Higher Baseline Heart Rate Research Articles

Resting heart rate does not predict growth in preterm infants

Background Previous reports indicate that preterm infants with higher baseline heart rate (HR) have greater weight gain than preterm infants with lower baseline HR. To verify this correlation and the potential utility of resting HR as a bench mark for risk of extrauterine growth restriction (EUGR), we studied preterm infants born between 32 and 36 weeks gestation. Earlier gestation infants (27 to 31 weeks) were included. Methods In retrospective chart review we collected heart rate (HR) and growth data on 156 infants between 27.0 and 34.0 weeks gestation from birth to hospital discharge. Results There was a significant increase in weight gain from day 10 of life in infants with higher resting HR compared to infants with lower resting HR. However, upon controlling for birth weight and gestational age, there was no significant relationship between HR and weight gain for any gestational age group of premature infants. Conclusions Contrary to previous reports, there was no significant relationship between HR and growth at any gestational age after controlling for birth weight and gestational age. It is important to continue to search for a clinical marker of risk for poor growth in preterm infants and to give an opportunity for nutritional interventions which may support better growth and developmental outcomes.

Predictors of sudden cardiac death change with time after myocardial infarction: results from the VALIANT trial

To determine whether predictors of sudden cardiac death (SCD) vary with time after myocardial infarction (MI). We analysed 11 256 patients enrolled in VALIANT. Landmark analysis and Cox proportional hazards modelling were used to predict SCD during hospitalization, from discharge to 30 days, 30 days to 6 months, and 6 months to 3 years. The cumulative incidence of SCD was 8.6% (n = 965). Initially, higher baseline heart rate [HR 1.20 per 10 b.p.m. (95% CI 1.06-1.37)] and impaired baseline creatinine clearance [HR 0.82 per 10 mL/min (95% CI 0.74-0.91)] were stronger predictors of SCD. With long-term follow-up, prior MI [HR 1.71 (95% CI 1.39-2.10)], initial left ventricular ejection fraction <40% [HR 0.67 per 10% (95% CI 0.58-0.78)], and recurrent cardiovascular events [HR 1.47 for rehospitalization (95% CI 1.17-1.86)] were more robust risk stratifiers for SCD. Atrial fibrillation post-MI was associated with an increased risk of SCD over the entire follow-up period. As time passed, the associations between baseline clinical characteristics and SCD decreased and time-updated assessments became more important. Predictors of SCD change with time after MI. Future studies of risk stratification for SCD should account for changes in these factors with time after MI.

A Single Exposure to Particulate or Gaseous Air Pollution Increases the Risk of Aconitine-Induced Cardiac Arrhythmia in Hypertensive Rats

Epidemiological studies demonstrate an association between arrhythmias and air pollution. Aconitine-induced cardiac arrhythmia is widely used experimentally to examine factors that alter the risk of arrhythmogenesis. In this study, Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats acutely exposed to synthetic residual oil fly ash (s-ROFA) particles (450 mug/m(3)) were "challenged" with aconitine to examine whether a single exposure could predispose to arrhythmogenesis. Separately, SH rats were exposed to varied particulate matter (PM) concentrations (0.45, 1.0, or 3.5 mg/m(3) s-ROFA), or the irritant gas acrolein (3 ppm), to better assess the generalization of this challenge response. Rather than directly cause arrhythmias, we hypothesized that inhaled air pollutants sensitize the heart to subsequent dysrhythmic stimuli. Twenty-four hour postexposure, urethane-anesthetized rats were monitored for heart rate (HR), electrocardiogram, and blood pressure (BP). SH rats had higher baseline HR and BP and significantly longer PR intervals, QRS duration, QTc, and JTc than WKY rats. PM exposure caused a significant increase in the PR interval, QRS duration, and QTc in WKY rats but not in SH rats. Heart rate variability was significantly decreased in WKY rats after PM exposure but increased in SH rats. Cumulative dose of aconitine that triggered arrhythmias in air-exposed SH rats was lower than WKY rats and even lower for each strain postexposure. SH rats exposed to varied concentrations of PM or acrolein developed arrhythmia at significantly lower doses of aconitine than controls; however, there was no PM concentration-dependent response. In conclusion, a single exposure to air pollution may increase the sensitivity of cardiac electrical conduction to disruption. Moreover, there seem to be host factors (e.g., cardiovascular disease) that increase vulnerability to triggered arrhythmias regardless of the pollutant or its concentration.

Baseline Heart Rate, Antihypertensive Treatment, and Prevention of Cardiovascular Outcomes in ASCOT (Anglo-Scandinavian Cardiac Outcomes Trial)

The aim of this study was to evaluate the effect of baseline heart rate on the efficacy of atenolol-based compared with amlodipine-based therapy in patients with hypertension uncomplicated by coronary heart disease in the ASCOT-BPLA (Anglo-Scandinavian Cardiac Outcomes Trial-Blood Pressure Lowering Arm). Heart rate is an established risk factor for cardiovascular events. Consequently, it is a widely held belief that beta-blockers should be prescribed for management of hypertension in patients with higher heart rates. Patients with atrial fibrillation or taking rate-limiting antihypertensive drugs at baseline were excluded. Primary analyses used Cox models to investigate the potential attenuation of the treatment effect with higher baseline heart rate on total cardiovascular events and procedures (TCVP) via introduction of an interaction term. Secondary analyses assessed coronary and total stroke outcomes. Primary unadjusted analyses included 12,759 patients and 1,966 TCVP. At the final visit, mean heart rate reduction from baseline was 12.0 (SD 13.7) and 1.3 (SD 12.1) beats/min in atenolol- and amlodipine-based groups, respectively. There was a reduction in TCVP in those allocated amlodipine-based therapy compared with atenolol-based therapy (unadjusted hazard ratio: 0.81, p < 0.001). This benefit was unattenuated at higher heart rates (interaction p value = 0.81). Similar results were obtained for coronary and total stroke outcomes. There was no evidence that the superiority of amlodipine-based over atenolol-based therapy for patients with hypertension uncomplicated by coronary heart disease was attenuated with higher baseline heart rate. These data suggest that, in similar hypertensive populations without previous or current coronary artery disease, higher baseline heart rate is not an indication for preferential use of beta-blocker-based therapy.

Movement-induced heart rate changes in epileptic and non-epileptic seizures

Heart rate changes are common in epileptic and non-epileptic seizures. Previous studies have not adequately assessed the contribution of motor activity on these changes nor have evaluated them during prolonged monitoring. We retrospectively evaluated 143 seizures and auras from 76 patients admitted for video EEG monitoring. The events were classified according to the degree of ictal motor activity (severe, moderate and mild/absent) in: severe epileptic (SE, N=17), severe non-epileptic (SNE, N=6), moderate epileptic (ME, N=28), moderate non-epileptic (MNE, N=11), mild epileptic (mE, N=35), mild non-epileptic (mNE, N=33) and mild aura (aura, N=13). Heart rate increased in the ictal period in severe epileptic, severe non-epileptic, moderate epileptic and mild epileptic events (p<0.05). Heart rate returned to baseline levels during the post ictal phase in severe non-epileptic seizures but not in severe epileptic patients. Aura events had a higher baseline heart rate. A cut-off of 20% heart rate increase may distinguish moderate epileptic and mild epileptic events lasting more than 30 seconds. In epileptic seizures with mild/absent motor activity, the magnitude of heart rate increase is proportional to the event duration. Heart rate analysis in seizures with different degrees of movement during the ictal phase can help to distinguish epileptic from non-epileptic events.

Reduced Heart Rate Response to Dipyridamole as a Marker of Left Ventricular Dysfunction in Diabetic Patients Undergoing Myocardial Perfusion Scintigraphy

This study sought to find among clinical, hemodynamic and left ventricular perfusion and function data obtained from myocardial perfusion scintigraphy (MPS), those associated with a reduced heart rate (HR) response to dipyridamole in diabetic patients. This phenomenon, although previously described as a marker of autonomic dysfunction in patients with diabetes, has not been fully elucidated. One hundred two consecutive diabetic patients undergoing dual-isotope (rest Tl-201/dipyridamole stress Tc-99m tetrofosmin) MPS were prospectively enrolled. A reduced HR response to dipyridamole was considered present if the ratio between maximal HR after dipyridamole infusion and rest HR was <or=1.20. MPS images were interpreted semiquantitatively, and perfusion scores were calculated. Left ventricular ejection fraction (LVEF) was automatically obtained. A logistic regression analysis was used to find variables independently associated with a reduced HR response to dipyridamole. A reduced HR response to dipyridamole was found in 46.1% of the patients and was associated with the presence of chronic renal failure (chi2 = 6.4), with high baseline HR (chi2 = 4.7) and low poststress LVEF (chi2 = 10.6). Attenuation of the HR response to dipyridamole was frequent and was strongly associated with reduced LVEF. Autonomic dysfunction may be reflected in the higher baseline HR but should not be considered the sole mechanism accounting for the reduction in HR response to dipyridamole in patients with diabetes.

Slower Heart Rates for Healthy Hearts

The management of atrial fibrillation, even in the modern era, remains complex and challenging. Preventing atrial fibrillation occurrence by identifying and favorably improving modifiable risk factors thus assumes great importance. It is well known that hypertension and resultant structural heart disease contributes significantly to the incidence of atrial fibrillation.1,2 The Losartan Intervention For End point reduction in hypertension (LIFE) study thus far has shown us that angiotensin-receptor blockade and reduction in left ventricular hypertrophy, irrespective of blood pressure–lowering, reduces the incidence of new-onset atrial fibrillation.1,3 Article see p 337 In recent years, accumulating evidence has linked high resting sinus heart rates (HR) directly and indirectly to adverse cardiovascular outcomes.4,5 Epidemiological studies show resting HR to be an independent predictor of cardiovascular and all-cause mortality in general population as well as in hypertensive patients.6 The cardiovascular benefits offered by β-blockade in coronary artery disease and heart failure have, in part, been attributed to β-blocker–mediated HR reduction.7,8 Other studies have linked high baseline HR to the development of hypertension, to the progression of coronary artery disease, and to the triggering of myocardial infarction, ventricular dysfunction, and ventricular arrhythmias.6,9–11 In this issue of Circulation: Arrhythmia and Electrophysiology , Okin and colleagues12 examines the relationship of HR changes over time on risk of atrial fibrillation in hypertensive patients as part of the LIFE study. In this post hoc analysis of the prospective LIFE study, 8828 hypertensive patients with left ventricular hypertrophy by ECG but without a history of atrial fibrillation were followed for a mean of 4.7±1.1 years. New onset atrial fibrillation was determined by 12-lead ECG performed on an intermittent, infrequent basis (at baseline, 6 months, and yearly thereafter). Hypertension was treated with losartan or atenolol. Using a variety of analyses, higher in-treatment HR on serial …

The Effect of Combination Therapy with an L/N-Type Ca2+ Channel Blocker, Cilnidipine, and an Angiotensin II Receptor Blocker on the Blood Pressure and Heart Rate in Japanese Hypertensive Patients: An Observational Study Conducted in Japan

Recently, the use of combination therapy with a calcium channel blocker (CCB) and an angiotensin II receptor blocker (ARB) has been rapidly increasing. Although this combination therapy is accepted as a standard treatment hypertension, there have been few large-scale, multicenter studies examining its safety and efficacy. The present study was designed to investigate the safety and efficacy of adding cilnidipine, a dual L/N-type CCB, to the regimen of patients whose blood pressure had been poorly controlled (systolic blood pressure [SBP] >140 mmHg or diastolic blood pressure [DBP] >90 mmHg) by antihypertensive monotherapy with an ARB. The percentage achievement of the blood pressure goals recommended by the JSH 2000 guidelines was also assessed for at least 12 weeks of treatment. A total of 2,920 patients were enrolled in the study at 471 institutions in Japan from February 2003 to July 2004. The incidence of adverse reactions related to cilnidipine was as low as 2.5%. A significant reduction from the baseline was found both in SBP (from 164.1 +/- 15.3 to 139.2 +/- 15.3 mmHg, p<0.0001) and DBP (from 91.7 +/- 11.4 to 79.3 +/- 10.7 mmHg, p<0.0001). A total of 31.5% of the patients achieved the blood pressure goals recommended by the JSH 2000 guidelines. Moreover, the heart rate also significantly decreased in these patients, particularly in those with a higher baseline heart rate. Our results indicate that cilnidipine can be used in combination with an ARB to control blood pressure without any significant adverse effects, and also that cilnidipine successfully reduces elevated heart rate, which is a possible risk factor for cardiovascular events.

190 Arrhythmic disorders and physiologic response during dobutamine stress echocardiography after acute myocardial infarction - influence of diabetes on

1 1 Medical University, II Chair of Cardiology, Lodz, Poland Aim: The purpose of the study was to evaluate long-term prognostic value of pharmacological stress echocardiography (SE) in patients with and with- out hypercholesterolemia (HCH). Methods: We followed 224 patients (62% men, age 55±10 yrs) who had undergone SE as the diagnostic test for ischemic heart disease. Myocardial infarction, need for revascularization or death were defined as endpoints (MACE) during the follow-up period of 53 months (range 12 to 91). The prog- nostic value of the test in patients with (50%) and without HCH was compared. Results: The prevalence of risk factors were: 44% for hypertension, 50% - hypercholesterolemia, 62% - history of smoking, 31% - previous myocardial infarction, 12% - diabetes. SE was positive for ischemia in 108 patients (48%). During then follow-up period 21 patients died (9%) and 102 (45%) experi- enced MACE. HCH and positive SE were independent predictors of events (Cochran-Cox: p=0.001, p<0.0001 respectively). However, positive result of SE in patients without HCH had higher prognostic value for MACE as com- pared with subset with HCH (HR: 3.57, p=0.0001 and HR: 2.05, p=0.003 respectively). Conclusion: In unselected patients undergoing diagnostic SE the presence of hypercholesterolemia limits the predictive value of positive SE for MACE. Patients and methods: The investigation comprised 128 patients, 55 diabet- ics (D) and 73 non-diabetics (ND) all with non-complicated AMI. 90 patients (70.3%) received thrombolityc therapy. After 10-12 days all of them underwent DSE testing and during the next 3-6 months coronary angiography. Results: Non-sustained ventricular and supraventricular tachycardia occurred in 7 D (12.7%) and 9 ND (12.3%) and in 6 D (10.9%) and 12 ND (16.4%). In 5 ND (6.8%) junction rhythm was developed, and in 4 D (7.2%) and 3 ND (4.1%) AV block II-III. Systolic blood pressure decrease of ≥ 40 mm Hg oc- curred in 6 D (10.9%) and 10 ND (13.7%). Significant coronary stenoses were found in 45 (81.8%) D and 42 (57.5%) ND. Diabetics vs non-diabetics had a higher baseline heart rate (83±11 vs 69±11 beats/min, p<0.001), with a higher age-predicted maximum heart rate at peak. In non-diabetics group there was no significant difference between patients with and without arrhythmias, regarding the mean number of diseased coronary arteries (1.61±0.7 vs 1.58±0.6). In diabetic group, patients with arrhythmias had greatest number of diseased coronary arteries (2.7±0.7 vs 1.52±0.4) Inde- pendent predictors of arrhythmias were: higher resting WMSI (p<0.01), and diabetes (p<0.1). Independent predictors of systolic blood pressure decrease of l 40 mm Hg were: higher baseline systolic pressure (p<0.0001); hyper- trophic left ventricle with diastolic dysfunction; and higher resting WMSI with systolic dysfunction. Conclusion: Physiological responses to dobutamine stress are comparable in diabetics and non-diabetics, except that a more rapid heart rate response is found in diabetics. Arrhythmic disorders during DSE in diabetic patients are predicted not only by the extent of systolic or diastolic left ventricular dysfunction, but also by the presence or the extent of CAD.

Psychophysiological responses in patients with fibromyalgia syndrome

Physical and emotional stress and altered reactivity of the autonomic nervous system have been implicated in the development and maintenance of fibromyalgia syndrome (FMS). This study investigated blood pressure, heart rate (HR), skin conductance levels (SCL), and surface electromyograms (EMG) from the trapezius muscle in 30 FMS patients and 30 age- and sex-matched healthy controls (HCs). All measures were continuously recorded during baseline (BL), social conflict, mental arithmetic, and relaxation tasks. The FMS patients showed significantly higher stress ratings and self-reported stress responses. Baseline EMG levels were significantly lower, and BL HR was significantly elevated. During both stress tasks, HR reactivity was significantly lower, and SCL reactivity was significantly higher in the FMS group. This pattern of low BL muscle tension and high BL HR, along with low HR and high SCL reactivity to stress, is discrepant to other chronic pain syndromes and suggests unique psychophysiological features associated with FMS. Several potential mechanisms for these psychophysiological responses are discussed.

Effect of Fish Oil on Heart Rate in Humans

The effect of fish oil on heart rate (HR), a major risk factor for sudden death, is not well established. We calculated this effect in a meta-analysis of randomized, double-blind, placebo-controlled trials in humans. Randomized trials of fish oil that evaluated HR were identified through MEDLINE (1966 through January 2005), hand-searching of references, and contact with investigators for unpublished results. Two investigators independently extracted trial data. A pooled estimate was calculated from random-effects meta-analysis. Predefined stratified meta-analyses and meta-regression were used to explore potential heterogeneity. Of 197 identified articles, 30 met inclusion criteria. Evidence for publication bias was not present. In the overall pooled estimate, fish oil decreased HR by 1.6 bpm (95% CI, 0.6 to 2.5; P=0.002) compared with placebo. Between-trial heterogeneity was evident (Q test, P<0.001). Fish oil reduced HR by 2.5 bpm (P<0.001) in trials with baseline HR > or =69 bpm (median) but had little effect (0.04-bpm reduction; P=0.56) in trials with baseline HR <69 bpm (P for interaction=0.03). Fish oil reduced HR by 2.5 bpm (P<0.001) in trials with duration > or =12 weeks but had less effect (0.7-bpm reduction; P=0.27) in trials with duration <12 weeks (P for interaction=0.07). HR reduction with fish oil intake did not significantly vary by fish oil dose (range, 0.81 to 15 g/d), type of HR measure, population age, population health, parallel versus crossover design, type of control oil, or study quality by Delphi criteria (P for interaction >0.25 for each). In randomized controlled trials in humans, fish oil reduces HR, particularly in those with higher baseline HR or longer treatment duration. These findings provide firm evidence that fish oil consumption directly or indirectly affects cardiac electrophysiology in humans. Potential mechanisms such as effects on the sinus node, ventricular efficiency, or autonomic function deserve further investigation.

Heart failure post-myocardial infarction in the new millennium: how often does it occur, can we predict it, and what are the consequences?

Purpose: Patients (pts) with acute myocardial infarction (MI) complicated by pulmonary edema and/or depressed ejection fraction (EF) are at heightened risk for chronic heart failure (HF) and/or death. We utilized the VALsartan In Acute myocardial iNfarcTion (VALIANT) trial experience to determine predictors of cardiovascular (CV) death and/or HF in high-risk MI pts undergoing modern therapy. Methods: VALIANT enrolled 14,703 pts with MI complicated by Killip class ≥2 and/or reduced EF between 0.5 and 10 days post-MI randomized to valsartan, captopril, or combination (median follow-up 24.7 months). Cox proportional hazards model was used to determine predictors of CV death and/or hospitalization for HF requiring intravenous therapy. Results: CV death occurred in 2484 (16.9%) pts, HF hospitalization in 2388 (16.2%), and 3992 (27%) died from CV cause and/or developed HF. Of the 2388 with HF hospitalization, 880 (36.9%) subsequently died. The most powerful independent predictors of HF and/or CV death were older age, higher baseline heart rate and diabetes mellitus (Table). There were no differences in outcomes between pts randomized to valsartan, captopril, or combination. Also, 73% (n=10,711) neither developed HF nor died from CV causes. Conclusion: Even among high-risk MI pts, the majority did not develop HF or die from CV causes. Age, diabetes, and rapid heart rate remain significant predictors of CV death and/or HF hospitalization. Mortality is twice as high among pts hospitalized for HF.VariableHazard Ratio (95% CI)Chi- squareVariableHazard Ratio (95% CI)Chi- squareAge (risk/10 years)1.35(1.30-1.40)256.9Prior MI1.33(1.24-1.46)54.8Heart rate (1 beat/min increase)1.02(1.01-1.02)172.8HF History1.34(1.24-1.46)49.6Diabetes mellitus1.48(1.37-1.59)112.9Pulse pressure (1 mm Hg increase)0.79(0.72-0.87)44.0BMI (1 kg/m2 increase)1.03(1.01-1.04)98.1Current smoker1.30(1.20-1.42)39.5Creatinine (0.1 mg/dL increase)1.05(1.04-1.07)95.2Hypertension History1.24(1.16-1.34)35.5Killip class (3 or 4)1.31(1.22-1.41)55.2Angioplasty Post-MI0.77(0.69-0.85)24.9

NCPAP improves abnormal autonomic function in at-risk-for-SIDS infants with OSA

We evaluated cardiovascular autonomic control and arousability during sleep in infants with obstructive sleep apnea (OSA) before and after 10 +/- 4 (mean +/- SD) days of treatment with nasal continuous positive airway pressure (nCPAP). Six OSA infants and 12 age-matched control infants were studied with polygraphic sleep studies at the age of 13 +/- 4 wk. During the study, 45 degrees head-up tilt tests were performed in slow-wave and rapid eye movement sleep. Blood pressure (BP) and heart rate (HR) were continuously monitored. All OSA infants had decreased initial BP and HR responses, followed by hypotension in two and hypertension in two. OSA infants displayed higher arousal thresholds in response to the tilt in rapid eye movement sleep (P < 0.005) and higher baseline HR (P < 0.05) than controls. nCPAP treatment normalized BP and HR responses as well as arousal thresholds to tilting and stabilized HR levels. OSA in infants may be linked with cardiovascular autonomic control disturbances and decreased arousability during sleep. These defects are improved by control of OSA with nCPAP.

Boys' and girls' responses to stress: affect and heart rate during a speech task.

To examine gender differences in heart rate and reports of negative and positive affect among adolescents during a speech task. Subjects were 133 adolescents, 73 girls and 60 boys, ages 14-18 years. Subjects were randomly assigned to speak for 10 minutes and asked either to free associate or to describe the most stressful event in their lives. Their heart rate was assessed at baseline and at 5 and 10 minutes after the task began. Self-ratings of negative and positive affect were assessed at baseline and at 10 minutes after the beginning of the task. Data were analyzed by Student's t-tests for independent samples, analyses of covariance, and Spearman rank-order correlation coefficients. Girls rated their negative affect significantly higher at baseline in comparison to boys. In addition, girls had a higher baseline heart rate. However, boys' increase in heart rate 5 minutes into the speech task was significantly greater than that of girls. Also, the free association task elicited significantly greater increases in heart rate compared to a task in which the adolescent described his or her most stressful life event. However, the stressful event task elicited greater negative and less positive affect. Significant relationships between change in heart rate and ratings of post-task affect were found among girls but not among boys, suggesting that the girls' ratings of their affect are more congruent with their physiological reactions to a stressful speech task. These results suggest that gender and task differences must be considered in assessing adolescents' stress.

Baseline heart rate may predict hypotension after spinal anesthesia in prehydrated obstetrical patients.

Hypotension is the most frequent complication of spinal anesthesia in pregnant patients. This study was designed to identify patients at risk for postspinal hypotension based on preoperative vital signs before and after an orthostatic challenge. Forty healthy women scheduled for elective Cesarean section were enrolled in this prospective trial. Blood pressure (BP) and heart rate (HR) were recorded with the patient in the lateral supine position and after standing up. After a bupivacaine spinal anesthetic, BP was obtained every two minutes for 30 min. Ephedrine treatment was administered based on the degree of hypotension observed. Hemodynamic parameters were correlated to ephedrine requirements (Spearman's rank order correlation). There was a significant correlation in baseline maternal HR and ephedrine requirements (P=0.005). The degree of orthostatic changes in mean arterial BP and HR did not correlate with postspinal hypotension. Baseline HR may be predictive of obstetric spinal hypotension. Higher baseline HR, possibly reflecting a higher sympathetic tone, may be a useful parameter to predict postspinal hypotension.

Cardiac autonomic function and oesophageal acid sensitivity in patients with non-cardiac chest pain

BACKGROUNDAcid reflux can elicit non-cardiac chest pain (NCCP), possibly through altered visceral sensory or autonomic function. The interactions between symptoms, autonomic function, and acid exposure are poorly understood.AIMTo examine autonomic...

Two sinusoidal heart rate patterns in fetal lambs undergoing extracorporeal membrane oxygenation

Objectives: The study analyzed the phase relationship between fetal heart rate and arterial blood pressure fluctuation during sinusoidal heart rate patterns in fetal lambs. Study Design: Thirty-two fetal lambs were placed on extracorporeal membrane oxygenation after cesarean delivery at ages ranging between 113 and 133 days’ gestation. Sinusoidal heart rate patterns persisting for >10 minutes were analyzed. The relationships between the sinusoidal heart rate cycles and the arterial blood pressure cycles were quantitatively expressed in degrees by timing the zenith and the nadir of each and assigning a phase-angle index (with 0 [360] and 180 degrees being synchronized and reciprocal, respectively). Simultaneous blood samples were taken from the 4 different sites of the fetal circulation for blood gas and acid-base analysis when the sinusoidal heart rate pattern appeared. Regional cerebral blood flow was determined by means of the colored microsphere technique in 8 fetuses with sinusoidal patterns and 7 control fetuses. Results: Sinusoidal heart rate patterns were observed in 13 (40.6%) of the 32 fetal lambs. Two types of fetal heart rate and arterial blood pressure relationship could be recognized during sinusoidal pattern, the reciprocal type (n = 7) and the synchronized type (n = 9). A reciprocal type of sinusoidal pattern preceded a synchronized type pattern in 3 lambs that showed sinusoidal patterns at different stages of the experiment. The reciprocal type was associated with a higher baseline heart rate and amplitude of the sinusoidal heart rate pattern than was the synchronized type. The synchronized type was associated with a lower pH and base excess than was the reciprocal type. The cerebral blood flow in the medulla oblongata was significantly lower during the synchronized type pattern than during the reciprocal type pattern. Conclusion: There are 2 types of sinusoidal heart rate pattern. A synchronized type sinusoidal heart rate pattern may indicate more advanced fetal compromise than is associated with a reciprocal type pattern. (Am J Obstet Gynecol 1999;180:462-8.)

Need for a Revision of the Normal Limits of Resting Heart Rate

The current definition of sinus tachycardia is a heart rate >100 beats per minute (bpm).1 This limit was set arbitrarily when heart rate was not yet regarded as a risk factor for cardiovascular disease, probably with the main purpose of distinguishing between a disease state (fever, thyrotoxicosis, anemia, congestive heart failure, etc) and a normal condition. In recent years, interest has been aroused by the awareness that fast heart rate is a potent precursor of hypertension, atherosclerosis, and their sequelae.2 3 4 5 6 7 8 9 10 In addition, many leading epidemiological studies have shown that tachycardia is associated with an increased risk of death from cardiovascular and noncardiovascular causes. This relationship has been found in general populations,3 4 5 6 7 in elderly individuals,9 and in hypertensive cohorts.10 In all of these studies, the heart rate value above that in which a significant increase in risk was observed was below the 100 bpm threshold (Table 1⇓). Only in the study by Levy et al3 was tachycardia defined as a heart rate >99 bpm, but in that study the cutoff between normal and high heart rate was chosen arbitrarily, and the highest heart rate value measured during the examination was taken to define the subject’s heart rate. In all the other studies, the threshold level between normal and fast heart rate was between 79 and 90 bpm. View this table: Table 1. Heart Rate Values Above Which a Significant Increase in Risk Was Found: Data From 9 Epidemiological Studies The normalcy limits of a clinical variable can be established according to different criteria. For many parameters, such as most biochemical indexes, the 95% confidence interval is calculated to identify the upper normal limit of the variable. This statistical approach does not appear suitable for those clinical variables …

Influence of Gender on Physiologic Response and Accuracy of Dobutamine Echocardiography

Dobutamine echocardiography (DE) has been shown to be safe, feasible, and accurate for identification of coronary artery disease (CAD) in mixed populations. The purpose of this study was to examine gender differences in physiologic response and accuracy of DE. We studied 2,886 consecutive DEs, performed in 2,748 patients, 1,209 of whom (44%) were women. A standard incremental protocol (5 to 40 μg/kg/min in 3-minute stages) was followed by atropine and/or an additional stage with 50 μg/kg/min, if the heart rate response was inadequate. Hemodynamic and echocardiographic findings were recorded at each stage. Three hundred sixty-nine patients without previous cardiac intervention (including 135 women) also underwent cardiac catheterization within 1 year of DE. Significant coronary stenoses (defined angiographically as >50% diameter) were present in 67% of women and 65% of men, of whom 55% and 65%, respectively, had multivessel disease. Women had a higher baseline heart rate (76 ± 13 vs 73 ± 14 beats/min, p <0.0001), and showed a more rapid increase in heart rate at low dose, with a higher age-predicted maximum heart rate at peak. This led to test termination at target heart rate but a submaximum dose in 22% of women versus 15% of men (p <0.0001) and less frequent administration of atropine (29% vs 34%, p <0.01). Dose-limiting side effects (8% vs 7%) and submaximum heart rate responses (14% vs 17%) were comparable in men and women. Even after the exclusion of negative DE at submaximal heart rate responses, the overall sensitivity was significantly lower in women than men (78% vs 88%, p <0.05), both for single (72% vs 78%, p <0.05) and for multivessel disease (82% vs 93%, p <0.05). The low specificity in both genders (55% vs 46%) probably reflected post-test referral bias. Thus, physiologic responses to dobutamine stress are comparable in men and women, except for a more rapid heart rate response in women, but the accuracy of DE for diagnosis of CAD in women is less than in men.

Patterns and predictors of hypertension incidence among Hispanics and non-Hispanic Whites

To determine whether Hispanics are at lower risk for the development of hypertension than non-Hispanic Whites. We also examined selected predictors of hypertension incidence and explored the role of markers of insulin resistance in the development of hypertension. A cohort study of a geographically-based sample of Hispanic and non-Hispanic white southern Colorado residents who were re-examined an average of 4 years after their baseline examination. These analyses included 664 participants who were normotensive and confirmed nondiabetic by an oral glucose tolerance test at their baseline examination. Hypertension was defined as systolic blood pressure > or = 140 mmHg or diastolic blood pressure > or = 90 mmHg or use of antihypertensive medication. Hispanics and non-Hispanic Whites had similar hypertension incidence rates. The strongest predictors of hypertension incidence were baseline blood pressure and age. Higher baseline heart rates and higher body mass index also predicted hypertension. Increased fasting insulin levels were associated with hypertension incidence among lean participants, though the association disappeared once baseline blood pressure levels were added to the models. Models investigating change in systolic or diastolic blood pressure levels found higher baseline levels of insulin area under the glucose tolerance curve predicted greater increases in systolic blood pressure in non-Hispanic Whites only. Hypertension incidence rates were similar in Hispanics and non-Hispanic Whites. Higher levels of insulin area were associated with larger increases in systolic blood pressure among non-Hispanic Whites only.