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Mechanisms of Fixed Splitting of the Second Heart Sound BY JOSEPIH K. P)ER10)1)'F, ANI.D. ANI) W%. PROCTOR MIARVEI Ml). Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 of WVilsoii.:i The criteria for the diagnosis of right ventricular failure were clinical and consisted of the presence of systemic venous lhypertension, pitting peripheral edemla, and cong-estive hepatomnegaly. The phonocardiogranis were logarithblie4 recordings at paper speeds of 50-75 amn. second, taken with either a standard twin-beani Sanborn, or a specially built Cambridge with the saime frequency response characteristics. Indirect carotid pulses were obtained with a light tamnbour applied to the neck. The interval between aortic valve closure and the inscription of the dicrotic notch of the carotid pulse varied 0.02 to 0.04 second, depending on where in the neck the carotid pick-up was located. The intracardiae pulses were, in certain instances, taken on a cathode ray photographic recorder. It is to be emphasized thiat all recorded events were appreciated by auscultation, and hence have direct clinical application. P ROPER elinical anialysis of the secondll heart sound has oily recently been emphasized.1 An ullderstalldill(r of the normal second heart sound has increased the diagnoslie usefulness of its variations in congenital and acquired heart disease. In atrial septal (lefeet, as emphasized by Wood,( the aortic aid pulmnonic coniponelits of the second heart sou]d(l are not o0ly widely separated, but the split remains fixed throughout the respiratory cycle. The following study was designed to investigate the physiology of fixed splitting of the second heart sound in atrial septal defect and iii 3 other categories in which this pheliomeflonl has been observed-right and left bundle-braneh block with right ventricular failure, and mitral instufficiency-i with right ventricular failure. RESULTS N'ormtal CoWatrols. The majority were younig adults, although the ages raniged from 5 to 50 years. During relaxed respiration the second heart sound varied from expiratorysychrony to inspiratory separation averaging 0.04 to 0.05 second. The youn-ger subjects differed somewhat ini that the second sound more often tended to remain slightly split during expiration (average 0.02 seconds) and tended to split more widely durinig inspiration. This expiratory asynchrony would often disappear if the subject expired more com1pletely. Wheim the respiratory excursions were increased ini magnitude, splittiiig tended to become more pronounced in all ages, but especially in the younger subjects in whom the inspiratory asymmchrony occasionally reached 0.08 to 0.09 seconds. When the records were takeni durinig held expiration, held inspiration, or ini the respiratory mid-position, the two components of the second sound tended to drift apart to varying degrees. It should be emphasized, therefore, that analysis of the second heart sound must be made during active respiration. MAATERIALS AND) METHODS A total of 69 cases were studied. They consisted of 25 noriaal controls, 13 patients with atrial septal defect, 10 with pure mitral insufficiency, 11 with right bundle-branch block, and 10 with left bundle-branch block. The material included patients in the Georgetown University Medical Center and in the Clinic of Surgery, NXational Heart Institute, Bethesda. All patients had electrocardiograias and chest fluoroscopy. In the group with atrial septal defect the diagnoses were established by right heart catheterization. The group with pure initral insufficiency had left heart catheterization. The preoperative diagnosis of atrioventricularis conmlmunis was established by the additional use of dye dilution curves with the injections mrcade into the left atrium and left ventricle.2 The patients with right and left bundle-branch block had congenital conduction defects (right), aclquired conduction defects associated with arteriosclerotic heart disease, and one acquired (left) after closure of a large patent ductus arteriosus. The diagnoses of complete right and left bundlebranch block were mnade on the basis of the criteria Supported in part by grants from the U.S. Public Health Service (H-3319), and the Washington Heart Association. 998 Circulation, Volume XVIJI, November 1958 FIXED SPLITTING OF SECOND HEART SOUND Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 A trial AReptal Ifcecl. TViirteeii patieiits were studied before and after surgical closure of the defect. In each iiistance the surgeon was satisfied with the technical result of the 1)roc.edure. Ten of the patients had the R8r'-V1 pattern9 in the electrocardiogram and oile patient had the pattern of complete right bundle-branch block.3 The QRS configuration of all 13 tracings remained unchanged at the time the postoperative study was done. Eight of these patients were recatheterized postoperatively. By this evidence the defect had been closed in all. In the preoperative phonocardiograms the splitting of the second heart sound remained fixed throughout respiration. In one patient not operated upon because the shunt was small (less than 1 L. per minute) and the right ventricle normal in size, the split widened 0.02 to 0.025 seconds during inspiration, but never achieved expiratory sylnchrony. Two patients had arrhythmias causing variations in cycle length, i.e., a wandering pacemaker in the sinoatrial node and episodes of sinus arrest. The split second sound widened after the longer cycle lengths and narrowed after the shorter cycle lengths. In 11 of the 13 patients the second sound on the postoperative phonocardiogram split normally during inspiration and became single during expiration. In 1 of the 13, however, the second sound did not normalize. Preoperatively, the split had been 0.08 second. Postoperatively, the split was 0.06 second (comparing complexes of the same cycle length) and during inspiration the pulmonic component moved less than 0.02 second. There was no delay in the onset of the right ventricular pressure pulse in the postoperative catheterization study. There was no clinical evidence of right ventricular failure. Postoperative catheterization proved the defect to be closed. The explanation for the findings in this case is not apparent. In the 1 patient with complete right bundlebranch block, the postoperative split of the second sound increased from an expiratory separation of 0.03 second to an inspiratory separation of 0.06 second. This can be consid- U 999) rT FIG. 1. Phonocardiograms with pulmonary and carotid arterial pulses in a patient with proven atrial septal defect. Note that in the upper tracing pulmonic valve closure (P2) times with the dicrotic notch (D.N.) of the pulmonary arterial pulse (interval betx. een P2 and D.N. accounted for by delay in transmission of pulse from pulmonic valve to catheter tip, plus instrumenwtal delay), and note that in the lower tracing aortic valve closure (A2) times with the dicrotic notch of the carotid arterial pulse (interval between A2 amid D.N. accounted for by delay in transmission of pulse from aortic valve to carotid pick-up plus instrumental delay). PA, pulmonary area, SP, first sound; SM, systolic murmur; L.S.E., lower left sternal edge. ered a normal inspiratory delay in pulmonic valve closure. The relationship of the two components of the second sound is typical of complete right bundle-branch block. This is of further interest since the onset of the right ventricular pressure pulse was not delayed, occurring 0.06 second after the onset of the QRS of the electrocardiogram.5 Complete Right Bundle-Branch Block. Eleven patients were studied. In the 8 with compensated right ventricles the split second sound widened on inspiration and narrowed on expiration but never became single. In the 3 patients with right ventricular failure, the split remained fixed throughout the respiratory cycle. Complete Left Bundle-Branch Block. Ten patients were studied. In the 6 with compensated right ventricles, the second heart sound split during expiration and became SYMPOSIUM ON CARDIOVASCULAR SOUND 1000 _ . PA S1 A2 Pa S. a- f- AP 22 o fl C A R Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 FIG. 2. Normal 22-year-old male medical student. Note that aortic (A,) and pulmonic (P,) components of the second sound are synclroniouis during expir.ationi (EXXP. n.tid split during inspiration (ILYSP.) Car., carotid pulse. single during inspiration. In the 4 patients with right ventricular failure, the second sound remained constantly split throughout the respiratory cycle. Pure Mitral Iiisufficic(lcy. Ten patients were studied. Ill the 6 with compensated right ventri(cles, the split second sound widened with inspiration aimd narrowed with expiration, but never became single. In the 4 patients with right ventricular failure, the split remained fixed. The width of the split varied from 0.04 to 0.10 second. None of these patients had the electrocardiographic pattern of right bunidle-branch block. DISCUSSION As early as 1866, Potain' was aware that the second heart sound (S2) split during the inspiratory phase of respiration. In 1950, Barber et al.6 emphasized this finding in children. Leatham and Towers7 subsequently confirmed its occurrence in the majority of healthy adults. The first component of the split is recorded at all valve areas and is synchronous with the dicrotic notch of the carotid pulse (fig. 1), a feature identifying it as the sound of aortic valve closure (A2). The second component is normally confined to the pulmonary area or the immediately subjacent left sternal edge and is synchronous with the dicrotic notch of the pulmonary arterial pulse (fig. 1), a feature identifying it as the soinid of pulmonary valve (losure (P2). Durilg inspiration the effective pulmo naar ty venous filling pressure remains unchanged, since pulnmonary veins, left atrium, and left ventricle share equally the inspiratory fall in intrathoracic pressure. However, the effective systemic venous filling pressure increases with ilms)iration since the inspiratory pressure in time right heart falls below that of the extrathoracic great veins. This results in selective inlsp)iratory augumentation of right-sided filling. The right ventricle takes longer to eject this increased volume and its prolonged ejection time is reflected in delayed pulmonary valve closure, giving rise to the normal inspiratory splitting of the second heart sound (fig. 2). It is to be emphasized that only P2 moves with respiration, the timing of A2 re- mnaining unchanged.* The phenomenon of fixed splitting of the second heart sound in atrial septal defect has been well documented.8 Our observations confirm the findings that even with deep inspiration and expiration the interval between aortic and pulmonic components of the second heart sound in atrial septal defect remains constant or moves very slightly (less than 0.02 second), the sounds never becoming single (fig. 3A). In 1 patient with a proven ostiumn *Ed.: Compare contradictory findings of Boyer .and in the succeeding paper. (llislolmi FIXED SPLITTING OF SECOND HEART SOUND 1001 ATRIAL SEPTAL DEFECT PRE-OPERATIVE A: PA 1AA Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 1 - CONTINUOUS TRACINS ATRIAL SEPTAL DEFECT POST. OPERATIVE B PA 'I~~41ft - - PE byP ~~~~~~~~~~~~~~~~~~~ n CAR FmI. 3. A. Proven atrial septal defect, preoperative. Note that the interval between the aortic (A2) and pulmonic (P2) components of the second sound remained fixed throughout the respiratory cycle. E, pulmonie ejection sound. B. Same patient after surgery. The atrial septal defect was proven to be closed by postoperative cardiac catheterization. Note that now the aortic (A2) and pulmonic (P2) components of the second sound are synchronous during expiration and split normally during inspiration. primum defect and normal mitral and tricuspid valves, and in 1 patient with ostium primum type of atrial septal defect with mitral incompetence, fixed splitting of the second sound occurred. Pulmonary hyper- tensive atrial defects are exceptions to this rule and are not included in this study. A basic hemodynamic expression of atrial septal defect is constant right-sided diastolic hypervolemia. The right ventricle apparently ON 1002 'SOUND Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 FIG. 4. Proven atrial septal. defect, preoperative, with variations in cycle le~lngth due to episodes of sinus arrest. Note that after longer cycle lengths the intersal between aortic (A4.,) After shorter cycle lengths and puholnoic (P2) comlpollnents of the second(l souniId incrcasc. this interval decreases. takes lomger to eject this ill( reasc(l volume, hence, its stroke time is prolontged aild the pulilloine valve eloses later than the aortic (fig. 3A). Because the overfilled state is present throughout the respiratory cycle, the right vveitricular volume dnriing expiration ay nlot diminiish. Conrverselv, as a resuilt of its alreadv exc(,,-s.sive dia tolic inflow, the right ventricle apparently (loes not accept the aflditional inspiratory: augmentation of filling. anid its stroke volume thus does not increase during inspiration. The result is that aortic and pulmoific valve closures remain constantly separated, their interval being affected little, if at all, by respiration (fig. 3A ). That the asvnchronv of semilunar valve closure is not a reflection of the electrocar(diographic patterni of "inicomplete right btundlebranch block'-l)erhaps better terllle(l the RSr'-V1 l)atterlil9-was demonstrated 1w studying 12 patients with the ostium seenimdun type of atrial septal defect, and 1 with the ostium primum type before and after surgical repair of these lesions. As soon as the second sound could be analyzed (often the day after surgerey). it was fouind to split normally (ur- illg inlsl)iratioll, acid (lose duri-iig ex)iration (fijr. .3) In 11o instance was there ans, changfe in the QRS pattern when the postoperative study was made. ()lne patient had complete right b)utldle-brallnch block and a fixed split before surgery. IPostoperatively. the split widened with illspiratioll and narrowe(l with expiration, but never became singrle, reflectinog the usual findinlr in eomplele rigrht bundle-branch block (see b(low) A residual left-to-righlt shunt through anomalous pulmonary veins nay result in a failure of the second s5011n1( to normalize plostoperatively, even thouglh the defect in the septum is closed. The followi mg ol)e(irvationis su0ggest that, althouigh the split seconl(I souiiid in atrial septal lefect remains fixed relative to respiration, it may vary w-ithl changes ill cyele length. Figlure 4 illustrates an increase ill the A,-P, iimtcv.al froil(0.04 to 0.08 secoll(d coilncident withi an inerease il cycle lengtll (caused b)periods of sinus arrest. It can be seen that tile imiterval betwe(,en S, anid A2 remains onistant, hence the increase in A2-P2 interval iiitIst hauve I)C(c11 (Ince to fillutier (delay ill pul- OF FIXED) 81-PIATT1NG SE(ONI) 1IART SO0ND) )I A. RIGHT Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 I- PA ,- -r - BUNDLE BRANCH 100)(3 BLOCK RIGHT BUNDLE BRANCH BLOCK RIGHT VENTRICULAR FAILURE 11 S.5 1 !11 5 , 1 1 T~~~~~ FIG. 5. A. Complete right bundle-branch block in a 60-year-old feimale with arteriosclerotic lheart disease. Note that during inspiration the interval betweemi aortic (A1,) anld pulinonic (P.,) components of the second sound inlereases a.ndif during expiration time interval decreases, but the two sounds never l)ecOOtC single. X, systolic cardiorespiratorv click. B. Complete right bundle-branch bmlock in 58-yea.lr -ol(l miale with leaioclhi-omii.atosis and riglht ventricular failure. Note that the interval between aortic (.,1) anl(l pulinonic (P,) comiponents of the sec-ond(l sound remains constant throughout the resl)iratory cycle. The first sound (8 ) is soft 1ec; of pmrolongedl P-R interval. a. use a monic valve (losure, reflecting a prolonigation of right ventricular stroke tine. Thus, after a long cycle lenegthi the right ventricular stroke time selectively le lgrtlhens. The same phenomenon was observed ill aiioth er patient with aii atrial sel)tal defect, in whichl the cyele leiigrtli varied because of a waimderinl peacemaker in the sinoatrial node. These events might be ex)lailled in the followingr fashion. When there is a defect in the atrial septum all 4 cardiac chambers are in common communicationl dliriltg diastole, but the rate of flow- into the rbrmt ventricle far exceeds ventricle. Au ilicrease iii the (iastolic filling period should thlerefore contribute disproportionately to right ratlher than to Icft ventricular filling. With longoeri cycle lengitlhs it is postulated that the rigrht enitric le may be the principle, if not the exclusive recipient of the added increnieiP of diastolie filling. Thl'is should reflect itself ill selectiv )rolongation of right v-enitriceuilar stroke time, delay in pulmonie valve closure and wider separation of the A2,-Pz interval (luring the longYer cycle lengths. Fixed splittiimr of the second heart sound the rate of flow into thie left 1004 SYMPOSIUM ON CARDIOVASCULAR SOUND A. _-4_ rr ; LEFT BUNDLE BRANCH BLOCK P2 A2 p AL- p- Fw- A- w~ lr-~,9.qr r .- A- a -4.T m ,S1(0 -1 EXPIRATION e rA PA I A 1 ---I i-r- - - - . he A.. ~ -9~-i CAR Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 INSPItRA1 IUN RATION LEFT BUNDLE BRANCH BLOCK WITH BIVENTRICULAR FAILURE B. -~~~~~~~;A PA_am~ U- - - ELD ' Af 1~ HELD INSPIRATION 0w* RESPIRATION EXPIRATION INSPIRATION Complete left bundle-branch block acquired after surgical closure of a large patent ductus arteriosus in a 37-year-old female. Note that the aortic (A,) component of the second sound falls after the pulmonic (P9) component of the second sounld. Hence during inspiration the second sound is single and during expiration the second sound is split. B. Complete left bundle-branch block in 72'-yea.(-ol white femiiale with arteriosclerotic heart disease and heart failure. Note that the inspiratory delay in pulnionic (P,) valve closure dloes not occur, hence the second souiindl remainis split throughout the iespirator-y cycle. FIG. 6. A. a is, therefore, valnlable (liaoiiosti( Sio'in of atrial septal (lef~et, and( possibly of the atrioventricularis commIIunis tvpe of anomnaly. This phenlomellon is probably a manifestation of the right-sided diastolic hypervolemiia, which prevents the right ventricle from unudergoi its normal respiratory changes in stroke volutme. The rather prompt return to the normal state after the defect is closed supports this a n concept. g OTHER OBSERVATIONS Altlhough1 heretofore fixed splitting of the seeond heart sound has beeii described onlyN in atrial septal defect, the following considertations led us to postulate its occurrence ini other. conditions. If the right ventricle ini a state of failure were operating, omi the plateaus of its Starling curve, it sliould not be able to colnvert the inspiratory augmentation of filling into increased stroke volume.10 10 1005 FIXED) SPLITTING OF SECOND HEART SOUND BIVENTRICULAR FAUWRE 3 I. C.S.A A~.L ~~~~~~~~~~~~~~~1 Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 / FRONTAL v S V f,*11 s 10 w SF IT-1-1-1I-1-11 1±4-i-H-H-I SAGITTAL * S * L ~~POST 9:* . 1 ANT ~~~~~~~~~~~~~~~~~~0 FIG. 7. Biventricular conduction defects in a 62-year old male with hypertensiv'~-arteriosclerotic heart disease and right venitr-l-ular failure. Note that in tihe phoniocardi(,grams (upper pair of tracings) the initial component of the split second sound times with the dicrotic notch of the synchronous carotid (CAR) pulse, thus establishing the normal sequence of semilunar valve closure. In tile scalar electrocardiogram (lowcer left) tile limb lead suggest complete left bundle branch block and the precordial leads suggest complete right bundlebranch block. The vectorcardiogram (10oUCr. right) reveals biventricular conduction defects. 31 I.CS., third left intercostal space. Ilein'.e, ini this state of failure, the right venltriele migiht be expec'ted to have a constant e~jeetioii time throughout the respiratory ('yele, resulting in a disappearance of the normal ilispiratory delay ini pulmonic valve closure. This thiesis was tested in 3 categories of 1)atients with sufficient splitting of the second. heart sound to allow detailed analysis. The first group consisted of patients with .olfllpletc right bundle-branch block. A cornmnonly observed mechanical sequel of this delay in right ventricular depolarization is a delay in pulmonic valve closure. This reflects itself in abnormally wide splitting of the second heart sound, 1 which fails to become single during expiration. During inspiration the normal augmentation of right-sided filling still occurs with the associated delay ini pulinonary valve closure. One finds accordingly that although the aortic and lpuliuonic, comlponents of the second sound widen their iiiterval (hiring inmsliration and narrow it durimigo expiration, they fail to become synchronous during the expiratory phase of respiration (fig. 5A). However, when right bundle-branch block occurs in the presence of right ventricular failure, the sp)litting of the second sound remains fixed (fig. 5B).-This is believed due to the inability of the failing right ventricle to convert its inspiratory augmentation of filling into increased stroke volume. As a consequence of this inability, the inspiratory delay in pulmonary valve closure should 1 (06)f Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 L.3rd LT. I.CS.S SYMPOSIUM ON CARD IOVASCU LAR SOUND MITRAL INCOMPETENCE A L So E _ t %SM_~ ~ ~ ~2s B da* MITRAL INCOMPETENCE 1 . 224 . RIGHT VENTRICULAR FAILURE si _ ql _ m -1 ]I CAR FIG. 8. A. Pure rheumatic mitral incompetence in a 28-vcar-old feillihle. Note tihat alltilougil the interval between aortic (A,) anid pulhonie (1`.,) components of the second sound w5idens with inspiration and narrows with expiration, the 2 coml)ollnelts iever become single. B. Pure rheumatic mitral incompetence in a 28->yea 011wite l female with associated right ventricular failure. Note tlhalt the second s(om1111( is not only wvidely split, lbut the interval between aortie (A,) and pulmuonic (P.,) coiil)omp(otets remains. fixed trlloliglonit the respiratory cycle. 3rd LT. I.C.S., third left intercostal space. iiot occur. The A2-P., interval would, therefore, remain unchanged. The secowd group consisted of )atiellts witlb left bundle-braneh block. It appears that a mechanical sequel of this delay in left ventricular depolarization is ani asso(iated delay, in aortic valve closure. The (lelay is usually sufficient to cause the aortie valve to close after the pulmonic, thlus reversing, the normal closing sequence of the semiluniar valves. This is demonstrated by timing A, with the dicrotie notch of the carotid pulse (fig. 6A). The result of tlis 'paradoxical oF)littilg of tlhe seoll(d1heart sound" is expiratory separation of its two components.. Dur ing inspiration the timing of pulmonary valve closure moves toward aorti(' closure and the second sound thus become.es single (fig. 6A). However, in the presence of right ventricular failure, S. does Iot become single during inspiration b)ecause the inspiratory delay in pulmonie valve closure does not occur (fig. 6B). This results in fixed splitting of the second heart sound in left bundle-branch block. In one ('ase this method of analysis was of p)articular interest. 'T'lhe pati(ent, a 7-year- FIXED SPLITTING OF SECOND HEART SOUND Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 old male with hypertensive-arteriosclerotic heart disease had an electrocardiogram which resembled left bundle-branch block in the limb leads, and right bundle-branch block in the precordial leads. The vectoreardiogram using the Schmidt-Simonson system'2 suggested biventricular conduction defects. This apparent electrocardiographic paradox has been variously interpreted. Some investigators13 consider these tracing- examples of right bundle-branch block, emnhasising the unreliability of the limb leads in distinguishing the side of the block. Others14 feel that in some cases this pattern should be regarded as left bundle-branch block with extensive posterolateral myoeardial infarction. Auscultatory examination of the patient disclosed a widely split second heart sound, but since marked right ventricular failure was present the split remained fixed, and therefore, could not be used to distinguish right from left bundle-branch block. The phonoeardiogram with synchronous carotid arterial pulse (fig. 7) revealed a normal sequence of aortic-pulmonic valve closures, suggesting in this instance the mechanical asynchrony of a right bundle-branch block. These observations further illustrate that in the presence of right ventricular failure, one cannot distinguish right from left bundle-branch block by auseultation. The third group consisted of patients with pure mitral insufficiency associated with wide splitting of the second heart sound. Unusually wide splitting of the second sound has been observed in this lesion'5 and attributed to premature aortic valve closure. It is sugaested that if the left ventricle can expel its contents not only into the systemic eirculation, but also into the left atrium, then its ejection time might be shortened, resulting in early aortic valve closure. If this is sufficiently pronounced, aortic and pulmonic valve closures may remain constantly separated (fig. 8A ). It is to be noted, however, thatas in norinals-inspiratory prolongation of right ventricular ejection time still occurs, resulting in inspiratory delay of pulmonic valve closure and increased splitting of the 1007 second heart sound (fig. 8A). It was found, however, that when the right ventricle decompensates in the presence of mitral insufficiency with wide splitting of the second heart sound, there is no inspiratory delay in pulmonic valve closure, hence, the split becomes fixed (fig. 8B). These data do not permit conclusions regarding the state of deCompensation at which the inspiratory delay in pulmonic valve closure would fail to occur. The severity of right ventricular failure will vary from time to time and from case to case. Even if the failing ventricle is operating on a depressed function curve, it still may be able to increase its stroke work if it has not yet reached the plateau of the curve.10 It might be anticipated, therefore, that not all patients in whom right ventricular failure coexists with complete bundle-branch block or mitral insufficiency will illustrate the phenomenon of fix' d splitting of the second heart sound. SUMMARY Forty-four patients with wide splitting of the second heart sound and 25 normal controls were studied with fast speed logarithmic phonoeardiograms. In the control group, inspiratory augmentation of right heart filling increased the right ventricular stroke volume, prolonged the right ventricular stroke time and delayed pulmonic valve closure, thus altering the second sound from expiratory synchrony to inspiratory separation of its 2 components. In the group with atrial septal defects, the second sound normalized postoperatively, reflecting the ability of the right ventricle to undergo its normal inspiratory increase and expiratory decrease in stroke volume when the defect was closed. Before closure, the right ventricular stroke time neither shortened with expiration nor lengthened with inspiration because of the constant diastolic right ventricular hypervolemia. Hence, preoperatively the interval between aortic and pulmonic valve closures remained characteristically wide and fixed. That the preoperative delay in pulinonic valve closure could SYMPOSIUM ON CARDIOVASCULAR SOUND 1008 Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 not have been a reflection of " incomplete right bundle-branch block " was illustrated by the postoperative normalization of the second sound without change in the QRS pattern of the electrocardiogram. Although the split of the second sound was not altered by respiration, it was altered by change in cycle length, widening after longer cycles and narrowing after shorter cycles. Wide splitting of the second heart sound was found in mitral insufficiency because of early aortic valve closure, in complete right bundle-branch block because of delayed pulmonic valve closure, and in complete left bundle-branch block because of a reversed sequence of aortic-pulmonic valve closure. When right ventricular failure coexisted with these lesions, the decompensated chamber did not convert its inspiratory augmentation of filling into increased stroke volume. The inspiratory increase in right ventricular stroke time and the inspiratory delay in pulmonic valve closure therefore could not occur so the split of the second sound remained fixed throughout the respiratory cycle. ACKNOWLEDGMENT The authors acknowledge with pleasure the freedom with which we were allowed to study the cases on Services of Dr. Andrew G. Morrow and Dr. Robert P. Grant at the National Heart Institute, Bethesda, and of Dr. Charles A. Hufnagel at the Georgetown University Medical Center, Washington, D. C. We are further indebted to Dr. Hubert V. Pipberger for taking and interpreting the vectoreardiograms. SUMMARIO IN INTERLINGUA QQuaranta-quatro patientes con large fission del setrunde sono cardiac 25 normal subjectos de cohtrolo esseva studiate per medio de phonocardiogrammas logarithmic a grande velocitate. In le gruppo de controlo, augmentation inspiratori del replenamento dextero-cardiac augmentava le volumine per pulso dexteroventricular, prolongava le tempore del pulso dextero-ventricular, e retardava le clausion del valvula pulmonic, de maniera que le secun- de sono esseva alterate ab synchronia expiratori a separation inspiratori de su 2 componentes. In le gruppo de patientes con defectos del septo atrial, le secunde sono se normalisava post le operation. Isto reflecteva le capacitate del ventriculo dextere de experientiar su normal augmento inspiratori e diminution expiratori in le volumine per pulso quando le defecto esseva claudite. Ante le clausion, le tempore per pulso dextero-ventricular non se reduceva in expiration e non se prolongava in inspiration a causa del constante diastolic hypervolemia dextero-ventricular. Per consequente, ante le operation le intervallo inter le clausion del valvula aortic e illo del valvula pulmonic remaneva characteristicamente large e fixe. Le facto que le retardo pre-operatori in le clausion del valvula pulmonic non poteva esser un reflexion de "incomplete bloco de branca dextere" esseva demonstrate per le normalisation post-operatori del sono que occurreva sin alteration in le formation de QRS in le electrocardiogramma. Ben que le fission del secunde sono non esseva alterate per le respiration, un alteration de illo occurreva como effecto de alterationes del longor de cyclo: illo deveniva plus large post cyclos prolongate e plus restringite post cyclos accurtate. Large fissiones del secunde sono cardiac esseva trovate in insufficientia mitral a causa de precoce clausion del valvula aortic, in complete bloco de branca dextere a causa del retardate clausion del valvula pulmonic, e in complete bloco de branca sinistre a causa de reversion del sequentia aortic-pulmonic in le clausiones valvular. In casos in que disfallimento dextero-ventricular co-existeva con iste lesiones, le camera discompensate non converteva su augmentation inspiratori del replenamento in un augmento del volumine per pulso. Le augmento inspiratori del tempore del pulso dextero-ventricular e le retardo inspiratori del clausion del valvula pulmonic non poteva, per consequente, occurrer. Le fission del secunde sono remaneva fixe durante le complete cyclo respiratori. FIXED SPLITTING OF SECOND HEART SOUND Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 REFERENCES 1. LEATHAM1, A.: Splitting of the first and second heart sounds. Lancet 2: 607, 1954. 2. BRAUNWALD, E., TANENBAUm, H., AND MORROW, A. G.: Dye-dilution curves from left heart and aorta for localization of left-toright shunts and detection of valvular insufficiency. Proc. Soc. Exper. Biol. & Med. 94: 510, 1957. 3. WILSON, F. N., ROSENBAUM, F. F., AND JOHNSON, F. D.: Interpretation of the ventricular complex of the electrocardiogram. Advances Int. Med. 2: 1, 1947. 4. RAPPAPORT, M. B., AND SPRAGUE, H. B.: Graphic registration of the normal heart sounds. Am. Heart J. 23: 591, 1947. 5. BRAUNWALD, E., AND MORROW, A. G.: Sequence of ventricular contraction in human bundle branch block. Am. J. Med. 23: 205, 1957. 6. BARBER, J. M., MADIGSON, 0., AND WOOD, P.: Atrial septal defect. Brit. 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L., AND WOLFF, L.: Left bundle branch block masquerading as right bundle branch block. Am. Heart J. 47: 383, 1954. 15. BRIGDEN, W., AND LEATHAM, A.: Mitral incompetence. Brit. Heart J. 15: 55, 1953. Mechanisms of Fixed Splitting of the Second Heart Sound JOSEPH K. PERLOFF and W. PROCTOR HARVEY Downloaded from http://circ.ahajournals.org/ by guest on April 29, 2017 Circulation. 1958;18:998-1009 doi: 10.1161/01.CIR.18.5.998 Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1958 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7322. 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