Effect of quinapril or metoprolol on heart rate variability in post-myocardial infarction patients

Comprehensive viewpoints on heart rate variability at high altitude

OBJECTIVES

Hypoxia is a physiological state characterized by reduced oxygen levels in organs and tissues. It is a common clinicopathological process and a major cause of health problems in highland areas.  Heart rate variability (HRV) is a measure of the balance in autonomic innervation to the heart. It provides valuable information on the regulation of the cardiovascular system by neurohumoral factors, and changes in HRV reflect the complex interactions between multiple systems. In this review, we provide a comprehensive overview of the relationship between high-altitude hypoxia and HRV. We summarize the different mechanisms of diseases caused by hypoxia and explore the changes in HRV across various systems. Additionally, we discuss relevant pharmaceutical interventions. Overall, this review aims to provide research ideas and assistance for in-depth studies on HRV. By understanding the intricate relationship between high-altitude hypoxia and HRV, we can gain insights into the underlying mechanisms and potential therapeutic approaches to mitigate the effects of hypoxia on cardiovascular and other systems.

METHODS

The relevant literature was collected systematically from scientific database, including PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), Baidu Scholar, as well as other literature sources, such as classic books of hypoxia.

RESULTS

There is a close relationship between heart rate variability and high-altitude hypoxia. Heart rate variability is an indicator that evaluates the impact of hypoxia on the cardiovascular system and other related systems. By improving the observation of HRV, we can estimate the progress of cardiovascular diseases and predict the impact on other systems related to cardiovascular health. At the same time, changes in heart rate variability can be used to observe the efficacy of preventive drugs for altitude related diseases.

CONCLUSIONS

HRV can be used to assess autonomic nervous function under various systemic conditions, and can be used to predict and monitor diseases caused by hypoxia at high altitude. Investigating the correlation between high altitude hypoxia and heart rate variability can help make HRV more rapid, accurate, and effective for the diagnosis of plateau-related diseases.

The Role of Heart Rate Variability (HRV) in Different Hypertensive Syndromes

Cardiac innervation by the parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS) modulates the heart rate (HR) (chronotropic activity) and the contraction of the cardiac muscle (inotropic activity). The peripheral vasculature is controlled only by the SNS, which is responsible for peripheral vascular resistance. This also mediates the baroreceptor reflex (BR), which in turn mediates blood pressure (BP). Hypertension (HTN) and the autonomic nervous system (ANS) are closely related, such that derangements can lead to vasomotor impairments and several comorbidities, including obesity, hypertension, resistant hypertension, and chronic kidney disease. Autonomic dysfunction is also associated with functional and structural changes in target organs (heart, brain, kidneys, and blood vessels), increasing cardiovascular risk. Heart rate variability (HRV) is a method of assessing cardiac autonomic modulation. This tool has been used for clinical evaluation and to address the effect of therapeutic interventions. The present review aims (a) to approach the heart rate (HR) as a CV risk factor in hypertensive patients; (b) to analyze the heart rate variability (HRV) as a "tool" to estimate the individual risk stratum for Pre-HTN (P-HTN), Controlled-HTN (C-HTN), Resistant and Refractory HTN (R-HTN and Rf-HTN, respectively), and hypertensive patients with chronic renal disease (HTN+CKD).

The VITAH Trial-Vitamin D Supplementation and Cardiac Autonomic Tone in Patients with End-Stage Kidney Disease on Hemodialysis: A Blinded, Randomized Controlled Trial

End-stage kidney disease (ESKD) patients are at increased cardiovascular risk. Vitamin D deficiency is associated with depressed heart rate variability (HRV), a risk factor depicting poor cardiac autonomic tone and risk of cardiovascular death. Vitamin D deficiency and depressed HRV are highly prevalent in the ESKD population. We aimed to determine the effects of oral vitamin D supplementation on HRV ((low frequency (LF) to high frequency (HF) spectral ratio (LF:HF)) in ESKD patients on hemodialysis. Fifty-six subjects with ESKD requiring hemodialysis were recruited from January 2013–March 2015 and randomized 1:1 to either conventional (0.25 mcg alfacalcidol plus placebo 3×/week) or intensive (0.25 mcg alfacalcidol 3×/week plus 50,000 international units (IU) ergocalciferol 1×/week) vitamin D for six weeks. The primary outcome was the change in LF:HF. There was no difference in LF:HF from baseline to six weeks for either vitamin D treatment (conventional: p = 0.9 vs. baseline; intensive: p = 0.07 vs. baseline). However, participants who remained vitamin D-deficient (25-hydroxyvitamin D < 20 ng/mL) after treatment demonstrated an increase in LF:HF (conventional: n = 13, ∆LF:HF: 0.20 ± 0.06, p < 0.001 vs. insufficient and sufficient vitamin D groups; intensive: n = 8: ∆LF:HF: 0.15 ± 0.06, p < 0.001 vs. sufficient vitamin D group). Overall, six weeks of conventional or intensive vitamin D only augmented LF:HF in ESKD subjects who remained vitamin D-deficient after treatment. Our findings potentially suggest that while activated vitamin D, with or without additional nutritional vitamin D, does not appear to improve cardiac autonomic tone in hemodialysis patients with insufficient or sufficient baseline vitamin D levels, supplementation in patients with severe vitamin D deficiency may improve cardiac autonomic tone in this higher risk sub-population of ESKD. Trial Registration: ClinicalTrials.gov, NCT01774812.

Short-term effect of percutaneous recanalization of chronic total occlusions on QT dispersion and heart rate variability parameters

Background

QT dispersion (QTd), which is a measure of inhomogeneity of myocardial repolarization, increases following impaired myocardial perfusion. Its prolongation may provide a suitable substrate for life-threatening ventricular arrhythmias. We investigated the changes in QTd and heart rate variability (HRV) parameters after successful coronary artery revascularization in a patient with chronic total occlusions (CTO).

Material/Methods

This study included 139 successfully revascularized CTO patients (118 men, 21 women, mean age 58.3±9.6 years). QTd was measured from a 12-lead electrocardiogram and was defined as the difference between maximum and minimum QT interval. HRV analyses of all subjects were obtained. Frequency domain (LF: HF) and time domain (SDNN, pNN50, and rMSSD) parameters were analyzed. QT intervals were also corrected for heart rate using Bazett’s formula, and the corrected QT interval dispersion (QTcd) was then calculated. All measurements were made before and after percutaneous coronary intervention (PCI).

Results

Both QTd and QTcd showed significant improvement following successful revascularization of CTO (55.83±14.79 to 38.87±11.69; p<0.001 and 61.02±16.28 to 42.92±13.41; p<0.001). The revascularization of LAD (n=38), Cx (n=28) and RCA (n=73) resulted in decrease in HRV indices, including SDDN, rMSSD, and pNN50, but none of the variables reached statistical significance.

Conclusions

Successful revascularization of CTO may result in improvement in regional heterogeneity of myocardial repolarization, evidenced as decreased QTcd after the PCI. The revascularization in CTO lesions does not seem to have a significant impact on HRV.

Electrocardiogram-based predictors of sudden cardiac death in patients with coronary artery disease

Current recommendations on which patients with coronary artery disease (CAD) should be offered an implantable cardioverter defibrillator for the primary prevention of sudden cardiac death (SCD) rely heavily on the presence of depressed left ventricular ejection fraction. Because the majority of SCD victims with CAD have preserved left ventricular function, additional cardiac investigations are likely to play an increasing role in the risk stratification of CAD patients. A number of studies have demonstrated that certain parameters on the traditional 12-lead electrocardiogram (ECG) and other ECG-based investigations (such as signal-averaged ECG, heart rate turbulence, T-wave alternans) can provide important information on the underlying cardiac substrate abnormality that may predispose to ventricular arrhythmias and SCD. This article reviews some of the evidence for these ECG-based tests as predictors of SCD in patients with CAD and addresses their advantages and limitations.

Risk Stratification for Sudden Cardiac Death after Acute Myocardial Infarction

Many patients who survive an acute myocardial infarction (AMI) remain at risk of recurrent cardiac events and sudden cardiac death after discharge, despite optimal medical treatment. Assessment of the degree of left ventricular dysfunction and residual myocardial ischaemia is useful to identify the patients at greatest risk. In addition, there is increasing evidence that a number of other cardiovascular tests can be used to detect autonomic dysfunction and myocardial substrate abnormalities postAMI that increase the risk of life-threatening ventricular arrhythmias. These investigations include ECG-based tests (signal averaged ECG and T-wave alternans), Holter-based recordings (heart rate variability and heart rate turbulence) and imaging techniques echocardiography and cardiac magnetic resonance), as well as invasive electrophysiological testing. This article reviews the current evidence for the use of these additional cardiac investigations among survivors of AMI to aid in their risk stratification for malignant ventricular arrhythmias and sudden cardiac death. Key words: Electrophysiological study, Holter recording, Non-invasive tests, Ventricular tachycardia

Quinaprilat: a review of its pharmacokinetics, pharmacodynamics, toxicological data and clinical application

BACKGROUND

Quinaprilat is an ACE inhibitor for intravenous use especially in patients with arterial hypertension or chronic heart failure. In contrast to the oral prodrug quinapril, it has not been approved for clinical application.

OBJECTIVE

In this review, the pharmacokinetic and pharmacodynamic profile of quinaprilat as well as toxicological data and results of preclinical and clinical studies are summarized.

METHODS

In a PubMed search for the terms "quinaprilat" and "quinapril", literature relevant for this review was selected.

RESULTS

Quinaprilat is a potent nonsulfhydryl selective ACE inhibitor with a short elimination half-life of 2 - 3 h, but due to slow dissociation from tissue ACE, once daily dosing is sufficient for effective ACE inhibition. Quinaprilat is excreted mainly in urine. In long-term animal studies, quinaprilat was not teratogenic, mutagenic or carcinogenic. However, due to the risk of fetal and neonatal morbidity and death, it should not be administrated in pregnancy. Quinaprilat is characterized by an excellent safety profile; adverse events occur infrequently and are rarely serious.

CONCLUSION

Quinaprilat is an attractive ACE inhibitor, which potently inhibits tissue ACE.

The electrocardiogram as a prognostic tool for predicting major cardiac events

Among patients with cardiac disease, the identification of those who are at low risk and those who are at high risk for major cardiac events is crucial for a rational clinical management of individual patients. A correct noninvasive risk stratification of cardiac patients, in particular, has relevant clinical implications because it would avoid unnecessary exposure to potentially risky invasive diagnostic or interventional procedures in low-risk patients, whereas it would allow an appropriate aggressive diagnostic and therapeutic approach in high-risk patients. Furthermore, the appropriate identification of low- and high-risk patients would also have social and economic implications by favoring optimization of resource distribution and costs. A large number of studies in previous decades provided evidence that several methods and variables derived from the analysis of the electrocardiogram (ECG) are powerful predictors of major cardiac events in several clinical conditions. Despite that, there has been limited attention about how several of these findings can be used in clinical practice. Furthermore, in recent years, most studies about risk stratification of cardiac patients have mainly been focused on the use of a number of serum/plasma biomarkers with reduced attention to ECG variables. Surprisingly, however, there have been few attempts to establish whether the various proposed risk markers add any significant information to that obtainable from ECG methods. In this article, the evidence for the prognostic value of variables derived from the assessment of the ECG signal by several methods and techniques will be briefly reviewed. Because of the largeness of the topic, this review will be necessarily incomplete. Because most of the clinical research in this field concerned risk stratification of patients with coronary artery disease, the article will be largely focused on this population of patients. The role of ECG methods in specific cardiac diseases and, in particular, in the general population of asymptomatic subjects will be briefly discussed when believed appropriate and helpful. Furthermore, only major clinical events (ie, cardiac death, arrhythmic events, acute myocardial infarction) will be taken into account as end points in this article. Minor clinical events (eg, coronary revascularization procedures, coronary artery restenosis, recurrences of symptoms) are indeed less robust as end points because they are widely biased by subjective judgments.

Autonomic modulation of the sinus node following electrical cardioversion of persistent atrial fibrillation: relation with early recurrence

BACKGROUND

The aim of this study was to correlate early atrial fibrillation (AF) relapses with heart rate variability (HRV) parameters immediately recorded after electrical cardioversion (EC) of persistent AF.

METHODS AND RESULTS

We performed the spectral analysis of short-term HRV 30 min after EC in 25 patients with persistent AF. The numbers of patients who maintained sinus rhythm at 48 h, 7, and 30 days were 22, 16, and 14, respectively. A very low low frequency/high frequency ratio (0.93+/-0.08 vs. 1.89+/-1.30; p<0.003) significantly identified patients with AF recurrence at 48 h in comparison to patients without AF recurrence. On the contrary, HRV parameters did not identify patients with AF recurrence at 7 or 30 days.

CONCLUSIONS

AF relapsed within the first 48 h more frequently in patients who presented a predominant vagal tone immediately after the restoration of sinus rhythm.

Effect of quinapril on the attenuated heart rate recovery of type 2 diabetic subjects without known coronary artery disease

BACKGROUND

Heart rate (HR) recovery at 1 min is a measure of the vagal reactivation that occurs after cessation of exercise. Despite ample evidence about the association of attenuated HR recovery with increased mortality, pharmacologic modification of this predictor has not been shown. On the other hand, angiotensin-converting enzyme (ACE) inhibitors are known to have vagomimetic activity.

HYPOTHESIS

We hypothesized that ACE inhibition would increase HR recovery in a group of subjects known to have reduced HR recovery, namely diabetics.

METHODS

Maximal treadmill exercise stress test was performed in 31 type 2 diabetic and 31 nondiabetic male subjects with similar age, body mass index, and hypertensive status. None of the subjects had known heart disease or evidence of myocardial ischemia during the test. The diabetic subjects, after 2 weeks of treatment with quinapril, underwent a second exercise test. A third test was performed 2 to 3 weeks after cessation of quinapril treatment.

RESULTS

At baseline, despite similar exercise capacity, the diabetics had a lower HR recovery at 1 min than nondiabetics (25 +/- 8 vs. 31 +/- 8 beats/min, p < 0.01). Quinapril significantly increased HR recovery at 1 min in diabetics (25 +/- 8 beats/min at baseline vs. 28 +/- 8 beats/min with quinapril vs. 25 +/- 7 beats/min off-therapy, p < 0.01 by analysis of variance).

CONCLUSIONS

The attenuated HR recovery of type 2 diabetics can be improved by quinapril. Whether the improvement in HR recovery with ACE inhibition can lead to decreased mortality is currently unknown.

Relationship between heart rate variability and left ventricular remodeling after reperfused first anterior wall acute myocardial infarction

The aim of the present study was to test the hypothesis that inadequate improvement in heart rate variability (HRV) in the healing stage of acute myocardial infarction (AMI) is associated with left ventricular (LV) remodeling. The study group comprised 20 patients (14 men, 6 women; mean age, 61+/-12 years) with a reperfused first anterior AMI (</=24 h). The standard deviation of normal RR intervals (SDNN) was calculated from the 24-h ambulatory electrocardiogram recorded on day 3 of admission and at predischarge from the hospital. Left ventriculography was performed immediately after primary angioplasty and at predischarge. The change in SDNN (deltaSDNN) was compared with the change in the LV end-systolic volume index (deltaLVESVI), a parameter of LV remodeling. SDNN increased from 73+/-19 ms on day 3 to 109+/-35 ms at predischarge (p=0.0003). SDNN at predicharge and deltaSDNN correlated negatively with deltaLVESVI (r=-0.52, p=0.02, and r=-0.61, p=0.004, respectively), whereas SDNN on day 3 did not correlate with deltaLVESVI. Multiple regression analysis selected deltaLVESVI (p=0.02) as an independent factor of deltaSDNN. This study indicates that deltaSDNN and SDNN at predicharge are associated with deltaLVESVI in patients with a reperfused first anterior wall AMI, indicating that persistently reduced HRV is associated with postinfarction LV remodeling.

Effects of propranolol on recovery of heart rate variability following acute myocardial infarction and relation to outcome in the Beta-Blocker Heart Attack Trial

This study evaluated the effects of propranolol on recovery of heart rate variability (HRV) after acute myocardial infarction and its relation to outcome in the Beta-blocker Heart Attack Trial (BHAT). Beta blockers improve mortality after acute myocardial infarction, but through an unknown mechanism. Depressed HRV, a measure of autonomic tone, predicts mortality after acute myocardial infarction. Whether beta blockers influence recovery of HRV after acute myocardial infarction, and thereby improve outcome, is unknown. We compared 24-hour HRV parameters at 1 week after acute myocardial infarction and after 6 weeks of treatment with propanolol (n = 88) or placebo (n = 96). The relation between 25-month outcome (death/acute myocardial infarction/congestive heart failure), propranolol treatment, and HRV was further analyzed. After 6 weeks, high-frequency (HF) power (log-normalized), an index of vagal tone, increased more in propranolol-treated patients (4.28 +/- 0.1 to 5.17 +/- 0.09 ms(2)) than in placebo-treated patients (4.26 +/- 0.09 to 4.77 +/- 0.1 ms(2), p <0.05). Sympathovagal balance measured by the low-frequency (LF) to HF ratio increased in placebo-treated patients (3.55 +/- 0.24 to 3.86 +/- 0.24) but decreased in those treated with propranolol (3.76 +/- 0.29 to 3.17 +/- 0.23, p <0.01). Other frequency-domain parameters increased over time but were not affected by propranolol. Propranolol blunted the morning increase in the LF/HF ratio. Recovery of HF, the strongest HRV predictor of outcome, and propranolol therapy independently predicted outcome. In summary, after acute myocardial infarction, propranolol therapy improves recovery of parasympathetic tone, which correlates with improved outcome, and decreases morning sympathetic predominance. These findings may elucidate the mechanisms by which beta blockers decrease mortality and reduce the early morning risk of sudden death after acute myocardial infarction.

Effect of preinfarction angina on heart rate variability in the early phase of the first anterior wall acute myocardial infarction

The aim of this study was to clarify the effect of preinfarction angina on heart rate variability (HRV) in anterior wall acute myocardial infarction (AMI). A total of 36 patients experiencing their first anterior wall AMI were prospectively examined. The patients were divided into 2 groups according to the presence (group A, n=24) or absence (group B, n = 12) of preinfarction angina. HRV was assessed on 24-h Holter electrocardiograms recorded on day 3. Peak creatine kinase activity was significantly lower in group A than in group B (2,747+/-1,939 vs 4,891+/-2,639 IU/L, p<0.05). The SD of all RR intervals and ultra-low frequency, very low frequency, and low frequency powers was significantly less reduced in group A than in group B (86+/-24 vs 64+/-22 ms, p<0.05; 2,098+/-1,462 vs 867+/-502 ms2, p<0.01; 1,430+/-1,042 vs 546+/-344ms2, p<0.01; and 354+/-272 vs 186+/-136ms2, p<0.05; respectively). High frequency power, low frequency/high frequency, and pNN50 did not differ significantly between the 2 groups. In conclusion, preinfarction angina has a favorable influence on HRV in the early phase of anterior wall AMI.

Recovery of cardiac autonomic responsiveness with low-intensity physical training in patients with chronic heart failure

BACKGROUND

A gradual worsening of autonomic control of cardiovascular function accompanies the progression of heart failure. Exercise training modulates autonomic balance, and may affect the prognosis of the disease.

AIMS

The sympathovagal balance was studied after 3 months of low-intensity rehabilitation compared with conventional therapy in 45 patients with heart failure (52% ischemic, 48% idiopathic), of whom 30 underwent rehabilitation and 15 did not. In 11 rehabilitated patients we also studied the effects on autonomic profile of 6 additional months of home-based training. Rehabilitated and non-rehabilitated patients had similar NYHA class, ejection fraction, exercise pVO2; 50% assumed carvedilol (39+/-5 mg/day).

METHODS AND RESULTS

Autoregressive power spectral density of RR intervals variability were assessed during 10 min of: (1) supine rest and free breathing; (2) supine rest and breathing at 20 acts/min (=vagal stimulus); (3) standing (=sympathetic stimulus). During each period, the ratio LF/HF of the individual autospectrum indicated the sympathovagal balance. After 3 months of rehabilitation, pVO2 increased (20%); LF/HF at rest was unchanged (8.7+/-1.2 vs. 9.2+/-1.2); it decreased with controlled breathing (-18%) and increased during standing (+79%) (P<0.05). These changes were more evident after 6 months of home-based training, when pVO2 was still high: LF/HF at rest was reduced (5.4+/-0.9 vs. 8.5+/-2.1), decreased during controlled breathing (-17%) and increased during standing (87%) (P<0.05). No changes in any variable were seen in non-rehabilitated patients.

CONCLUSIONS

A low intensity rehabilitation program restores autonomic tone and reactivity to vagal and sympathetic stimuli. Some of these effects are already evident after the initial hospital-based phase.

Different baseline sympathovagal balance and cardiac autonomic responsiveness in ischemic and non-ischemic congestive heart failure

BACKGROUND

A profound autonomic unbalance is present in heart failure: its correlation with the etiology of the disease has never been investigated.

AIMS

We characterized the sympatho-vagal balance and autonomic responsiveness of 42 patients (21 with ischemic heart failure, 21 with idiopathic dilated cardiomyopathy). Patients had comparable NYHA class, ejection fraction, exercise pVO(2), exercise ventilatory response, incidence of beta-blocking treatment. None showed periodic breathing or nocturnal arterial desaturation.

METHODS

Heart rate variability was assessed in the time and frequency domain during: (1) 10 min of quiet supine resting and free breathing; (2) 10 min of regular breathing at a frequency of 20 acts/min (=parasympathetic stimulus); and (3) 10 min of active standing (=sympathetic stimulus). The ratio of the low- to high-frequency components of each autospectrum obtained in the frequency domain (LF/HF) was used as an index of sympathovagal balance.

RESULTS

Patients with ischemic heart failure had a greater baseline sympathetic activation (higher LF/HF) than those with idiopathic dilated cardiomyopathy, maintaining some parasympathetic responsiveness as well (reduced LF/HF with regular breathing).

CONCLUSIONS

There is a distinct autonomic control according to the etiology of heart failure, a finding that may help understanding its pathophysiology, and could be useful in the clinical management of patients.

Cardiovascular responses to anesthetic induction in patients chronically treated with angiotensin-converting enzyme inhibitors

PURPOSE

To investigate the effects of chronic ACE inhibition on cardiac neural function following induction of general anesthesia in patients with underlying coronary artery disease.

METHOD

In a prospective case-control study, heart rate variability (HRV) and baroreflex control were compared preoperatively and 30 min after anesthesia induction in patients receiving, or not, ACEI (n=16, control group and n=16, ACEI group). All patients had normal cardiac function and anesthesia consisted of a fixed dose regimen of fentanyl and midazolam. Anesthesia-related hypotension was defined by systolic blood pressure < 90 mmHg. Spectral density of HRV was calculated for low frequency and high frequency bands (LF, from 0.05 to 0.15 Hz and HF, from > 0.15 to 0.6 Hz). Baroreflex sensitivity was estimated after blood pressure changes induced by injections of phenylephrine (PHE) and nitroglycerin (NTG).

RESULTS

The HRV parameters and baroreflex sensitivity were not different between groups, during the awake and anesthesia periods. Anesthesia produced similar reduction in total HRV in the Control and ACEI groups (-93 +/- 28% vs -89 +/- 32%), and in baroreflex sensitivity during NTG (-64 +/- 21% vs -54 +/- 17%) or PHE tests (-74 +/- 25% vs -72 +/- 22%). Anesthesia-related hypotension occurred in nine patients in the ACEI group (vs two controls). Although the hypertensive response to phenylephrine was greater after anesthesia in both groups, the sensitivity to phenylephrine was attenuated in those patients experiencing hypotension in the ACEI group.

CONCLUSIONS

Chronic preoperative treatment with ACEIs does not influence cardiac autonomic regulation and anesthetic-induced hypotensive episodes are mainly attributed to decreased alpha-adrenergic vasoconstrictive response.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

Effect of quinapril or metoprolol on circadian sympathetic and parasympathetic modulation after acute myocardial infarction

Abnormal autonomic nervous system impairment in patients with acute myocardial infarction (AMI) has a circadian pattern with the greatest manifestation in the morning hours; it probably plays an important role in the pathogenesis of cardiac arrhythmias and acute ischemic syndromes. Angiotensin-converting enzyme inhibitors improve autonomic function in patients with AMI, but the circadian pattern of this effect has not been studied. Heart rate variability-normalized frequency domain indexes were assessed 5 days (baseline) after the onset of uncomplicated AMI and 30 days after therapy with quinapril (n = 30), metoprolol (n = 30), or placebo (n = 30) with a solid-state digital Holter monitor. Normal subjects (n = 30) were used as controls. Quinapril increased parasympathetic and decreased sympathetic modulation, and improved sympathovagal interactions manifested by an increase in normalized high-frequency power (HFP), and a decrease in normalized low-frequency power (LFP), and their ratio (LFP/HFP) during the entire 24-hour period (p<0.001), with maximal effect on the ratio (p<0.0001) between 02.00 to 04.00 A.M., 08.00 to 11.00 A.M., and 19.00 to 22.00 P.M. (delta% ratio -30%, -32%, and -26%, respectively). Metoprolol increased HFP and decreased LFP and the LFP/HFP ratio mainly between 08.00 A.M. to 12.00 noon, and 19.00 to 22.00 P.M. (delta% ratio -21%, and -12% respectively, p<0.001). Heart rate variability indexes in the placebo group and controls remained unchanged 30 days after the baseline study. In conclusion, quinapril increased parasympathetic, and decreased sympathetic and partially restored sympathovagal interaction in patients with uncomplicated AMI during the entire 24-hour period, with peak effect in the early and late morning and evening hours. Metoprolol had a similar effect during the late morning and evening hours, but at a lower level. These effects may prove beneficial in reducing cardiac arrhythmias and acute ischemic syndromes in past-AMI patients.

Predicting the effect of D,L-sotalol on ventricular tachycardia inducibility from the RR variability response

AIM

To find a rapid way of identifying non-responders to D, L-sotalol in patients with ventricular tachycardia.

METHODS

Programmed ventricular stimulation and RR variability were studied in the control state and 10 days after treatment with 160 to 320 mg of D,L-sotalol in 36 consecutive patients with ventricular tachycardia.

RESULTS

In 14 patients (group I) D,L-sotalol suppressed ventricular tachycardia inducibility. In 22 patients (group II) sustained ventricular tachycardia remained inducible during D,L-sotalol treatment. The ventricular tachycardia rate was slowed in eight patients and unchanged or accelerated in 14. At baseline, heart rate variability was similar in both groups. During treatment with D,L-sotalol, variables reflecting parasympathetic activity (pNN50, rMSSD, and high frequency amplitude (HF)) increased in both groups: HF increased from (mean (SD)) 75 (68) to 146 (134) in group I (p < 0.05) and from 60 (49) to 125 (79) in group II (p < 0.05). Other variables were unchanged in group I. In group II, the variables associated with sympathetic activity (coefficient of variance (CV), ratio of low frequency amplitude (LF) to HF) decreased significantly: CV decreased from 13 (4) to 9 (2) (p < 0. 001) and LF/HF from 4.74 (3.02) to 3.00 (2.02) (p < 0.05).

CONCLUSIONS

The beta blocking effect of D,L-sotalol produced a significant improvement over control values in indices of parasympathetic tone in all treated patients. However, the heart rate variability indices related to sympathetic activity were decreased only in non-responders. This effect of D,L-sotalol on heart rate variability could help detect non-responders to the drug and avoid an electrophysiological study.

Cardiovascular autonomic dysfunction and hemodynamic response to anesthetic induction in patients with coronary artery disease and diabetes mellitus

Autonomic neuropathy is a major complication of diabetes mellitus and is reported to be associated with increased perioperative hemodynamic instability. We investigated the relationship between autonomic dysfunction and hemodynamic response to anesthetic induction in diabetic and nondiabetic patients with coronary artery disease. We studied 60 patients scheduled for coronary artery surgery, 30 suffering from diabetes mellitus. Preoperative evaluation included traditional cardiovascular autonomic function tests (coefficient of variation of 150 beat-to-beat intervals in heart rate at rest, heart rate response to deep breathing, and heart rate and arterial blood pressure response to standing), spectral analysis of blood pressure and heart rate variability (HRV), and the computation of spontaneous baroreflex sensitivity. After premedication with clorazepate, anesthesia was induced with sufentanil (0.5 microg/kg), etomidate (0.1-0.2 mg/kg), and vecuronium (0.1 mg/kg). Heart rate and blood pressure before anesthetic induction and before and after tracheal intubation were compared between groups. Autonomic function tests, spectral analysis of HRV, and spontaneous baroreflex sensitivity revealed significant differences between patient groups. Most diabetic patients (n = 23) had one or more abnormal test results, in contrast to most nondiabetic patients, who did not show signs of autonomic neuropathy (n = 23). There was no relationship between cardiovascular autonomic function and hemodynamic behavior during anesthetic induction. The blood pressure response to anesthetic induction was not different between patient groups, even when comparing the subgroups with and without abnormal autonomic function tests. These findings indicate that increased hemodynamic instability during anesthetic induction is not obligatory in patients with diabetes mellitus and autonomic dysfunction.

IMPLICATIONS

This study indicates that increased hemodynamic instability during anesthetic induction is not obligatory in patients with coronary artery disease and autonomic dysfunction.

Effect of angiotensin converting enzyme inhibition on sudden cardiac death in patients following acute myocardial infarction. A meta-analysis of randomized clinical trials

Estimate the effect of angiotensin converting enzyme (ACE) inhibitors on the risk of sudden cardiac death (SCD) following myocardial infarction (MI).

BACKGROUND

Trials in post-MI patients have shown that ACE inhibitor therapy reduces mortality. However, the effect on SCD as a mechanism has not been clarified.

METHODS

Trials of ACE inhibitor therapy following MI reported between January, 1978 and August, 1997 were identified. Studies were included if they met the following criteria: 1) randomized comparison of ACE inhibitor to placebo within 14 days of MI; 2) study duration/blinded follow-up of > or =6 weeks; 3) the number of deaths and modes of death were reported or could be obtained from the investigators.

RESULTS

We identified 374 candidate articles, of which 15 met the inclusion criteria. The 15 trials included 15,104 patients, 2,356 of whom died. Most (87%) fatalities were cardiovascular and 900 were SCDs. A significant reduction in SCD risk or a trend towards this was observed in all of the larger (N > 500) trials. Overall, ACE inhibitor therapy resulted in significant reductions in risk of death (random effects odds ratio [OR] = 0.83; 95% confidence interval [CI] 0.71-0.97), cardiovascular death (OR = 0.82; 95% CI 0.69-0.97) and SCD (OR = 0.80; 95% CI 0.70-0.92).

CONCLUSIONS

This analysis is consistent with prior reports showing that ACE inhibitors decrease the risk of death following a recent MI by reducing cardiovascular mortality. Moreover, this analysis suggests that a reduction in SCD risk with ACE inhibitors is an important component of this survival benefit.

The natural history of recently diagnosed autonomic neuropathy over a period of 2 years

BACKGROUND

Patients with diabetic autonomic neuropathy (DAN) have an increased cardiovascular mortality rate compared with normals or diabetic patients without DAN. Indices of standard cardiovascular autonomic function tests and heart rate variability (HRV) are reliable markers of the presence and severity of DAN.

OBJECTIVE

The present prospective study investigated the natural history of values of HRV indices and cardiovascular reflex tests in patients with recently diagnosed asymptomatic DAN, over a period of 2 years, at 3 month intervals.

PATIENTS AND METHODS

A total of 30 consecutive patients (nine men and 21 women), of median age 51 (range 25-65) years, eight with type 1 and 22 with Type 2 diabetes mellitus, were included in the study, at the time that the presence of DAN was confirmed, as this was established if at least two of cardiovascular autonomic function tests became abnormal. The expiration/inspiration (E/I) ratio. S.D. and mean circular resultant of R-R intervals, the Valsalva index, the 30:15 ratio, and the blood pressure response to standing as well as normalised spectral power indices of HRV were used.

RESULTS

All measured indices, except the Valsalva index, deteriorated in all 30 patients during the 2 year follow-up. Most of HRV indices values deteriorated significantly in comparison to baseline at month 12, while the values of cardiovascular reflex tests displayed significant deterioration, in comparison to baseline, between months 15 and 21. Fourteen patients developed symptoms of DAN during the 2 year period. Patients with better glycemic control exhibited deterioration of DAN markers at the same time period with those with poor glycemic control.

CONCLUSIONS

Our data suggest that the progression of DAN is significant during the 2 years subsequent to its discovery. This was defined by the deterioration of the mean values of HRV indices and standard cardiovascular autonomic function tests, and by the development of autonomic symptoms in some patients. HRV indices are the earlier markers of DAN deterioration.

Mechanisms underlying very-low-frequency RR-interval oscillations in humans

BACKGROUND

Survival of post-myocardial infarction patients is related inversely to their levels of very-low-frequency (0.003 to 0.03 Hz) RR-interval variability. The physiological basis for such oscillations is unclear. In our study, we used blocking drugs to evaluate potential contributions of sympathetic and vagal mechanisms and the renin-angiotensin-aldosterone system to very-low-frequency RR-interval variability in 10 young healthy subjects.

METHODS AND RESULTS

We recorded RR intervals and arterial pressures during three separate sessions, with the patient in supine and 40 degree upright tilt positions, during 20-minute frequency (0.25 Hz) and tidal volume-controlled breathing after intravenous injections: saline (control), atenolol (0.2 mg/kg, beta-adrenergic blockade), atropine sulfate (0.04 mg/kg, parasympathetic blockade), atenolol and atropine (complete autonomic blockade), and enalaprilat (0.02 mg/kg, ACE blockade). We integrated fast Fourier transform RR-interval spectral power at very low (0.003 to 0.03 Hz), low (0.05 to 0. 15 Hz), and respiratory (0.2 to 0.3 Hz) frequencies. Beta-adrenergic blockade had no significant effect on very-low- or low-frequency RR-interval power but increased respiratory frequency power 2-fold. ACE blockade had no significant effect on low or respiratory frequency RR-interval power but modestly (approximately 21%) increased very-low-frequency power in the supine (but not upright tilt) position (P<0.05). The most profound effects were exerted by parasympathetic blockade: Atropine, given alone or with atenolol, abolished nearly all RR-interval variability and decreased very-low-frequency variability by 92%.

CONCLUSIONS

Although very-low-frequency heart period rhythms are influenced by the renin-angiotensin-aldosterone system, as low and respiratory frequency RR-interval rhythms, they depend primarily on the presence of parasympathetic outflow. Therefore the prognostic value of very-low-frequency heart period oscillations may derive from the fundamental importance of parasympathetic mechanisms in cardiovascular health.

Effects of cardiac rehabilitation and beta-blocker therapy on heart rate variability after first acute myocardial infarction

After acute myocardial infarction (AMI), rehabilitation with physical training increases parasympathetic tone. It is unknown whether such a favorable effect of exercise on the sympathovagal balance interacts with effects of other widespread therapies, such as beta blockers. In 53 patients after a first, uncomplicated AMI, we studied the combined short- and long-term influence on heart rate variability (HRV) of rehabilitation and beta blockade. Patients were divided into 3 groups: group 1 (n = 19) underwent rehabilitation with physical training; group 2 (n = 20) was taking beta blockers and underwent rehabilitation; group 3 (n = 14) was taking beta blockers and did not enter the rehabilitation program for logistic reasons. Patients were similar as to age, site of infarction, ejection fraction, left ventricular diameter, and baseline stress test duration. Measures of HRV (obtained from a 15-minute resting electrocardiogram) were the standard deviation of the mean RR interval (RRSD), the mean squared successive differences (MSSD), the percent of RR intervals differing >50 ms from the preceding one (pNN50), the low-(LF) and high-(HF) frequency components of the autoregressive power spectrum of the RR intervals and their ratio (LF/HF). Four weeks after AMI, there was less sympathetic predominance in groups 2 and 3 (i.e., patients taking beta blockers [p <0.05]). Rehabilitation modified HRV in groups 1 and 2 (p <0.05), with signs of increased parasympathetic tone (group 1: MSSD +25%, pNN50 +69%, LF/HF -40%; group 2: MSSD +41%, pNN50 +48%, LF/HF -39%). These changes persisted in the long term. In group 3, HRV was unchanged over time. Hence, after AMI, the effects of rehabilitation and beta blockers on HRV are not redundant: their association induces a more favorable sympathovagal balance, accelerating the recovery of a normal autonomic profile.

Heart rate variability after acute myocardial infarction in patients treated with atenolol and metoprolol

Heart rate variability (HRV) reflects autonomous activity that influences the heart. It has been shown that HRV is depressed during acute myocardial infarction (AMI) and that it recovers with time. Beta-blockers reduce mortality after AMI and changes in sympathico-vagal activity have been suggested to be of importance. Under certain animal experimental conditions, metoprolol has been reported to increase vagal tone more than atenolol, which could have clinical implications. The purpose of the present study was to compare the effects of atenolol and metoprolol treatments on HRV during 6 weeks after AMI and to follow the post MI changes in HRV in patients on betablockers.

METHODS

In an open, randomised cross-over study, 28 patients were randomised to 3+3 weeks' treatment with atenolol or metoprolol starting 2-5 days after AMI. Twenty-four hour Holter recordings were made before randomisation and after 3 and 6 weeks. HRV was analysed as HR, SDRR, SDANN, SD, rMSSD and pNN50 in the time domain and as coefficient of component variance (CCV) of HF and LF, and as LF/HF ratio in the frequency domain.

RESULTS

The average daily dose in our study population was 106 mg of metoprolol and 54 mg of atenolol. There were trends toward lower heart rates daytime, lower LF/HF ratio daytime and higher rMSSD on atenolol compared to metoprolol. In the total group of 28 patients we found during the first 3 weeks, a significant increase of SDNN, SDANN (p<0.0001) and LF/HF ratio daytime and CCV-HF night-time (p<0.01). All differences and trends were unchanged between 3 and 6 weeks.

CONCLUSIONS

There was no evidence of more increased vagal tone with metoprolol compared to atenolol as has been suggested from animal models. In patients also on chronic treatment with beta blockers, an increase of HRV was seen during the first weeks post MI.

Lisinopril. A review of its pharmacology and clinical efficacy in the early management of acute myocardial infarction

Following establishment of its efficacy in hypertension and congestive heart failure, the ACE inhibitor lisinopril has now been shown to reduce mortality and cardiovascular morbidity in patients with myocardial infarction when administered as early treatment. The ability of lisinopril to attenuate the detrimental effects of left ventricular remodelling is a key mechanism; however, additional cardioprotective and vasculoprotective actions are postulated to play a role in mediating the early benefit. The GISSI-3 trial in > 19 000 patients has demonstrated that, when given orally within 24 hours of symptom onset and continued for 6 weeks, lisinopril (with or without nitrates) produces measurable survival benefits within 1 to 2 days of starting treatment. Compared with no lisinopril treatment, reductions of 11% in risk of mortality and 7.7% in a combined end-point (death plus severe left ventricular dysfunction) were evident at 6 weeks. Advantages were apparent in all types of patients. Thus, those at high risk-women, the elderly, patients with diabetes mellitus and those with anterior infarct and/or Killip class > 1 -also benefited. These gains in combined end-point events persisted in the longer term, despite treatment withdrawal after 6 weeks in most patients. At 6 months, the incidence rate for the combined end-point remained lower than with control (a 6.2% reduction). The GISSI-3 results concur with those from recent large investigations (ISIS-4, CCS-1, SMILE) of other ACE inhibitors as early management in myocardial infarction. However, the results of the CONSENSUS II trial (using intravenous enalaprilat then oral enalapril) were unfavourable in some patients. These findings, together with the development of persistent hypotension and, to a lesser extent, renal dysfunction among patients in the GISSI-3 trial, have prompted considerable debate over optimum treatment strategies. Present opinion generally holds that therapy with lisinopril or other ACE inhibitors shown to be beneficial may be started within 24 hours in haemodynamically stable patients with no other contraindications; current labelling in the US and other countries reflects this position. There is virtually unanimous agreement that such therapy is indicated in high-risk patients, particularly those with left ventricular dysfunction. The choice of ACE inhibitor appears less important than the decision to treat; it seems likely that these benefits are a class effect. Lisinopril has a tolerability profile resembling that of other ACE inhibitors, can be given once daily and may be less costly than other members of its class. However, present cost analyses are flawed and this latter points remains to be proven in formal cost-effectiveness analyses. In conclusion, early treatment with lisinopril (within 24 hours of symptom onset) for 6 weeks improves survival and reduces cardiovascular morbidity in patients with myocardial infarction, and confers ongoing benefit after drug withdrawal. While patients with symptoms of left ventricular dysfunction are prime candidates for treatment, all those who are haemodynamically stable with no other contraindications are also eligible to receive therapy. Lisinopril and other ACE inhibitors shown to be beneficial should therefore be considered an integral part of the early management of myocardial infarction in suitable patients.