Academy of Doctors of Audiology

Author: Carol Knightly, Au.D.

According to the Centers for Disease Control and Prevention, 11.5% of adults in the US have cardiovascular disease (CVD), the most common cause of death worldwide (CDC, 2016). Likewise, congenital heart malformations in children are the most common birth defect, affecting some 40,000 newborns in the United States each year (CDC, 2018). Thirty percent of those newborns will require some sort of intervention during the first year of life; very often, that intervention is surgical. It is likely, therefore, that the caseload of an audiologist will include individuals with some type of cardiovascular disorder.

We have long been aware of genetic abnormalities and syndromes that include both hearing loss and heart defects, such as Down syndrome, Goldenhar syndrome, CHARGE syndrome, Velocardiofacial syndrome and Jervell Lange-Nielsen syndrome. There also appears to be a relationship between CVD and hearing loss. Perhaps most importantly, however, there is evidence for a predictive relationship between hearing loss and sub-clinical CVD, before other, better-known, symptoms appear. Finally, just recently, we have begun to examine the relationship between congenital heart defects requiring surgery in infancy and permanent childhood hearing loss.

Myocardial infarction (heart attack) and stroke are common causes of death resulting from CVD, and those two events are generally caused by atherosclerosis, thromboses, hypertension, valve malformations or atrial fibrillation. Atherosclerosis, commonly referred to as “hardening of the arteries” is a build-up of a substance called plaque on the interior walls of the blood vessels, of which cholesterol is a key component. Plaque build-up can severely restrict blood flow, resulting in the formation of blood clots called thrombi, or obstruct the flow of blood through a vessel entirely. If a thrombus breaks off and begins to travel through the body, it is referred to as an embolism. An embolism can travel unimpeded through the body until it comes to narrower blood vessels, where it can lodge resulting in ischemia, or insufficient blood flow beyond that point to provide adequate oxygenation, and localized death of cells and tissue.

Hypertension, or high blood pressure, damages the interior walls of the blood vessels, making them more susceptible to the build-up of plaque. Hypertension can also result in “leaky” blood vessels.

There are four valves in the heart, which are responsible for ensuring that the blood flows in only one direction. If the valves do not function properly as a result congenital malformation or scarring from an infection, they can restrict blood flow, as in stenosis, or allow some amount of regurgitation, resulting in embolism.

Finally, atrial fibrillation is an irregular heartbeat, or arrhythmia. In cases of arrhythmia, the blood does not empty from the heart completely with each contraction, leading to the formation of blood clots in the heart, which can then travel to lodge in smaller blood vessels, resulting in ischemia. Significant restriction of blood flow to the heart itself will result in myocardial infarction.

The relationship between CVD and hearing loss is straightforward. The inner ear is a large consumer of energy, relying on metabolism of both glucose and oxygen supplied by the blood to fuel the stria vascularis. The stria vascularis maintains the overall health of the cochlea, important to the organ of Corti and, in turn, endocochlear potentials.

Damage to the cochlea from CVD can occur for a number of reasons. First, the blood supply to the cochlea is delivered via extremely small vessels, or capillaries. Capillaries are very susceptible to damage from high blood pressure and embolism, or even microembolism (Gyo, 2013). An embolism that passes through other arteries unimpeded because of their relatively larger size can become lodged in the supply vessels to the cochlea. In addition, few arteries feed the cochlea. If they become damaged or blocked from hypertension or embolism, there is no collateral blood supply. Finally, the blood supply to the cochlea is relatively sparse at the apex, compared to that of the base.

Given the likely insults to the cochlea from CVD, there are somewhat predictable patterns of associated sensorineural hearing loss (SNHL). There are a number of different types of presbycusis affecting older adults: sensory, neural, metabolic and mechanical (Lee, 2013). Of particular interest here is metabolic, or strial, presbycusis. Any degeneration in health of the stria vascularis from embolism or micro-bleeds will impact the quality of endolymph. And, since endolymph flows throughout the cochlea, the resulting SNHL is often of flat configuration.

Sudden-onset unilateral SNHL has been associated with embolism in the arteries supplying the cochlea, and there here have been cases reported of sudden onset unilateral hearing loss followed by stroke (Gur, 2006). High frequency SNHL has been associated with micro-bleeds of the capillaries supplying specific regions of the cochlea. Finally, as mentioned, the blood supply to the apical portion of the cochlea is relatively sparse in comparison to that of the basal section. Degradation of the blood supply to the cochlea, therefore, has been implicated in low frequency SNHL.

Because the blood supply to the cochlea is so susceptible to the CVD process, it is possible that hearing loss would appear in advance of other symptoms of CVD. In fact, hearing loss has been shown to be predictive of larger, more serious, CV events. In 1993, Gates, et al. showed that the odds ratio (OR) of having any CV event and low frequency PTA presbycusis of 40 db HL was 3.06 for women. For men, the OR for coronary artery disease and low frequency PTA presbycusis of 40 db HL was 1.68. However, the OR increased to 3.46 for stroke in men. A 2009 study by Friedland, et al. showed that approximately 85% of individuals suffering a stroke had low-frequency or flat hearing loss. Consequently, Friedland has suggested that individuals with low frequency SNHL be regarded as at-risk for CVD, and that consideration be given to referral for appropriate follow-up.

Treatment for CVD includes lifestyle changes and sometimes medication and surgery. Many cases of CVD are preventable though lifestyle changes. Smoking cessation or adhering to specific diets may, in fact, reverse CVD. In addition, it has been suggested that increasing aerobic activity for a period of as little as 6 months results in faster recovery from temporary threshold shift, evidence of a protective effect for the ear.

Surgical intervention theoretically introduces an entirely new set of potential risks for hearing loss. While extended high-frequency audiometry and TEOAEs have shown evidence of sub-clinical hearing loss, there is somewhat conflicting evidence in the literature that techniques used during cardiac surgery, including cardiac bypass and deep hypothermic circulatory arrest, have any significant measureable or self-reported impact on hearing sensitivity (Aytacoglu, 2005; Munjal, 2013) except in the pediatric population.

Neurodevelopmental disabilities are the most common sequelae in children following infant cardiac surgery (International Cardiac Collaborative on Neurodevelopment Investigators, 2016), but the impact is highly variable and may lessen over time. There are comparatively few studies examining hearing loss following cardiac surgery in children.

The prevalence of permanent childhood hearing loss (PCHL) is 1-3 per 1000 in the general population, and 2-4 per 1000 in NICU survivors (Delaney, 2018). Recent studies (Bork, 2018; Grasty, 2018) have suggested that the prevalence of PCHL in children following infant cardiac surgery ranges from 59 to 69 per 1000, an almost twentyfold increase. The risk factors, as well as the degree and configuration of hearing loss, vary. In addition, not all study participants had reviewable newborn hearing screening results, but for those that did, the results were a pass. Regardless of the cause of hearing loss in these cases, infant cardiac surgery should be considered a risk factor for hearing loss.     Carol Knightly, Au.D., CCC-A, is director of clinical operations in the Center for Childhood Communication and the Center for Rehabilitation at CHOP. She received her Bachelor of Arts degree in Speech& Hearing Science & Psychology form Thiel College, her Master of Arts degree from The Ohio State University and her Doctor of Audiology degree from the University of Florida. Aytacoglu BN, Ozcan C, Sucu N, Gorur K, Doven O, Camdeviren H, Kose N, Dikmengil M. (2006) Hearing loss in patients undergoing coronary artery bypass grafting with or without extra corporeal circulation. Medical Science Monitor. 12(6): CR253-9.

Bork KT, To BP, Leonard NJ, Douglas CM, Dinon DA, Leonard EE, Valeriote HA, Usher LF, Robertson CMT. (2018) Prevalence of Childhood Permanent Hearing Loss after Early Complex Cardiac Surgery. Journal of Pediatrics. Jul; 198:104-109.

Centers for Disease Control and Prevention. (2016) Summary Health Statistics: National Health Interview Survey. https://ftp.cdc.gov/pub/Health_Statistics/NCHS/NHIS/SHS/2016_SHS_Table_A-1.pdf

Centers for Disease Control and Prevention. (2018) Congenital Heart Defects. https://www.cdc.gov/ncbddd/heartdefects/data.html

Delaney A, Meyers A. (2018) Newborn Hearing Screening. Medscape. https://emedicine.medscape.com/article/836646-overview

Friedland D, Cederberg C, Tarima S. (2009) Audiometric Pattern as a Predictor of Cardiovascular Status: Development of a Model for Assessment of Risk. Laryngoscope. 119(3): 473-86.

Gates G, Cobb J, D’Agostino R. (1993) The relation of hearing in the elderly to the presence of cardiovascular disease and cardiovascular risk factors. Archives of Otolaryngology Head and Neck Surgery. 119(2): 156-161.

Grasty MA, Ittenbach RF, Knightly C, et al. (2018) Hearing loss after cardiac surgery in infancy unintended consequence of life-saving care: Journal of Pediatrics. Jan; 192: 144-151.

Gur C, Lalazar G, Raphaeli G, Gilon D, Ben-Chetrit, E. (2006) Mitral stenosis presenting with acute hearing loss. Public Library of Science Medicine. Jun; 3(6): e 233.

Gyo K. (2103) Experimental study of transient cochlear ischemia as a cause of sudden deafness. World Journal of Otorhinolaryngology. 3(1): 1-15.

International Cardiac Collaborative on Neurodevelopment (ICCON) Investigators. (2016) Impact of Operative and Postoperative Factors on Neurodevelopmental Outcomes after Cardiac Operations. Annals of Thoracic Surgery. 102(3):843-849.

Lee K. (2013) Pathophysiology of age-related hearing loss (peripheral and central). Korean Journal of Audiology. 17(2):45-49.

Munjal SK, Malik P, Sharma A, Panda NK, Thingnum SK. (2013) Effects of cardiopulmonary bypass surgery on auditory function: a preliminary study. ISRN Otolaryngology. Aug 29; 2013:453920