872

Short PR Interval and Narrow QRS Complex Associated WithPheochromocytoma: Electrophysiologic Observations

JACC Vol. 3. No.3March 1984:872-5

SHOE! K. HUANG, MD, FACC,* MICHAEL J. ROSENBERG, MD, PABLO DENES, MD, FACC

Chicago, Illinois

A patient with a short (0.10 second) PR interval, narrowQRS complex and palpitation is described. Electro­physiologic studies demonstrated the presence of accel­erated atrioventricular (AV) nodal conduction. Subse­quently, a pheochromocytoma was found. Surgical

In 1952, Lown, Ganong and Levine (1) described a syn­drome of short PR interval, normal QRS complexes andparoxysmal rapid heart action. There has been considerablecontroversy in regard to the mechanism of the short PRinterval and the types of tachyarrhythmias associated withthis syndrome. A short PR interval has been described inpatients with chronic lung disease (2), acute myocardialinfarction (3), endocrine disorders (hyperthyroidism andCushing's disease) (4), and glycogen storage disease (Pompe'sdisease) (5). Other causes of short PR interval include ab­breviated atrioventricular (AV) conduction noted in childrenand young adults, ectopic impulse formation (atria, coronarysinus or AV junction) and erroneous measurement utilizingonly one or two electrocardiographic leads (6).

Electrocardiographic changes are frequent in patients withpheochromocytoma (7); these consist of left ventricular hy­pertrophy, T wave changes and sinus tachycardia. Occa­sionally, changes suggestive of acute myocardial damage,including marked and diffuse T wave changes and transientST segment elevation or depression, have been reported(8,9). The acute changes are usually transient and revert tonormal after removal of the tumor or after pharmacologicblockade (10).

In the present report, we describe a patient who had ashort PR interval and narrow QRS complexes. Electro­physiologic studies demonstrated the presence of enhancedAV nodal conduction. Subsequently, she was found to have

From the Section of Cardiology, Department of Medicine, Rush-Pres­byterian-St. Luke's Medical Center, Rush Medical College, Chicago, Il­linois. Manuscript received August 8,1983, accepted September 30,1983.

*Present address and address for reprints: Shoei K. Huang, MD, Sec­tion of Cardiology, Department of Medicine, University of Arizona HealthSciences Center, Tucson, Arizona 85724.

© J984 by the American College of Cardiology

removal of the tumor resulted in normalization of thePR interval. These findings suggest that the short PRinterval and the accelerated AV nodal conduction weredue to the effect of excess catecholamines on the AVconduction system.

a left adrenal pheochromocytoma. After resection of thistumor, the PR interval returned to normal.

Case ReportThe patient, a 45 year old black woman, had a history

of labile hypertension, palpitation and atypical chest pain.On February 26, 1981, she presented to the emergency roomof a local hospital with the chief complaints of severe chestpain and dizziness. Her blood pressure was 2341140 mmHg. After admission, she had a cardiopulmonary arrest fromwhich she was successfully resuscitated. A diagnosis ofacute myocardial infarction was made based on markedelevation of cardiac serum enzymes and ST-T wave changes.She was discharged on March 28. An electrocardiogramtaken on June 25 (Fig. lA) showed a sinus rate of 75/min,a short PR interval (0.10 second) and an otherwise normaltracing.

On August 23, she was admitted to our centerfor cardiaccatheterization and electrophysiologic study. The bloodpressure was 1501100 mm Hg in both the supine and sittingpositions. Cardiac examination was normal. Chest X-rayfilm showed a normal heart size. The electrocardiogramshowed a short PR interval and was unchanged from herprevious electrocardiogram. Complete blood count, urinal­ysis and blood chemistry determinations including thyroidfunction studies were normal. She had a maximal treadmillexercise test that did not show electrocardiographic evidenceof ischemia; there were no arrhythmias. A 24 hour Holterelectrocardiographic recording demonstrated normal sinusrhythm with occasional ventricular premature complexesand a six beat run of ventricular tachycardia at a rate of 110to 130 beats/min. Her symptoms of palpitation and chestpain did not correlate with the presence of arrhythmias. The

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JACC Vol. 3, No, 3March 1984:872-5

HUANG ET AL.SHORT PR INTERVAL AND PHEOCHROMOCYTOMA

873

Figure 1. Standard 12 lead electrocardiogramstaken before (A) and after (B) resection of pheo­chromocytoma, The longest PR interval was 0,08second in A and 0.16 second in B,

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Figure 2. Demonstration of I: I AV nodal conduction at an atrialpacing cycle length of 280 ms with AH increment less than 100ms (from 60 ms during basic sinus rhythm to 110 ms) and sinusnode recovery time of 540 ms, Both the AH interval (60 ms)during sinus rhythm and the HV interval (35 ms) were borderlineshort, A = atrial activity; H = His bundle activity; HRA = highright atrium; HBE = His bundle electrogram; RVA = right ven­tricular apex; S = pacemaker stimulus artifact; V = ventricularactivity, Interval between time markers equals 1,000 ms, The paperspeed was 100 mmls,

two-dimensional and M-mode echocardiograms were nor­mal as were the results of cardiac catheterization and coro­nary angiography,

Electrophysiologic study was performed using previouslydescribed methods (11) because of the history of cardiacarrest and recurrent palpitation, All cardiac medications werediscontinued for 48 hours before the study, At the time ofelectrophysiologic testing, her sinus rate was 92 beats/min.The AH interval was 60 ms, the HV interval 35 ms and the

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874 HUANG ET AL.SHORT PR INTERVAL AND PHEOCHROMOCYTOMA

JACC Vol. 3. No.3March 1984:872-5

PA interval 25 ms. Incremental atrial pacing from the highright atrium (cycle length from 600 to 300 ms) demonstrateda gradual but small increment in AH interval from 60 to110 ms (A AH = 50 ms). At an atrial pacing cycle lengthof 280 ms (rate 214 beats/min), I: I AV nodal conductionwas still present (Fig. 2). The AV nodal effective «260ms) and functional «300 ms) refractory periods at thedriven pacing cycle of 500 ms were short. Similarly, I: Iretrograde ventriculoatrial (VA) conduction was present upto a ventricular pacing rate of 200 beats/min (cycle length300 ms) with gradual prolongation of VA interval. Therewas no inducible supraventricular or ventricular tachycardiaby programmed single and double extrastimulus technique.

The possibility ofpheochromocytoma as a cause for thepatient's hypertension and symptoms was suggested. Thisdiagnosis was substantiated by the elevation of urinary cate­cholamines (675 JLg/24 hours, normal 38 to 100), meta­nephrine (1.9 mg124 hours, normal 0.3 to 0.9) and vanil­lylmandelic acid (VMA) (8.4 mg124 hours, normal 0.7 to6.8). Subsequently an abdominal aortic angiogram dem­onstrated a 5 to 6 cm circumscribed hypervascular mass inthe left suprarenal region (Fig. 3). Two months later, a leftadrenal pheochromocytoma weighing 50 g was removed.

An electrocardiogram taken I week after the operationas well as 4 months later while the patient was not takingany cardiac medication showed a normal PR interval (0.16second) (Fig. IB). The patient had no further complaintsof palpitation or chest pain. Blood pressure returned to nor­mal. The patient denied consent for repeat electrophysio­logic study. The two follow-up 24 hour Holter monitorrecordings did not show any ectopic rhythm.

DiscussionDisorders associated with short PR interval and nar·

row QRS. In their original article, Lown, Ganong and Lev­ine (1) commented on the possible relation between theirfindings and the endocrine system (particularly the adrenals)and autonomic nervous system. They quoted several en­docrine disorders that may affect the PR interval. Hyper­thyroidism and Cushing's syndrome are associated with shortPR interval and Addison's disease is occasionally associatedwith first degree atrioventricular (AV) block. They alsodescribed several other conditions (neurosis, emotional in­stability, hypothalamic overfunction, standing position) as­sociated with increased sympathetic tone that may result inshortening of the PR interval and paroxysmal rapid heartaction. It is surprising that pheochromocytoma has not beenpreviously associated with this syndrome.

Electrophysiologic studies. Many electrophysiologicstudies (12-19) have been reported in subjects with a shortPR interval and narrow QRS complexes, with or withoutdocumented tachyarrhythmias. Most studies (12-17) foundthat the short PR interval reflects a shortening of the AH

interval, although in some (17-19) there was a shorteningof the HV interval. A short PR interval associated with ashort AH interval may be explained by the presence of a"partial" AV nodal bypass (James fibers) (20), a total AVnodal bypass (Brechenmacher tract) (21), a small or im­mature AV node or an intranodal "fast pathway" (22).Gallagher et al. (23) introduced the term "enhanced AVnodal conduction" to describe the following electrophysi­ologic phenomena: I) an AH interval during sinus rhythmof 60 ms or less; 2) I: I atrio-His bundle conduction duringhigh right atrial pacing up to a cycle length of 300 ms, and3) an increment in the AH interval that does not exceed 100ms with rapid atrial pacing up to a cycle length of 300 ms.

Present case. We describe a patient who had pheo­chromocytoma and a short PR interval, narrow QRS com­plex and episodes of palpitation. Electrophysiologic studiesbefore surgery demonstrated a short AH interval (60 ms)during sinus rhythm, with an increment of only 50 ms inthe AH interval during rapid atrial pacing, and I: I AVconduction at a paced cycle length of 280 ms. These findingsfulfill the criteria for the presence of enhanced AV nodalconduction. We also demonstrated short AV nodal refrac-

Figure 3. Abdominal aortic angiogram demonstrating a hyper­vascular mass approximately 5 to 6 em in the left suprarenal region(delineated by solid arrows).

JACC Vol. 3, No.3March 1984:872-5

HUANG ET AL.SHORT PR INTERVAL AND PHEOCHROMOCYTOMA

875

tory periods. There was excellent retrograde ventriculoatrial(VA) conduction through the AV node (I: I VA conductionat a ventricular pacing rate of 200/min). After resection ofthe tumor, the PR interval returned to normal and the symp­toms subsided. These observations confirm the role of cate­cholamines, particularly epinephrine and norepinephrine, inthe genesis of short PR interval and enhanced AV nodalconduction.

The short PR interval in our patient was not dependenton the presence of sinus tachycardia, but was recorded dur­ing normal sinus rates. We hypothesize that chronic sym­pathetic hyperstimulation resulted in a short PR intervalsecondary to enhanced AV nodal conduction. This accel­erated AV nodal conduction was not accompanied by aconcomitant chronic increase in sinus nodal discharge rate,suggesting a differential adaptation process between the sinusand AV nodes to chronic catecholamine excess. Resectionof the pheochromocytoma resulted in normalization of AVconduction time.

We deeply appreciate the secretarial assistance of Cheryl Bahrychuk.

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