Acta Med. Okayama, 2019Vol. 73, No. 2, pp. 147‑153
CopyrightⒸ 2019 by Okayama University Medical School.

Original Article

http://escholarship.lib.okayama-u.ac.jp/amo/

Prolonged Tachycardia with Higher Heart Rate Is Associated with
Higher ICU and In-hospital Mortality
Masao Hayashia＊, Arata Taniguchia, Ryuji Kakua, Shusaku Fujimotob,
Satoshi Isoyamaa, Sei Manabec, Tsubasa Yoshidad, Satoshi Suzukia,
Kazuyoshi Shimizua, Hiroshi Morimatsua, and Ryusuke MomotaeaDepartment of Anesthesiology and Resuscitology, Okayama University Hospital, bOkayama University Medical School,
Department of Human Morphology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences,
Okayama 700-8558, Japan, cDepartment of Anesthesiology and Intensive Care Medicine, National Cancer Center Hospital,
Tokyo 104-0045, Japan, dDepartment of Anesthesiology, Tottori Municipal Hospital, Tottori 680-8501, Japane

Tachycardia is common in intensive care units (ICUs). It is unknown whether tachycardia or prolonged tachycardia affects patient outcomes. We investigated the association between tachycardia and mortality in criticallyill patients. This retrospective cohort study’s primary outcome was patient mortality in the ICU and the hospital. We stratified the patients (n = 476) by heart rate (HR) as LowHR, MediumHR, and HighHR groups. We
also stratified them by their durations of HR > 100 (prolonged HR; tachycardia): MildT, ModerateT, andSevereT groups. We determined the six groups’ mortality. The ICU mortality rates of the LowHR, MediumHR,and HighHR groups were 1.0%, 1.5%, and 7.9%, respectively; significantly higher in the HighHR vs. LowHR
group. The in-hospital mortality rates of these groups were 1%, 4.5%, and 14.6%, respectively; significantly
higher in the HighHR vs. LowHR group. The ICU mortality rates of the MildT, ModerateT, and SevereTgroups were 0.9%, 5.6%, and 57.1%, respectively. The mortality of the HRT = 0 (i.e., all HR ≤ 100) patients was
0%. The in-hospital mortality rates of the MildT, ModerateT, and SevereT groups were 1.8%, 16.7%, and85.7%, respectively; that of the HRT = 0 patients was 0.5%. Both higher HR and prolonged tachycardia wereassociated with poor outcomes.
Key words: tachycardia, mortality, ICU, in-hospitalT

he morbidity due to tachycardia seems to be relatively higher in critically ill patients than in other
patients, but the relationship between tachycardia andmortality has not been well studied. In contrast, theassociation between arrhythmia (mostly consisting ofatrial fibrillation [Af]) and postoperative [1], criticallyill [2-4], and septic patients [5-15] has been investigated in many studies. Tachycardia is commonly seen in
intensive care unit (ICU) settings, e.g., intensive surgiReceived November 30, 2018 ; accepted December 5, 2018.
Corresponding author. Phone : +81-86-235-7778; Fax : +81-86-235-6984
E-mail : mao893@aol.com (M. Hayashi)＊cal, neurological, and medical settings. There havebeen few investigations regarding whether a higher
heart rate (HR) or a prolonged higher HR actuallyaffects patient outcomes. We conducted the present
study to evaluate the association between tachycardia
and mortality in critically ill patients. The association
between tachycardia and mortality was investigated in
critically ill patients in a University Hospital ICU(Okayama University Hospital, Okayama, Japan). Our
hypothesis was that higher HR and prolonged tachycarConflict of Interest Disclosures: No potential conflict of interest relevantto this article was reported.

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Hayashi et al.

Acta Med. Okayama Vol. 73, No. 2

dia cause worse patient outcomes.

Patients and Methods
Study design. This study was approved by theInstitutional Review Board (IRB) of Okayama University
Hospital. The requirement of written informed consent
was waived by the IRB due to the retrospective cohort
design of the study. This manuscript adheres to theapplicable STROBE guidelines. The primary outcome
was patient mortality in the ICU and in the hospital.
After the IRB’s approval was obtained, we reviewed therecords of patients in the ICU and in the hospital from
September 1, 2014 to August 31, 2015, and the patients’HR values were extracted from automatically recorded
vital signs.
A total of 1,863 patients were admitted to Okayama
University Hospital’s ICU during this period of time. Of
these patients, we excluded the cases of the patients
who were admitted to the ICU more than twice, orwere discharged from the ICU within 48 h of theiradmission to the ICU, or were under 17 years old(Fig. 1). The remaining 476 patients were eligible andenrolled.
We first stratified the patients into three groups
based only on their HR values: LowHR (100 ≤ HR
< 110), MediumHR (110 ≤ HR < 120) and HighHR (HR≥ 120). All patients’ HR values were recorded automatically in the ICU every 60 sec. For this stratification,
when we describe a patient as having had an HR value≥ 100, the HR was > 100 continuously for > 10 min inthat patient. When HR values that were in-between
each group’s thresholds were observed for > 10 min, the
1,863

1,387

Fig. 1 Exclusion criteria. Of the total of 1,863 patients, 476 patientswere eligible and enrolled.

enrolled group was determined. For example, when apatient’s HR values were 105, 106, 108, etc. for> 10 min, the patient was assigned to the 100 ≤ HR
< 110 (LowHR) group.
We then created another three patient groups basedon the duration of higher HR (tachycardia), according
to our hypothesis that a prolonged higher HR is morelife-threatening. The duration of higher HR was measured using the patients’ HR records, and when the HR
value was over 100, it would have been counted as(HR-100). The concept of prolonged tachycardia isexpressed by the following formula: (HR-100) × thetime duration (min) during which the HR was > 100.
Since the result of this calculation is HR × time, we
named this value the “HRT.” As a result, we created theformula HRT = (HR-100) × the time duration (min)during which the patient’s HR was > 100. This expresses
a variable equal to the areas under the curve (AUC)
over 100 beats per min.
Using this formula and the patients’ data, we stratified the 476 patients into the MildT (1 ≤ HRT < 50400),
ModerateT (50400 ≤ HRT < 151200), and SevereT(HRT ≥ 151200) tachycardia groups. The label ‘1 ≤ HRT< 50400’ indicates that the HR value 105 was recordedin the patient for 1 week: (105-100) × 60 × 24 × 7.
The statistical analyses were performed with JMP
Pro® ver. 12.2.0 (Tokyo), and differences were considered significant when the p-values were < 0.05. The
p-values for mortality were calculated with Fisher’s
exact test. The p-values for the Kaplan-Meier curves
were calculated by log lank test.

Results
The mean age of all patients was 58.4 ± 0.9 years(Table 1). Of the 476 patients, 200 (42%) were female.
The severity of illness was validated with the acutephysiology and chronic health evaluation II (APACHE
II) score, and the average score was 16.6 ± 0.3 (Table 1).
β-blockers were administered to 117 (24.6%) patients,and sinus rhythm was preserved in 391 (82.1%) patients(Table 1).
The characteristics of the patients in the LowHR,
MediumHR, and HighHR groups (stratification by HR
only) are summarized in Table 1. The ICU mortality
rates of the LowHR, MediumHR, and HighHR groups
were 1.0%, 1.5%, and 7.9%, respectively; the mortality of the HR < 100 group was 0%. The ICU mortality

Tachycardia Is Associated with Mortality

April 2019was significantly higher in the HighHR group comparedto the LowHR group (Fig. 2A). The in-hospital mortality rates of the LowHR, MediumHR, and HighHR
groups were 1.0%, 4.5%, and 14.6%, respectively; thatof the HR < 100 group was 0.5%. In-hospital mortality
was significantly higher in the HighHR group comparedto the LowHR group (Fig. 2A , B).
The odds ratios (ORs) of MediumHR and HighHR
against LowHR were calculated. In terms of ICU mor-

149

tality, the ORs of MediumHR and HighHR were 1.5(95%CI: 0.1-37.2) and 7.3 (95%CI: 1.2-138.0, p < 0.05),
respectively. With respect to in-hospital mortality, theORs of MediumHR and HighHR were 4.5 (95%CI:
0.6-91.7) and 13.7 (95%CI: 2.5-256.6, p < 0.01),
respectively (Table 2).
We next analyzed the three groups stratified by the
duration of HR > 100: MildT, ModerateT, and SevereT.
The groups’ patient characteristics are shown in Table 3.

Table 1 Stratiﬁcation of patients by HR
Total

LowHR

MediumHR

HighHR

HR＜100(n ＝ 222)

100≦HR＜1110(n ＝ 98)

110≦HR＜120(n ＝ 67)120≦HR(n ＝ 89)

59.8 ± 1.2
92(41.4)

60.9 ± 1.9
53(54.1)

55.4 ± 2.3
23(34.3)†

54.6 ± 2.0

200
(42)
16.6 ± 0.3

15.7 ± 0.4

16.3 ± 0.7

16.9 ± 0.8

18.8 ± 0.7

117(24.6)

45(20.3)

23(23.5)

17(25.4)

41(46.1)＊

Sinus rhythm(%)

391(82.1)

195(87.8)

81(82.7)

55(82.1)

60(67.4)†

Int. Med. (%)
GI Surg.
Lung Surg.
Esop h. Surg.
Cardiac surg.
Neuro Surg.
Others38 (8.0)138 (29.0)
26 (5.5)
13 (2.7)
54 (11.3)
40 (8.4)
167 (35.1)

13 (5.9)61 (27.5)
6 (2.7)7 (3.2)23 (10.4)
24 (10.8)
88 (39.6)

4 (4.1)30 (30.6)
4 (4.1)2 (2.0)18 (18.4)
7 (7.1)33 (33.7)

4 (10.5)
10 (26.3)
4 (10.5)2 (5.3)2 (5.3)1 (2.6)15 (39.5)

17 (14.4)
37 (31.4)
12 (10.2)
2 (1.7)
11 (9.3)
8 (6.8)31 (26.3)

Variables(n ＝ 476)

Age58.4 ± 0.9

The numberof Female (%)
APACHEⅡ
Score
Use ofβ-blockers (%)

32(36.0)†（†: ＜ 0.05, ＊: ＜ 0.01）

A

B

Mortality in the ICU
Mortality in the hospital

1.00
＊

0.98

16.00%
14.00%

MediumHR

0.96

12.00%

0.94†

10.00%
8.00%

0.92

6.00%

0.90

4.00%

HR100_110

0.88

2.00%
0.00%

LowHR

HR<100 100≦HR<110 110≦HR<120 120≦HR
LowHR

MediumHR

HighHR

HR110_120
HR120<

0.86
0

20

40

HighHR＊
60

80
100
timeline (days)

120

140

Fig. 2 A, The mortality in the ICU and in the hospital. The patients were stratiﬁed by HR alone as LowHR (100 ≤ HR ＜ 110),
MediumHR (110 ≤ HR ＜ 120), and HighHR (HR ≥ 120). Both the ICU and in-hospital mortality rates were signiﬁcantly higher in the
HighHR group compared to the LowHR group. †p ＜ 0.05, ＊p ＜ 0.01 by Fisherʼs exact test; B, The Kaplan-Meier curves of the LowHR,
MediumHR, and HighHR groups. These results conﬁrmed those illustrated in panel A. †p ＜ 0.05, ＊p ＜ 0.01 by log rank test.

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Hayashi et al.

Acta Med. Okayama Vol. 73, No. 2

Table 2 Odds Ratio of group MediumHR and HighHR to LowHR
GroupsLowHR
MediumHR
HighHR

OR of mortality in ICU

OR of mortality in hospital

OR

95%CI

p value

OR

95%CI

p value1
1.5
7.3

0.1-37.2
1.2-138.0

0.79＜ 0.05†

1
4.5
13.7

0.6-91.7
2.5-256.6

0.16＜ 0.01＊（†: ＜ 0.05, ＊: ＜ 0.01）
Table 3 Stratiﬁcation of patients by HRT
Total

MildT

ModerateT

SevereT

HR × duration0(n ＝ 222)

HR × duration
1-50,400(n ＝ 229)

HR × Duration
50,400-151,200(n ＝ 18)

HR × Duration
151,200(n ＝ 7)

200
(42)

59.8 ± 1.2
92(41.4)

60.9 ± 1.9
97(42.4)

57.2 ± 5.59(50.0)

47.3 ± 8.3
2(28.6)

16.6 ± 0.3

15.7 ± 0.4

17.0 ± 0.4

20.1 ± 1.6

22.9 ± 2.5

Use ofβ-blockers (%)

117(24.6)

45(20.3)

23(23.5)

11(61.1)＊

5(71.4)†

Sinus rhythm(%)
Int. Med. (%)
GI Surg.
Lung Surg.
Esop h. Surg.
Cardiac surg.
Neuro Surg.
Others391(82.1)
38 (8.0)138 (29.0)
26 (5.5)
13 (2.7)
54 (11.3)
40 (8.4)
167 (35.1)

195(87.8)
13 (5.9)61 (27.5)
6 (2.7)7 (3.2)23 (10.4)
24 (10.8)
88 (39.6)

81(82.7)
4 (8.7)30 (29.3)
4 (6.6)2 (2.6)18 (13.1)
7 (7.0)33 (32.7)

11(61.1)
4 (22.2)
10 (33.3)
4 (22.2)0 (0)1 (5.6)0 (0)3 (16.7)

5(71.4)
1 (7.7)4 (30.8)
1 (7.7)
0 (0)
0 (0)
0 (0)
7 (53.8)

Variables(n ＝ 476)
Age
The numberof Female (%)
APACHEⅡ
Score

58.4 ± 0.9（†: ＜ 0.05, ＊: ＜ 0.01）

The usage of β-blockers was significantly higher in theModerateT and SevereT groups compared to the MildT
group. For the MildT, ModerateT, and SevereT groups,
the ICU mortality rates were 0.9%, 5.6%, and 57.1%,
respectively, while that of the HRT = 0 group was 0%,
since HR ≤ 100 means HRT = 0. The ICU mortality wassignificantly higher in the SevereT group than in the
MildT group (p < 0.01) (Fig. 2A). The in-hospital mortality rates of the MildT, ModerateT, and SevereTgroups were 1.8%, 16.7%, and 85.7%, respectively;that of the HRT = 0 group was 0.5%. In-hospital mortality was significantly higher in the ModerateT and
SevereT groups compared to the MildT group (p < 0.05
and p < 0.01, respectively) (Fig. 3A , B).
We calculated the ORs of ModerateT and SevereT

against MildT. In terms of ICU mortality, the ORs of
ModerateT and SevereT were 3.3 (95%CI: 0.2-24.0)
and 75.0 (95%CI: 12.9-514.9, p < 0.01), respectively.
For in-hospital mortality, the ORs of ModerateT and
SevereT were 5.5 (95%CI: 1.1-21.5, p < 0.05) and 165.8(95%CI: 24.6-3333.7, p < 0.01), respectively (Table 4).

Discussion
Our retrospective analyses revealed three major
findings. First, higher HR was associated with poor
patient outcomes and tachyarrhythmia. Second, prolonged tachycardia and higher HR were also profoundly
associated with poor patient outcomes. Finally,
patients with HR < 100 had substantially lower mortal-

Tachycardia Is Associated with Mortality

April 2019

A

151

B

Mortality in the ICU
Mortality in the hospital
80%
70%

MildT

1.0

＊

90%

ModerateT＊

0.8

＊

60%

0.6

50%
40%

0.4

†

30%

HRT1_50400

20%

HRT50400_151200
HRT151200＜

0.2

10%
0%

0

1-50400

MildT

50400-151200

ModerateT

151200-0

SevereT

20

40

SevereT＊
60

80
100
timeline (days)

120

140

Fig. 3 A, The mortality in the ICU and in the hospital. The patients were stratiﬁed by (HR-100) × duration of time (min) when HR is＞ 100: MildT (1 ≤ HRT ＜ 50400), ModerateT (50400 ≤ HRT ＜ 151200), and SevereT (HRT ≥ 151200). In terms of both the ICU andin-hospital mortality, the mortality rates of the SevereT group were signiﬁcantly higher than those of the MildT group. †p ＜ 0.05, ＊p ＜0.01 by Fisherʼs exact test; B, The Kaplan-Meier curve of the MildT, ModerateT, and SevereT groups. The survival rates of ModerateTand SevereT groups were signiﬁcantly higher than those of the MildT group, conﬁrming the results shown in panel A. †p ＜ 0.05, ＊p ＜0.01 by log rank test.

Table 4 Odds Ratio of group SevereT and ModerateT to MildT
Group

MildT
ModerateT
SevereT

OR of mortality in ICU

OR of mortality in hospital

OR

95%CI

p value

OR

95%CI

p value

1
3.3
75.0

0.2-24.0
12.9-514.9

0.35＜ 0.01＊

1
5.5
165.8

1.1-21.5
24.6-3333.7＜ 0.05†＜ 0.01＊（†: ＜ 0.05, ＊: ＜ 0.01）

ity.

Regarding the first finding that higher HR alone
contributed to poor patient outcomes, our results suggest that both the ICU mortality and the in-hospitalmortality of patients with HR ≥ 120 (the HighHR group)
were significantly higher than those of the patients with100 ≤ HR < 110 (the LowHR group) (Fig. 2A , B). With
this patient stratification, the modality of arrhythmia,
which is predominantly Af, was significantly higher
compared to the LowHR patients with HR < 100, theLowHR group, or the MediumHR group (Table 1).
This suggests that higher HR has a significant association not only with Af or other arrhythmias but also withsignificantly increased mortality. Although the association between arrhythmia and mortality was unclear in
the present study, there were no cardiac deaths, such as
those due to ventricular fibrillation.
Our second major finding was that prolonged tachy-

cardia with higher HR contributed to higher mortalityof patients in the ICU and hospital. Interestingly, eventhough mortality was highest in the SevereT group, thenumber of patients with arrhythmia in this group was
not significantly higher than the other groups’. This
result suggests that prolonged tachycardia with higher
HR contributes independently to increased mortality.
Finally, the most surprising finding was that critically ill patients with HR <100 had 100% survival in the
ICU, and their hospital survival rate was still > 99%.
Overall, 12.2% of the 222 patients with HR < 100 had
arrhythmias, which suggests that even if a patient has
an arrhythmia, maintaining his or her HR at < 100 may
be beneficial.
To the best of our knowledge, the association
between tachycardia and mortality has been investigated very rarely [16], but the relationship between Af
and mortality has been investigated several times [4-12 ,152

Hayashi et al.

15-17]. Several studies have shown an association
between Af and sepsis or septic shock [5-9 , 11-17].
Annane concluded that supraventricular arrhythmias
did not significantly impact the hospital survival of critically ill patients [3], while other researchers suggested
that supraventricular arrhythmia, especially new-onset
Af, had quite a large impact on the survival of patientswith sepsis [5 , 7-9 , 11 , 12]. Our hospital’s ICU has amixed-function design, and it functions relatively more
like a surgical ICU, but the present HighHR group still
had significantly more patients with arrhythmias andhad higher mortality rates. Theerwit noted that critically ill patients with HR > 130 had a higher mortality
than patients with HR ≤ 130 [6]; our present findings
might reflect that result.
Although there have been few reports of the association between HR and patient outcomes, a few researchgroups have investigated the effect of the β1-receptor
blocker esmolol in patients with septic shock [13 , 15].
They concluded that esmolol could achieve HR reduction to the target level without adverse events [15] andwithout changing cardiac output, whereas norepinephrine requirements were reduced [13]. There is only one
report of an investigation of the relationships of HR andprolonged tachycardia with patient outcomes [18], andthe report’s authors concluded that critically ill patientswith high cardiac risk and HR values > 95 for ≥ 12 h intheir ICU stay had a significant risk of major cardiac
events [19]. Whether HR reduction would have had any
survival benefit in critically ill patients remains
unknown. Further studies are needed to determine
whether HR reduction contributes to better patient outcomes.
Study limitations.
This investigation had some
limitations. First, since this was a single-center retrospective, observational, cohort study, the results have
limited generalizability. Second, the cohort consisted
mainly of postoperative patients, and the baseline characteristics of each group were not similar. This could
have resulted in some confounding bias to the outcomes. Third, regarding the stratification of the groups,
each cut off-level of HR or HRT was arbitrary. These
cut-off levels were sensible but not statistically generated, and the numbers of patients categorized to theModerateT and SevereT groups were very low. Fourth,the HRT might have been relatively shorter if criticallyill patients died soon after being admitted to the ICU.
In conclusion, the results of our analyses indicate

Acta Med. Okayama Vol. 73, No. 2that not only higher HR but also prolonged tachycardia
are associated with poor patient outcomes.
Acknowledgments. We thank Mr. Toshihiro Fujinuma and Mr. Koken
So, employees of Nippon Koden Co. Ltd., who extracted and provided hugeamounts of data.

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