Is there increased sympathetic activity in patients with hypertrophic cardiomyopathy?

Heart rate variability and haemodynamic function in individuals with hypertrophic cardiomyopathy

OBJECTIVES

Heart rate variability (HRV) is a measure of cardiac autonomic function. This study: (1) evaluated the differences in HRV and haemodynamic function between individuals with hypertrophic cardiomyopathy (HCM) and healthy controls, and (2) determined the relationship between HRV and haemodynamic variables in individuals with HCM.

METHODS

Twenty-eight individuals with HCM (n = 7, females; age 54 ± 15 years; body mass index: 29 ± 5 kg/m2 ) and 28 matched healthy individuals (n = 7 females; age 54 ± 16 years; body mass index: 29 ± 5 kg/m2 ) completed 5-min HRV and haemodynamic measurements under resting (supine) conditions using bioimpedance technology. Frequency domain HRV measures (absolute and normalized low-frequency power (LF), high-frequency power (HF) and LF/HF ratio) and RR interval were recorded.

RESULTS

Individuals with HCM demonstrated higher vagal activity (i.e., absolute unit of HF power (7.40 ± 2.50 vs. 6.03 ± 1.35 ms2 , p = 0.01) but lower RR interval (914 ± 178 vs. 1014 ± 168 ms, p = 0.03) compared to controls. Stroke volume (SV) index and cardiac index were lower in HCM compared with healthy individuals (SV, 33 ± 9 vs. 43 ± 7 ml‎/beat‎/m², p < 0.01; cardiac index,2.33 ± 0.42 vs. 3.57 ± 0.82 L/min/m2 , p < 0.01), but total peripheral resistance (TPR) was higher in HCM (3468 ± 1027 vs. 2953 ± 1050 dyn·s·m2 cm-5 , p = 0.03). HF power was significantly related to SV (r = -0.46, p < 0.01) and TPR (r = 0.28, p < 0.05) in HCM.

CONCLUSIONS

Short-term frequency domain indices of HRV provide a feasible approach to assess autonomic function in individuals with HCM. Vagal activity, represented by HF power, is increased, and associated with peripheral resistance in individuals with HCM.

Autonomic dysfunction in cardiac amyloidosis assessed by heart rate variability and heart rate turbulence

BACKGROUND

Cardiac amyloidosis (CA) is characterized by left ventricular hypertrophy (LVH) and autonomic nervous imbalance due to amyloid infiltration. However, autonomic dysfunction is often seen in heart failure (HF) with LVH from other etiologies. We aimed to characterize autonomic dysfunction in CA from other etiologies of LVH.

METHODS

Fifty-five HF patients with LVH (35 males, mean age 65 ± 16 years) were enrolled. LVH was defined as left ventricular mass index measured by echocardiography >95 g/m2 in women and 115 g/m2 in men. The etiology was as follows: amyloid light chain (AL)-CA, n = 14; hypertrophic cardiomyopathy, n = 21; and aortic stenosis (AS), n = 20. With the patient in a clinically stable condition, heart rate variability (HRV) and heart rate turbulence (HRT), which reflect autonomic dysfunction, were measured using Holter monitoring and compared among the three groups.

RESULTS

Brain natriuretic peptide levels, LVH severity, left ventricular ejection fraction, and tissue Doppler index E/e' did not differ among the three groups. However, severe abnormalities of HRV and HRT were obtained in AL-CA. In the ROC analysis to identify AL-CA in HF with LVH, the best cutoff value for standard deviation of all R-R intervals, standard deviation of the 5-min mean R-R intervals, turbulence onset, and turbulence slope were 68.5 ms (AUC: 0.865), 58.5 ms (AUC: 0.834), 0.25% (AUC: 0.813), and 1.00 ms/RR (AUC 0.736), respectively.

CONCLUSION

Autonomic dysfunction is a hallmark of AL-CA, and its noninvasive assessment by Holter monitoring may be a useful tool for differential diagnosis of HF with LVH.

Heart Rate and Heart Rate Variability of Rhesus Macaques (Macaca mulatta) Affected by Left Ventricular Hypertrophy

Hypertrophic cardiomyopathy (HCM) is frequently associated with sudden cardiac death, presumably due to the development of malignant arrhythmias. The risk of sudden cardiac death due to HCM has been reported to be predicted by assessing electrocardiographic (ECG) changes including frequencies and complexities of arrhythmias as well as heart rate variability (HRV) as an assessment of autonomic balance. Sudden cardiac death in association with naturally-occurring left ventricular hypertrophy (LVH) has been reported in a colony of rhesus macaques and is under investigation as a potential non-human primate model of human HCM. In the present study, 10 rhesus macaques with LVH and 10 without the signs of LVH confirmed by an echocardiographic examination were recruited for assessing ECG and HRV parameters. ECG morphology on 10-s, 6-lead ECG analysis, and the frequency and complexity of arrhythmias as well as HRV on 20-h ambulatory ECG Holter analyses were assessed. On the standard 10-s 6-lead ECG analysis, P wave and QRS complex duration as well as the QRS complex amplitude were significantly increased in the LVH-affected rhesus macaques compared to control rhesus macaques. Analysis of 20-h Holter monitoring revealed no statistically significant differences in the frequency or the complexity of arrhythmias between the LVH and the control groups. Several HRV parameters were smaller in the LVH group than the control group throughout the majority of Holter recordings showing periods of reduced variability, however, no statistically significant differences were achieved across groups and/or time points. These findings indicate that ECG analysis and Holter monitoring of rhesus macaques are feasible and that ECG morphological changes in association with LVH could be used as a possible component of an antemortem screening tool. The rhesus macaques of this study did not reveal clear indications of risk for sudden cardiac death. Further studies are necessary to determine the etiology of sudden cardiac death due in LVH affected rhesus macaques and identify if any parameters of arrhythmia assessment or HRV can be used to predict the development of sudden cardiac death.

Slowed atrial and atrioventricular conduction and depressed HRV in a murine model of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common heritable cardiac disorder with diverse clinical outcomes including sudden death, heart failure, and stroke. Depressed heart rate variability (HRV), a measure of cardiac autonomic regulation, has been shown to predict mortality in patients with cardiovascular disease. Cardiac autonomic remodelling in animal models of HCM are not well characterised. This study analysed Gly203Ser cardiac troponin-I transgenic (TG) male mice previously demonstrated to develop hallmarks of HCM by age 21 weeks. 33 mice aged 30 and 50 weeks underwent continuous electrocardiogram (ECG) recording for 30 min under anaesthesia. TG mice demonstrated prolonged P-wave duration (P < 0.001) and PR intervals (P < 0.001) compared to controls. Additionally, TG mice demonstrated depressed standard deviation of RR intervals (SDRR; P < 0.01), coefficient of variation of RR intervals (CVRR; P < 0.001) and standard deviation of heart rate (SDHR; P < 0.001) compared to controls. Additionally, total power was significantly reduced in TG mice (P < 0.05). No significant age-related difference in either strain was observed in ECG or HRV parameters. Mice with HCM developed slowed atrial and atrioventricular conduction and depressed HRV. These changes were conserved with increasing age. This finding may be indicative of atrial and ventricular hypertrophy or dysfunction, and perhaps an indication of worse clinical outcome in heart failure progression in HCM patients.

Clinical correlates of autonomic response during tilting test in hypertrophic cardiomyopathy

AIMS

The aim is to investigate autonomic nervous system imbalance in hypertrophic cardiomyopathy (HCM) by combining echocardiographic morphological and functional parameters with the analysis of the autonomic responses to orthostatic stress.

METHODS

A 10-min tilting test and a transthoracic echocardiogram focused on ventricular septal systolic (S wave) and diastolic function (isovolumic relaxation time) were performed. Low frequency on high frequency ratio (LF/HF) and RR variation (variation of beat to beat intervals) in response to passive orthostatism were used as measures of sympathetic reflex activation [delta LF/HF (D-LF/HF) and delta RR (DRR), respectively]. Brain natriuretic peptide was measured.

RESULTS

A total of 50 HCM patients were categorized in two groups: D-LF/HF more than 0 (group 1, sympathetic response) and D-LF/HF 0 or less (group 2, parasympathetic response). Patients in group 2 had higher New York Heart Association class, a more frequent history of atrial fibrillation (38 versus 9% P = 0.04) or syncope (46 versus 12% P = 0.01) and an increased septal isovolumic relaxation time (122 versus 82 ms P = 0.02). The same categorization was made according to lowest quartile DRR (DRR at least 23 ms, group 1: sympathetic response; DRR less than 23 ms, group 2: parasympathetic response). In group 2, patients were older, with advanced New York Heart Association class and higher history of atrial fibrillation.

CONCLUSIONS

Autonomic response to passive orthostatism in HCM appears correlated with specific functional features of the hypertrophic heart. Altered neural afferent traffic from the localized area of segmental hypertrophy resulted in autonomic changes with a blunted sympathetic response, and an inappropriate vagal activation, especially in patients with history of atrial fibrillation or syncope.

Can QT/RR relationship differentiate between low- and high-risk patients with hypertrophic cardiomyopathy?

BACKGROUND

Abnormal dynamicity of repolarization is considered to be a marker of myocardial vulnerability contributing to increased risk of arrhythmic events and sudden death. However, little is known about QT dynamics in hypertrophic cardiomyopathy (HCM). In this study, we aimed to evaluate ventricular repolarization by QT dynamicity in patients with HCM, focusing on its value to define if it is able to differentiate among low- and high-risk HCM patients.

METHODS

The linear regression slopes of the QT interval, measured to the apex and to the end of the T wave plotted against RR intervals (QTapex/RR and QTend/RR slopes, respectively) were calculated from 24-hour Holter recordings using a standard algorithm in 36 HCM patients and 64 control subjects.

RESULTS

QTapex/RR and QTend/RR slopes were significantly steeper in the HCM patients in contrary to healthy control subjects (QTapex/RR = 0.22 + 0.08 vs 0.20 + 0.05, P = 0.0367; QTend/RR = 0.25 + 0.10 vs 0.20 + 0.06, P = 0.023). Moreover, the slopes of QTend/RR and QTapex/RR of high-risk patients were significantly steeper than those of control subjects while no significant differences were found among low-risk HCM patients and control subjects and only QTe/RR of high-risk patients was significantly different between low- and high-risk HCM patients.

CONCLUSIONS

Our study results suggest that QT dynamicity is impaired in patients with HCM and may help to differentiate among low- and high-risk patients. Further studies are needed to elucidate the prognostic significance and clinical implications of impaired ventricular repolarization in patients with HCM.

Heart rate recovery in patients with hypertrophic cardiomyopathy

Recovery in heart rate (HR) after exercise is a measure of autonomic function and a prognostic indicator in cardiovascular disease. The aim of this study was to characterize heart rate recovery (HRR) and to determine its relation to cardiac function and morphology in patients with hypertrophic cardiomyopathy (HC). We studied 18 healthy volunteers and 41 individuals with HC. All patients underwent clinical assessment and transthoracic echocardiography. Continuous beat-by-beat assessment of HR was obtained during and after cardiopulmonary exercise testing using finger plethysmography. HRR and power spectral densities were calculated on 3 minutes of continuous RR recordings. Absolute HRR was lower in patients than that in controls at 1, 2, and 3 minutes (25.7 ± 8.4 vs 35.3 ± 11.0 beats/min, p <0.001; 36.8 ± 9.4 vs 53.6 ± 13.2 beats/min, p <0.001; 41.2 ± 12.2 vs 62.1 ± 14.5 beats/min, p <0.001, respectively). HRR remained lower in patients at 2 and 3 minutes after normalization to peak HR. After normalization to the difference in HR between peak exercise and rest, HRR was significantly impaired in individuals with obstructive HC at 3 minutes compared with controls. HR at 3 minutes correlated with peak left ventricular outflow tract gradient (B 0.154 beats/min/mm Hg, confidence interval 0.010 to 0.299, p = 0.037) and remained a significant predictor of HRR after multivariable analysis. Spectral analysis showed a trend toward an increased low-frequency to high-frequency ratio in patients (p = 0.08) suggesting sympathetic predominance. In conclusion, HRR is impaired in HC and correlates with the severity of left ventricular outflow tract gradient. Prospective studies of the prognostic implications of impaired HRR in HC are warranted.

Abnormal heart rate regulation in murine hearts with familial hypertrophic cardiomyopathy-related cardiac troponin T mutations

Mutations in cardiac troponin T (cTnT), Δ160E and R92Q, have been linked to familial hypertrophic cardiomyopathy (FHC), and some studies have indicated that these mutations can lead to a high incidence of sudden cardiac death in the relative absence of significant ventricular hypertrophy. Alterations in autonomic function have been documented in patients with hypertrophic cardiomyopathy. We hypothesize that alterations in autonomic function may contribute to mutation-specific clinical phenotypes in cTnT-related FHC. Heart rate (HR) variability (HRV) has been used to assess autonomic function from an electrocardiograph. Nontransgenic, Δ160E, or R92Q mice were implanted with radiofrequency transmitters to obtain continuous electrocardiograph recordings during 24-h baseline and 30-min recordings after β-adrenergic receptor drug injections. Although Δ160E mice did not differ from nontransgenic mice for any 24-h HRV measurements, R92Q mice had impaired HR regulation, as measured by a decrease in the SD of the R-R interval, a decrease in the low frequency-to-high frequency ratio, a decrease in normalized low frequency, and an increase in normalized high frequency. β-Adrenergic receptor density measurements and HRV analysis after drug injections did not reveal any significant differences for Δ160E or R92Q mice versus nontransgenic mice. Arrhythmia analysis revealed both an increased incidence of heart block in R92Q mice at baseline and frequency of premature ventricular contractions after isoproterenol injections in Δ160E and R92Q mice. In addition, Δ160E and R92Q mice exhibited a prolonged P duration after drug injections. Therefore, between two independent and clinically severe cTnT mutations within the same functional domain, only R92Q mice exhibited altered autonomic function, whereas both mutations demonstrated abnormalities in conduction and ventricular ectopy.

Heart rate variability in patients with cardiac hypertrophy--relation to left ventricular mass and etiology

BACKGROUND

Decreased heart rate variability (HRV) has been shown to reflect disturbances of the autonomic nervous system that is related to increased cardiovascular mortality. Most studies investigated HRV in patients with systolic left ventricular dysfunction due to remote myocardial infarction or dilated cardiomyopathy. To date, only few data are available on HRV in patients with predominant diastolic dysfunction in the presence of cardiac hypertrophy of different etiologies.

METHODS

Time domain analysis of HRV was performed from digital 24-hour Holter electrocardiogram recordings in 86 patients with sinus rhythm and cardiac hypertrophy, which was due to aortic valve stenosis in 33 patients, hypertrophic cardiomyopathy in 29 patients, and hypertensive heart disease in 24 patients. Heart rate variability analysis was compared with 91 healthy controls.

RESULTS

The SD of all normal-to-normal R-R intervals (SDNN) was reduced in patients with aortic valve stenosis, hypertrophic cardiomyopathy, and hypertensive heart disease when compared with controls (SDNN 119 +/- 42 vs 154 +/- 36 milliseconds, P < .001). The extent of cardiac hypertrophy indexed by echocardiography based left ventricular mass calculation and increased patient age were independent predictors for depression of SDNN.

CONCLUSIONS

Cardiac hypertrophy of various etiologies is related to decreased HRV on 24-hour Holter electrocardiogram. Both the patient age and the extent of left ventricular hypertrophy are independently associated with depression of HRV. These findings are independent of the cause of cardiac hypertrophy. The significance of these findings remains to be determined by future studies.

Prognostic value of heart rate variability in patients with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) have been reported to display impaired heart rate variability, although little is known regarding its prognostic value. By using fast Fourier transformation of 24-hour Holter recordings in 73 HCM patients at a stable clinical condition, we computed 4 spectral components: very low frequency, low frequency, high frequency, and total power. During 28 months, 7 HCM patients experienced death or acquired hospitalization for heart failure. Sudden death did not occurred. High frequency component was lower in HCM patients with cardiac events than that in patients without cardiac events (3.78 +/- 0.66 vs. 4.43 +/- 0.92 In(ms(2)), P =.045). There were no significant differences in other heart rate variability variables between HCM patients with and without cardiac events. In multivariate analysis, high frequency component remained to be an independent predictor of cardiac events (relative risk=0.10, 95% CI 0.01-0.73, P =.023). Heart rate variability analysis is predictive of heart failure in our cohort of HCM patients, whereas its predictive value of sudden death remains unclear.

Heart rate and heart rate variability of healthy cats in home and hospital environments

To investigate heart rate and its variability, a telemetry device was affixed to 16 healthy, young cats. Prior to inclusion in the study, cats were subject to echocardiographic examination. The heart rate (HR) when cats were restrained for echocardiography (HR(r)) was calculated from 4-5 consecutive RR intervals obtained from a simultaneously recorded electrocardiogram. Electrocardiographic data were then acquired by telemetry in a quiet room in the veterinary hospital (VTH) and later, in the owner's home (home). The ambulatory data were digitally sampled and the RR interval tachogram from a 4 min epoch subject to Fast Fourier Transform to yield measures of heart rate variability (HRV). Sinus arrhythmia was often observed in resting cats. Heart rates (bpm) expressed as mean (+/-SD) were: HRr: 187 (+/-25), HRVTH: 150 (+/-23), HR(home): 132 (+/-19); each of these rates was significantly different from the others. Significant differences in profiles of HRV suggested that sympathetic tone was higher (and parasympathetic tone lower) when cats were in the hospital.

Parasympathetic dysfunction in hypertrophic cardiomyopathy assessed by heart rate variability: comparison between short-term and 24-h measurements

In this study, we evaluate cardiac autonomic function in hypertrophic cardiomyopathy (HCM) by assessing heart rate variability (HRV), comparing a short-term laboratory method with an ambulatory (24-h) method, in patients with and without beta-blockade. Reduced HRV is a risk factor for adverse events in some cardiac diseases, but is not a proven risk indicator in HCM. Analysis of HRV has been based on either short- or long-term electrocardiographic recordings and previous studies in HCM have shown conflicting results. There is no consensus on which method to prefer, and we evaluate, for the first time, both short- and long-term analyses in patients with HCM. Long- and short-term HRV analyses were performed in 43 patients with HCM. They were divided in two groups, 22 patients on beta-blockade and 21 non-treated patients. As controls, 121 healthy subjects were used. Young patients without beta-blockade showed a reduction in HRV parameters reflecting parasympathetic function, both in the short- and long-term registrations, which was attenuated by beta-blockade. Parasympathetic autonomic regulation was found to be impaired in young patients with HCM. This may be of clinical relevance as abnormal autonomic function might be a substrate for malignant dysrhythmias. The impairment was attenuated by beta-blockade, which might indicate a clinically useful effect. We also show that short- and long-term methods yield similar results, suggesting that a short-term registration might be sufficient to assess HRV in patients with HCM.

Do variable age-related secondary factors affect ventricular geometry in hypertrophic cardiomyopathy?

The relationship between cardiac shape and the age of patients with hypertrophic cardiomyopathy (HCM) has been established, and echocardiography has been accepted as the best method to quantitate ventricular cavity geometry. Recently, real-time three-dimensional volumetric data have demonstrated that children and young, middle-aged, and elderly patients with HCM have different morphologic and prognostic characteristics. This review discusses the importance of phenotypic expression and describes secondary factors that may affect ventricular cavity geometry during the progression of HCM.

Vascular mechanisms of sudden death in hypertrophic cardiomyopathy, including blood pressure responses to exercise

Approximately a third of patients with hypertrophic cardiomyopathy fail to increase blood pressure appropriately during exercise, a consequence of an inappropriate vasodilator response in nonexercising beds, leading to an exaggerated fall in systemic vascular resistance. The precise mechanism responsible for this abnormal vascular control in hypertrophic cardiomyopathy is still unclear, but is thought to be secondary to enhanced cardiac baroreceptor activity. However, alternate or synergistic mechanisms, including enhanced release of brain natriuretic peptide, may be involved. Normal exercise blood pressure responses have been shown to have a high (97%) negative predictive accuracy for sudden death during an average follow-up of approximately 3 years, providing considerable reassurance. Patients with abnormal blood pressure responses on exercise were at markedly increased risk of sudden cardiac death, although the positive predictive accuracy during this brief follow-up period was low (15%). It is likely that vascular instability may act as a trigger for sudden cardiac death in patients with an underlying electrophysiologic substrate. Recent evidence suggests that this vascular instability may also result in hypotension during ordinary daily activity, or even at rest, and may be an important cause of syncope in hypertrophic cardiomyopathy. Further studies are required to identify mechanisms of attenuating or reversing this vascular instability. Such measures might have the potential to improve symptoms of recurrent syncope and perhaps reduce the risk of sudden cardiac death.

Heart rate decline after exercise in patients with hypertrophic cardiomyopathy

To evaluate the heart rate recovery, submaximal exercise, echocardiographic examination, and Holter monitoring were performed on 30 patients with hypertrophic cardiomyopathy and 11 controls. The time constant of heart rate decline after exercise was calculated. Spectral analysis was performed on Holter recordings. The time constant did not correlate with heart rate, left ventricular end-diastolic pressure, ejection fraction, or wall thickness. There was no correlation between the time constant and any mean spectral indices over 24 hours in patients. However, the time constant correlated with high frequency component in the night. Nocturnal high frequency component in patients with short time constant was significantly less than in those with long time constant, but did not significantly differ from that in controls. In conclusion, the heart rate decline after exercise does not primarily reflect the severity of hypertrophy or hemodynamic impairment but is associated with nocturnal parasympathetic modulation in patients with hypertrophic cardiomyopathy.

Heart rate variability in hypertrophic obstructive cardiomyopathy: association with functional classification and left ventricular outflow gradients

BACKGROUND

The aim of this study was to investigate cardiac autonomic control in patients with hypertrophic obstructive cardiomyopathy (HOCM) and to assess the indexes of heart rate variability (HRV) in relation to the clinical and echocardiographic features.

METHODS AND RESULTS

Twenty-three patients (17 male, six female: mean age 43+/-11) with HOCM and 18 healthy volunteers were included. M-mode and two-dimensional echocardiography, pulsed and continuous-wave Doppler studies were obtained. All patients and volunteers underwent continuous 24-h ambulatory ECG monitoring. Time domain variables considered in this study were standard deviation of mean R-R intervals (SDNN), root mean-squared successive difference (RMSSD) and percentage of cycles differing from the preceding one by more than 50 ms (PNN 50%). Patients were compared to detect associations between indices of heart rate variability, left ventricular outflow tract obstruction and clinical status. Heart rate variability parameters were also correlated with the echocardiographic and clinical characteristics of the patients. Both New York Heart Association (NYHA) functional class I-II patients (group I) and NYHA III-IV patients (group II) had lower values of SDNN, RMSSD and PNN 50% when compared with the control group (P<0.001, P<0.05 and P<0.01, respectively, for group I and P<0.001, P<0.001 and P<0.001, respectively, for group II). Time domain heart rate variability parameters were found to be significantly correlated with the subaortic dynamic obstruction.

CONCLUSION

Heart rate variability is reduced in HOCM and well correlated with the degree of subaortic obstruction. Heart rate variability indices are also sensitive markers of the functional status.

Impact of chronic DDD pacing on time-domain indexes of heart rate variability in patients with hypertrophic obstructive cardiomyopathy

The aim of this study was to examine whether DDD pacing affects time-domain indexes of heart rate variability (HRV) in patients with hypertrophic obstructive cardiomyopathy (HOCM). We studied 11 patients (7 men, age 52 +/- 8 years) with HOCM refractory to drugs. In all patients a DDD pacemaker was implanted and the atrioventricular delay was programmed to ensure a full ventricular activation sequence. Time-domain indexes of HRV (mean NN, SDANN, SDNN, SD, rMSSD, pNN50) were determined from 24-hour Holter recordings 3 days before and 1 year after pacemaker implantation. The pacemaker was turned off during the second recordings. The same indexes were determined in ten healthy controls at the same time points. The controls showed no significant differences in any of the measured parameters between the two time points. The HOCM patients showed an increase in SD (from 27 +/- 13 to 41 +/- 13 ms, P < 0.001), rMSSD (from 18 +/- 5 to 32 +/- 8 ms, P < 0.001), and pNN50 (from 1.03 +/- 1.06 to 8.52 +/- 4.84%, P < 0.0001). As a result, the values of these three parameters, which were lower in the HOCM patients than in the controls before pacing, were restored to normal levels by the end of the study. In conclusion, our findings indicate that long-term pacing in HOCM patients restores the sympathovagal balance in the heart by increasing vagal activity.

Impaired peripheral vasoconstriction in response to alpha-adrenergic stimulation in patients with idiopathic hypertrophic cardiomyopathy

Exercise hypotension has been documented in patients with hypertrophic cardiomyopathy (HCM). Some investigators reported that this is due to an inadequate increase of systemic vascular resistance during or after exercise. The aim of this study was to investigate the pathogenesis of limb vascular response abnormalities in patients with idiopathic HCM. Thirteen patients with HCM and 9 healthy controls were administered an endothelium-dependent dilator (acetylcholine), a direct smooth muscle dilator (nitroglycerin), an alpha-adrenergic stimulator (phenylephrine), and a beta-adrenergic stimulator (isoproterenol) by intra-arterial infusion. Peripheral vascular resistance was assessed by forearm plethysmography at rest and during each infusion to obtain the percentage change in vascular resistance. Isoproterenol, acetylcholine and nitroglycerin produced dose-related vasodilatation with no significant differences between HCM patients and healthy controls. The percentage increase in vascular resistance was significantly less in HCM patients than in healthy controls after phenylephrine infusions of 0.5 microg/min (155+/-38% vs 195+/-47%, mean+/-SD, p<0.05) and 1.0 microg/min (174+/-49% vs 238+/-65%, p<0.05). Vasoconstriction mediated by alpha-adrenergic receptors appeared to be impaired in the peripheral vasculature of patients with HCM.

Heart rate variability

Heart rate variability (HRV), usually performed from 24 hour ambulatory ECG recordings, measures the variability of the heart rate. Alterations in autonomic balance and baroreceptor function, increased plasma norepinephrine levels, and reduced HRV have been associated with progressive myocardial failure. Not only has reduced HRV been associated with the degree of myocardial failure, possibility of prognostic significance, but also increased sudden death risk in both ischemic and nonischemic cardiomyopathy in humans. Heart rate variability analysis in the dog is confounded by pronounced sinus arrhythmia, and whether or not this technique has clinical utility in the dog remains to be demonstrated.

Reduced cardiopulmonary baroreflex sensitivity in patients with hypertrophic cardiomyopathy

OBJECTIVES

We sought to assess baroreflex function in patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

We have previously demonstrated a specific abnormality in the afferent limb of the cardiopulmonary baroreflex in patients with vasovagal syncope. Patients with HCM exhibit abnormal control of their vasculature during exercise and upright tilt; we therefore hypothesize a similar abnormality in the afferent limb of the cardiopulmonary baroreflex arc.

METHODS

We investigated 29 patients with HCM and 32 control subjects. Integrated baroreceptor sensitivity was assessed after administration of phenylephrine. Cardiopulmonary baroreceptor sensitivity was assessed by measuring forearm vascular resistance (FVR) during lower body negative pressure (LBNP). Carotid artery baroreflex sensitivity was assessed by measuring the in RR interval during manipulation of carotid artery transmural pressure. The integrity of the efferent limb of the reflex arc was determined by studying responses to both handgrip and peripheral alpha-receptor sensitivity.

RESULTS

During LBNP, FVR increased by only 2.36+/-9 U in patients, compared with an increase of 123+/-8.76 U in control subjects (p=0.001). FVR paradoxically fell in eight patients, but in none of the control subjects. Furthermore, FVR fell by 4.9+/-5.6 U in patients with a history of syncope, compared with an increase of 4.7+/-7.2 U in those without syncope (p=0.014). Integrated and carotid artery baroreflex sensitivities were similar in patients and control subjects (14+/-7 vs. 14+/-6 ms/mm Hg, p=NS and -3+/-2 vs. -4+/-2 ms/mm Hg, p=NS, respectively). Similarly, handgrip responses and the dose/response ratio to phenylephrine were not significantly different.

CONCLUSIONS

This study suggests that patients with HCM have a defect in the afferent limb of the cardiopulmonary reflex arc.

[Appraisal of the state of the autonomic nervous system in hypertrophic cardiomyopathy by the analysis of heart rate variability]

INTRODUCTION

The analysis of heart rate variability has been accepted as a non-invasive method to evaluate the influence of the autonomic nervous system over the heart. Although heart rate variability has been used during the last decade in several illnesses the studies in hypertrophic cardiomyopathy are scarce.

OBJECTIVES

We report the activity of the autonomic nervous system in patients with hypertrophic cardiomyopathy using the analysis of heart rate variability.

PATIENTS AND METHODS

Heart rate variability was evaluate by the analyzing 24-h ambulatory electrocardiograms (Holter) in 20 patients with hypertrophic cardiomyopathy and in 15 controls. This method has been used to measure heart rate variability. Spectral analysis of the frequencies were calculated using fast Fourier transformation. Spectral heart rate variability was computed as high (0.15 to 0.40 Hz) low (0.04 to 0.15 Hz) and total (0.01 to 1.0 Hz). We compared the relation between low/high frequency as an index of the sympathetic/parasympathetic balance. All data are expressed as mean value +/- SD. The unpaired Student t-test was used. A two tailed p valued < 0.05 was considered statistically significant.

RESULTS

There were no differences in the mean heart rates among the patients with hypertrophic cardiomyopathy and normal subjects (mean +/- SD: 71 +/- 9 versus 74 +/- 11 beats/minute; p = NS) while there was a significant decline in total spectral (mean +/- SD: 7.14 +/- 1.1 versus 7.57 +/- 0.6 ln [ms2]; p = 0.02) and high (mean +/- SD: 5.22 +/- 0.8 versus 5.63 +/- 1.3 ln [ms2]; p = 0.04) as well as in low spectral frequency of heart rate variability (mean +/- SD: 22 +/- 0.8 versus 5.63 +/- 1.3 ln [ms2]; p = 0.04) in patients with hypertrophic cardiomyopathy. There were no differences in the low/high frequency component ratio in these patients (mean +/- SD: 1.1 +/- 0.1 versus 1.2 +/- 0.1 ln [ms2]; p = NS).

CONCLUSIONS

These facts suggest that the patients with hypertrophic cardiomyopathy have an alteration in the autonomic nervous system: sympathetic (low spectral frequencies) and parasympathetic activity (high spectral frequencies), although this does not reflect an imbalance between sympathetic and parasympathetic activities (relation of low to high spectral frequencies).

Heart rate variability and ventricular arrhythmia in clinically stable patients with hypertrophic cardiomyopathy

To investigate whether autonomic nervous dysfunction exists and to determine the relationship between autonomic nervous activity and ventricular arrhythmias in clinically stable patients with hypertrophic cardiomyopathy (HCM), we studied heart rate variability (HRV) in 21 patients with HCM and 10 age-matched healthy control subjects. Patients were divided into 2 groups: HCM I (14 patients without nonsustained ventricular tachycardia, defined as 3 or more consecutive ventricular premature beats) and HCM II (7 patients with nonsustained ventricular tachycardia). HRV was measured on 24-h ECG monitorings using both nonspectral and spectral methods (fast Fourier transform, FFT). We assessed autonomic nervous activity based on high-frequency (HF; 0.15-0.40 Hz, an index of parasympathetic nervous activity) and the low- to high-frequency power ratio (L/H ratio; an index of sympathetic nervous activity) during daytime and night-time separately. There were no significant differences in any index of HRV between the HCM I and control groups. HF in the HCM II group was significantly lower than that of both the HCM I and control groups during the day and at night, whereas the L/H ratio at night-time was significantly higher in the HCM II group than in the HCM I and control groups. These data demonstrate that, in clinically stable HCM patients without nonsustained ventricular tachycardia, autonomic nervous activity was not different to that of healthy control subjects, whereas in HCM patients with nonsustained ventricular tachycardia, parasympathetic nervous activity was reduced throughout the 24-h period, and sympathetic nervous activity at night was increased compared with healthy control subjects. Thus, HCM patients with nonsustained ventricular tachycardia have to be treated even if they do not exhibit significant clinical manifestation.

Heart rate variability in patients with hypertrophic cardiomyopathy: association with clinical and echocardiographic features

Autonomic dysfunction has been reported in patients with hypertrophic cardiomyopathy. To evaluate the influence of different clinical and echocardiographic features of the disease on sympathovagal balance, as assessed by heart rate variability, 33 patients with hypertrophic cardiomyopathy and 33 healthy volunteers underwent echocardiographic examination and 24-hour electrocardiogram Holter recording. Measures of vagal modulation of heart rate were lower in patients with hypertrophic cardiomyopathy than in controls, particularly in those exhibiting syncope, exertional chest pain, dyspnea, or moderate or severe mitral regurgitation. Furthermore, the age-corrected multiple regression analysis showed that the parasympathetic cardiac control was inversely related to left atrial dimension and directly related to left ventricular end-systolic dimension. Therefore in hypertrophic cardiomyopathy the parasympathetic withdrawal is more evident in patients with symptoms than in those without; the reduction in left ventricular end-systolic dimension and the increase in left atrial size are the echocardiographic features that most influence the sympathovagal balance.

New diagnostic options in hypertrophic cardiomyopathy

The pathophysiologic features and clinical manifestations of HCM have been elucidated by the introduction of several new diagnostic options. Knowledge of the molecular defects of HCM has advanced rapidly, and genetic screening studies have reemphasized the value of the standard electrocardiogram as an initial screening tool. Analysis of heart rate variability, late potentials, and QT dispersion were not found to be reliable prognostic markers in HCM. However, measurement of dispersion of conduction is probably a sensitive technique in identifying a high risk for sudden cardiac death. Significant developments include transthoracic and transesophageal echocardiography and their role in studying the mitral valve, early detection of left ventricular chamber dilatation, analysis of coronary flow, and intraoperative echocardiography. Finally, advances in the application of magnetic resonance imaging and positron-emission tomography are underway.