Heart Journal, Atrial fibrillation in patients idiopathic

British Heart_Journal, I970) 32, 652-659.

Atrial fibrillation in patients with idiopathichypertrophic subaortic stenosis

D. Luke Glancy, Kevin P. O'Brien', Herman K. Gold, and Stephen E. EpsteinFrom the Cardiology Branch, National Heart and Lung Institute, Bethesda, Maryland, U.S.A.

Atrial fibrillation occurred in I6 (io%) of I67 patients with idiopathic hypertrophic subaorticstenosis. The clinical and haemodynamic findings in these I6 patients are presented.

Atrial fibrillation appeared late in the course of the disease, and its occurrence did not seemto be related to the severity of left ventricular outflow obstruction or to the amount of associatedmitral regurgitation. In each patient the onset of the arrhythmia was accompanied by severeclinical deterioration, which often necessitated urgent medical treatment. Digitalis was adminis-tered to all I6 patients with subsequent clinical improvement in i5. Electrical cardioversion wasuniformly successful in restoring sinus rhythm, but atrialfibrillation usually recurred. In each of8 patients catheterized during atrial fibillation, cardiac output was strikingly low (average,I. 9 l./min./m.2), whereas it was normal in xo of '3 patients studied in sinus rhythm. The durationoffollow-up from the onset of atrial fibrillation has averaged 5 years, and 3 of the I6 patientshave died of causes related to their heart disease. Four have suffered cerebral emboli. Only 5patients are now in stable sinus rhythm; in general, they are less symptomatic than the patientsin whom atrial fibrillation has recurred.

The unusually severe clinical deterioration at the onset of atrialfibrillation and the low cardiacoutput measured during catheterization are thought to be related to the loss of the importantcontribution to ventricular filling of atrial systole in patients with poorly compliant ventricles,and to the effect of an irregular ventricular rhythm on the variable nature of the outflowobstruction.

Atrial fibrillation was initially believed tooccur rarely in patients with idiopathic hyper-trophic subaortic stenosis (Hancock and El-dridge, I966; Lannigan, I965; Hollister andGoodwin, 1963). As experience with this dis-order grew, however, it became apparent thatthis disturbance in rhythm was not uncom-mon. In a previous review from this insti-tution, Frank and Braunwald (I968) foundthat atrial fibrillation was present in I0 of 123patients, and since then we have studied 6additional patients with idiopathic hyper-trophic subaortic stenosis and atrial fibrilla-tion. Thus, of the I67 patients with thisanomaly who have now been studied at theNational Heart and Lung Institute, i6 havedeveloped atrial fibrillation during the courseof their illness, and in most of them its onsetappeared to represent an ominous milestonein the course of the disease. The presentinvestigation was undertaken in order to

Received 2 February I970.I Present address: Greenlane Hospital, Auckland, NewZealand.

characterize the haemodynamic findings inpatients with hypertrophic stenosis and atrialfibrillation, and to determine the course ofthe disease once atrial fibrillation appeared.

Subjects and methodsIn each patient the diagnosis was established bycardiac catheterization (Braunwald et al., I964),and atrial fibrillation was documented electro-cardiographically. In each of the patients whounderwent operative treatment, the initial bout ofatrial fibrillation preceded the operation. Patientswhose only episode of atrial fibrillation was a tran-sient post-operative one have been excluded fromthe study.

ResultsA summary of the clinical information con-cerning the i6 patients is presented in Table i.The average age of the Io men and 6 womenat the onset of atrial fibrillation was 40 years(range, i8 to 58 years). Paroxysmal atrialfibrillation led to the recognition of heartdisease in one patient (M.K.); in each of theother iS patients a praecordial murmur had

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Atrial fibrillation in idiopathic hypertrophic subaortic stenosis 653

TABLE I Clincal summary of patients with idiopathic hypertrophic subaortic stenosis (IHSS)and atrial fibrillation

Patient Sex Age No. of Clinical No. of Operation Follow-up Current statusepisodes deterioration electrical for IHSS from onset

When cardiac At onset of AF with AF* cardio- of AFdisease noted of AF versions (yr.)

P.K. F I2 i8 Several (Pre-S) (CHF) 0 0 8 Died in AF of CHF, age 26M.H. F 28 41 5 (H,D, Pre-S) 0 0 I Died suddenly, age 42P.S. M 9 20 Many (Pre-S) (CHF) I 0 I3 Died in AF of multiple systemic

emboli, age 33J.K. M 28 52 Many (S, CHF) 2 0 5 Died in AF and CHF of gastric

carcinoma, age 57R.P. M i8 42 3 (CHF) 2 0 5 AF, Class IIItR.S. M I5 29 12 (S,D) (LVF) (A) I0 Age 3I 4 AF, Class IIW.D. M 2I 44 Many (CHF) (H) (A) Io Age 44 5 AF, Class IIW.Q. M I7 56 Many (A,D) (S) (CHF) I Age 59 4 AF, Class IIIS.B. F i6 25 6 (Fa) 5 0 4 AFP.Sc. F I4 40 Many (Fa, D) o 0 7 Paroxysmal AF

Class I (NSR), Class II (AF)M.K. F 50 50 Many (HA) (H,C) (CHF) o 0 6 Paroxysmal AF

Class II (NSR), Class IV (AF)M.W. F 23 38 I (H, S, POe) I 0 2 NSR, hemiparesis due to cerebral

embolusJ.L. M 29 42 2 (HA) (CHF) I Age 42 7 NSR, Class IIW.A. M 32 58 2 (POe,CHF) I Age 58 I NSR, Class ID.E. M 35 43 2 (D) 2 0 4 NSR, Class IIG.E. M 35 47 3 (A,D) 0 0 5 NSR, Class II

*Those signs and symptoms which developed during the same episode(s) of AF have been enclosed together within parentheses.t Functional capacity, New York Heart Association classification. Two patients could not be classified because of mental retardation (S.B.)and hemiparesis (M.W.).A=angina; AF=atrial fibrillation; C= convulsions; CHF= congestive heart failure; D = dyspnoea; Fa=fatigue; H=hypotension; LVF=left ventricular failure; NSR=normal sinus rhythm; POe=pulmonary oedema; S=syncope.

been noted 6 to 39 years (average, i8 years)before the onset of atrial fibrillation. Of thei6 patients, i5 have had more than one epi-sode of atrial fibrillation.Three of the i6 patients were sibs (P.K.,

P.S., and M.W.), and 4 others had a familyhistory of idiopathic hypertrophic subaorticstenosis. One patient (J.K.) had a family his-tory of atrial fibrillation but no family historyof hypertrophic subaortic stenosis.

Clinical deterioration with onset ofatrialfibrillation All i6 patients experienced adecrease in exercise tolerance with the onsetof atrial fibrillation. In addition, more strikingmanifestations of cardiac dysfunction (Tablei) occurred with one or more episodes of atrialfibrillation in each of 13 patients: cardiacfailure in i i, syncope or presyncope in 7,angina pectoris in 6, documented systemicarterial hypotension in 5, and a generalizedseizure in one. In 9 of the i i patients withcardiac failure, signs of both right and leftventricular failure were present. In 7 patientsclinical deterioration was dramatic and re-quired urgent treatment.

Response to treatment Each patient re-ceived digitalis, usually in combination with

a diuretic drug, soon after the onset of atrialfibrillation, and distinct clinical improvementwas noted after the institution of therapy inall but one patient (M.W.). She was not bene-fited by digitalis, vasopressors, and proprano-lol, and systemic arterial hypotension dis-appeared only after electrical cardioversion.Eight patients reverted to sinus rhythm whilereceiving digitalis. All, however, subsequentlyreturned to atrial fibrillation. One (G.E.) ofthe 8 is now in sinus rhythm after a thirdreversion associated with the administrationof digitalis.

Electrical cardioversion was attempted ini i patients and restored sinus rhythm in each.However, atrial fibrillation recurred from iday to 8 months later (average, 2 months) in8 of the ii, despite maintenance doses ofquinidine. Six of these 8 underwent additionalcardioversions; though one patient (D.E.) hasremained in sinus rhythm for 4 years after asecond cardioversion, atrial fibrillation soonrecurred in the other 5.

Systemic embolism Systemic emboli oc-curred in 4 of the i6 patients. In one (P.S.),multiple systemic emboli caused death I7 daysafter successful cardioversion and I5 daysafter cardiac catheterization. Seven days be-

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654 Glancy, O'Brien, Gold, and Epstein

FIG. I Postero-anterior (left) and lateral (right) chest x-rays in patient M.W. Both the leftatrium and the left ventricle are enlarged.

fore death atrial fibrillation had recurred, and2 days before death this patient had suffereda major cerebrovascular accident. At necropsyan antemortem thrombus was found in theapex of the left ventricle. His sister (M.W.)experienced a cerebral embolus 4 days afterthe onset of atrial fibrillation and one dayafter electrical cardioversion. She remainslimited by hemiparesis. Six years before atrialfibrillation was documented electrocardio-graphically, W.D. suffered a cerebral embolus,which probably occurred during a bout ofparoxysmal atrial fibrillation. P.Sc. had acerebral embolus one year after the onset ofatrial fibrillation. Both of these last 2 patientsmade complete recoveries. During a paroxysmof atrial fibrillation one additional patient(W.Q.) developed syncope and a transienthemiparesis that may have been due to eitheran embolus or poor cerebral perfusion duringthe arrhythmia.

Radiological features The plain chest x-ray showed moderate to severe left atrialenlargement in I3 of the i6 patients (Fig. I).The 3 patients without left atrial enlargementhad paroxysmal atrial fibrillation.A satisfactory left ventricular angiogram

was available for review in I2 patients. Theangiogram showed no mitral regurgitation in2 patients, mild regurgitation in 4, and con-

siderable regurgitation in 6 (Fig. 2). In manypatients the association of mitral regurgitation,atrial fibrillation, and radiological evidence ofleft atrial enlargement suggested the diagnosisof rheumatic mitral valve disease.

Haemodynamic data (Table 2) Eightpatients were in sinus rhythm when cardiaccatheterization was performed and 3 were inatrial fibrillation. The remaining 5 patientsunderwent one catheterization while in sinusrhythm and another while in atrial fibrillation.In addition, in 4 ofthese last 5 patients haemo-dynamic measurements were made duringboth atrial fibrillation and sinus rhythm at thesame catheterization.

Cardiac output was low ( < 2-5 l./min../m.2)in each of 8 patients studied during atrialfibrillation, whereas it was normal in IO of I3studied in sinus rhythm. In each of the 5patients in atrial fibrillation during one studyand in sinus rhythm during another, cardiacoutput was higher during sinus rhythm.Moreover, cardiac output was measured in 3of the 4 patients who reverted from atrialfibrillation to sinus rhythm during catheter-ization, and in each the output was higherafter reversion. In the one patient (W.D.)studied in atrial fibrillation after operation,cardiac output was lower (2-2 l./min./m.2)than during a pre-operative study in sinus

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FIG. 2 Antero-posterior (left) and lateral (right) x-rays. After the injection of contrast materialinto the left ventricle (LV) of patient M.W., mitral regurgitation produces denseopacification of the large left atrium (LA). The wall of the left ventricle is hypertrophied, andthe configuration of its cavity is typical of idiopathic hypertrophic subaortic stenosis. Theascending aorta (Ao.) is of normal size.

rhythm, despite post-operative absence of apressure gradient across the left ventricularoutflow tract. In the 2 patients (J.L. and R.S.)studied in sinus rhythm after operation, car-diac output was normal.

Resting left ventricular outflow gradientswere recorded during at least one catheteriza-tion in I5 of the i6 patients, and tended to beslightly larger in patients studied during sinusrhythm. In 5 patients, including 3 of the 4who subsequently died, the peak systolicgradient was less than 30 mm. Hg. Left ven-tricular end-diastolic pressure was abnormal( > I2 mm. Hg) on at least one occasion in allbut 4 patients, 3 of whom were studied duringatrial fibrillation. Though left ventricular end-diastolic pressures were on the average slightlyhigher in patients studied during sinusrhythm, left atrial mean pressure was approx-imately the same in patients with sinusrhythm as in those with atrial fibrillation. Leftatrial mean pressure was abnormally high(> I2 mm. Hg) in 10 of I4 patients.

Long-term clinical course The durationof follow-up from the onset of atrial fibrilla-

tion has ranged from I to 13 years (average,5 years). During the period of observation, 3of the i6 patients died from causes related totheir heart disease: one (P.S.) of multiple sys-temic emboli 13 years after the initial onset ofatrial fibrillation; his sister (P.K.) of conges-tive heart failure 8 years after fibrillation be-gan; and a third patient (M.H.) suddenly oneyear after the development of paroxysmalatrial fibrillation. In a fourth patient (J.K.),atrial fibrillation recurred 6 months after hissecond electrical cardioversion and was associ-ated with the development of congestive heartfailure, but death resulted from gastriccarcinoma.

Five patients underwent left ventricularmyotomy and/or myectomy (Morrow et al.,I968), were cardioverted after operation, andimproved clinically. Though atrial fibrillationrecurred in 3 of them, in each the arrhythmiahas been better tolerated than it was beforeoperation.

Seven patients who did not undergo opera-tion have survived. Of the 3 now in sinusrhythm, 2 are in functional Class II: one(D.E.), whose only 2 episodes of atrial fibrilla-

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TABLE 2 Haemodynamic and angiographic findings

Patient Age Cardiac Ventricular Resting LV LVEDP LA mean CI Mitral(yr.) rhythm rate outflow (mm. Hg) pressure (l./min./m.') regurgitation

(beats/min.) gradient (mm. Hg) on LV(mm. Hg) angiogram

J.L. 42 NSR 79 I33 26 - 2-9M.K. 5I NSR 85 0 20 io PAW 3-5 NoneP.Sc. 43 NSR 78 53 I4 I5 2-8 NoneG.E. 49 NSR 70 20 12 6 3-3 MildW.A. 58 NSR 56 55 22 14 2-1 MildD.E. 37 NSR 60 90 15 20 2-2M.W. 32 NSR go 55 25 I2 2.7 ConsiderableW.D. 42 NSR 8o 75 I5 2.7 ConsiderableW.Q. 59 AF 70 0-75 I0 I4 i-6 ConsiderableJ.K. 56 AF 96 0-20 4 5 I-8P.K. 25 AF 8o 10 Io II8 -R.P. 44 AF (NSR) 70 (69) 80 i8 i8 (I5) 21I

45 NSR 63 I07 37 24 2-8 ConsiderableS.B. I9 NSR 105 70 12 15 PAW 3-7 -

25 AF (NSR) ioo (90) 80 (9o) I3 (i6) 17 PAW 2-I (2-9) MildM.H. 40 NSR I02 90 25 I9 4-0 Considerable

41 AF I05 o-85 i8 22 i-8R.S. 29 AF (NSR) 90 (79) 50-IOO (85) 17 (I7) i8 2-2 (2-4) Considerable

30 NSR 68 53 I7 i8 2-5P.S. 26 AF (NSR) I46 (9°) (30) (26) (i8) I-3 (2-I) (Mild)

33 NSR 60 0 26 22 PAW 2-0 Mild

AF=atrial fibrillation; CI= cardiac index; LA=left atrial; LV=left ventricular; LVEDP =left ventricularend-diastolic pressure; NSR=normal sinus rhythm; PAW=pulmonary arterial wedge pressure; ( )=dataobtained during the same catheterization following electrical cardioversion of long-standing AF to NSR,except for patient P.S. who developed a paroxysm of AF during catheterization and who reverted withouabain.

tion occurred in association with uretero-lithotomy, has remained in sinus rhythm for4 years after a second cardioversion; the other(G.E.) reverted from atrial fibrillation on 3occasions after the administration of digitalisand has now been in sinus rhythm for 4 years.The third patient (M.W.) has been in sinusrhythm for 2 years after electrical cardiover-sion, but remains limited by hemiparesis.Two patients have paroxysms of atrial fibril-lation during which they symptomaticallydeteriorate, and 2 are continuously in atrialfibrillation. One (R.P.) of the latter is in ClassIII, and in the other (S.B.) functional capacitycannot be adequately assessed because ofmental retardation.

Thus, of the 9 patients with persistent atrialfibrillation, 4 have died and only 2, both ofwhomhavehadoperations foridiopathichyper-trophic subaortic stenosis, are in functionalClass II. In contrast, 4 of the 5 patients nowin sinus rhythm are in Class I or I I, and the fifthpatientis limited byhemiparesis. The2 patientswith paroxysmal atrial fibrillation do well insinus rhythm but deteriorate symptomaticallywith episodes of the arrhythmia. All but onepatient (M.W.) are currently being treated withdrugs. Each of the 5 patients in stable atrialfibrillation receives digitalis; 2 are also takingdiuretics, and 3, propranolol. Among the 7

patients with sinus rhythm or paroxysmalatrial fibrillation, 4 are receiving quinidine,3 digitalis, 3 propranolol, and i diuretics.

DiscussionThe results of this investigation show that theonset of atrial fibrillation in patients with idio-pathic hypertrophic subaortic stenosis is oftenassociated with obvious clinical deteriorationand an increased risk of systemic emboli. Themechanism responsible for the onset of atrialfibrillation in these patients is not clear. Itdoes not appear to be related to the severityof left ventricular outflow obstruction, leftventricular end-diastolic pressure, or leftatrial pressure. Though the majority ofpatients had mitral regurgitation, 2 did not.Furthermore, mitral regurgitation occurs fre-quently in patients with idiopathic hyper-trophic subaortic stenosis and sinus rhythm(Simon, Ross, and Gault, I967). Perhaps thebest correlation can be made with left atrialsize. Of the i6 patients with atrial fibrillation,I3 had moderate to severe enlargement of theleft atrium. Moreover, only paroxysmal boutsof the arrhythmia occurred in patients with-out left atrial enlargement. Atrial fibrillationdevelops relatively late in the course of sub-aortic stenosis (average age at onset, 40 years;average duration of known heart disease, i6

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years), and therefore may also be related toprogression of the basic myocardial disease.Once present, however, the arrhythmia in itselfseems to cause further clinical deterioration.The onset of atrial fibrillation leads to an

increase in symptoms in patients with manytypes of heart disease, but the clinical deterior-ation observed in these patients with idiopa-thic hypertrophic subaortic stenosis wasunusually striking. Several physiologicalmechanisms may have been responsible forthis. First, atrial systole contributes signifi-cantly to the filling of hypertrophied andpoorly compliant ventricles (Burchell, I964;Braunwald, I964), and the loss of atrial systoledecreases stroke output on the basis of theStarling mechanism. Very low cardiac out-puts were seen in the 8 patients studied duringatrial fibrillation, despite left atrial mean pres-sures that were high in 7 of them. For left ven-tricular stroke volume to have been main-tained, left atrial mean pressure would havehad to rise even higher.

Second, atrial fibrillation causes large vari-ations in stroke volume and thus arterial pres-sure. The beat following a short diastole ejectslittle or no blood into the aorta, resulting in alow systemic arterial pressure (Fig. 3). Inpatients in atrial fibrillation without left ven-tricular outflow obstruction or with fixedobstruction, arterial pressure is restored bythe increased left ventricular stroke volumeand pulse pressure that result from the longdiastole that usually follows (Fig. 4, above). Inpatients with idiopathic hypertrophic sub-aortic stenosis, however, this compensatoryincrease in stroke volume probably does notoccur. Instead, a long diastole is followed bya fall in arterial pulse pressure and a furtherfall in arterial systolic pressure (Fig. 4, below).The change in arterial pulse contour after along diastole suggests that this response iscaused by an increase in the degree of obstruc-tion to left ventricular ejection. This conclusionis also suggested by studies which have shownthat interventions that raise arterial pressuredecrease the degree of obstruction in patientswith idiopathic hypertrophic subaortic steno-sis, while interventions that lower arterialpressure produce the opposite effect (Braun-wald et al., I964). The low distending pressureafter a long diastole presumably causes thewalls of the hypertrophied outflow tract toapproximate each other more closely, andthereby increases the degree of obstruction(Lewis et al., I965; Wigle et al., I963). Inaddition, the low arterial pressure present atthe end of a long diastole may cause a baro-receptor mediated increase in sympatheticstimulation to the heart, a change known to

increase outflow tract obstruction in patientswith idiopathic hypertrophic subaortic steno-sis.

Finally, in these patients any increase in theinotropic state of the myocardium may in-crease left ventricular outflow obstruction. Instrips of mammalian myocardium, Koch-Weser and Blinks (I963) have shown an in-crease in contractility after an early contrac-tion (postextrasystolic potentiation), after along interval between contractions (restpotentiation), and after a series of rapidlyoccurring contractions (poststimulation po-tentiation). Early beats, long diastolic inter-vals, runs of rapidly occurring beats, andvarious combinations of these are the hall-marks of atrial fibrillation, and indeed,Edmands, Greenspan, and Fisch (I969) havefound beat-to-beat changes in ventricularinotropic state with the varying cycle lengthsof atrial fibrillation. These transient increasesin ventricular contractility seen in atrial fibril-lation might well be accompanied by an in-

FIG. 3 Simultaneous electrocardiogram(ECG) and left ventricular (LV) and brachialarterial (BA) pressure tracings in patient J.K.The cardiac rhythm is atrial fibrillation. Onlya small pressure gradient is present between theleft ventricle and the brachial artery on mostbeats. After a long diastole, however, the pres-sure gradient increases considerably, the bra-chial arterial pulse assumes the bifid configura-tion typical of idiopathic hypertrophicsubaortic stenosis, and the pulse pressure in thebrachial artery decreases. Consequently,brachial arterial pressure is not restored by thebeat after a long diastole.

200r ECG

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J.K. 06-24-65 F- I sec --

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crease in left ventricular outflow obstructionin patients with idiopathic hypertrophic sub-aortic stenosis, and thus lead to symptomaticdeterioration.

Digitalis, in combination with diuretics,resulted in symptomatic improvement in allbut one of the patients with atrial fibrillation.This at first seems paradoxical, since digitalisincreases the degree of obstruction in thesepatients in normal sinus rhythm (Braunwaldet al., I964). Such an increase in obstructionduring sinus rhythm was documented afteracute digitalization in the catheterizationlaboratory in patient P.S. When he was inatrial fibrillation, however, the administrationof digitalis was associated with clinical im-provement. Thus, it appears likely that thesalutary effects observed in patients with idio-pathic hypertrophic subaortic stenosis andatrial fibrillation after the administration ofdigitalis result from a slower and more regularventricular response, rather than from an in-crease in myocardial contractility.Though the onset and persistence of atrial

fibrillation were associated with obvious symp-tomatic deterioration, the restoration of sinusrhythm was always associated with clinicalimprovement, and those patients able tomaintain a normal rhythm have fared muchbetter than those who returned to atrial fibril-lation. Unfortunately, in most patients sinusrhythm could be restored only transiently.Atrial fibrillation recurred after the firstelectrical cardioversion in 8 of i i patientsand after additional cardioversions in 5 of 6patients. In addition, cerebral emboli occurredsoon after electrical cardioversion in 2 pa-tients, causing death in one and permanenthemiparesis in the other.

ReferencesBraunwald, E. (I964). Symposium on cardiac arrhyth-

mias. Introduction, with comments on the hemo-dynamic significance of atrial systole. AmericanJournal of Medicine, 37, 665.

-, Lambrew, C. T., Rockoff, S. D., Ross, J., Jr.,and Morrow, A. G. (I964). Idiopathic hypertrophicsubaortic stenosis. I. A description of the diseasebased upon an analysis of 64 patients. Circulation,29 and 30, SuppI. 4, p. 3.

Burchell, H. B. (I964). A clinical appraisal of atrialtransport function. Lancet, I, 775.

Edmands, R. E., Greenspan, K., and Fisch, C. (I969).Ventricular function in atrial fibrillation: A variableinotropic state. (Abstract.) American Journal ofCardiology, 23, IIO.

Frank, S., and Braunwald, E. (1968). Idiopathic hyper-trophic subaortic stenosis. Clinical analysis of 126patients with emphasis on the natural history.Circulation, 37, 759.

Hancock, E. W., and Eldridge, F. (I966). Muscularsubaortic stenosis: Reversibility with varying car-diac cycle length. American Journal of Cardiology,I8, 5I5.

E

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ai

FIG. 4 Simultaneous electrocardiogram(ECG) and left ventricular (LV) and brachialarterial (BA) pressure tracings in patient V.H.with valvular aortic stenosis (above) and inpatient R.P. with idiopathic hypertrophic sub-aortic stenosis (below). Both patients haveatrial fibrillation. In the patient with valvularstenosis brachial arterial pulse and systolicpressures increase after a long diastole (arrow)despite a slight increase in the systolic pressuregradient between the left ventricle and brachialartery. In contrast, in the patient with idio-pathic hypertrophic subaortic stenosis brachialarterial pulse pressure does not increase aftera long diastole (arrow), and the systolic pres-sure falls. In addition, after a long diastole alarge pressure gradient develops between theleft ventricle and brachial artery, and thebrachial arterial pulse becomes more bifid.

Hollister, R. M., and Goodwin, J. F. (I963). Theelectrocardiogram in cardiomyopathy. British Heart'ournal, 25, 357.

Koch-Weser, J., and Blinks, J. R. (I963). The influ-ence of the interval between beats on myocardialcontractlity. Pharmacological Reviews, IS, 6oi.

Lannigan, R. (I965). Hypertrophic subaortic stenosiswith myocardial fibre degeneration. British HeartJ7ournal, 27, 772.

Lewis, R. P., Bristow, J. D., Farrehi, C., Kloster, F. E.,and Griswold, H. E. (I965). Idiopathic left ven-tricular hypertrophy. A hemodynamic reappraisal.American Journal of Medicine, 38, 842.

Morrow, A. G., Fogarty, T. J., Hannah, H., III, andBraunwald, E. (I968). Operative treatment in idio-

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pathic hypertrophic subaortic stenosis: Techniques,and the results of preoperative and postoperativeclinical and hemodynamic assessments. Circulation,37, 589.

Simon, A. L., Ross, J., Jr., and Gault, J. H. (I967).Angiographic anatomy of the left ventricle andmitral valve in idiopathic hypertrophic subaorticstenosis. Circulation, 36, 852.

Wigle, E. D., Lenkei, S. C. M., Chrysohou, A., andWilson, D. R. (i963). Muscular subaortic stenosis:Effect of peripheral vasodilatation. Canadian Medi-cal Association Journal, 89, 896.

AddendumSince this manuscript was prepared, we havestudied two additional men with idiopathic hyper-

trophic subaortic stenosis and atrial fibrillation. InJ. G. fibrillation began at age 37 and at first wasparoxysmal, but 5 years later (and 2 years after leftventricular myectomy) persistent atrial fibrillationoccurred. R. M. developed persistent fibrillationat age 45. Both patients deteriorated clinically withtheonset ofatrialfibrillation. Digitalis and diureticsimproved both of them, but in R. M. heart rateand symptoms were better controlled when pro-pranolol also was given. Electrical cardioversionrestored sinus rhythm in each patient, but J. G.has undergone a second cardioversion because,despite quinidine therapy, atrial fibrillation recur-red 2 months later. Four hours after cardioversionR. M. suffered a large pulmonary embolus: hegradually recovered.

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Heart Journal, Atrial fibrillation in patients idiopathic