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CLINICAL USES OF HRV — and that reduced HRV was associated with disease
severity measures such as NYHA functional class,
• Prediction of risk of cardiac death or arrhythmic
events post-myocardial infarction (MI) left ventricular diastolic dimension, reduced left ven-
tricular ejection fraction, and peak O2 consumption
• Detection and quantification of autonomic neurop- . Prognostically, reductions in HRV have been shown
athy in patients with diabetes mellitus to be independent predictors of overall mortality,
Prediction of mortality in the early post-MI period: The mortality from heart failure, sudden cardiac death,
impact of HRV on prognosis post-myocardial infarc- ventricular arrhythmias, and the need for transplant .
tion (MI), initially reported in the era prior to treat- Improvements in HRV are seen with effective heart
ment with thrombolysis, has also been validated in failure therapy (eg cardiac resynchronized therapy
patients with an MI treated with thrombolytic therapy . [CRT]). Patients with improved HRV after CRT have
Patients with reduced indices of HRV measured early been shown to have better outcomes than those in
following an MI (within 14 days) have a three- to four- whom HRV is not improved.
fold greater risk of death within three years following
an MI. However, the sensitivity of measures like Heart rate variability in diabetes patients: Diabetes
SDNN <50 ms as predictors of mortality, originally mellitus is one of the main causes of autonomic neu-
estimated to be about 30 percent, have declined ropathy. Cardiovascular autonomic neuropathy can
simply because improvements in post-MI treatment cause abnormalities in heart rate control. Diabetic
have resulted in markedly fewer patients having autonomic neuropathy frequently coexists with oth-
SDNN at those levels.. er diabetic complications. This complication, which is
present in 20 – 40% of diabetes patients, is a cause of
Prediction of mortality in the late post-MI period: While increased morbidity and mortality. Cardiac autonom-
reduced HRV in the early post-MI period is clearly ic dysfunction has been diagnosed since the 1970s
associated with a worse prognosis among patients by manoeuvres that elicit cardiovascular reflexes. In
from the pre-PCI era, the substantial recovery of HR recent years, the use of time-domain and frequen-
variability within the three months after myocardial cy-domain parameters of heart rate variability has
infarction, particularly following an inferior infarct, been recommended as a reliable and easy method.
raises a question as to whether recovery values for Diabetes caused progressive autonomic dysfunction
HR variability predict death . Among the 68 place- and decreased variability in heart rate. When cardio-
bo-treated patients entered into the Cardiac Arrhyth- vascular autonomic neuropathy is identified in a pa-
mia Pilot Study (CAPS) who had 24-hour ECG record- tient with diabetes, there should be aggressive treat-
ings at baseline and at 3, 6, and 12 months after MI, ment to control cardiovascular risk factors, because
there was a substantial increase in all measures of these may be associated with the development of
HRV between three weeks and three months . On cardiovascular mortality . Insulin therapy can cause
average, recovery of HRV was completed by three regression of cardiovascular autonomic neuropathy.
months post-MI; between 3 and 12 months, the val- In conclusion, patients with diabetes had lower val-
ues were stable for the group as a whole and for ues of heart rate variability parameters than healthy
individual patients. controls, and among diabetes patients those with
Patients with stable CHD: An association between microvascular complications had the lowest heart
decreased HRV and the presence of significant rate variability parameters. Patients with microvas-
coronary heart disease (CHD) has been suggested. cular complications should be followed up more in-
Among 470 consecutive patients undergoing elec- tensely than others and should be treated with insu-
tive coronary angiography, patients with obstructive lin to prevent the progression of cardiac autonomic
CHD (>50 percent stenosis) had significantly reduced dysfunction. Diabetes patients had lower values for
HRV based on five-minute supine measurement, es- time-domain and frequency-domain parameters than
pecially in the low frequency range (180 with versus controls. Most heart rate variability parameters were
267 ms without obstructive CHD) . In a multivariate lower in diabetes patients with chronic complications
2
analysis using a cutoff of 250 ms , persons with low than in those without chronic complications.
2
frequency power below 250 ms were at significantly
2
greater risk of obstructive CHD ,independent of base- SUMMARY AND RECOMMENDATIONS
line Framingham Risk Scores. • There are three major noninvasive or minimally in-
vasive assessment approaches to evaluating the
Patients with heart failure: Several studies have
shown that patients with heart failure and/or cardio- autonomic nervous system which provide comple-
myopathy have reduced HRV compared with controls, mentary information about autonomic as well as

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