of this observation remains

unknown.

Most children with SND and structurally normal hearts are asymptomatic.”4 They are discovered

incidentally because of irregular cardiac rhythms or

abnormally slow heart rates. Children with

symp-tomatic SND usually are first seen with one or more

syncopal episodes. Although syncope is frequently

the result of neurologic or metabolic disorders,

syn-cope of cardiac origin is generally sudden and brief and leaves few, if any, permanent sequelae. Other

symptoms that should suggest the presence of SND

include dizziness, seizures, paresis, palpitations

(sec-ondary to tachyarrhythmias), and chest pain,

par-ticularly during or following exertion.

Electrocardiographically, SND presents with

in-appropriate sinus bradycardia for age, episodes of

sinus arrest, with or without a junctional escape

rhythm, or sinus node exit block.”4 The last

diag-nosis can be made easily using previous published criteria.’ Previously, most instances of bradycardia

occurring

in

athletic children have been regarded as

benign. In view of recent experience, the clinician

should carefully differentiate physiologic sinus

bradycardia from the pathologic variety that occurs

inappropriately and fails to respond in a normal

fashion to exercise and atropine.

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thor-ARTICLES 593

ough evaluation. In healthy children, submaximal

exercise and intravenous atropine (0.01 mg/kg)

in-crease

the

resting

sinus

rate

by at least

30%.1.5.13

Failure to respond appropriately to these interven-tions supports the diagnosis of SND. Particularly

helpful is 12-to 24-hour ambulatory monitoring as the ECG abnormalities diagnostic of SND are

fre-quently intermittent. Furthermore, Holter-type re-cordings may help to establish a correlation

be-tween clinical symptoms and ECG findings. If the

above studies support the diagnosis ofSND, cardiac

catheterization and invasive electrophysiologic evaluation should follow. These procedures will

de-lineate the mechanisms that underlie SND and will

help to determine whether structural heart disease and other electrophysiologic abnormalities are also present. Inasmuch as clinical SND results either from a disorder of impulse formation (decreased

sinus node automaticity) or impaired sino-atrial conduction (sinus node exit block),’4 one should

specifically look for both disorders. As was the case

in

patients 1 and 2, disorders of sinus node auto-maticity and sinoatrial conduction frequently

co-exist. Disorders of A-V conduction should also be

looked for because patients with SND seem to have a higher incidence ofthese problems.’5 This impres-sion is substantiated by our finding of an A-V node conduction abnormality in patient 1 and the finding

by James et &l12 of A-V node pathology in two children with sinus node abnormalities who died suddenly.

All children with symptomatic SND should be treated with a permanent pacemaker to prevent

syncope and sudden death. Inasmuch as atrial

pac-ing results in a normal A-V contraction sequence

(assuming normal

A-V

conduction), it is most

phys-iologic and provides the most optimal

cardiac

out-put. Right ventricular demand pacemakers, how-ever, continue to be used most frequently in

chil-then. Each of our three patients received a

trans-venous ventricular pacemaker. All had complete

disappearance of symptoms and have been able to

lead nearly normal lives.

This report is intended to stress that sympto-matic SND may occur in children of any age and in the absence ofstructural heart disease. Accordingly, SND should be considered and specifically investi-gated whenever a child presents with unexplained

dizziness or syncope and has an abnormal cardiac

rhythm.

REFERENCES

1. Yabek SM, Jarmakani JM: Sinus node dysfunction in

chil-then, adolescents and young adults. Pediatrics 61:593, 1978

2. Greenwood RD, Rosenthal A, Sloss LI, et al: Sick sinus

syndrome after surgery for congenital heart disease.

Circu-lation 52:208, 1975

3. El-Said GM, Gillette PC, Cooley DA, et al: Protection of the

sinus node in Mustard’s operation. Circulation 53:788, 1976 4. Kugler JD, Gillette PC, Mullins CE, et al: Sinoatrial con-duction in children An index of sinoatrial node function.

Circulation 59-.1266, 1979

5. Scott 0, Macartney FJ, Deverall PB: Sick sinus syndrome in children. Arch Die Child 51:100, 1976

6. Nordenberg A, Varghese PJ, Nugent EW: Spectrum ofsinus node dysfunction two siblings. Am Heart J 91:507, 1976 7. ROberts N1(, Gillette PC: Electrophysiologic study of the

conduction system in normal children. Pediatrics 60:858, 1977

8. Brodaky SJ, Mirowski M, Krovetz U, et al: Recordings of His bundle and other conduction tissue potentials in

chil-dren.J Pediat,r 79:61, 1971

9. Yabek SM, Jarmakani JM, ROberts N: Postoperative trifas-cicular block complicating tetralogy of Fallot repair.

Pedi-atrics 58:236, 1976

10. Yabek SM, Jarmakani JM, Roberts NK: Sinus node function in children: Factors influencing its evaluation. Circulation

53:28, 1976

11. Yabek SM: Evaluation of sinus node automaticity and si-noatrial conduction in children with normal and abnormal

sinus node function. Clin Cardiol 1:136, 1978

12. James TN, Froggatt P, Marshal! TK: Sudden death in young athletes. Ann Intern Med 67:1013, 1967

13. Dauchot P, Gravenstein JS: Effects of atropine on the

elec-trocardiogram indifferent age groups. Clin Pharmacol Ther

12:274, 1971

14. Jordan JL, Yamaguchi I, Mandel WJ: Studies in the

mech-anism of sinus node dysfunction in the sick sinus syndrome. Circulation 57:217, 1978

15. Rosen KM, Loeb HS, Sinno MZ, et al: Cardiac conduction

in patients with symptomatic sinus node disease. Circulation

43:836,1971

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1982;69;590

Pediatrics

Steven M. Yabek, Terrence Dillon, William Berman, Jr and Colleen J. Niland

Symptomatic Sinus Node Dysfunction in Children Without Structural Heart Disease

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