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the square root of the mean sum of squares differences Table 2: The results of time‑domain analysis of HRV
between adjacent NN intervals; (4) SDNN index (ms): Variable Patients (n = 20) (%) Controls (n = 20) P
mean of the standard deviations of all NN intervals SDNN (ms) 12 (60) 0 0.001
for all 5-min segments of the entire recording; (5) 45.30‑111.20 86.33‑198.70
SDSD (ms): standard deviation of differences between SDANN (ms) 55.70 ± 20.23 152.75 ± 15.66 0.001
9 (45)
0
adjacent NN intervals; (6) NN50 count: number of pairs 44.50‑116.35 94.40‑180.68
of adjacent NN intervals differing by more than 50 ms in 58.19 ± 13.80 142.23 ± 12.09
0
12 (60)
the entire recording; three variants are possible counting SDNN index (ms) 42.30‑138.56 92.43‑166.62 0.001
all such NN intervals pairs or only pairs in which the 56.46 ± 20.02 112.64 ± 16.22
first or second interval is longer; and (7) pNN50%: RMS‑SD (ms) 8 (40) 0 0.001
percentage of differences between adjacent normal NN 12.30‑45.70 5.64‑95.55
intervals that are greater than 50 ms computed over the pNN50 (%) 20.51 ± 6.06 46.57 ± 4.24 0.001
0
6 (30)
entire 24-h ECG recording. 0.10‑14.50 0.60‑23.22
1.40 ± 0.32 14.42 ± 2.86
The warning signs of cardiac problems include: VEs in Data are expressed as number of patients with abnormalities, range, mean ± SD.
SD: Standard deviation; HRV: Heart‑rate variability
excess of 10/h, VE Pair, V-Runs, R on T beats, SV-Runs,
A-Fib, pauses in excess of 2.5 s, QTc in excess of 460 reduced indices of HRV (SDNN, SDANN, SDNN Index,
ms, ST depressions of 1 millimeter or more (a strong RMS-SD and pNN50) (P = 0.001 for all). No significant
indication of cardiac ischemia) and SDNN of 50 ms correlations were reported between SDNN, RMS-SD,
or less. pNN50 and duration of illness.

Statistical analysis DISCUSSION
Calculations were done with the statistical package SPSS,
version 12.0. Data were presented as mean ± standard In this study, dynamic ECG showed evidence of
deviation. Unpaired two-sided Student’s t test was utilized subclinical autonomic cardiac dysfunction in patients
for comparison among means of normally distributed with MG with mild/moderate severities. Cardiac
parameters, while Mann-Whitney U-test was for all other autonomic functions were assessed by measuring the
cases. Correlations were assessed using Pearson’s and cyclic variation of the heart beat intervals (i.e., HRV).
Spearman’s methods for normally and non-normally HRV reflects the complex interplay of sympathetic
distributed data, respectively. For all tests, values of and parasympathetic innervation of heart. The lack
P < 0.05 were considered statistically significant. of intra-individual variability over time makes the
measurement of HRV an excellent tool for studying
RESULTS autonomic input of the heart. [31] In the present study,
components of the time-domain analysis (SDNN,
This study included 20 patients with MG. They had RMS-SD, pNN50) were significantly reduced in
mean age of 28.45 ± 8.89 years and mean duration patients with MG. No significant correlations were
of illness of 3.52 ± 1.15 years. None of the patients identified between HRV indices and duration of
reported symptoms related to arrhythmias as syncope, illness. Accordingly, previous studies did not report
dizziness, palpitation, shortness of breath, chest significant correlations between autonomic nervous
discomfort, diaphoresis, or neurological symptoms system dysfunction and disease duration, clinical
such as transient ischemic attack. Conventional manifestations, cardiovascular risk factors and diseases
echocardiographic measures were normal for all activity were reported. [19,23]
patients. The total ambulatory 24-h ECG recording
period was ranged between 18 and 24 h (mean: SDNN reflects overall autonomic modulation of the
22.00 ± 0.35). The minimum heart-rates were found heart but does not provide no information regarding
during sleeping and ranged from 47 to 75 beats/min isolated sympathetic and parasympathetic activities,
(mean: 58 ± 8) and the maximum heart-rates trends while RMSSD and pNN50 which reflect very short-term
were found during awake and ranged from 112 to 145 HRV are predominantly mediated by the vagus nerve. [32]
beats/min (mean: 90 ± 12). Minimum R-R ranged from Reduced HRV is well known to be associated with
296 to 560 ms (mean: 421 ± 47) and the maximum susceptibility to cardiac arrhythmias. Previous studies
[33]
R-R intervals ranged from 868 to 1,618 ms (mean: had also shown that reduced HRV is an independent
1,255 ± 205). VEs and SVEs were found in 11 (55%) risk factor for arrhythmic sudden death after myocardial
and 7 (40%) of patients (versus none for controls) infarction. In their study, Vernino et al. reported
[34]
[19]
respectively. SVEs were less than 25/24 h. Depressed impaired HRV and a low vagal tone and modified cardiac
ST-T was reported in 4 (20%) patients. Table 2 shows parasympathetic modulation, orthostatic hypotension
the results of HRV in the time-domain. Patients had and gastrointestinal manifestations (severe abdominal

Neuroimmunol Neuroinflammation | Volume 2 | Issue 1 | January 15, 2015 23