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Low heart rate variability and sudden cardiac death
D H Singer1, G J Martin, N Magid
1Reingold ECG Center, Northwestern University Medical School, Chicago, IL 60611.
Insights
Reduced heart rate variability (HRV) indicates depressed cardiac parasympathetic function, a risk factor for sudden cardiac death (SCD). HRV may serve as a noninvasive screen for identifying individuals at high risk of SCD.
Area of Science:
- Cardiology
- Autonomic Nervous System Function
- Cardiac Electrophysiology
Background:
- Sudden cardiac death (SCD) remains a significant cause of mortality.
- Altered autonomic function, particularly reduced parasympathetic activity, is implicated in cardiac electrical instability.
- Existing risk factors for SCD, such as coronary artery disease and hypertension, are associated with diminished parasympathetic activity.
Purpose of the Study:
- To investigate the relationship between heart rate variability (HRV) and the risk of SCD.
- To determine if HRV can serve as an independent predictor of SCD inducibility.
- To explore the potential of HRV as a noninvasive screening tool for individuals at risk of SCD.
Main Methods:
- Analysis of heart rate variability (HRV) in patients with a history of inducible SCD and in patients with asymptomatic ventricular ectopy.
- Comparison of HRV in inducible versus noninducible patients.
- Correlation of HRV with established SCD risk factors and autonomic function.
Main Results:
- HRV was markedly depressed in inducible SCD survivors and in patients with inducible asymptomatic ventricular ectopy.
- HRV depression in inducible patients paralleled that of SCD survivors.
- HRV did not differ in noninducible asymptomatic ventricular ectopy patients compared to normal controls.
- Findings suggest depressed cardiac parasympathetic function in individuals prone to SCD.
Conclusions:
- Depressed cardiac parasympathetic activity, as indicated by reduced HRV, contributes to electrical instability and SCD risk.
- HRV measurements show potential as an independent predictor of SCD inducibility.
- HRV may serve as a valuable noninvasive screening tool for identifying individuals at increased risk of SCD.
Abstract:
Our results indicate the following. 1. HRV is markedly depressed in inducible SCD survivors, a group at high risk of a subsequent episode of SCD. 2. Studies on patients who developed SCD during Holter monitoring indicate that HRV is depressed prior to SCD. 3. HRV is markedly depressed in inducible "asymptomatic ventricular ectopy" patients, with the degree of reduction paralleling that observed in inducible SCD survivors. In contrast, HRV of noninducible "asymptomatic ventricular ectopy" patients did not differ statistically from normal. 4. The findings provide additional evidence that cardiac parasympathetic function is depressed in patients prone to development of SCD and that altered autonomic function contributes to the development of electrical instability in such individuals. This accords with findings that such risk factors for sudden death as coronary artery disease, myocardial infarction, congestive failure, and hypertension all have been associated with reduced parasympathetic activity or attenuation of parasympathetically mediated reflexes. It is tempting to believe that diminished cardiac parasympathetic activity, perhaps by failing to counter excess sympathetic activity, contributes to SCD. 5. It may be inferred that HRV measurements have potential for serving as an independent predictor of inducibility in response to programmed ventricular stimulation and that they could represent a noninvasive screen for patients referred for evaluation of risk of SCD because of asymptomatic ventricular ectopy or other causes. In a larger sense, the data suggest that HRV measurements may provide information pertinent to the identification of individuals at increased risk of SCD that is independent of that provided by other risk factors. Given the human and economic stakes, further study is clearly warranted.