The Apical A Wave versus the Fourth Heart Soundin Assessing the Severity of Aortic StenosisBy MORTON A. KAVALIER, M.D., JANIE STEWART, AND MORTON E. TAVEL, M.D.
SUMMARYThe height of the "a" wave of the apexcardiogram was evaluated as a marker for critical aortic stenosis in
patients over 40. Critical aortic stenosis was defined as an aortic valve area < .75 cm2 with no more thanmild aortic insufficiency. Phonocardiograms and apexcardiograms were performed on 72 patients withcatheterization proven aortic stenosis and on 14 normal controls, all over age 40. The height of the " a" waveof the apexcardiogram was measured as a percentage of the e to o excursion (a/e-o). Fourth heart soundgallops (S4G) were recorded in 71% (11 of 14) of normal controls, 86% (6 of 7) of patients with less thancritical aortic stenosis, and 85% (55 of 65) of patients with critical aortic stenosis. The a/e-o was less than16% in all normals or patients with less than critical aortic stenosis. The a/e-o exceeded 16% in 45% (29 of65) with critical aortic stenosis. Audibility of the S4G bore no relationship to recordability, apical "a" waveheight, or the severity of the aortic stenosis.
In conclusion, therefore, we believe that when one is confronted with findings suggestive of aorticstenosis, the finding of a palpable apical "a" wave (or an "a" wave height of greater than 16% of the totalcomplex on the apexcardiogram) is an important positive feature, suggesting severe aortic stenosis. Itsabsence, however, does not exclude severe valvar obstruction. Probably because of auscultatory inaccuracyin this condition, the apparent presence or absence of an S4G has not been of much aid in this evaluation.This sound, however, might be more useful in a carefully performed prospective study.
THE NONINVASIVE ASSESSMENT of the se-verity of aortic stenosis remains a problem despite
the long list of clinical and graphic criteria.1Goldblatt et al., noting the correlation between afourth heart sound gallop (S4G) and a thickened non-compliant left ventricle, concluded that the presenceof an S4G in aortic stenosis predicted a peak aorticvalve gradient of at least 75 mm Hg.5 Caulfield et al.modified these conclusions when they noted that thereliability of an S4G as a predictive factor of severeaortic stenosis diminished in patients over the age of40.6 While the absence of S4G was felt to indicate lessthan severe aortic stenosis, its presence did not in-dicate severe aortic stenosis with significant reliability.
In the present study, we examined phonocar-diograms and apexcardiograms from normal patientsand those with less than critical aortic stenosis as wellas critical aortic stenosis. Correlations between the
From the Department of Medicine, Indiana University School ofMedicine, and the Krannert Institute, Indianapolis, Indiana.
Supported in part by the Herman C. Krannert Fund, and byGrants HL-06308, HL-05363 and HL-05749 from the NationalHeart and Lung Institute.
Address for reprints: M. E. Tavel, M.D., 110 Fesler Hall, IndianaUniversity School of Medicine, 1100 West Michigan Street, In-dianapolis, Indiana 46202.
Received August 14, 1974; revision accepted for publication Oc-tober 9, 1974.
S4G, apical "a" wave height, left ventricular "a" wavepressure and severity of the aortic stenosis were madeto better assess the severity of aortic stenosis inpatients over 40 years of age.
Methods
Phonocardiograms and apexcardiograms were recorded in14 normal controls, seven patients with less than critical aor-tic stenosis, and 65 patients with critical aortic stenosis, allover age 40. Critical aortic stenosis was defined as an aorticvalve area of less than 0.75 cm2 with no more than mild aor-tic insufficiency. One patient had mild mitral insufficiency.Patients with idiopathic hypertrophic subaortic stenosis orsignificant coronary artery disease were excluded from thestudy. Normal patients were screened for a history ofhypertension or coronary artery disease. All had normalelectrocardiograms and chest X-rays. Less than critical aor-tic stenosis was defined as an aortic valve area of greaterthan 0.75 cm2 and less than a 50 mm Hg aortic valvular peaksystolic pressure gradient.
Phonocardiograms were obtained with a Cambridgemicrophone and were routinely recorded in the second rightand second left intercostal space, lower left sternal borderand apex. All recordings were made within 24 hours of car-diac catheterization.
Electronic signals were recorded graphically with an Elec-tronics for Medicine recorder (Model DR-8). The apexcar-diogram was recorded using the technique of Benchimoland Dimond.7 The time constant for this circuit was deter-mined to be 1.8 second as described in previous work fromthis laboratory.' We have compared these tracings with
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those recorded with an infinite time constant and havefound no significant differences in wave morphology or "a"wave height measurements. This observation is in agree-ment with that of Kesteloot et al.8 Apical sounds wererecorded simultaneously with a dynamic microphone(Hewlett Packard #62-1500-C13). Band-pass filters were setas follows: Apexcardiograms, 0.1 to 20 cycles per second;sounds, 120-500 cycles per second. Attenuation of wavesoutside these frequency limits was at the rate of 6 decibelsper octave.
Clinical records were reviewed to determine theaudibility of the fourth heart sound (S4G) at the bedside.Phonocardiograms were analyzed for the presence orabsence of a recordable S4G. The height of the "a" wave ofthe apexcardiogram was measured as a percentage of the eto o height (fig. 1). The height of the "a" wave of the leftventricular pressure tracing at rest was measured and cor-related with the apical "a" wave excursion.
Results
An S4G was recorded in 11 (71%) of 14 normals, six(86%) of seven patients with less than critical aorticstenosis and in 55 (85%) of 65 patients with criticalaortic stenosis. The height of the "a" wave as apercentage of the e to o height was less than 16% in allseven patients with less than critical aortic stenosis(fig. 2). The " a wave height exceeded 16% in 29 of 65patients (45%) with critical aortic stenosis. An S4G wasthought to be audible in 43%9 (3 of 7) of those with lessthan critical aortic stenosis and in 29%5 (19 of 65) ofthose with critical aortic stenosis (table 1). The "a"wave of the left ventricular tracing correlated weaklywith the apical "a" wave height (a/e-o), with an rvalue of 0.53.
Discussion
The " a wave of the apexcardiogram has beenshown to be due to the late diastolic anterior displace-ment of the left ventricular wall as a result of atrialsystole.9 It synchronizes with the fourth heart sound,and is frequently more easily palpated than is thefourth heart sound heard. An S4 has been shown to bephonocardiographically present in a high percentageof normal patients over age 50,1011 but an "a" wave of> 12% is felt to be an abnormal finding. 12 Whether ornot this recordable S4 is commonly audible is lessclear.'3-"1 An S4 was recorded in 71Y% of our normalpatients, 86% of patients with less than critical aorticstenosis and in 85% of patients with critical aorticstenosis, clearly a poor discriminator in detecting theseverity of the aortic obstruction. We also observedpoor correlation between severity of aortic stenosisand the audibility of the S4G, noting detection of anS4G in 43% of the patients with less than critical aorticstenosis and in only 29% of those with critical aorticstenosis. The audibility of the S4G did not correlatewith the height of the " a" wave of the apexcar-diogram. These data support those of Caulfield et al.,fwho noted that in patients over age 40 the presence of
ECG!1
A
Figure 1
Sirniltan2eot.s phonocardiogram arnd apexcardiograni from a putierntivitl/ critical aortic stenosis. a = a wave height; c-o = total heighlt ofapexcardiogramn from e point to pOint; S4 = fourth heart sointld;SM = systolhc murmunr; 2 aortic sec.nd soutnd.
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SM 2PHONO
ACG0.1 \~SEC
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Figure 2
'dill aortic stenosis int a 66-year-old male with systolic aorticpressure gradienft of 20 rum fig. A fourth heart sound (4) isrecorded, but in this exanmple, the apical A wave is dimrinutive andnwll within nornmal liniits.
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Clinical and Phonocardiographic Data of Normal Patients and Patients wth Aortic Stenosis
Normal patients Mild AS patients Critical AS patients
Number of patients 14 7 65S4 heard 0 3 (43 %7) 19 (29 '6co)S4 recorded 11 (71Cc) 6 (86%) 55 (85%)a/e-o > 16C,G 0 0 29 (45%c)Average age 53.8 54.3 57.2
Abbreviations: a/e-o = a wave height percentage; AS
an S4G was an unreliable predictor of significant dis-ease. When the accompanying "a" wave of the apex-cardiogram was analyzed in the same group ofpatients a clear discriminator was evident. While asmall "a" wave did not rule out significant aorticstenosis, in every instance that the "a" wave ratio wasgreater than 16%, critical aortic stenosis was present.The "a" wave ratio has been shown by others to cor-relate with the peak "a" wave pressure in the leftatrium. 12 In addition, the palpability of the "a" wavehas been correlated with an "a" wave ratio of 14%,12suggesting that if one is able to feel this presystolicapical impulse in a given patient, aortic stenosis, ifpresent, is apt to be severe. One of course must takeinto consideration such factors as emphysema, chestwall configuration, obesity, large breasts, and shortP-R intervals, any of which might reduce the palpabil-ity of the S4G.
Similar to the finding of Voigt and Friesinger,'6 wenoted a poor correlation between left ventricular end-diastolic pressure and apical "a" wave height, notingmany elevated pressures which were not associatedwith large "a" wave percentages. There was,however, a weak correlation between left ventricular"a" wave height and apical "a" wave size. This is ex-pected since both these phenomena reflect the resultsof a vigorous atrial contraction on a noncompliantventricle. The low order of correlation and degree ofscatter, however, precludes the clinical use of apexcar-diography in prediction of left ventricular "a" waveheight in the individual patient. The work of Gibsonet al. using a diastolic stiffness factor more thoroughlyexplores these interrelationships.'7Our study was not specifically designed to test the
clinician's ability to detect the S4G, although ex-perienced auscultators were used for most of the ex-aminations. We feel that the masking effect of theloud systolic murmur likely interfered with detectionof this sound, since in other conditions these soundsare usually heard in the presence of large apical "a"waves.
In conclusion, therefore, we believe that when oneis confronted with findings suggestive of aortic
aortic stenosis; S4 = fourth heart sound.
stenosis, the finding of a palpable apical "a" wave (oran "a" wave of greater than 16% of the total complexon the apexcardiogram) is an important positivefeature, suggesting severe aortic stenosis. Its absence,however, does not exclude severe valvar obstruction.Probably because of auscultatory inaccuracy in thiscondition, the apparent presence or absence of an S4Ghas not been of much aid in this evaluation. Thissound, however, might be more useful in a carefullyperformed prospective study.
References
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14. FOWLER NO, ADOLPH RJ: Fourth sound gallop or split firstsound? Am J Cardiol 30: 441, 1972
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