European Journal of Cardiovascular Medicine

Sense of hearing is of utmost importance to humans as it bridges communication with the outside world. Hearing loss equates to handicap as it denies an individual normal life. Various etiologies like Inflammatory, vascular, metabolic, traumatic, idiopathic etc, have been proposed to explain Sensorineural hearing loss (SNHL) in the general population. (1)

SNHL can be explained as a surgical complication of otological surgeries. However, development of SNHL with non-otological surgeries has become an area of concern and interest in recent times. (2) The first documented case of sudden unilateral deafness (SUD) following cardiac surgery was reported by Arenberg in 1972. Since then, this rare complication has gained attention. (3)

The incidence rate of approximately 1 in 1,000 for SUD associated with cardiac surgeriesis reported. (4)

Although the exact pathophysiology of hearing loss remains unclear, several hypotheses like micro-emboli formation, ischemic injury to the cochlea or auditory nerve, and hemodynamic fluctuations during the procedurehave been proposed. Many researchers have postulated a genetic basis behind this sudden development of hearing loss after surgery. (5,6) Extracorporeal circulation usage seems to bring an additional risk in terms of hearing loss. (7)

Routine assessment of hearing pre and post operatively is not commonly practiced in India despite hearing loss reported as a frequent complication, hence the need of this study.

This single-center, prospective observational study involved 210 diagnosed cases of Coronary artery disease (CAD), aged 18 to 60 years, undergoing primary Coronary artery bypass grafting (CABG).The study was conducted over a 12-month period in the department of CVTS and ENT at a tertiary care center in Kanpur, India with an aim to evaluate the effect of CABG on audiological parameters. Informed consent was obtained from all participants following approval from the institution’s ethics committee.

Objectives

1. To evaluate pre-operative hearing status by Pure Tone Audiometry (PTA)
2. To evaluate post-operative hearing by Pure Tone Audiometry
3. To corelate any change in hearing threshold post operatively

Inclusion Criteria

• Diagnosed cases of coronary artery disease (CAD) undergoing primary CABG
• Aged 18 to 60 years

Exclusion Criteria

• Patients of CAD with low ejection fraction
• Patients undergoing revision CABG
• Patients aged >60 years
• Patients with pre-existing hearing loss
• Patients with history of pervious ear surgery or ear trauma

Patients with confirmed diagnosis of CHD, undergoing primary CABG with or without extracorporeal circulation, were included in the study.

Detailed history, thorough cardiovascular, ENT and systemic examination of patients were obtained.

All the patients were subjected to otoscopic examination followed by audiological assessment via Pure Tone Audiometry (PTA) in a sound proof room pre-operatively, a day prior to surgery, and at 1week, 1 and 3 months post-operatively. Air and bone conduction thresholds were obtained by PTA. Thresholds below 25 dB were considered normal. Hearing loss was indicated by thresholds above 25 dB.

PTA results were evaluated and hearing loss was classified according to ASHA classification of hearing impairment(8).

Participants who required further audiologic workup were followed up at the ENT department.

The categorical data obtained was recorded and tabulated in MS excel worksheet and analyzed by using SPSS software/ window excel. Chi square tests were applied and significant findings recorded.

Demographic profile

Out of 210 patients undergoing CABG, the majority (148) were in the age bracket of 51-60 years (70.5%).

Males 154(73.3%) outnumbered females 56(26.7%), with a male-to-female ratio of 2.7:1.

Urban areas accounted for most of the cases, 128(61%) surpassing those in rural areas 82 (39%).

Table 1 showing the demographic profile:

COMORBIDITIES

Among the 210 patients included in the study, hypertension was the most common comorbidity, affecting 183 patients (87.1%). Dyslipidemia was also highly prevalent, observed in 156 patients (74.3%). Diabetes mellitus was present in 87 patients (41.4%), with 48 patients (22.9%) having both hypertension and diabetes, indicating a significant burden of metabolic syndrome components. Tobacco use was widespread, with 182 patients (86.7%) reporting regular use, and 139 patients (66.2%) having a history of smoking.

Figure 1: showing the distribution of comorbidities among coronary artery disease patients

INTRA-OPERATIVE VARIABLES

Of the 210 patients undergoing primary coronary artery bypass graft (CABG) surgery, 167 patients (79.5%) underwent off-pump CABG (OPCAB), while 43 patients (20.5%) underwent the procedure with the use of cardiopulmonary bypass (on-pump CABG) involving extracorporeal circulation.

Table2 showing the intra-operative variables of patients undergoing CABG

Intraoperative hypotension was notably more common among on-pump patients (27.9% vs. 12.6%, p = 0.017), suggesting a possible hemodynamic mechanism contributing to cochlear stress or ischemia.

OTOSCOPY

Tympanic membrane was found intact in all 210 patients. Membrane was mobile on siegelization in all cases.  

AUDIOLOGICAL ASSESSMENT

Pre-operative PTA was performed 1-2 day prior to surgery.Auditory threshold mean was calculated at speech frequency i.e. 500, 1000 and 2000Hz for both air and bone conduction.

Table 3 showing the Pure Tone Auditory threshold for speech frequencies:

POST-OPERATIVE PTA

PTAwas performed at one week, one month, and three months postoperatively in both the off-pump and on-pump groups.

In the off-pump group (n = 167), bilateralsensorineural hearing loss was observed in 1 patient (0.6%), which persisted across all three time points, indicating a sustained hearing loss up to 3 months post-surgery.

In contrast, in the on-pump group (n = 43), 2 patients (4.6%) exhibited bilateral SNHL on PTA performed at 1 week. At the 1-month follow-up, an additional patient developed right sidedhearing loss, increasing the total to 3 patients (6.9%). However, by the 3-month assessment, 1 patient showed recovery, and 2 patients (4.6%) continued to have persistent SNHL.These findings indicated a higher incidence and variability of hearing loss in the on-pump group.

No of patients with SNHL                Off-pump(n=167)                         On-pump(n=43)

                                             01                     01                   01                 02                  01                02

Table 4 showing the Pure Tone Auditory threshold for speech frequencies at 1 week, 1month and 3 months post-operatively:

Auditory thresholds at 500, 1000, and 2000 Hz, conducted at one week, one month, and three months post-operatively, did not reveal any statistically significant change in either the off-pump or on-pump groups when compared to pre-operative values. This suggested that coronary artery bypass grafting (CABG) did not lead to a generalized deterioration in hearing thresholds.

Out of three patients with SNHL, 2 (66.6%) exhibited mild hearing impairment, whereas one(33.3%) presented with moderate hearing loss, indicating that while the overall risk is low, individual susceptibility exists, especially in the on-pump group.

Figure 2 showing pre and post-operative hearing threshold difference at three months

Table 5 showing relation of comorbidities with hearing loss:

DM- Diabetes mellitus; HTN- Hypertension; S- Smoker; T- Tobacco chewer

The patient with moderate hearing loss had multiple co-morbidities, including diabetes mellitus, hypertension, history of smoking, and tobacco chewing. In contrast, the two patients with mild hearing loss showed lesser PTA changes of 11 dB and 8 dB, respectively. One of these patients had diabetes, hypertension, and a history of smoking, while the other had hypertension and smoking as the only identifiable risk factors. Notably, the patient with the least degree of hearing loss had undergone off-pump surgery. These findings suggested a potential association between the cumulative burden of vascular and lifestyle-related co-morbidities and the severity of post-operative hearing loss.

In the present study majority of patients (70.5%) were in the age group of 51–60 years. This age-related distribution reflected the typical demographic affected by advanced coronary artery disease. Mohammadi S. et al. also reported a similar pattern, with most patients undergoing CABG being over 50 years of age, highlighting the progressive nature of atherosclerosis with advancing age (9).

With regard to gender, our study showed a clear male predominance (73.3%), with a male-to-female ratio of approximately 2.7:1. This result is in accordance with findings reported by Hlatky M.A. et al., who observed that males constituted the majority of patients undergoing bypass (10).

61% of the patients in our study were from urban areas, while the remaining 39% were from rural backgrounds. This urban predominance may be attributed to easier access to tertiary care centers, higher health awareness, and better referral systems in urban regions. These findings agree with those reported in national data from the Registrar General of India (11)and Bhan N. et al. (12).

In the present study,out of 210 patients, 3 individuals (1.4%) developed postoperative sensorineural hearing loss (SNHL). Of these, 2 patients (4.6%) belonged to the on-pump group and 1 patient (0.6%) to the off-pump group, suggesting a relatively higher incidence of SNHL in the on-pump population. This finding is in accordance with the study by Plasse et al., who reported a higher incidence of sudden unilateral deafness in patients undergoing cardiopulmonary bypass (CPB), likely due to microemboli or ischemic injury during extracorporeal circulation (4).

Among the three affected patients, two exhibited mild hearing loss, while one developed moderate SNHL. Interestingly, the patient in the off-pump group who developed SNHL had only mild threshold elevation (8 dB), while one on-pump patient had a moderate shift of 24 dB, implying a possible correlation between extracorporeal circulation and the degree of hearing impairment. Similar observations were made by Aytacoglu et. al. (13).

Statistical analysis of PTA thresholds at 500, 1000, and 2000 Hz showed no significant threshold change at 3 months post-op in either on-pump or off-pump groups (p > 0.05). This study is in concordance with the findings ofBrowne et al. (14) and Munjal et. al. (15)Howevercontrary to our results, Gianoliet al.(16) reported hearing changes in a small subset of patients post-CPB surgery  in his study.

Additionally, in the present study, all three patients who developed SNHL had one or more vascular comorbidities, such as diabetes, hypertension and smoking. The results aligned with the observations of Kaidzuet al.(17), Sadeghi et. al. (18) and Kapil et. al. (19)

Our study suggested that while CABG did not led to a statistically significant decline in auditory thresholds, individuals with multiple comorbidities, particularly those undergoing on-pump CABG, were at elevated risk for postoperative SNHL. This was further supported by the higher rate of intraoperative hypotension observed in the on-pump group (27.9% vs. 12.6%, p = 0.017), which may had contributed to transient or permanent cochlear hypoperfusion.

While coronary artery bypass grafting appears to be largely safe in terms of preserving hearing, the small but notable risk of SNHL, particularly in patients undergoing on-pump CABG with vascular comorbidities, merits further attention. Routine pre- and post-operative audiological assessment, especially in high-risk individuals, may be valuable for early identification and rehabilitation of hearing loss.

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