Shortened left ventricular filling time in dilated cardiomyopathy: additional effects on heart rate variability?

OBJECTIVE--To assess possible mechanical influences underlying the reduced heart rate variability in patients with dilated cardiomyopathy. DESIGN--Comparison of standard non-spectral indices of heart rate variability with echocardiographic Doppler measures of left ventricular function in patients and normal controls. PATIENTS--20 patients with dilated cardiomyopathy and 15 normal subjects of similar ages were studied. METHODS--Standard non-spectral indices of heart rate variability were measured over 24 hours. These were correlated with left ventricular cavity size, shortening fraction, and isovolumic relaxation time measured by M mode echocardiography, and the duration of functional mitral regurgitation and left ventricular filling time assessed by continuous wave Doppler. RESULTS--Mean RR interval and estimates of short term variability (root mean square difference of successive RR intervals, proportion of adjacent RR intervals > 50 ms different, and SD indices) were not different from normal. The overall mean (SD) of the RR interval (65 (35)), and SD of five minute mean RR intervals (55 (30)), however, were reduced compared with normal values (115 (40) and 105 (45); p < 0.01 for both). Neither correlated with left ventricular cavity size or shortening fraction, but both were strongly related to left ventricular filling time (coefficient of variation, r = 0.82 and r = 0.81 respectively). Correlation persisted when the SD was corrected for RR interval (r = 0.69) although this correlation was not found in the controls. In individual patients, the difference between RR interval at the time of echo and minimum value during the 24 hours, a measure of ability to increase heart rate, also correlated closely with filling time (r = 0.92). CONCLUSION--As the duration of functional mitral regurgitation is effectively fixed, its presence can limit the time available for left ventricular filling in dilated cardiomyopathy when heart rate is high. This may become the mechanism by which maximum heart rate is set, becoming fixed to optimise cardiac output. This manifestation of dilated cardiomyopathy may be an important factor in reduction of heart rate variability in these patients.     

Patients Operated for Tetralogy of Fallot and with Non-Sustained Ventricular Tachycardia Have Reduced Heart Rate Variability

BACKGROUND: To study heart rate variability (HRV) in patients operated for tetralogy of Fallot (ToF) and to identify any correlation between HRV and ventricular tachycardia (VT). PATIENTS AND METHODS: We studied HRV in 23 consecutive patients operated for ToF (mean age 14 +/- 6.6 years; mean follow-up 10.6 +/- 5.2 years). Seven patients had non-sustained VT on Holter monitoring. Two control groups were included: 18 healthy subjects and 15 patients operated for other congenital heart disease. There were no differences in age, age at surgery (in the operated groups), follow-up, and mean heart rate between the three groups. Four time and four frequency domain indices were calculated: mean duration of RR intervals, standard deviation of all RR intervals (SD), square root of the mean squared differences of successive RR intervals (r-MSSD), percent of differences between adjacent RR intervals (pNN50), total power (TP), low frequency (LF), high frequency (HF), and LF/HF ratio. RESULTS: HRV indices were identical in the two control groups but were significantly reduced in patients with ToF. Within the patients who had been operated on for ToF, HRV indices were significantly lower in the seven with non-sustained VT than in those without arrhythmias: SD (95 +/- 15 vs. 135 +/- 54 ms; p = 0.01), r-MSSD (26 +/- 9 vs. 45 +/- 20 ms; p = 0.03), pNN50 (4.4 +/- 3.4 vs. 16.5 +/- 12.5%; p = 0.001) and HF (111 +/- 97 vs. 352 +/- 291 ms(2); p = 0.009). Using stepwise multivariate regression analysis, pNN50, age at surgery, degree of pulmonary regurgitation and higher right/left ventricular ratio were independent predictive variables for VT (p < 0.0001; r(2) = 0.85). CONCLUSIONS: ToF patients, particularly those with ventricular arrhythmias, have significant impairment of sympatho-vagal balance, characterized by a reduction of vagal drive.     

Depressed Heart Rate Variability as an Independent Predictor of Death in Chronic Congestive Heart Failure Secondary to Ischemic or Idiopathic Dilated Cardiomyopathy

After acute myocardial infarction, depressed heart rate variability (HRV) has been proven to be a powerful independent predictor of a poor outcome. Although patients with chronic congestive heart failure (CHF) have also markedly impaired HRV, the prognostic value of HRV analysis in these patients remains unknown. The aim of this study was to investigate whether HRV parameters could predict survival in 102 consecutive patients with moderate to severe CHF (90 men, mean age 58 years, New York Heart Association [NYHA] class II to IV, CHF due to idiopathic dilated cardiomyopathy in 24 patients and ischemic heart disease in 78 patients, ejection fraction [EF], 26%; peak oxygen consumption, 16.9 ml/kg/min) after exclusion of patients in atrial fibrilation with diabetes or with chronic renal failure. In the prognostic analysis (Cox proportional-hazards model, Kaplan-Meier survival analysis), the following factors were investigated: age, CHF etiology, NYHA class, EF, peak oxygen consumption, presence of ventricular tachycardia on Holter monitoring, and HRV measures derived from 24-hour electrocardiography monitoring, calculated in the time (standard deviation of all normal RR intervals [SDNN], standard deviation of 5-minute RR intervals [SDANN], mean of all 5-minute standard deviations of RR intervals [SD], root-mean-square of difference of successive RR intervals [rMSSD], and percentage of adjacent RR intervals >50 ms different [pNN50]) and frequency domain (total power [TP], power within low-frequency band [LF], and power within high-frequency band [HF]). During follow-up of 584 ± 405 days (365 days in all who survived), 19 patients (19%) died (mean time to death: 307 ± 315 days, range 3 to 989). Cox's univariate analysis identified the following factors to be predictors of death: NYHA (p = 0.003), peak oxygen consumption (p = 0.01), EF (p = 0.02), ventricular tachycardia on Holter monitoring (p = 0.05), and among HRV measures: SDNN (p = 0.004), SDANN (p = 0.003), SD (p = 0.02), and LF (p = 0.003). In multivariate analysis, HRV parameters (SDNN, SDANN, LF) were found to predict survival independently of NYHA functional class, EF, peak oxygen consumption, and ventricular tachycardia on Holter monitoring. The Kaplan-Meier survival curves revealed SDNN <100 ms to be a useful risk factor; 1-year survival in patients with SDNN <100 ms was 78% when compared with 95% in those with SDNN >100 ms (p = 0.008). The coexistence of SDNN <100 ms and a peak oxygen consumption <14 ml/kg/min allowed identification of a group of 18 patients with a particularly poor prognosis (1-year survival 63% vs 94% in the remaining patients, p <0.001). We conclude that depressed HRV on 24-hour ambulatory electrocardiography monitoring is an independent risk factor for a poor prognosis in patients with CHF. Whether analysis of HRV could be recommended in the risk stratification for better management of patients with CHF needs further investigation.

In 102 consecutive patients with stable chronic congestive heart failure and sinus rhythm, several heart rate variability measures derived from 24-hour electrocardiographic recording were significant prognostic risk markers, independent of clinical variables (New York Heart Association class, peak oxygen consumption, left ventricular ejection fraction). The coexistence of the standard deviation of all normal RR intervals <100 ms and peak oxygen consumption <14 ml/kg/min had the worst prognosis, and it is concluded that heart rate variability analysis is useful for noninvasive heart transplant assessment.     

Total cavopulmonary and atriopulmonary connections are associated with reduced heart rate variability

AIM—To determine whether cavopulmonary connections are associated with abnormalities of heart rate variability.
METHODS—Heart rate variability was studied by 24 hour Holter monitoring in 39 patients (mean (SD) age 12.2 (4.1) years) who underwent cavopulmonary connection operations (partial in 12, total in 13, and atriopulmonary in 14). Two control groups were used: 18 healthy children (11.1 (2.5) years) and 16 patients (11.7 (4.3) years) undergoing cardiovascular surgery for biventricular repair of congenital heart disease. All patients were in sinus rhythm and had normal left ventricular function. Four time domain indices were calculated: mean duration of RR intervals (RR), standard deviation of all RR intervals (SD), square root of the mean squared differences of successive RR intervals (r-MSSD), and percentage differences of successive RR intervals of > 50 ms duration (pNN50). Four frequency domain indices were calculated: total power (TP), low frequency (LF), high frequency (HF), and the LF:HF ratio.
RESULTS—Heart rate variability indices were identical in the two control groups. Significantly reduced heart rate variability was found in patients with total cavopulmonary connections and atriopulmonary connections compared with the two control groups. In patients with partial cavopulmonary connections, heart rate variability was reduced compared with healthy controls. No differences in heart rate variability could be related to clinical status (New York Heart Association functional class), number of surgical interventions, or presence of right atrial enlargement.
CONCLUSIONS—Patients with cavopulmonary connections have significantly reduced heart rate variability and a particularly low vagal drive.


     

Heart rate turbulence and left ventricular ejection fraction in Chagas disease.

AIMS: Chagas disease patients often present premature ventricular complexes (PVCs), depression of left ventricular ejection fraction (LVEF) and autonomic dysfunction, which is generally evaluated by heart rate variability (HRV) analysis. As frequent PVCs may complicate HRV computation, we measured heart rate turbulence (HRT) and evaluated the correlation between ejection fraction and HRT or HRV in Chagas disease. METHODS: We studied 30 patients (47+/-11 years, 20 men) with Chagas cardiomyopathy and left ventricular dilatation who underwent clinical evaluation, ejection fraction (EF: 45+/-14%) determination and 24-h Holter monitoring (median PVC=1781). In all patients, the standard deviation of normal RR intervals (SDNN), the square root of the mean square differences of successive RR intervals (RMSSD) and values of turbulence onset (TO) and turbulence slope (TS) were calculated. RESULTS: HRT indices were independent of mean RR interval and presented high correlation with EF: TO (-0.11+/-0.01%, r=-0.60, P<0.001) and TS (5.8+/-3.7 ms/RR-interval, r=0.73, P<0.001). Of HRV parameters, only SDNN, corrected for mean RR interval, showed a weak but not significant correlation with EF (r=0.41). The comparison of HRT/EF and HRV/EF correlation coefficients, indicated the presence of a significant difference (P=0.017). CONCLUSIONS: HRT indices appear to correlate better with EF than SDNN in Chagas disease. Thus, an analysis based on heart rate transient adaptation seems to perform better than HRV in detecting the autonomic alterations that parallel left ventricular dysfunction in Chagas disease patients. The high number of PVCs observed in these patients further support the use of HRT methodology.     

高血压病患者胰岛素抵抗与心率变异的关系

目的探讨高血压病患者心率变异指标变化和胰岛素抵抗之间的关系。方法３７例高血压病患者和１６例正常人行糖耐量试验和测定胰岛素释放曲线的同时测定心率变异各项指标。结果高血压病人中６２％存在高胰岛血素症和胰岛素抵抗，其２４小时ＲＲ间期均值的标准差指数（ＳＤＮＮＩ）明显高于正常人，而２４小量内ＲＲ间期的标准差（ＳＤＮＮ）５分钟ＲＲ间期均值标准差指数（ＳＤＡＮＮＩ）和相邻心搏ＲＲ间期差值的均方根（ｒＭＳＳＤ）及相邻心搏ＲＲ间期大于５０ｍｓ的百分比（ＰＮＮ５０）明显低于正常人。结论高血压病患者的心率变异和胰岛素抵抗所引起的交感神经增强和副交感神经的活性减弱有关     

QT intervals and heart rate variability in hypertensive patients

Low heart rate variability and increased QT dispersion are risk factors for cardiac mortality in various patient populations. We studied dispersion of QT interval, i.e. an index of inhomogeneity of repolarization, and heart rate variability (HRV) i.e., a measure of cardiac autonomic modulation in 76 essential hypertension cases (45 women, 53.0 +/- 11.1 years, body mass index: 25.1 +/- 1.4 kg/m2) and 70 healthy cases (42 women, 54.0 +/- 10.2 years, body mass index: 25.5 +/- 1.6 kg/m2, p > 0.05). QT-corrected QT intervals and their dispersions were significantly higher in the hypertensive group (p < 0.0001), all showing a direct relation with the level of systolic and diastolic blood pressures, ventricular mass index and high Lown grade ventricular rhythm problems. Time domain measures like standard deviation of RR intervals, standard deviation of the means of all corrected RR intervals calculated at 5 min intervals (p < 0.0001), proportion of adjacent RR intervals differing by > 50 msec (p = 0.005), HRV triangular index (p = 0.007), the square root of the mean squared differences of successive RR intervals (p = 0.011), and the high frequency (HF, 0.16-0.40 Hz, p < 0.0001) part of the frequency domain measure of HRV were all decreased, whereas the low frequency (LF, 0.04-0.15 Hz, p = 0.013) part of the frequency domain measures and LF / HF ratio (p < 0.0001) were increased in hypertensive cases. Time domain and the HF part of frequency domain measures of heart rate variability showed an inverse relation with the increased levels of both systolic and diastolic blood pressures and Lown grading system of ventricular rhythm problems, whereas LF and LF / HF showed direct relations with high levels of systolic and diastolic blood pressures and high Lown grade ventricular rhythm problems. The measures of heart rate variability apart from LF and LF / HF were inversely related with the QT intervals and dispersions, whereas LF / HF was directly related with them. Therefore, we conclude that the levels of both systolic and diastolic blood pressures are related to the generation of ventricular rhythm problems either via increasing left ventricular mass which results in an increase in QT parameter measurements, or by altering heart rate variability measures indicating a disturbance in cardiac autonomic balance in essential hypertension.     

Effect of sotalol on heart rate variability assessed by Holter monitoring in patients with ventricular arrhythmias

Reduced vagal activity has been demonstrated to be associated with an increased risk of sudden death. Assessing the heart rate variability as a measure of the autonomic control of the heart has been established as a useful tool for the risk stratification of patients after myocardial infarction. In the current study, heart rate variability assessed by time- and frequency-domain measures was determined from Holter recordings before and during treatment with sotalol in 28 patients wtth chronic ventricular arrhythmias. The heart rate variability at baseline was independent of the presence or absence of spontaneous arrhythmias and of left ventricular function. Therapy with sotalol produced a significant improvement over control values in indices of parasympathetic tone (root mean square of the difference in successive RR intervals, proportion of adjacent RR intervals different by > 50 msec, high-frequency power spectrum). This improvement was not related to drug-induced changes in the mean heart rate or the suppression of ventricular ectopic activity. These effects on heart rate variability may contribute significantly to the overall efficacy profile of sotalol.     

Effect of metoprolol on heart rate variability in symptomatic patients with mitral valve prolapse

Metoprolol is widely used to eliminate symptoms in patients with mitral valve prolapse (MVP), a condition associated with enhanced sympathetic tone. In this study, effects of metoprolol on heart rate variability (HRV) indices were investigated in symptomatic patients with MVP. Thirty-nine symptomatic patients with MVP (26 women, mean age 26 +/- 7 years) and 16 age- and gender-matched controls were studied. After a baseline 24-hour Holter evaluation in all subjects, patients with MVP were started on metoprolol succinate therapy at a dose of 25 to 100 mg/d, and Holter analysis was repeated at the end of 3 months of metoprolol therapy. At the basal evaluation, all time-domain HRV indices with the exception of proportion of adjacent RR intervals differing by >50 ms in the 24-hour recording were significantly lower in patients with MVP than controls (SD of all normal-to-normal [NN] intervals, p = 0.013; SD of average NN intervals calculated during 5-minute periods of the entire recording, p = 0.03; triangular index, p = 0.025; and square root of mean squared differences in successive NN intervals, p = 0.026). After metoprolol treatment, all HRV indices significantly improved compared with baseline (SD of all NN intervals, p = 0.028; SD of average NN intervals calculated during 5-minute periods of the entire recording, p = 0.043; triangular index, p = 0.004; square root of the mean squared differences in successive NN intervals, p = 0.021; and proportion of adjacent RR intervals differing by >50 ms in the 24-hour recording, p = 0.014), and HRV indices after metoprolol treatment were similar to those of the control group (p >0.05). In conclusion, metoprolol significantly improved impaired HRV parameters in symptomatic patients with MVP.     

Left ventricular diastolic filling and its association with age

Thirty normal subjects, aged 22 to 80 years, were studied by radionuclide ventriculography to determine the age dependence of cardiac ventricular diastolic function and to evaluate the association of other factors with ventricular diastolic performance. A strong negative correlation was found between peak diastolic filling rate and age (r = -0.82, p less than 0.0001). Partial correlation analysis was used to factor out the strong age dependence and yielded additional significant correlations of peak filling rate with heart rate (r = 0.48, p less than 0.01) and time to peak filling rate (r = -0.48, p less than 0.01). Time to peak filling rate is also correlated with heart rate but not definitely with age. Analysis by multiple linear regression yields an equation predicting peak filling rate from age and heart rate. Thus, the rate of rapid diastolic filling declines markedly with age in normal subjects. The association of peak filling rate with age and with other factors indicates the need for careful consideration of these factors in the interpretation of scintigraphic findings in patients with heart disease.     

Two-Dimensional Vector Analysis of Beat-to-Beat Dynamics of Ventricular Repolarization

Objective: Duration of ventricular repolarization is a result of complex interaction between autonomic modulation and heart rate (HR). Methods: To study the dynamics of ventricular repolarization of the human right ventricle, beat-to-beat variability of ventricular repolarization was measured by plotting the duration of each monophasic action potential at the 90% phase of repolarization (APD₉₀) as a function of the previous APD90 both in sinus rhythm and during steady-state atrial pacing (cycle length of 600 rns) in 12 subjects without structural heart disease. Results: Quantitative analyses of APD₉₀ and RR interval variability in sinus rhythm showed that the total standard deviation (SD) of APD90 was only 8% of the SD of all RR intervals. Both longterm, continuous variability (SD2) of APD90 (3.9 ± 1.5 ms) and instantaneous beat-to-beat variability (SD1) of APD₉₀ (1.2 ± 0.3 ms) were smaller than the SD2 and SD1 of RR intervals (46 ± 17 ms and 15 ± 9 ms, respectively) (P < 0.001 for both), but the shapes of the APD₉₀ and RR interval plots and the SD1/SD2 ratio did not differ. SD1 of APD90 correlated well with the SD1 of RR intervals (r = 0.64, P < 0.05) but no significant correlation was observed between the SD2 of APD₉₀ and SD2 of RR intervals (r = 0.32, NS). During steady-state atrial pacing, only minimal instantaneous beat-to-beat variability in APD₉₀ (0.9 ± 0.3 rns) was observed but the SD2 was larger than the SD2 of RR intervals (2.3 ± 1.0 ms vs. 1.6 ± 0.8 ms, P < 0.001). Conclusion: The results suggest that instantaneous beat-to-beat variability of ventricular repolarization is mainly due to beat-to-beat fluctuation of HR, but the long-term dynamics of repolarization are partly influenced by other factors than the HR variability.     

Prognostic Value of Heart Rate Variability in Time Domain Analysis in Congestive Heart Failure

AIMS: Analysis of heart rate variability is a noninvasive tool that allows to study autonomic control of the heart. Several studies have shown disturbed heart rate variability in patients with chronic heart failure (CHF). We sought to assess the prognostic value of time domain measures of heart rate variability in CHF. METHODS AND RESULTS: We prospectively enrolled 190 patients with CHF in sinus rhythm, mean age 61+/-12 years, 109 (57.4 %) in NYHA class II and 81 (42.6 %) in class III or IV, mean cardiothoracic ratio 57.6+/-6.4 % and mean left ventricular ejection fraction 28.2+/-8.8 %, 85 (45 %) with ischemic and 105 (55 %) with idiopathic dilated cardiomyopathy. Time domain measures of heart rate variability were obtained from 24 h Holter ECG recordings. During follow-up (22+/-18 months), 55 patients died. In multivariate analysis, independent predictors for all-cause mortality were: ischemic heart disease, cardiothoracic ratio > or =60 % and standard deviation of all normal RR intervals <67 ms (RR=2.5, 95 % CI 1.5--4.2). CONCLUSIONS: Depressed heart rate variability has independent prognostic value in patients with CHF.     

Heart rate variability and ischaemia in patients with coronary heart disease and stable angina pectoris; influence of drug therapy and prognostic value. TIBBS Investigators Group. Total Ischemic Burden Bisoprolol Study.

AIMS: Determination of the influence of therapy with bisoprolol and nifedipine on the heart rate variability of patients from the Total Ischemic Burden Bisoprolol Study and examination of the prognostic value. METHODS AND RESULTS: Four hundred and twenty-two patients with stable angina were included. The heart rate variability was determined over a period of 24 h. Parameters determined: standard deviation of the mean of all corrected RR intervals, standard deviation of all 5 min mean cycle lengths, square root of the mean of the squared differences of successive corrected RR intervals. Nifedipine reduced the mean values of all heart rate variability parameters tested. Square root of the mean of the square differences of successive corrected RR intervals increased under bisoprolol. Standard deviation of the mean of all corrected RR intervals and standard deviation of all 5 min mean cycle lengths increased from low baseline values and declined from higher baseline values. The increase in heart rate variability under therapy was accompanied by a tendency towards a better prognosis. Patients with an increase in heart rate variability and simultaneous complete suppression of ischaemia under therapy displayed no serious events in the course of one year. CONCLUSIONS: The increase in the heart rate variability, which can be regarded as prognostically favourable, was predominantly observed under bisoprolol. The parameter constellation of an increase in heart rate variability and complete ischaemia suppression on the 48-h Holter ECG was associated with the greatest benefit.     

Differential index, a novel graphical method for measurements of heart rate variability

BACKGROUND: Commonly used methods to evaluate heart rate variability require extensive filtering of the registrations in order to exclude artefacts and ectopic beats. We developed and validated a novel graphical method for time-domain measurements of heart rate variability, the differential index, which does not require filtering and is simple to use. METHODS: The 24-h ambulatory long-term electrocardiogram recordings from 120 patients with angina pectoris and 49 control subjects were computerised without any filtering process. Sample density histograms of differences in the RR interval for successive beats were constructed and the widths of the histograms were used to obtain the differential index. For comparison, the same registrations were analysed by conventional methods. RESULTS: The differential index was most closely related (P<0.001) to conventional short-term time domain (e.g. percent of differences between adjacent normal RR intervals >50 ms, pNN50, r=0.81) and frequency-domain (e.g. high frequency power, r=0.84) components, but also to long-term time domain (e.g. standard deviation of all normal-to-normal RR intervals for all 5-min segments of the entire registration, SDNNIDX, r=0.72) and frequency-domain (e.g. low frequency power, r=0.64) components. CONCLUSION: The differential index method shows good agreement with established indices of heart rate variability. The insensitivity to recording artefacts and short-lasting disturbances of sinus rhythm make the differential index method particularly suited when data quality is imperfect. The simplicity of the method is valuable when large numbers of registrations are to be evaluated.     

Patients with uncomplicated coronary artery disease have reduced heart rate variability mainly affecting vagal tone

AIM: To investigate whether uncomplicated chronic coronary artery disease causes changes in heart rate variability and if so, whether the heart rate variability pattern is different from that described in patients with acute myocardial infarction. METHODS: Heart rate variability was studied in 65 patients with angina who had no previous myocardial infarcts, no other diseases, and were on no drug that could influence the sinus node. Results were compared with 33 age matched healthy subjects. The diagnosis of coronary artery disease in angina patients was established by coronary angiography in 58, by thallium scintigraphy in six, and by exercise test only in one. Patients and controls were Holter monitored 24 hours outside hospital, and heart rate variability was calculated in the frequency domain as global power (GP: 0.01-1.00 Hz), low frequency peak (LF: 0. 04-0.15 Hz), high frequency peak (HF: 0.15-0.40 Hz), LF/HF in ms(2), and in the time domain as SDNN (SD of normal RR intervals), SDANN (SD of all five minute mean normal RR intervals), SD (mean of all five minute SDs of mean RR intervals), rMSSD (root mean square of differences of successive normal RR intervals) (all in ms), and pNN50 (proportion of adjacent normal RR intervals differing more than 50 ms from the preceding RR interval) as per cent. RESULTS: The mean age in patients and controls was 60.4 (range 32-81) and 59.1 (32-77) years, respectively (NS), the male/female ratio, 57/65 and 24/33 (NS), and the mean time of Holter monitoring, 23.0 (18-24) and 22.8 (18-24) hours (NS). Mortality in angina patients was 0% (0/65) at one year, 0% (0/56) at two years, and 3% (1/33) at three years. Compared with healthy subjects angina patients showed a reduction in GP (p = 0.007), HF (p = 0.02), LF (p = 0.02), SD (p = 0.02), rMSSD (p = 0.01), and pNN50 (p = 0.01). No significant difference was found in RR, LF/HF, SDNN, or SDANN. CONCLUSIONS: Uncomplicated coronary artery disease without previous acute myocardial infarction was associated with reduced high and low frequency heart rate variability, including vagal tone. SDANN and SDNN, expressing ultra low and very low frequencies which are known to reflect prognosis after acute myocardial infarction, were less affected. This is in agreement with the good prognosis in uncomplicated angina in this study.     

Circadian blood pressure variability is associated with autonomic and baroreflex-mediated modulation of the sinoatrial node

OBJECTIVE: The day-night variability of blood pressure (BP) is of interest in the analysis of ambulatory blood pressure monitoring (ABPM). The aim of this study was to investigate whether the nocturnal BP reduction was associated with the autonomic and baroreflex-mediated modulation of the sinoatrial node in normotensive and hypertensive subjects. METHODS AND RESULTS: 63 consecutive untreated male subjects (40 hypertensive and 23 normotensive) were studied. Spectral parameters of RR interval variability and the alphaLF index (a measure of baroreflex gain) were calculated at rest.Then all the subjects performed a 24-h ABPM. RESULTS: As regards the relationships involving 24-h BP and resting heart rate (HR) and HR variability parameters, a significant correlation was found between mean RR and both systolic and diastolic nocturnal BP falls (r = 0.40, p < 0.001, r = 0.32, p < 0.01, respectively); moreover, a significant correlation was found between the nocturnal fall of systolic BP and both the LF/HF ratio and absolute power of HF (r = -0.25, p < 0.05 and r = 0.29, p < 0.05, respectively). The alphaLF index was significantly associated with the nocturnal diastolic BP fall (r = 0.26, p < 0.05) whereas the association with the systolic fall did not reach statistical significance (r = 0.23, p = 0.07). CONCLUSIONS: The relationship found between the nocturnal reduction of BP and both the LF/HF ratio and HF power of RR variability suggests that factors influencing the sympatho-vagal modulation to the heart are associated with the day-night variability of blood pressure. Moreover, the relationship between BP fall and the spontaneous baroreflex sensitivity index alphaLF, may indicate a role of the baroreflex-mediated arc function in the BP adjustments occurring during the night.     

Heart rate variability in dilated cardiomyopathy

Chronic heart failure is associated with excessive neurohormonal activation. Analysis of heart rate variability is considered a valid technique for assessment of the autonomic balance of the heart. Twenty symptomatic patients of dilated cardiomyopathy in NYHA class II-IV symptomatic status and as many normal controls were subjected to 24 hours Holter monitoring to assess the heart rate variability with both time domain and frequency domain analysis. Age of the patients ranged from 12 to 67 years (mean +/- SD 38.6 +/- 7 years), the male-female ratio was 4:1. The left ventricular ejection fraction of the patients was between 18-42 percent (mean +/- SD 30.2 +/- 9%) and all received diuretics, digoxin and angiotensin-converting enzyme inhibitors. Heart rate variability parameters measured included mean heart rate with standard deviation, hourly heart rate with SD and the mean of all normal RR intervals from the 24-hour recording. Time domain measures calculated were SD of all normal RR intervals, SD of 5 minute mean RR intervals and root mean square of difference of successive RR intervals. Using spectral plots, frequency domain subsets of low frequency and high frequency were analysed and expressed in normalised units. Total power was also measured. In the dilated cardiomyopathy patients, mean 24-hour heart rate in beats per minute was significantly higher in comparison to controls (82 +/- 13 vs 72 +/- 8; p < 0.001) whereas mean hourly heart rate with standard deviation (msec) was significantly lower (97 +/- 41 vs 232 +/- 25; p < 0.001), SD of all normal RR intervals (msec) was 85.5 +/- 26.3 vs 139.4 +/- 16.9 in controls (p < 0.001), SD of 5 minute mean RR intervals (msec) was also significantly less in patients in comparison to controls (75.8 +/- 39.6 vs 130.8 +/- 20.3; p < 0.001). However, although root mean square of difference of successive RR intervals (msec) was reduced in patients (30.1 +/- 9.3 vs 37.3 +/- 11.7; p < 0.05), the difference was non-significant. Low frequency power (0.05-0.15 Hz) (normalised units) was reduced in the dilated cardiomyopathy group (0.0721 +/- 0.003 vs 0.136 +/- 0.047 in the control group; p < 0.001). High frequency power (0.35-0.50 Hz) (normalised units) (0.08 +/- 0.05 in patients vs 0.09 +/- 0.02 in controls; p > 0.1) and total power frequency (0.02-0.50 Hz) (normalised units) (0.34 +/- 0.05 in patients vs 0.35 +/- 0.12 in controls; p > 0.1) was non-significantly different in the two groups. Regression analysis showed a significant decrease in SD of all normal RR intervals, SD of 5 minute mean RR intervals, low frequency, high frequency, total power and a non-significant decrease in root mean square of difference of successive RR intervals with a decrease in ejection fraction percent whereas there was a significant decrease in SD of all normal RR intervals, SD of 5 minute mean RR intervals, low frequency and total power and a less significant decrease in root mean square of difference of successive RR intervals and high frequency power with an increase in NYHA class. At 6 months duration, 6 patients were lost to follow-up, 3 patients were readmitted (2 for congestive cardiac failure, one of paroxysmal supraventricular tachycardia). One patient who was NYHA class IV at baseline was readmitted for congestive cardiac failure and showed much lower heart rate variability parameters compared to the average of the patients. We conclude that in symptomatic dilated cardiomyopathy patients, heart rate variability parameters are significantly reduced in comparison to control subjects.     

Assessment of stiffness of the hypertrophied left ventricle of bicyclists using left ventricular inflow Doppler velocimetry

Sixteen male bicyclists and 16 control subjects were studied to assess whether the left ventricular hypertrophy of athletes is associated with changes in diastolic left ventricular function. The cyclists had a larger left ventricular internal diameter on echocardiography (55.2 versus 47.9 mm; p less than 0.001) and a disproportionate increase in wall thickness relative to the internal diameter (0.48 versus 0.41; p less than 0.01), indicating a mixed eccentric-concentric type of hypertrophy. Left ventricular inflow Doppler velocimetry showed similar results in athletes and control subjects for peak flow velocities in the atrial contraction phase (30 versus 32 cm/s; p = NS) and in the early diastolic rapid filling phase (71 versus 67 cm/s; p = NS). The similar ratio of both velocities, that is, 0.43 in the cyclists and 0.49 in the control subjects, suggests that left ventricular distensibility is unaltered in cyclists. It is concluded that the left ventricular hypertrophy observed in cyclists is not associated with changes in ventricular stiffness, as estimated from left ventricular inflow Doppler velocimetry.     

Relationships between heart rate variability, functional capacity, and left ventricular function following myocardial infarction: an evaluation after one week and six months

BACKGROUND: Relationships between heart rate (HR) variability and different prognostic markers such as ejection fraction, functional capacity, and patency of the infarct-related artery, as well as the comparison of their time courses are not fully elucidated. HYPOTHESIS: The aim of study was to assess prospectively the early postinfarction changes in HR variability and its evolution over a period of 6 months: the relationships between HR variability and functional capacity in exercise testing; left ventricular function in cardiac catheterization: status of the infarct-related artery; and the comparison of their time courses. METHODS: In 42 patients with anterior myocardial infarction, a study was made of the early changes in HR variability analyzed by the complex demodulation method, its evolution over a period of 6 months. and the relationships between HR variability and (1) functional capacity in exercise testing, (2) left ventricular function in cardiac catheterization, and (3) status of the infarct-related artery. RESULTS: At 1 week HR variability parameters correlated directly with functional capacity indicators such as METS, percent change in HR from rest to peak exercise (%deltaHR), difference between initial and peak HR (HR range), percent peak theoretical HR (% peak HR), left ventricular ejection fraction (EF), and, inversely, with end-systolic volume (ESV). Stepwise multiple regression analysis to establish HR variability parameters (recorded at 1 week) as related to functional capacity and left ventricular function at 1 week and 6 months postinfarction established the following variables: (1) At 1 week: standard deviation (SD) of the RR cycles in relation to %deltaHR (r = 0.60, p <0.0001), HR range (r = 0.43, p < 0.01), and EF (r = 0.79, p < 0.0001). (2) At 6 months, the sole accepted HR variability parameter was the SD in relation to %deltaHR (r = 0.38, p < 0.05) and HR range (r = 0.45, p < 0.01). No variability parameter was accepted in relation to METS, % peak HR, or ESV. Relationship between EF or ESV and HR variability parameters was not significant when both were evaluated at 6 months. At that time, there was a significant increase in all HR variability parameters among all surviving patients (n = 39), with the exception of the LF/HF ratio and mean RR cycle. The percent increase in HR variability between the first week and 6 months was greater among those patients with the lowest basal EF. No relation was established between HR variability and patency of the infarct-related artery. CONCLUSION: The decrease in HR variability observed following myocardial infarction is associated with a diminished functional capacity and an increased alteration of the EF. This does not affect the recovery of HR variability, which was observed in all surviving patients.     

Influence of heart rate on stroke volume variability in atrial fibrillation in patients with normal and impaired left ventricular function

Both resting tachycardia and irregular ventricular rhythm may contribute to impaired cardiac performance in atrial fibrillation (AF). This study assesses the relation between resting heart rate and beat-to-beat changes in left ventricular (LV) ejection and filling in patients with normal and impaired LV systolic function. Beat-to-beat variation in LV outflow and inflow velocity-time integral was measured using pulsed Doppler ultrasound in 39 patients with chronic AF and normal (n = 22) or impaired (n = 17) LV systolic function. Aortic velocity-time integral variability increased with mean heart rate (p = 0.003) even though RR interval variability decreased (p <0.001). Aortic velocity-time integral was more sensitive to the duration of both the preceding (p <0.001) and prepreceding (p <0.001) RR intervals at higher heart rates. These relations were similar for patients with normal and impaired LV systolic function. The sensitivity of the filling velocity-time integral to RR interval variability also increased with heart rate (p <0.001). However, at higher heart rates the filling velocity-time integral (p = 0.009 ) and filling time (p = 0.005) were less sensitive to change in RR intervals in patients with impaired LV function. We conclude that beat-to-beat stroke volume variability in AF increases with heart rate. Stroke volume variability was not influenced by LV systolic function.