Prognostic value of heart rate turbulence for risk assessment in patients with unstable angina and non-ST elevation myocardial infarction

Figures & data

Table 1 Characteristics of patients with unstable angina or NSTEMI

Variable	Patients (n = 166)	Patients with cardiac-related events (n)		Event-free patient (n = 77)
		30 days (n = 26)	One year, including 30-day outcomes (n = 89)
Mean age, years	65 ± 13	65 ± 12	66 ± 13	65 ± 12
Male	91 (55%)	13	44	47
Race
African American	31 (19%)	4	24	7
Asian	44 (27%)	9	20	24
Caucasian	79 (48%)	12	36	43
American Native/Pacific Islander	12 (7%)	1	9	3
Latino ethnicity, n (% of total)	15 (9%)	2	12	3
ACS diagnoses
Unstable angina	126 (64.7%)	21	72	54
NSTEMI	40 (24.6%)	5	17	23
History or comorbidity
Prior history of coronary artery disease	115 (69%)	19	70	45
Family history of coronary artery disease	88 (53%)	12	41	47
Diabetes	44 (27%)	12	30	14
Hypertension	128 (77%)	18	73	55
Hypercholesterolemia	113 (68%)	16	64	49
Current smoker	30 (18%)	3	17	13
Inhospital therapy
Beta-blocker	147 (89%)	23	78	69
Percutaneous coronary intervention	52 (31%)	10	27	25
Coronary artery bypass graft	12 (7%)	3	6	6
24-hour electrocardiographic data
Mean heart rate, beats per minute	65 ± 11	68 ± 13	65 ± 11	65 ± 10
Mean number of VPCs per hour (median)	20 ± 38 (4)	28 ± 40 (12)	24 ± 35 (7)	15 ± 40 (3)
Mean turbulence onset (n = 139), %	−0.0053 ± 0.0264	−0.0 ± 0.0241	−0.006 ± 0.0286	−0.0129 ± 0.0212
Mean turbulence slope (n = 139), msec per RR interval	6.411 ± 4.684	3.4716 ± 3.640	5.673 ± 5.738	7.354 ± 5.984

Note: Percentages refer to % of total and are rounded to nearest half percent.

Abbreviations: ACS, acute coronary syndrome; VPC, ventricular premature contraction; NSTEMI, non-ST elevation myocardial infarction.

Table 2 Cardiovascular outcomes

30-day cardiovascular outcomes
• Returned to ED (16 patients were admitted to hospital from ED)	21 (13%)
• Died	5 (3%)
• Total 30-day cardiovascular outcomes	26 (16%)
One-year cardiovascular (including 30-day) outcomes
• Returned to ED (60 patients were admitted to hospital from the ED)	80 (48%)
• Died	9 (5%)
• Total one-year cardiovascular outcomes	89 (54%)

Abbreviation: ED, emergency department.

Table 3 Frequency of patients within each category of Thrombolysis in Myocardial infarction (TIMI) risk score

TIMI category	Patients in category (n)	Percentage of total (n = 166)
0–1 lowest risk	9	5.4
2 low risk	17	10.2
3 medium-low risk	60	36.1
4 medium risk	49	29.5
5 medium-high risk	28	16.9
6–7 high risk	3	1.8
Total	166	100.0

Table 4 Frequency of patients within each category of heart rate turbulence risk score

HRT category	Score parameters	Patients in category (n)	Percentage of total (n = 166)
Low risk	TO < 0% and TS > 2.5 msec per RR interval or too few VPCs to calculate	101	60.8
Medium risk	TO > 0% or TS < 2.5 msec per RR interval	43	25.9
High risk	TO > 0% and TS < 2.5 msec per RR interval	22	13.3
Totals		166	100.0

Abbreviations: HRT, heart rate turbulence; TO, turbulence onset; TS, turbulence slope; VPC, ventricular premature contraction.

Table 5 Comparison of heart rate turbulence and TIMI risk scores in univariate Cox regression (n = 166)

Risk score measure	Model Chi square	Model P value	HR (95% CI)	C-statistic
Outcomes at 30 days
HRT risk	7.923	0.005	1.911 (1.198–3.048)	0.647
TIMI risk	6.702	0.010	1.613 (1.121–2.320)	0.687
Outcomes at one year
HRT risk	22.553	<0.001	1.851 (1.42–2.41)	0.657
TIMI risk	9.905	0.002	1.371 (1.13–1.67)	0.605

Abbreviations: CI, confidence interval; HRT, heart rate turbulence; HR, hazards ratio; TIMI, Thrombolysis in Myocardial infarction.

Table 6 Heart rate turbulence and TIMI risk scores in multivariate Cox regression (n = 166)

Single model with HRT and TIMI risk scores: adverse outcomes at 30 days (26 events)
Model chi square (model P value) = 13.200 (0.001)
Model C-statistic = 0.725
Risk score measure	Wald statistic	Variable P value	HR (95% CI)
HRT risk	7.572	0.013	1.818 (1.33–2.915)
TIMI risk	3.352	0.018	1.570 (1.080–2.283)
Single model with HRT and TIMI risk scores: adverse outcomes at one year (89 events)
Model chi square (model P value) = 31.089 (<0.001)
Model C-statistic = 0.695
Risk score measure	Wald statistic	Variable P value	HR (95% CI)
HRT risk	20.776	<0.001	1.860 (1.424–2.428)
TIMI risk	9.667	0.002	1.383 (1.127–1.696)

Abbreviations: CI, confidence interval; HRT, heart rate turbulence; HR, hazards ratio; TIMI, Thrombolysis in Myocardial infarction.

Figure 1 Comparison of TIMI and heart rate turbulence risk scores in acute coronary syndrome. Outcomes of emergent cardiac readmission or cardiac death at one year.

Notes: In total, 100% of patients (proportionately equal to 1.0) start at time zero (time of emergency department discharge) without an adverse event, ie, event-free (upper left hand corner). The lines represent the proportion of patients in each group who are event-free at the end of one year.
Abbreviation: TIMI, Thrombolysis In Myocardial Infarction.