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Cardio Diabetes Medicine 2017 261

Heart Rate Variability in Ischemic

Heart Disease and Diabetes

Dr. R. Hari hara Krishnan MD., DM(Cardio).,
Asst.Prof. cardiology,
Stanley medical college Chennai.

INTRODUCTION to-day basis and over periods of days to weeks when
Evaluation of beat-to-beat heart rate dynamics, as a there are no major intervening clinical events.
noninvasive albeit indirect probe of autonomic ner-
vous system function, is of interest from a number of AUTONOMIC NERVOUS SYSTEM
basic perspectives with potential translational appli- INTERACTIONS WITH CARDIAC RATE AND
cations. For example, a large body of clinical and ex- RHYTHM
perimental evidence that indicates an important role Modulation of heart rate and the autonomic nervous
for the autonomic nervous system in the triggering system: The autonomic nervous system is the pri-
or sustaining of malignant ventricular arrhythmias . mary regulator of heart rate in the presence of sinus
Higher sympathetic activity unopposed by vagal ac- rhythm . The intrinsic sinus node rate at rest (ie, the
tivity promotes arrhythmia in a variety of ways:
rate after pharmacologic or surgical denervation of
• Reducing ventricular refractory period and the the sinus node) is 95 to 110 per minute . Under nor-
ventricular fibrillation threshold mal supine resting conditions, there is little efferent
sympathetic neural input, and the concentration of
• Promoting triggered activity after potentials
circulating catecholamines is low; however, there is
• Enhancing automaticity substantial efferent parasympathetic traffic on the
vagus nerves, which slows the sinus node rate to 60
Vagal stimulation opposes these changes and reduc-
es the effects of sympathetic stimulation by prolong- to 70 per minute in most adults. Keep in mind that
ing refractoriness, elevating the ventricular fibrillation resting heart rate is determined by both sympathetic
threshold, and reducing automaticity. There are three and parasympathetic tone (ie, the basic firing rate of
major noninvasive or minimally invasive assessment the nerves). Heart rate variability (HRV) measures the
approaches to evaluating the functioning of the au- fluctuations in the RR intervals (also referred to as NN
tonomic nervous system. intervals for presumed sinus beats) related primarily
to autonomic control
• RR interval (RRI) or heart rate variability (HRV) Triggering of cardiac arrhythmias and the autonom-
from short-term or longer term monitoring
ic nervous system: Both branches of the autonomic
• Baroreflex sensitivity (BRS) testing nervous system have an important role in the trig-
gering or sustaining of malignant ventricular arrhyth-
• Bedside autonomic function tests (eg, Valsalva
maneuver, tilt testing, and other orthostatic chal- mias, particularly post-myocardial infarction (MI). This
lenges) relationship partly explains the predictive value of
abnormal HR variability for such events to the ex-
The utility of HRV measures for prediction of out- tent that the arrhythmogenesis is a consequence of
come or detection of changes in clinical status de- alterations in autonomic functioning.
pends on their stability over time. HRV is influenced
significantly by age, race, sex, physical fitness, clini- The sympathetic nervous system: Chronically in-
cal conditions, and drug treatment, but most 24-hour creased sympathetic activity and elevated plasma
HRV appears to be stable when measured on a day- catecholamines can be found in the setting of myo-
cardial dysfunction . These alter the electrophys-

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