New risk factor for sudden cardiac death: Untreated Obstructive Sleep Apnoea

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New risk factor for sudden cardiac death: Untreated Obstructive Sleep Apnoea

A long-term study found that 7 out of 100 sleep apnoea sufferers can die of sudden cardiac death (SCD) if obstructive sleep apnoea (OSA) is left untreated.

Snoring, choking episodes at night, sleep associated with multiple episodes of wakefulness and shortness of breath or daytime drowsiness are the symptoms present; if an individual has any two or more of these symptoms, then he/she is most likely to be suffering from OSA. OSA has been found to be associated with multiple conditions like diabetes, hypertension, heart disease and also SCD.

Sudden Cardiac Death

SCD is an unexpected loss of life due to loss of heart function which has been reported as a leading cause of natural death in United States. It is responsible for 4.5 lakh annual deaths in United States alone. Moreover, it is the young people, adults in their mid-30s to mid-40s, without known, traditional cardiac risk factors that run the highest risk of SCD. Recent studies have probably unravelled one such unrecognised factor, not known traditionally, for SCD, which is OSA.

People with untreated and undiagnosed OSA may have higher episodes of irregular heart beat. Impaired wake-up mechanism due to apnoea (cessation of breathing) in these patients leads to low oxygen levels to the brain that may eventually turn fatal.

Dark hour of sudden cardiac death with Obstructive Sleep Apnoea

A study spanning over 5 years, which included 10,000 adults referred to sleep disorders clinic, found OSA to be independently responsible for SCD, with men at double the risk in comparison to women.

In patients with OSA, the nights are not safe or rested. They tend to run a higher risk of SCD during the night hours between midnight and 6 am. The chances of reviving a patient from sudden cardiac arrest are already known to be low and during night a cardiac event, such as ischaemia (reduced blood flow to the heart) or arrhythmia (irregular heart beat) even if recognised by patient may not be useful as appropriate help may not be available within the right hour and hence the risk of death further increases. In heart diseases, time is of great importance. Receiving help within the golden hour can make all the difference. At nights, the inability to receive this help at the right time may further decrease the survival chances.

Likelihood of death more than double for untreated severe obstructive sleep apnoea (Apnoea-hypopnea index [AHI] > 30)

The Wisconsin sleep study spanning over eighteen years found a high number of deaths among untreated people with OSA. Age, gender, body mass index (BMI) or even symptoms of sleepiness were not identified as recurrent factors in this study. The number of pauses in breathing and choking episodes were the measurements used for finding how serious was the condition and how high was the risk of SCD.

Fig 1

Fig. 1: Survival probability in patients with OSA, adapted from original article in Sleep, 2008

AHI shown in the above graph represents number of pauses that occur in breathing through the night. Lesser the pauses in breathing (AHI < 5) calculated by sleep study, double was the survival chance in comparison to those with mild-to-moderate OSA. While, in those with severe OSA, with 30 or more episodes of pause in breathing, the risk of dying was the highest.

Continuous positive airway pressure (CPAP) therapy prevents health problems associated with OSA

The best approach to treat all the associated, serious conditions with OSA is by prevention, that is by treatment of OSA with CPAP or other therapies. CPAP therapy used for the treatment of OSA reduces the nighttime stress, which is evident by reduction in the associated stress hormones (catecholamine levels) during those hours. Reduction in the daytime blood pressure has also been reported which further minimizes the risk of heart disorders.

Patients who are diagnosed and actually follow the doctor's instructions are the ones that can reduce the chances of suffering from SCD. A long-term study of over 7 years among patients who diligently followed their treatment with CPAP reported no deaths in the group treated for OSA with CPAP. However, 7% deaths due to SCD among those untreated for OSA were reported. A number of studies have reported low death risk among those treated with CPAP.

It is important to note that those who have symptoms of loud snoring or wake-up feeling "short of breath" must consult a sleep specialist who may recommend a sleep study or polysomnography to diagnose sleep apnoea. Sleep study comprises of overnight monitoring of breathing and other body functions during sleep. Patient may be hooked to multiple equipments to monitor heart, lung and brain activity, breathing patterns, arm and leg movements and blood oxygen levels while they are asleep.

The specialist would recommend treatment such as lifestyle changes, CPAP or surgery based on individual case merits for reducing the risk of several diseases associated with OSA, including SCD.

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