Influence of age on ambulatory electrocardiogram-derived heart rate variability

OBJECTIVE

To evaluate the quantitative change in heart rate variability with age by using 24 h Holter ambulatory monitoring of electrocardiogram and to set the lower limit of heart rate variability depending on age.

PARTICIPANTS

Eighty healthy subjects without any medication (male to female ratio 40:40, 45.6 +/- 14.1 years of age, range 16 to 68 years).

METHODS

Holter monitoring was performed, and frequency and time domain heart rate variability was obtained.

RESULTS

A significant inverse relationship was found between age and heart rate variability, especially in the frequency domain, and, in the time domain analysis, in the root mean square of the difference in the RR intervals of sinus rhythm (NN) between successive beats and in the portion of NN cycles greater than 50 ms apart. Except for the standard deviation of the mean of RR intervals taken every 5 mins and averaged over 24 h and the ratio of low frequency high frequency power spectra, all parameters decreased to a certain age and did not change thereafter, and the rate of decrease differed among the parameters of heart rate variability. Because age had a strong influence on heart rate variability, the lower limit of heart rate variability for a certain age was determined by using the polynomial curve fitting of the moving average minus 2 SD of 10 consecutive subjects. By using these equations, it could be determined whether heart rate variability was normal or abnormal depending on age.

Application of mechanical restitution: variation of inotropic effects of vagal stimulation or verapamil administration during irregular cardiac rhythm

The effects of verapamil administration or vagal stimulation on the mechanical restitution curve (MRC) were studied in order to better understand the modulation of left ventricular (LV) function by interventions that lower the ventricular rate of atrial fibrillation. The MRC and the postextrasystolic MRC were obtained in 11 dogs using peak single beat elastance (Emax). The MRC was fitted by a monoexponential curve. Vagal stimulation or verapamil administration decreased the peak of the MRC and right-shifted the MRC. The postextrasystolic MRC was located upward compared with the control MRC, and was shifted downward by vagal stimulation or verapamil administration. If interventions having a negative inotropic effect effectively slow a rapid heart rate, the net effect of the ventricular contractile state may not always be negative. It was concluded that the MRC is useful in understanding LV contractility during irregular rhythm, especially when assessing the net effect of the negative dromotropic and inotropic action of antiarrhythmic drugs.

Association between preinfarction angina and a lower risk of right ventricular infarction

BACKGROUND

Right ventricular infarction occurs in conjunction with inferior myocardial infarction caused by proximal occlusion of the right coronary artery. However, right ventricular infarction occurs infrequently, and the reasons for this are uncertain.

METHODS

We retrospectively assessed the association between preinfarction angina and right ventricular infarction, as well as the short-term outcome, in 113 patients with a first acute inferior myocardial infarction caused by right-coronary-artery occlusion. The association between the timing of angina during the week before infarction and the clinical outcome was also assessed.

RESULTS

The absence of preinfarction angina predicted the development of right ventricular infarction (odds ratio, 6.3; 95 percent confidence interval, 2.7 to 15.1; P<0.001), complete atrioventricular block (odds ratio, 3.6; 95 percent confidence interval, 1.4 to 10.3; P=0.01), and combined hypotension and shock (odds ratio, 12.4; 95 percent confidence interval, 4.5 to 40.6; P<0.001). Angina 24 to 72 hours before infarction was most strongly associated with reductions in the rates of right ventricular infarction (adjusted odds ratio, 0.2; 95 percent confidence interval, 0 to 0.8; P=0.02) and combined hypotension and shock (adjusted odds ratio, 0.1; 95 percent confidence interval, 0 to 0.5; P=0.02).

CONCLUSIONS

Preinfarction angina was an independent predictor of the absence of right ventricular infarction in patients with acute inferior myocardial infarction. The patients with preinfarction angina also had better short-term outcomes than those without preinfarction angina.

Structural evolution in boron nitrides during the hexagonal-cubic phase transition under high pressure at high temperature

Structural evolution during the phase transition from h (hexagonal)- to c (cubic)-boron nitrides (BN) under high pressure (6.5-7.7 GPa) at high temperature (1,700-2,150 degrees C) was examined by using high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). At the initial stage of the evolution, some starting h-BN plates were strongly folded, while others were slightly bent. As a result, a strong texture was formed. HRTEM revealed that the interplanar distance between sp2 sheets became slightly shortened and they were slightly sheared to each other during the folding and bending. As a result, m (monoclinic)-BN was formed near the folding plane with lattice parameters; a = 0.433 nm, b = 0.250 nm, c = 0.32-0.33 nm, and beta = 90-92 degrees. In a succeeding stage, the value of beta increased to 92-95 degrees. c-BN grains appeared with nano-scale twins and sometimes partly included wurtzite-type BN. They started to grow with secondary twins at higher temperature. EELS analysis revealed that the band structure of sp2 sheets changed during the transition from h-BN to m-BN; the density of state for the pi* bond became prominently high in m-BN as compared to that in h-BN.

A case of widely split double P waves with marked intra-atrial conduction delay

We report a 78-year-old man as the first documented case of double P waves separated by 400 msec on 12-lead ECG. These P waves had different polarities on lead V1. The first P wave represented activation of the lateral wall of the right atrium, and the latter P wave represented activation of the medial right atrium and the left atrium. Widely spaced double potentials were recorded craniocaudally along the line, presumably corresponding to the crista terminalis during sinus rhythm. For this to occur, conduction disturbance has to be present both in the upper and lower right atrium. Conduction disturbance in the upper right atrium would interrupt excitation from the sinus node to the medial wall, and conduction disturbance in the lower right atrium would interrupt excitation spreading from the lower lateral right atrium to the isthmus area where fragmented potentials were recorded. These multiple discrete lesions appear to constitute a unique electrical atriopathy in this patient.

C-reactive protein as a predictor of infarct expansion and cardiac rupture after a first Q-wave acute myocardial infarction

BACKGROUND

Pump failure after acute myocardial infarction (AMI) can be predicted by several indices that estimate infarct size. However, there are few indices that predict infarct expansion and cardiac rupture. We focused on the prognostic significance of serum C-reactive protein (CRP) after AMI.

METHODS AND RESULTS

Serum CRP levels were measured every 24 hours in 220 patients with a first Q-wave AMI. In-hospital complications, predischarge left ventriculographic findings, and long-term prognosis were assessed in relation to peak CRP levels. Peak levels of both CRP and creatine kinase (CK) were higher in patients with pump failure than in those without pump failure. In patients with cardiac rupture, peak CRP levels were higher than in those without rupture (P=.001); peak CK levels were not predictive. Higher CRP levels were found in patients with left ventricular aneurysm (P=.001 versus those without), aggravated heart failure (P=.03 versus those without), and cardiac death (P<.0001 versus survivors) during the first year after AMI. Multivariate analysis confirmed that an elevation of the peak CRP level > or = 20 mg/dL was an independent predictor of cardiac rupture (relative risk, 4.72; P=.004), left ventricular aneurysmal formation (relative risk, 2.11; P=.03), and 1-year cardiac death (relative risk, 3.44; P<.0001).

CONCLUSIONS

Cardiac rupture, left ventricular aneurysmal formation, and 1-year cardiac death were associated with an elevation of serum CRP early after AMI, suggesting that elevation of CRP levels after AMI may predict infarct expansion.

[Effect of barnidipine hydrochloride on the autonomic nervous system: difference between short- and long-acting components of calcium antagonist]

Short-acting calcium antagonists have a deleterious effect on the prognosis for patients with myocardial ischemia, possibly caused by overactivation of sympathetic nerves due to vasodilatation, negative inotropism, or coronary steal. However, there is considerable debate about whether long-acting calcium antagonists as well as the short-acting calcium antagonists have the same effect. Barnidipine-HCl is a newly-developed calcium antagonist with 1:2 short- and long-acting particles. This study evaluated the changes of autonomic tone due to barnidipine. Both the short- and long-acting effect of the calcium antagonist was evaluated. Eleven patients with primary hypertension underwent 24-hour ambulatory electrocardiogram and blood pressure monitoring before and after the treatment with barnidipine. Heart rate and blood pressure were compared before and after the medication. Heart rate variability was analyzed with a Marquette 8000/T. High frequency power (HF), as a parameter of vagal tone, and the ratio to low frequency power (LF), as a parameter of sympathetic tone, were obtained. Twenty-four-hour average blood pressure decreased significantly during the day, but nocturnal hypotension was not observed. Heart rate did not increase. HF decreased at the peak of the short- and long-acting components. LF/HF increased at the peak of the short-acting component. Short-acting particles of barnidipine had a deleterious effect on the autonomic tone, that is overactivation of sympathetic tone and suppression of vagal tone. Long-acting particles of barnidipine suppressed the vagal tone. These findings suggest that short-acting calcium antagonists may cause arrhythmia or deterioration of coronary ischemia.

Increase in heart rate after radiofrequency catheter ablation is mediated by parasympathetic nervous withdrawal and related to site of ablation

To assess the mechanism for the increased sinus rate after radiofrequency catheter ablation performed for atrioventricular nodal reentrant tachycardia (AVNRT), we studied heart rate variability before and after radiofrequency catheter ablation in 17 patients with AVNRT and in 38 patients with an accessory pathway. The accessory pathway was located at the left ventricular free wall, the right ventricular free wall, or the posterior interventricular septum. An increased sinus rate was observed in patients with AVNRT or with the accessory pathway at the posterior septum or left free wall after radiofrequency ablation. In these groups, high-frequency power, root mean square of successive difference and percent of adjacent cycles that were more than 50 ms apart, all of which are indices reflecting parasympathetic nervous activity, were decreased. The ratio of low-frequency to high-frequency power reflecting sympathovagal balance, was increased in patients with AVNRT or with an accessory pathway at the posterior septum or left free wall. Increases in sinus rate were correlated with decreases in high-frequency power, and percent of adjacent cycles more than 50 ms apart that the increase in heart rate was due to parasympathetic nervous withdrawal.

[Clinical significance and mechanism of ST-segment changes during the post-exercise recovery period in male patients with coronary artery disease]

The treadmill exercise test (TET) is evaluated by exercise-induced ST-segment depression (delta ST). However, the depression sometimes only appears during the post-exercise period. Depression appearing only during the post-exercise period may be as useful as depression during exercise to predict coronary artery disease, but little is known about factors that may affect ST depression after exercise. The clinical significance and mechanism of post-exercise ST depression were investigated in patients with coronary artery disease. Target heart rate- or symptom-limited TET was performed in 531 male patients with definitive effort angina pectoris or myocardial infarction using the Bruce protocol. Patients were divided into four groups according to delta ST during exercise and 1-2 min after exercise; 1) no TET or post-exercise delta ST (Nn, n = 192), 2) only post-exercise delta ST (Np, n = 36), 3) only TET delta ST (Pn, n = 112), 4) both TET and post-exercise delta ST (Pp, n = 66). Patient profiles, parameters during TET, echocardiographic and coronary angiographic findings and outcome during the year after TET were compared between the Nn and Np or Pn and Pp groups. The percentage of patients treated with beta-blocker was higher in the Np than that in the Nn group (Nn: 45%, Np: 64%, p < 0.05) and systolic blood pressure declined at 1 min after exercise from peak exercise in the Nn, but not in the Np group (Nn: 175 --> 167 mmHg, p < 0.05; Np: 170 --> 170 mmHg, not significant). There was no difference in age, other parameters during TET, echocardiographic and coronary angiographic findings and outcome between the Nn and Np group. The incidence of right coronary artery stenosis and that of patients with multi-vessel disease were higher in the Pp than those in the Pn group (Pn: 41%, 58%, Pp: 65%, 73%, both p < 0.05). The occurrence of chest pain during exercise was higher in the Pp than the Pn group in spite of less delta ST at peak exercise. However, systolic blood pressure declined after exercise in the Pn group, but not in the Pp group (Pn: 164 --> 158 mmHg, p < 0.05; Pp: 166 --> 164 mmHg, not significant). These results confirmed that the clinical significance of post-exercise delta ST in patients without TET delta ST differs from that in patients with TET delta ST and suggests that post-exercise delta ST without delta ST during exercise may be associated with an abnormal response to imbalances in the cardiovascular sympathetic system in the post-exercise period rather than with myocardial ischemia.

Effect of a new beta-blocker, nipradilol, on cardiac function and neurohumoral factors in idiopathic dilated cardiomyopathy

This study investigated the therapeutic efficacy of a new beta-blocker, nipradilol, a non-selective agent with vasodilating activity, for the treatment of idiopathic dilated cardiomyopathy (DCM). The New York Heart Association functional class improved in the nipradilol group (n = 9, p < 0.01), but not in the control group who received conventional therapy (n = 9). The observation period was 19 +/- 7 months in the nipradilol group, and 20 +/- 9 months in the control group. Before therapy there was no difference in heart rate between the 2 groups (76 +/- 12 vs 79 +/- 15 beats/min). The end-diastolic and end-systolic left ventricular dimensions decreased in the nipradilol group (p < 0.05), but not in the control group. Radionuclide ventriculography revealed that the left ventricular ejection fraction increased in the nipradilol group (27 +/- 8 to 41 +/- 18%, p < 0.05), but not in the control group (27 +/- 11 to 27 +/- 8%). Plasma norepinephrine tended to be lowered, although not significantly, whereas plasma alpha atrial natriuretic peptide significantly decreased after the therapy (p < 0.01) in the treatment group. Lymphocyte beta-adrenoceptors were up-regulated in the nipradilol group (p < 0.05). None of these parameters changed during the observation period in the control group. Thus, nipradilol improved symptoms and cardiac function with a favorable effect on neurohumoral factors in patients with DCM.

[Usefulness of the newly developed transtelephonic electrocardiogram and computer-supported response system]

The "Cardiophone System" is a system designed to expand the relationship between patients and medical services using a transtelephonic electrocardiogram and computer-assisted answering system. The transtelephonic electrocardiogram, or so-called "Cardiophone", developed by Nihon Kohden, Inc., allows the patients to carry a "Cardiophone" to record electrocardiograms during paroxysmal occurrences of palpitation, chest pain, and other symptoms. The Cardiophone may function as a terminal of the host computer at the hospital, which stores the electrocardiogram and print it as soon as the computer receives the electrocardiogram over the phone. Cardiologists can examine the electrocardiogram immediately after it is printed. Cardiologists and operators are on duty 24 hours a day. Judgments based on the electrocardiogram are made by the cardiologist on duty, and stored in the computer by the operator. The patients may listen to the judgment over the phone within 30 min of sending the electrocardiogram. In the case of potentially lethal findings on the electrocardiogram, the cardiologist on duty calls the patient directly to give a medical advice. We studied 184 outpatients who were enrolled in the Cardiophone System of our hospital. The average number of transtelephonic electrocardiograms was 10 per day. Abnormal electrocardiographic changes were observed in 42 patients, and the diagnoses were as follows: paroxysmal supraventricular tachycardia in 18 patients, paroxysmal atrial fibrillation in 17, ventricular tachycardia in 3, and angina in 7. Among seven patients in whom ST changes were documented by Cardiophone, six were diagnosed as variant angina. In several patients with diagnoses already made by Holter monitoring, the Cardiophone was used to monitor the drug effects and the correlations between symptoms and arrhythmic events. We conclude that the Cardiophone System is useful for diagnosing the causes of paroxysmal cardiac symptoms in some patients and for improving home medical services.

Early reduction of neurohumoral factors plays a key role in mediating the efficacy of beta-blocker therapy for congestive heart failure

This study examined the role played by neurohumoral factors in mediating the effects of beta-blocker therapy for congestive heart failure. Fifteen patients with congestive heart failure underwent beta-blocker therapy. Plasma norepinephrine and alpha-atrial natriuretic peptide concentrations decreased 2 weeks after initiation of beta-blocker therapy. Decrease in plasma norepinephrine level persisted for 6 months. Lymphocyte beta-adrenoceptor density increased 2 weeks after therapy but was not increased 6 months later. Left ventricular ejection fraction was unchanged 2 weeks after therapy, but it increased 6 months after introduction of beta-blockers. Plasma norepinephrine level decreased 2 weeks after the therapy in the responders (increase in ejection fraction > 0.10) but not in the nonresponders. Thus early reduction of neurohumoral factor levels preceded the late improvement of left ventricular contractile function and may therefore be partly responsible for the efficacy of beta-blocker therapy for congestive heart failure.

Preinfarction angina as a major predictor of left ventricular function and long-term prognosis after a first Q wave myocardial infarction

OBJECTIVES

The purpose of this study was to assess the prognostic significance of preinfarction angina after a first Q wave myocardial infarction. Patients with anterior or inferior myocardial infarction were compared.

BACKGROUND

The effect of preinfarction angina on prognosis after anterior and inferior myocardial infarction remains unclear.

METHODS

A total of 291 patients with a first Q wave anterior (n = 171) or inferior (n = 120) myocardial infarction were examined to assess the effect of preinfarction angina on short- and long-term prognosis. The relation between predischarge left ventriculographic findings and preinfarction angina was also examined.

RESULTS

The presence of preinfarction angina was associated with lower peak creatine kinase activity, a lower in-hospital incidence of sustained ventricular tachycardia and fibrillation and a lower incidence of pump failure and cardiac mortality in patients with either anterior or inferior infarction. Among patients with anterior infarction, preinfarction angina was associated with a lower incidence of cardiac rupture and less need for readmission for heart failure within 1 year after the onset of infarction. In this subgroup it was also associated with a higher ejection fraction, a smaller end-diastolic volume and a lower incidence of aneurysm formation noted on ventriculography during convalescence. In patients with inferior infarction, these variables did not differ significantly in the presence or absence of preinfarction angina. Multivariate analysis confirmed that the presence of preinfarction angina was an independent predictor of development of ventricular aneurysm, late phase heart failure and 1-year cardiac mortality.

CONCLUSIONS

The presence of preinfarction angina has a favorable effect on infarct expansion and late phase left ventricular function, especially in patients with anterior myocardial infarction. The mechanisms responsible for this phenomenon are not known but may be secondary to limitations of infarct size through unidentified mechanisms other than collateralization (e.g., ischemic preconditioning).

Beta-1-selectivity is not essential to achieve therapeutic efficacy with beta-blockade therapy for idiopathic dilated cardiomyopathy

This study investigated the therapeutic efficacy of two different beta-blockers, metoprolol (beta 1-selective) and nipradilol (nonselective) for the treatment of idiopathic dilated cardiomyopathy (DCM). The New York Heart Association functional class improved in the metoprolol group (n = 9) and the nipradilol group (n = 9), but not in the control group who received conventional therapy (n = 8). The left ventricular ejection fraction increased in both the beta-blocker groups (p < 0.01, p < 0.05). Lymphocyte beta-adrenoceptors were upregulated in the nipradilol group (p < 0.01). Cardiac events were less common in both the beta-blocker groups than in the control group (both p < 0.05). Thus, nipradilol improved symptoms and cardiac function with a favorable effect on sympathoneuronal activity as well as metoprolol in patients with DCM. Therefore, beta 1-selectivity is not essential to achieve therapeutic efficacy with beta-blockade therapy for DCM.

Effect on short-term prognosis and left ventricular function of angina pectoris prior to first Q-wave anterior wall acute myocardial infarction

The prognostic significance of angina pectoris before the development of first Q-wave anterior wall acute myocardial infarction (AMI) was assessed in 153 patients. A total of 100 patients in this study had angina before Q-wave AMI, whereas 53 patients had no antecedent symptoms of angina. The presence of angina before AMI was associated with a lower incidence of complications including sustained ventricular tachycardia or fibrillation (7% vs 25%, p = 0.0022), pump failure (24% vs 47%, p = 0.0035), cardiac rupture (1% vs 17%, p = 0.0001), and a lower in-hospital mortality rate (11% vs 28%, p = 0.0067). The peak creatine phosphokinase activity was lower in patients with than without antecedent angina (1,727 +/- 1,238 vs 2,675 +/- 2,569 IU/liter, respectively, p = 0.023). There was no difference in the prevalence of multivessel coronary artery disease or the presence of collateral circulation between the 2 groups. Left ventriculography revealed a higher left ventricular ejection fraction (54 +/- 13% vs 46 +/- 11%, p = 0.034) and smaller left ventricular end-diastolic volumes (75 +/- 15 vs 86 +/- 18 ml/m2, p = 0.017) in patients with than without antecedent angina. These findings suggest that the presence of angina before AMI may be associated with a protective effect on left ventricular function during anterior wall AMI. Although the precise mechanisms underlying the beneficial effects are unknown, they may be related to the development of collateral channels or ischemic preconditioning.

Clinical evaluation of the use-dependent QRS prolongation and the reverse use-dependent QT prolongation of class I and class III antiarrhythmic agents and their value in predicting efficacy

We measured the QRS duration during a treadmill exercise test and the QT interval using a 24-hour Holter electrocardiogram at various heart rates to identify use-dependent QRS prolongation and reverse use-dependent QT prolongation of class I and III antiarrhythmic drugs. Use-dependent QRS prolongation was detected in 61%, 53%, and 64% of patients receiving disopyramide, mexiletine, and pilsicainide, respectively. Reverse use-dependent QT prolongation was found in 40% and 70% of patients receiving disopyramide and E4031. Drugs suppressed > or = 75% of the total premature ventricular contractions in all patients who had both use-dependent QRS prolongation and reverse use-dependent QT prolongation, in 79% of patients with use-dependent QRS prolongation alone, in 70% with reverse use-dependent QT prolongation alone, and in 11% with neither use-dependent QRS prolongation nor reverse use-dependent QT prolongation. Use-dependent QRS prolongation and reverse use-dependent QT prolongation were identified noninvasively and were useful in evaluating antiarrhythmic efficacy.

Calcium concentration during anoxic perfusion modifies post-ischemic hypercontraction in the canine heart

The purpose of this study was to clarify the role of calcium flux in the pathogenesis of transient overshoot in regional myocardial contractile function after brief ischemia (post-ischemic hypercontraction). Six open-chest anesthetized dogs were examined. The left anterior descending coronary artery (LAD) was cannulated with a bypass system from the left carotid artery. Two minutes of total coronary occlusion of the LAD resulted in a post-ischemic hypercontraction 1 minute after reperfusion. Post-ischemic hypercontraction was abolished after reperfusion following 2 minutes of perfusion with anoxic Krebs-Henseleit solution containing 2.5 mM calcium. Post-ischemic hypercontraction occurred after calcium-free anoxic perfusion. The regional myocardial contractile function remained depressed 1 minute after reperfusion following anoxic perfusion with 5.0 mM calcium solution. Thus, post-ischemic hypercontraction was modified by the calcium concentration during anoxia. Alteration in transsarcolemmal calcium influx during reperfusion, which was modified by alterations in the calcium environment during anoxia, could be responsible for this phenomenon.

Acute myocardial infarction without warning: clinical characteristics and significance of preinfarction angina

We investigated the clinical characteristics of acute myocardial infarction (AMI) not preceded by angina in 256 patients with first AMIs. Complications, including sustained ventricular tachycardia or ventricular fibrillation, pump failure and cardiac rupture, were more frequent in patients with AMI not preceded by angina (group 1, n = 92) than those preceded by angina (group 2, n = 164). The in-hospital mortality rate was higher in group 1 than in group 2. Poor preexisting collateral channels or lack of ischemic preconditioning may be responsible for the poorer outcome in group 1 patients.

Postischaemic hypercontraction is enhanced in ischaemically injured canine myocardium

OBJECTIVE

The aim was to identify the role of calcium flux in the pathogenesis of transient overshoot of regional myocardial contraction after brief ischaemia, ie, postischaemic hypercontraction.

METHODS

Ten anaesthetised mongrel dogs were examined under open chest conditions. The left anterior descending coronary artery was initially occluded for 2 min and reperfused for 10 min. A further period of coronary occlusion of 15 min duration was followed by 15 min reperfusion to produce postischaemic regional dysfunction. A third occlusion of 2 min duration was followed by 10 min reperfusion to induce postischaemic hypercontraction. Coronary blood flow was measured using an ultrasonic transit time flow meter. Segment length was measured by ultrasonic microcrystals.

RESULTS

Postischaemic hypercontraction after 2 min coronary occlusion was exaggerated in ischaemically injured myocardium. The 10 dogs were divided into two groups, a control group (n = 5) and a verapamil treated group (n = 5), and were exposed to a final 2 min period of coronary occlusion with or without verapamil in the ischaemically injured myocardium. Postischaemic hypercontraction was attenuated in the verapamil treated group compared with the control group.

CONCLUSIONS

Exaggeration of postischaemic hypercontraction in ischaemically injured myocardium may be mediated by a trans-sarcolemmal calcium flux. Changes in calcium flux may play a role in the pathogenesis of this phenomenon in the normal myocardium.