Heart Rate Variability in Acute Myocardial Infarction and Its Association with Infarct Site and Clinical Course Athanase Pipilis, MD, Marcus Flather, MRCP, Oliver Ormerod, DM, MRCP, and Peter Sleight, MD
eart rate (HR) variability is now recognizedas an important independentprognosticfactor after an acute myocardial infarction, in addition to other traditional measures(e.g., left ventricular dysfunction, positive exercisetest results and ventricular arrhythmias). Wolf et al’ were the first to observethat lack of respiratory sinus arrhythmia in the Coronary Care Unit carried a poor prognosiseven in patients matched for other variables such as size of infarct or presenceof heart failure. Survivors of acute myocardial infarction with low HR variability at the time of discharge have a higher mortality rate than patients with high HR variability.* HR variability may be quantified by powerspectral analysis3and standard deviation (SD) of RR intervals,* or by the mean of differencesbetweenconsecutive RR intervals.4 HR variability is influenced by the balance between sympathetic and parasympathetic tone3; differences in parasympathetic activity between night and daytime in patients with high or low 24-hour HR variability5 and between anterior and inferior infarcts during the early phase of infarction6y7have been described. However, other studies3found no influence of the infarct site on HR variability. In this study we compared the night and daytime HR variability in patients with anterior and inferior wall acute myocardial infarction during the first day of admission to hospital.
H
We studied 56 men and I4 women (mean age f SD 62 f 9 years) who presented to the coronary care unit with a diagnosis of anterior or inferior wall acute myocardial infarction based on electrocardiographic criteria (ST-segment elevation in either anterior or inferior leads). All patients were admitted within 24 hours from the onset of chest pain and none had atria1 fibrillation, heart block or sustained ventricular arrhythmias during the time of analysis. The mean time ofpresentation was 4.8 ( f 4.1) hours after the onset of pain. Thirty-six patients had an inferior and 34 an anterior wall acute myocardial infarction. The clinical characteristics of these 2 groups of patients are listed in Table I. All patients had a 24-hour Holter tape (Oxford Medilog MR 35 FM) starting at a mean of 12.8 ( f
From the Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU England. Manuscript received October 16, 1990; re.visedmanuscript received January 22, 1991, and acceptedJanuary 24.
6.6) hours after the onset of pain. The tapes were analyzed using a Medilog 3000 FM analyzer. The trigger pulse and the off-tape crystal clock signals were processed to create a continuous beat-to-beat interval file on an IBM computer. Cycles with length duration different by >20% from the preceding cycle length were discarded, thus excluding premature ectopic beats or artefacts from T-wave sensing. For the remaining cycles (length duration within 20% of the preceding cycle length) histograms of RR intervals and of RR interval differences were generated. This permitted the following calculations to express HR variability for each patient: (1) mean RR interval (mean cycle length), (2) SD of the mean RR interval (SD&, and (3) SD of the mean difference of each RR interval from the preceding one (SDD&. All these parameters were calculatedfor each patient from two I-hour periods of the Holter recording: one during the night (1 to 5 hours A.M.) and one during the day (8 to 12 hours A.M.). We compared the night and daytime HR variability indexes for each patient and also the differences between the anterior and the inferior infarction groups. We also correlated the HR variability values with the subsequent development of heart failure (presence of rules, gallop rhythm or radiologic evidence ofpulmonary congestion). All patients with these findings were discharged with a diuretic drug regimen by the responsible physician. We also included the 2 patients who died during the first 2 weeks after admission. All values are presented as mean f SD. Paired and unpaired Student’s t test and chisquare test were usedfor statistical analysis of our data.
TABLE
I Clinical
Characteristics
of Patients Location of Infarction
No. of patients Age (years) Male/female Time to admission (hours) Time to Holter start (hours) Heart failure on day 1 Peak AST activity (U/liter) Thrombolysis therapy Beta blocker on day 1
Anterior
Inferior
34 62zt9
36 62k9 28/8 4.7 f 3.5 12.7 f 6.4 2 (6%) 308 f 223 33 (92%) 5(14%)
28/6 4.8 f 4.8
12.9f 6.9 4(12%) 410 A 332 33 (97%) 3 (9%)
Values are mean j, standard deviation or number of patients Diierences between the 2 groups are not signkant. AST = aspartate ammotransferase.
BRIEF REPORTS
1137
TABLE II Heart Rate Variability Parameters During Night and Day 1 Variables Mean RR interval (ms) SDRR (ms)
Nighttime
Daytime
pValue
797 f 136
779 f 133 71f28 28f14
eart rate (HR) variability is now recognizedas an important independentprognosticfactor after an acute myocardial infarction, in addition to other traditional measures(e.g., left ventricular dysfunction, positive exercisetest results and ventricular arrhythmias). Wolf et al’ were the first to observethat lack of respiratory sinus arrhythmia in the Coronary Care Unit carried a poor prognosiseven in patients matched for other variables such as size of infarct or presenceof heart failure. Survivors of acute myocardial infarction with low HR variability at the time of discharge have a higher mortality rate than patients with high HR variability.* HR variability may be quantified by powerspectral analysis3and standard deviation (SD) of RR intervals,* or by the mean of differencesbetweenconsecutive RR intervals.4 HR variability is influenced by the balance between sympathetic and parasympathetic tone3; differences in parasympathetic activity between night and daytime in patients with high or low 24-hour HR variability5 and between anterior and inferior infarcts during the early phase of infarction6y7have been described. However, other studies3found no influence of the infarct site on HR variability. In this study we compared the night and daytime HR variability in patients with anterior and inferior wall acute myocardial infarction during the first day of admission to hospital.
H
We studied 56 men and I4 women (mean age f SD 62 f 9 years) who presented to the coronary care unit with a diagnosis of anterior or inferior wall acute myocardial infarction based on electrocardiographic criteria (ST-segment elevation in either anterior or inferior leads). All patients were admitted within 24 hours from the onset of chest pain and none had atria1 fibrillation, heart block or sustained ventricular arrhythmias during the time of analysis. The mean time ofpresentation was 4.8 ( f 4.1) hours after the onset of pain. Thirty-six patients had an inferior and 34 an anterior wall acute myocardial infarction. The clinical characteristics of these 2 groups of patients are listed in Table I. All patients had a 24-hour Holter tape (Oxford Medilog MR 35 FM) starting at a mean of 12.8 ( f
From the Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU England. Manuscript received October 16, 1990; re.visedmanuscript received January 22, 1991, and acceptedJanuary 24.
6.6) hours after the onset of pain. The tapes were analyzed using a Medilog 3000 FM analyzer. The trigger pulse and the off-tape crystal clock signals were processed to create a continuous beat-to-beat interval file on an IBM computer. Cycles with length duration different by >20% from the preceding cycle length were discarded, thus excluding premature ectopic beats or artefacts from T-wave sensing. For the remaining cycles (length duration within 20% of the preceding cycle length) histograms of RR intervals and of RR interval differences were generated. This permitted the following calculations to express HR variability for each patient: (1) mean RR interval (mean cycle length), (2) SD of the mean RR interval (SD&, and (3) SD of the mean difference of each RR interval from the preceding one (SDD&. All these parameters were calculatedfor each patient from two I-hour periods of the Holter recording: one during the night (1 to 5 hours A.M.) and one during the day (8 to 12 hours A.M.). We compared the night and daytime HR variability indexes for each patient and also the differences between the anterior and the inferior infarction groups. We also correlated the HR variability values with the subsequent development of heart failure (presence of rules, gallop rhythm or radiologic evidence ofpulmonary congestion). All patients with these findings were discharged with a diuretic drug regimen by the responsible physician. We also included the 2 patients who died during the first 2 weeks after admission. All values are presented as mean f SD. Paired and unpaired Student’s t test and chisquare test were usedfor statistical analysis of our data.
TABLE
I Clinical
Characteristics
of Patients Location of Infarction
No. of patients Age (years) Male/female Time to admission (hours) Time to Holter start (hours) Heart failure on day 1 Peak AST activity (U/liter) Thrombolysis therapy Beta blocker on day 1
Anterior
Inferior
34 62zt9
36 62k9 28/8 4.7 f 3.5 12.7 f 6.4 2 (6%) 308 f 223 33 (92%) 5(14%)
28/6 4.8 f 4.8
12.9f 6.9 4(12%) 410 A 332 33 (97%) 3 (9%)
Values are mean j, standard deviation or number of patients Diierences between the 2 groups are not signkant. AST = aspartate ammotransferase.
BRIEF REPORTS
1137
TABLE II Heart Rate Variability Parameters During Night and Day 1 Variables Mean RR interval (ms) SDRR (ms)
Nighttime
Daytime
pValue
797 f 136
779 f 133 71f28 28f14
