Ann Thorac Surg 1996;61:594-602
© 1996 The Society of Thoracic Surgeons
Original Article: Cardiovascular
Impact of Mechanical Heart Valve Prosthesis Sound on Patients' Quality of Life
Sigrid A. Blome-Eberwein, MD,
Dieter Mrowinski, PhD,
Joseph Hofmeister, MD,
Roland Hetzer, MDPhD
Universitätsklinikum Rudolf Virchow, ENT Clinic and Polyclinic, Department of Audiology, Deutsches Herzzentrum Berlin, Berlin, Germany
Accepted for publication September 19, 1995.
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Abstract
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Background. The ``click'' sound of mechanical heart valve prostheses has been recognized as a disturbing factor for some patients after mechanical heart valve implantation. The factors determining the extent of disturbance remain controversial.
Methods. Ninety-five unmatched patients with six different valve types were examined (Duromedics-Edwards, Björk-Shiley, St. Jude Medical, Medtronic, CarboMedics, and Omnicarbon), including 12 patients with double-valve replacement. Three groups (Björk-Shiley, Duromedics-Edwards, and St. Jude Medical) were comparable in size. All patients were examined and interviewed, a hearing test was performed, and valve sounds were analyzed. Sound transmission was evaluated.
Results. The loudest valve was the Duromedics-Edwards prosthesis (mean, 84.2 dB[A] impulse) and the St. Jude Medical was the quietest (mean, 73.5 dB[A] impulse). This ranking was independent of patient variables and valve position. Discomfort level correlated with hearing loss and loudness of the valve. Patients desiring a quieter valve had better hearing, had louder valve sounds, felt disturbed by the sound, had partners who felt disturbed, and were receiving coumarin for anticoagulation. Sound was transmitted predominantly by air conduction. The frequency analysis to identify different valves was unsatisfactory, but louder frequencies did correspond with hearing-impaired patients' audiograms.
Conclusions. Our results emphasize the need for valve design changes, preoperative education about the sound, and inclusion of routine hearing tests into the preoperative workup.
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Introduction
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Within the past 16 years the metallic ``click'' sound of mechanical heart valve prostheses has been recognized as one major problem for some patients after valve replacement, in addition to the thromboembolic complications and necessary anticoagulation. Although some work has been done in the past to evaluate the severity of this problem and to distinguish the various models of heart valves according to their ``noisiness'' [1–8], more needs to be done to identify the group of patients who will later have a problem with the click.
The mechanism that causes different sound levels in different valves in vivo is not well understood. Clearly the type of materials adjoining and the impact of collision determine the loudness of each individual prosthesis. However, in an implanted mechanical heart valve the sound it produces is expected to be dependent on the resonant properties of the body. Some authors have suggested sound transmission to the patient's ear by body conduction [4, 7].
The present study compares various mechanical heart valves (three with comparable group sizes) in vivo according to their noisiness and tries to elucidate criteria to specify the patient group who will have problems with the generated sound. An attempt was made to categorize the valves by frequencies of their sounds and to correlate these with the perception of different valves.
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Material and Methods
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Valves
Six different commercially available mechanical valve models were examined in this study (three with comparable group sizes): three were bileaflet valves (St. Jude Medical, Duromedics-Edwards, and Carbomedics) and three were tilting-disc valves (Björk-Shiley, Medtronic Hall, and Omnicarbon). All have pyrolitic carbon-covered surfaces of leaflets and disks, and the Omnicarbon valve is made entirely of this material. The hinge mechanisms are quite different in different valve types and range from annulus-integrated hinges to prongs that stick out from the flat surface of the valve. The Duromedics-Edwards valve was withdrawn from the market because of reports of leaflet escape and fractures, and the Björk-Shiley valve has been modified in the meantime.
Patients
Ninety-five patients between 23 and 80 years old, 55 male and 40 female, were examined. Twenty-two patients (23%) were less than 50 years old. All patients were recruited from a cardiologic outpatient clinic, and the time between operation and examination varied between 3 days and 19 years. The distribution of valve types and patient parameters was incidental. We recorded thorax circumference, heart rate, systolic and diastolic blood pressure, height and weight, and heart rhythm for all patients. Patient-specific parameters were evenly distributed throughout the groups (Table 1
). Eighty-six of 95 patients were taking coumarin for anticoagulation, 6 were taking subcutaneous heparin, and 2 patients took only aspirin. Twenty-six patients took loop diuretics and 20 patients took thiazides. Twenty-seven patients took combination diuretics.
Interview
All patients underwent a standardized interview before examination about perception of the valve sound now and previously, the impact on daily life, the impact on patients' partnerships, which situations possibly intensified the sound, and whether they would choose a quieter valve if they could.
Tone Audiometry
All patients underwent bilateral tone audiometry before valve sound measurements in a professional sound-insulated chamber (Sapper & Hortmann GmbH Phonax 218). Hearing capability was defined as ``normal'' (<30 dB hearing loss at >2,000 Hz), ``slight'' (30 dB to 60 dB hearing loss at >2,000 Hz), ``moderate'' (60 dB to 90 dB loss at >2,000 Hz) and ``severe'' (>90 dB loss at >2,000 Hz).
Valve Sound Measurements
The valve sound level was measured with the patient in a seated position and without clothes. First a microphone was positioned 10 cm from the thoracic wall. A second microphone was integrated into a stethoscope membrane and placed on the thoracic wall in the aortic area and the ``Erb'' auscultation area in the third intercostal space left parasternally. We used a Brüel & Kjaer microphone type 4179 (1" omnidirectional; Brüel & Kjaer, Copenhagen, Denmark) and a Brüel & Kjaer measuring amplifier (type 2607). Measurements were taken in two settings. A peak sound pressure (impulse) measurement and an integrated (effective) sound pressure measurement with the integration constant set to ``fast'' (RMS fast) were recorded for all positions. An A-filter was added to the measurements (DIN 45633), and the microphone was calibrated with a sound level calibrator (Brüel & Kjaer 4220). All valve sounds were recorded on high-bias CrO2 cassettes for frequency analysis at a later date (Fig 1). The measurements were taken in a soundproof chamber.
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Fig 1. . Time record of the sound of a Duromedics-Edwards aortic prosthesis, 23 mm annulus diameter, recorded with microphone 10 cm away from thoracic wall.
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Bone Versus Air Conduction
The outer auditory canal was inspected and occluded with headphones in all patients, who were then asked whether they still heard their valve sound and if it was the same quality as before. In those who claimed they did, we attempted to mask the sound via broad spectrum and band noise. The sound intensity at which this was successful was recorded.
Frequency Analysis
The recordings were analyzed by a frequency analyzer (Brüel & Kjaer type 2033) according to frequency spectrum and time. For the frequency spectrum 64 single beats were analyzed and the sum recorded. This type of analytic sum was examined to find specific valve patterns and to compare the most prominent frequencies to the tone audiograms and to correlate them with the patient's negative perception. This was attempted by picking the loudest frequencies, indicated by a ``peak'' in the graphic recording of the sum spectrum (Fig 2), and categorizing them into sections of frequencies from 5 to 10 kHz, 9 to 13 kHz, 13 to 15 kHz and 15 to 20 kHz. We tried to eliminate the noise of breathing by running a frequency analysis on those ``room'' noises (see Fig 2). The ``frequency maxima'' were then entered into the correlation as a variable for each patient and later analyzed according to valve groups as well as individual perception. The stethoscope recordings were not interpretable because the membrane vibration blotted out most of the valve frequencies (Fig 3).
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Fig 2. . Frequency analysis of a Duromedics-Edwards prosthesis (microphone at 10 cm distance from thoracic wall). The frequency spectrum recorded is a sum of 64 consecutive beats. The intensity peaks were categorized (5–10 kHz, 9–13 kHz, 13–15 kHz, and 15–20 kHz). The graph labeled room shows a frequency analysis of environmental sounds in the sound-insulated chamber with the microphone facing away from the patient. It shows clearly that these ``environmental sounds'' could be negated.
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Fig 3. . Time record of the sound of a Duromedics-Edwards aortic prosthesis recorded with microphone integrated in stethoscope membrane.
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Statistics
Common statistical methods were used for calculations (Pearson 
2 test, analysis of variance, multiple regression). They were performed with the help of SPSS and a personalized computer program by Dr Howard McGuire, Long Island University, Brooklyn, NY.
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Results
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Variability
Each patient, in unchanged upright position and without any physical stress, exhibited a definite beat-to-beat variability (Figs 4, 5).
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Fig 4. . Time record of 12 consecutive beats of a Duromedics-Edwards prosthesis, recorded with microphone 10 cm away from thoracic wall. This recording shows a small beat-to-beat variability of the generated sound in 1 patient under controlled conditions.
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Fig 5. . Time record of 10 consecutive beats of a Medtronic-Hall aortic prosthesis, recorded with microphone 10 cm away from thoracic wall. This recording shows a large beat-to-beat variability of the generated sound in 1 patient under controlled conditions.
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Measurements
Patients with double-valve replacement were excluded for the analysis of data regarding mean sound pressures and correlation analysis. The statement expressing preference for a quieter valve includes the double-valve replacement patients. For values of all measurements for all valves please refer to Table 2.
Correlation Analysis
Correlation analysis is shown in Table 3.
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Table 3. . Extract of the Performed Correlation Analysis for Duromedics-Edwards, Björk-Shiley, and St. Jude Medical Valves in All Positions as Well as in Mitral and Aortic Position (Double Valves Excluded)
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Tone Audiometry
Thirty-seven patients (38%) had a normal right tone audiogram, and 27 patients (28%) had a normal left tone audiogram. Thirty-five patients (36%) had slight hearing loss of the right ear, and 33 patients (35%) of the left ear. Moderate was the hearing impairment in 12 patients for the right (12%) and 23 patients for the left ear (24%). Ten patients had severe hearing loss of the right ear, and 11 patients had severe hearing loss of the left ear. One patient was deaf (Fig 6).
Interview
Forty-nine patients said they heard their valve sound clearly (51.5%), 32 patients heard it faintly (33.6%), and 14 patients (15%) denied any auditory perception of their valve sound. When asked about the past, 78 patients (82%) stated they had heard their valves clearly versus 10 patients (10.5%) who had never heard their valve. Seven patients had heard the sound faintly in the past (7.5%). Eighty-two patients (86%) reported that their partners or others in their environment heard the valve sound; 13 patients (14%) denied this. Twenty-two patients (23%) had experienced uncomfortable situations because of their valve sounds, and 47 patients (50%) wished for a quieter valve or would have chosen a quieter valve, had they been given the option. Ten patients (10%) explicitly did not wish for a quieter valve, and 38 (40%) patients were indifferent. Virtually all patients had not been told about the valve sound preoperatively (or did not remember being told).
Sound Transmission
Sixty-two patients (65%) did not hear their valves with occluded outer auditory canal, 9 patients (9%) heard the sound clearly with occluded outer auditory canal, and 24 patients (25%) heard a somewhat distorted sound. In 7 patients with Duromedics valves a mean of 82.8 dB(A) was needed to mask that perception. In 7 patients with Björk-Shiley prostheses a mean of 40.7 dB(A) was needed, and in 4 patients with St. Jude Medical valves a mean of 52 dB(A) was needed to mask their perception. These measurements were not consistent with the loudness of the different valves outside of the body.
Measurements for Patients With Double-Valve Replacement
In 12 patients (7 male, 5 female) with double-valve replacement 50% had a sound intensity of more than 80 dB(A) in impulse mode; the integrated sound level measured between 41 and 50 dB(A) for 63% of patients (see Table 3
). The two valves did not produce a sum of each individual valve's sound level, but they did cause an amplification of the sound. Five of those patients would have preferred quieter valves. Please refer to Table 4 for results.
Frequency Analysis
In correlation analysis there was a significant correlation between frequency maximums 3 and 4 (13 to 20 kHz) and the disturbance of the patients or their wish for a quieter valve. We found a significant distribution of the peaks between 9 kHz and 13 kHz for different valve models (p = 0.04) (see Fig 2).
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Comment
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Most of the emphasis in heart valve development has concerned hemodynamic performance, durability, and biocompatibility. These phenomena have been previously studied in detail in vivo and in vitro. The long-term follow-up results for the Björk-Shiley, St. Jude Medical, Starr-Edwards, and Duromedics valves have been comparable in this regard [9–15]. In our investigation the subject of interest was the ``sound'' that mechanical heart valves produce.
The fact that different valves produce different sound levels has already been established in vitro in studies by Thulin and associates [3] for the Omniscience, Hall-Kaster, Björk-Shiley, Duromedics, St. Jude Medical, Starr-Edwards, polyurethane, and Carpentier-Edwards valves and by Wieting and colleagues [16] for the Edwards-Duromedics, Björk-Shiley Monostrut, Medtronic-Hall, and St. Jude Medical valves. In vivo studies dealing with the sound level of various mechanical models were done by Moritz and associates [1, 5] for the St. Jude Medical, Duromedics-Edwards, and Björk-Shiley valves; Laurens and colleagues [6] for Björk-Shiley, CarboMedics and St. Jude Medical valves; and Moritz and co-workers [7, 8] for St. Jude Medical, Duromedics-Edwards, Björk-Shiley Monostrut, and Carbomedics valves.
In accordance with the previous studies (Table 5) the Duromedics-Edwards prosthesis was the loudest in all measurements (84.2 dB[A]). This is despite the fact that the mean annulus diameter of this valve was small (26 mm). The St. Jude Medical prosthesis was quietest (73.5 dB[A]), even though the mean annulus diameter was second largest (28 mm). The difference between the valves regarding loudness in impulse mode was significant (p = 0.0001). In the integrated mode (RMS fast) the difference was not significant (see Table 2).
In most previous studies the investigators chose the integrated (RMS) sound levels as their means of reference, except Moritz and co-workers [1, 5, 7, 8], who measured the sound intensity in ``impulse'' mode, but at 100 cm distance. We hypothesized that the method to measure valve sounds would have to be impulse because the important factor for disturbance by the valve sound would be the loudest element of it, as opposed to a leveled average. We confirmed this hypothesis by finding no correlation between disturbance of the patient and RMS values (see Table 3, no. 52).
The sequence in loudness of valve types remained unchanged when adjusted for only the three comparable valve types (St. Jude Medical, Duromedics-Edwards, and Björk-Shiley) and for the same valves in aortic position only. In mitral position the Björk-Shiley valves were quieter than the St. Jude Medical valves; however, considering the range of values in the Björk-Shiley mitral group, the rank order is maintained (see Table 2).
Thulin and associates suggested in their in vitro study [3] that the loudness would be influenced by other factors such as systemic blood pressure, position of the valve, and heart rhythm. Laurens and colleagues [6] doubted that the loudness was dependent on any individual patient-related factors, but considered loudness mainly attributable to the valve design. Moritz and co-workers [7, 8] also suggested that details in design influence sound generation more than closing energy of different valves. In Moritz and co-workers' first study [1] they found the loudness to be dependent on annulus diameter in valves in the aortic position. In their second study [5] the same investigators found larger valves implanted in patients with larger body surface area, but this did not influence the loudness. In their third study [8] the heart rhythm did influence the loudness of the valve, as well as the disturbance. Also, in a different comparison of St. Jude and Björk-Shiley valves, a higher dB(A) level was found in patients with larger body surface area [5]. According to our data (see Table 3) the loudness of the valves was not dependent on body surface area (no. 43), heart rhythm (no. 14), or blood pressure (No. 54). It was not dependent on annulus size, even when examined for mitral and aortic position separately (p = 0.08 and p = 0.19, respectively) or warfarin therapy (no. 56).
The beat-to-beat variability, observed in vitro, was again demonstrated in this study. This variability can not be explained only by such factors as inspiration and expiration, blood pressure changes, and heart rhythm, because it also appears under controlled conditions in the pump-simulator [3]. Major contributors to this variability in vivo are probably the blood viscosity and turbulence, as well as the varying contraction sequence of each heart beat (see Figs 4, 5).
The hearing deficit of the patients influenced the hearing of the valve sound. At least 10 patients could not hear their valve sounds (of approximately 80 dB[A]) because of their hearing impairment, and only approximately 30 patients had normal hearing. All patients with normal hearing heard their valve sound, whereas only 80% of patients with slight and 60% of patients with moderate hearing impairment heard their valve sound. The hearing deficit increased with age (Table 3, nos. 1, 2). The valve type had no influence on the patients' hearing of the sound (no. 31). Only for Duromedics valves was there a correlation of loudness and perception (hearing) of the valve sound (p = 0.03). Time of operation and age of the patients had no influence on hearing of the sound (p = 0.6 and p = 0.3), although hearing impairment did increase with age. The hearing impairment was preexistent in some patients with exposure to high noise levels or presbyacusis. Some patients, however, did not have any previous history of hearing impairment. Perioperative treatment with diuretics and aminoglycosides was suspected to have an impact on their hearing. Furosemide therapy seemed to have an influence on the hearing of the sounds, even if not significant (Table 3, nos. 49, 50, 51): 33.3% of those patients who did take furosemide versus only 8.5% of those patients who did not take the medication were unable to hear the sound.
Nineteen of 49 patients who reported a loud valve sound felt disturbed by it. Five of 32 patients who heard their valve faintly felt disturbed by it, and none of the patients who did not hear their valve click felt disturbed. The disturbance of the patient was dependent on the loudness of the valve (no. 53). Fifteen (62.5%) of 24 patients who did feel disturbed by the sound had a sound level greater than 80 dB(A). We found 25% of our patients disturbed by the sound of mechanical valves, even years after their implantation. Patients with this problem have been found in numerous studies [1, 2, 4, 6–8]. We were able to further identify those patients who would feel disturbed by the valve sound because of simultaneously tested hearing capabilities and interviews of all patients. Patients with valve sounds greater than 75 dB(A) tended to feel disturbed, independent of time since the operation, age or sex of the patient, valve type or position, and heart rhythm (see Table 3, nos. 35 and 18; additional data not shown), but dependent on hearing impairment. We did find a significant correlation between loudness of a valve and the wish for a quieter prosthesis in the aortic position and overall (see Table 3, no. 47) and most of those patients whose valve sound was greater than 75 dB(A) wished they had a quieter valve (59.3%).
From our correlation analysis (see Table 3) and supported by multiple regression analysis it becomes clear that the three major factors influencing the wish for a quieter valve are disturbance and hearing of the sound and disturbance of significant others, and the two factors influencing the disturbance are whether a patient hears the click now and whether significant others are disturbed. In one-way analysis of variance for the St. Jude Medical, Björk-Shiley, and Duromedics-Edwards valves the valve type the patient received per se had no influence on the patient's perception. The fact that coumarin therapy had an impact on wishing for a quieter valve (no. 44) can probably be explained by the fact that the inconvenience of this treatment in itself is reason for many people to just wish they had a ``different'' valve.
The means of transmission of the sound remains controversial. Thulin and associates [2] quoted some unpublished studies from their audiology laboratory suggesting that the main transmission of valve sounds would depend on air conduction. Moritz and co-workers found that in only 15% of patients the valve sound perception could be suppressed by occlusion of the outer auditory canal [1] and that patients with body conduction had significantly more sleep disturbance and wished to have a quieter valve more often [7, 8]. Schöndube and colleagues [4] found an intensified sound with occlusion of the outer ear canal in their 20 patients with Björk-Shiley valves. This implies that body conduction plays a major role in sound transmission. To really evaluate the means of transmission, one would have to employ objective audiometry (registration of acoustically evoked potentials on electroencephalograms). Air conduction seems to play a major role in our study, although 34% of patients did report hearing with occluded outer auditory canal.
The analysis of frequencies related to the different valves was unsatisfactory in this study design. The individual valve groups were too small and the variability too large even in the same patient to actually find patterns of frequency bands. The stethoscope measurement analysis had a significant artifact caused by the stethoscope membrane vibration. Furthermore, we used a very broad classification for ``frequency maxima.'' Despite those limitations we found some significant distributions of the frequency maxima in different valves and concluded that patients with at least one side normal hearing heard their valve sounds independent of the distribution of frequencies in the valve sound. To diagnose valve malfunction, a more detailed classification and a more sophisticated statistical approach may lead to more satisfactory results. Studies by Cloutier and associates [17], Suobank and colleagues [18], Schöndube and co-workers [4], and Köymen and associates [19] show some of these analytic approaches.
The high percentage of patients who felt disturbed shows that the impact the valve sound has on patients' quality of life is not a rarity but presents a real postoperative problem. There were multiple reasons why not all patients felt disturbed by the valve sounds or wished for a quieter valve. A severe hearing impairment of the patient clearly diminished his or her irritation with the valve sound but did not eliminate it. The sound was sometimes a problem for the patients' partners or it had a detrimental effect on their social life, even if the patient did not hear the sound.
Our data lead us to the conclusion that many previously suspected cofactors for loudness of the different valves and disturbance with the ``click'' sound of mechanical heart valve prostheses are probably coincidental. In particular, factors such as valve size, heart rhythm, blood pressure, and body surface area did not seem to have an influence on sound perception. The finding by Thulin and associates [2] that especially younger and female patients feel disturbed by their valve ``click'' cannot be supported by our data. On the contrary, there was a slight predominance of men who heard their sound (see Table 3, no. 3). Our data analysis suggests that the group of patients who will be disturbed by their valve sounds cannot be determined without individualized testing of hearing impairment. Therefore patients should be evaluated for hearing impairment and sensitivity preoperatively with routine tone audiograms. All patients should be warned about the valve sound to be expected and, if possible, the loudness of a valve should become one of the selection criteria for mechanical heart valves. The major heart valve manufacturers should be encouraged to include the sound factor in their research protocol. The frequency analysis approach for valve diagnosis is promising but needs further investigation.
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Acknowledgments
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We are indebted to Dr Howard McGuire (Long Island University, Brooklyn, NY), who was our consultant statistician in the United States, Mr Axel Mohnhaupt, who was our consultant statistician in Germany, Professor Dr Horst Schmutzler and his staff in the cardiology outpatient clinic of the Universitätsklinikum Rudolf-Virchow, Standort Charlottenburg, and Professor Dr Volker Jahnke for use of the tone-audiometry equipment and chamber.
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Footnotes
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Address reprint requests to Dr Hofmeister, Deutsches Herzzentrum Berlin, Augustenburger Platz 1, 13353 Berlin, Germany.
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References
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Abstract
Introduction
