Parasympathetic activity is a major modulator of the circadian variability of heart rate in healthy subjects and in patients with coronary artery disease or diabetes mellitus

Autonomic heart rate control was assessed by power spectral analysis of heart rate variability in 24-hour ambulatory electrocardiographic recordings from 23 healthy subjects, 14 patients with coronary artery disease without cardiac dysfunction, and 14 patients with diabetes mellitus. The log value of the ratio of the low-frequency component (LF = 0.04 to 0.15 Hz) to the high-frequency component (HF = 0.15 to 0.5 Hz) and logHF were employed as indexes of sympathetic and parasympathetic activity, respectively. Diurnal and nocturnal logLF, logHF, and log(LF/HF) values were calculated for heart rates of 60, 70, and 80 beats/min. Intergroup differences among these three variables were not significant at any heart rate. Although a heart rate-related decrease in logHF was generally observed, the relationship between log(LF/HF) and heart rate was not consistent. The correlation between diurnal and nocturnal logHF values was significant at all three heart rates (r = 0.63, 0.87, and 0.59), whereas the diurnal log(LF/HF) was correlated with the nocturnal value only at 70 beats/min (r = 0.77). These results suggest that the heart rate during normal daily activities is a reliable indicator of parasympathetic tone, if not sympathetic tone, in healthy subjects and patients with coronary artery disease or diabetes mellitus.     

Effect of benazepril on complex ventricular arrhythmias in older patients with congestive heart failure, prior myocardial infarction, and normal left ventricular ejection fraction

Sixty patients, mean age 82 +/- 8 years, with congestive heart failure, prior myocardial infarction, normal left ventricular ejection fraction, and > or = 30 ventricular premature complexes per hour detected by 24-hour ambulatory electrocardiograms, and who were treated with diuretics, were randomized to treatment with benazepril 20 to 40 mg/day (30 patients) or to no benazepril (30 patients). At a median of 6 months after treatment, follow-up 24-hour ambulatory electrocardiograms showed that compared with no benazepril, benazepril caused no significant reduction in the number of ventricular premature complexes per hour or in the number of runs of ventricular tachycardia per 24 hours.     

A new method for evaluating antiarrhythmic drug efficacy

To develop standards for distinguishing antiarrhythmic drug effect from spontaneous variability of premature ventricular complexes (PVCs), 21 males (mean age 56 +/- 8 years) with chronic ischemic heart disease and PVCs underwent symptom-limited treadmill exercise testing and 24-hour ambulatory monitoring before and after 2 weeks of placebo medication. Linear regression analysis was used to describe the relationship between baseline and placebo PVC frequency for various indexes of ventricular ectopic activity and to establish 95% and 99% one-tailed confidence intervals for this relationship within the group of 21 patients. The lower limit of baseline PVC frequency for which the procedure could distinguish a placebo from a true drug response, termed the "sensitivity threshold," was an average frequency of 2.2 PVCs/hour for ambulatory electrocardiographic monitoring and 1.2 PVCs/min for treadmill exercise testing. All patients exceeded the sensitivity threshold on baseline ambulatory ECGs, but only 38% of patients did so on baseline treadmill exercise tests. To establish antiarrhythmic efficacy with 95% confidence, the minimal percent reduction of PVCs between baseline and placebo visits was 68% for treadmill exercise testing and 65% for ambulatory electrocardiography. Although these standards were developed in patients with chronic ischemic heart disease, the model can be used to establish antiarrhythmic drug efficacy in any patient group.     

Impact of ambulatory blood pressure on left ventricular diastolic dysfunction in uncomplicated arterial systemic hypertension

To determine the relations of 24-hour blood pressure (BP) and its different phases with left ventricular (LV) diastolic filling, 125 subjects (mean age 46 years) not taking cardiac drugs were studied by Doppler echocardiography and ambulatory BP recording. Subjects (excluding those with coronary artery or valvular heart disease, heart failure, or diabetes) were classified into 2 groups according to the level of Doppler-derived ratio of peak early to atrial velocity (E/A ratio): 59 had E/A >1 (normal diastole), 62 had E/A <1 (impaired diastole), and 4 had E/A = 1. Patients with E/A <1 were older and had higher LV mass indexed for height, average 24-hour BP, average nighttime BP, and lower day-night BP decrease, whereas average daytime BP did not differ significantly between the 2 groups. Negative correlations of E/A were found with age, heart rate, office, average 24-hour and average nighttime systolic and diastolic BP, and LV mass index. In a multivariate model that included potentially confounding factors, only age (standardized beta coefficient = -0.52, p<0.00001), nighttime BP (beta = -0.28, p<0.0001), and heart rate (beta = -0.22, p<0.001) were independent predictors of E/A in the pooled population. In conclusion, LV diastolic function is more closely related to ambulatory, rather than to clinic, BP measurements, and high average nocturnal diastolic BP is a powerful marker of LV filling impairment.     

Long-term reproducibility and usefulness of daytime recording of noninvasive 24-hour ambulatory blood pressure monitoring in borderline hypertension: a two-year follow-up study

We investigated the long-term reproducibility of noninvasive 24-hour ambulatory blood pressure monitoring (ABPM) compared with casual blood pressure measurements in 54 individuals (47 +/- 11 years) with borderline hypertension. ABPM and casual blood pressure measurements were obtained 3 times over 2 year period. ABPM data were analyzed to determine the average 24-hour blood pressure (24-BP), the average blood pressure during the waking hours (Day-BP), and the average blood pressure from the time the subject went to bed until he awoke (Night-BP). ABPM measurements were similar for Year 1, 2, and 3 (24-BP: Year 1; 130 +/- 10/79 +/- 6 mmHg; Year 2; 130 +/- 10/79 +/- 7 mmHg; and Year 3; 130 +/- 10/78 +/- 7 mmHg). Bland-Altman analysis and standard deviation of the difference also indicated the reproducibility of 24-BP was better than casual pressure. The 24-BP was significantly correlated with both Day-BP and Night-BP for each year. Day-BP showed the stronger correlation. Our results suggest that Day-BP provides reproducible estimation in subjects with borderline hypertension.     

The capsule biosynthetic locus of Pasteurella multocida A:1

OBJECTIVES: The purpose of this study was to investigate the progression of autonomic dysfunction in patients with Duchenne-type progressive muscular dystrophy (DMD) over time by using heart rate variability. BACKGROUND: Although previous studies suggest the presence of autonomic dysfunction in patients with DMD, the precise cause is not known. On the other hand, it is well known that analysis of heart rate variability provides a useful, noninvasive means of quantifying autonomic activity. High frequency power is determined predominantly by the parasympathetic nervous system, whereas low frequency power is determined by both the parasympathetic and sympathetic nervous systems. METHODS AND RESULTS: Frequency and time domain analyses of heart rate variability during ambulatory electrocardiographic monitoring were performed in 17 patients with DMD over a 9-year period. At the time of entry, the mean patient age was 11 years and the mean Swinyard-Deaver stage was 4. In the first year, high frequency power was significantly lower and the ratio of low frequency to high frequency was significantly higher in patients with DMD than in the normal control subjects. These differences become significantly greater as the disease progressed. At the time of entry, low and high frequency powers increased at night in both groups. However, over time, high and low frequency powers at night tended to decrease. All of the time domain parameters were significantly lower in the patients with DMD at all time points compared with the normal control subjects. CONCLUSIONS: We concluded that DMD patients have either a decrease in parasympathetic activity, an increase in sympathetic activity, or both as their disease progresses.     

Nutritional aspects of neuromuscular diseases

Evidence suggests that individuals with DMD have reduced skeletal development, including decreased linear growth and bone mineral density, compared to normal subjects. Despite their reduced muscle mass, a high percentage of DMD patients are overweight. Body composition measurements can assist with monitoring changes in fat mass and skeletal muscle mass as the disease progresses. Weight management in overweight DMD patients is indicated because excess adiposity burdens mobility and breathing, but only one study in two DMD patients has documented that weight reduction can be done safely. In the latter stages of the disease most DMD subjects become underweight because of an acceleration in skeletal muscle protein degradation relative to its synthesis. Studies of energy, protein and branched chain amino acid supplementation in DMD have yielded promising but inconclusive results, and more well-designed studies are needed in this area. Although there is currently no cure for DMD, studies on the role of nutritional therapy in increasing the quality of life in these patients are urgently needed. Studies in adults with various SP-NMDs indicate a reduction in fat-free mass and an increase in fat mass relative to controls. The newly developed method of air displacement plethysmography for measuring body composition is ideally suited for SP-NMD subjects because it requires very little effort and the measurement procedure is relatively fast. Dual energy x-ray absorptiometry technology has been proposed for distinguishing myogenic from neurogenic SP-NMDs from calculation of the fat-to-lean soft tissue ratio, which is higher in patients with myogenic muscular atrophy. Studies on the energy metabolism of ambulatory SP-NMD subjects indicate that their basal metabolic rate is either similar to or slightly lower than controls, but 24-hour energy expenditure is about 25% lower than controls. This reduction in 24-hour energy expenditure is due to a reduction in physical activity in SP-NMD. Studies examining the roles of energy expenditure, physical activity, and diet in the development of adiposity and risk for secondary chronic diseases in SP-NMD subjects are currently underway.     

Arrhythmias documented by 24-hour continuous ambulatory electrocardiographic monitoring in young women without apparent heart disease

Results are reported of 24-hour ambulatory ECG recordings in 50 young women without apparent heart disease. During waking periods, maximum (sinus) rates ranged from 122 to 189 beats/min (bpm) (153 +/- 14 mean +/- SD) and minimum rates from 40 to 73 bpm (56 +/- 7). During sleeping periods, maximum and minimum rates ranged from 71 to 128 bpm (105 +/- 13) and from 37 to 59 bpm (48 +/- 6), respectively. Thirty-two subjects (64%) had atrial premature beats, with only one subject (2%) having greater than 100 beats/24 hrs. Twenty-seven subjects (54%) had ventricular premature beats, with only three subjects (6%) having greater than 50 beats/24 hrs. One subject (2%) had one three-beat episode of ventricular tachycardia. Two subjects (4%) had transient type I second-degree atrioventricular block.     

Seasonal variations in home and ambulatory blood pressure in the PAMELA population. Pressione Arteriose Monitorate E Loro Associazioni

OBJECTIVE: Clinic blood pressure values are known to change according to seasonal influences. We therefore examined home and 24 h ambulatory blood pressure values to determine whether these measurements are also affected by the seasons. DESIGN AND METHODS: In 2051 subjects of the Pressione Arteriose Monitorate E Loro Associazioni (PAMELA) study, we measured clinic (sphygmomanometric measurements), home (semi-automatic device) and ambulatory (Spacelabs 90207) systolic blood pressure, diastolic blood pressure and heart rate. Because the overall sample was evenly distributed over each month (except August), we were able to make a cross-sectional determination of whether the values differed between seasons. The corresponding heart rates were also evaluated. RESULTS: As expected, summer was associated with the lowest clinic blood pressure and winter with the highest, and this was the case also for home and 24 h average blood pressure, although seasonal differences in the latter were less pronounced. Seasonal clinic, home and ambulatory blood pressure patterns were similar for normotensive subjects (n = 1152), untreated hypertensives (n = 540) and treated hypertensives (n = 359). Heart rate values did not differ by season. CONCLUSIONS: Seasonal influences on blood pressure are not limited to conventional measurements but characterize daily values as well. These effects are visible in both normal and elevated blood pressure values, regardless of the effect of antihypertensive drugs. This has implications both for the clinician and for studies aimed at evaluating the effects of antihypertensive treatment.     

Cardiac autonomic function and sensitivity to pain in postmenopausal women with angina and normal coronary arteries

An increased sensitivity to painful stimuli and an abnormal cardiac autonomic function have previously been reported in patients with angina and angiographically normal coronary arteries, a syndrome that mainly affects postmenopausal women. In this study we compared both general sensitivity to pain, by evaluating time to forearm ischemic pain (FIP) provoked by sphygmomanometer cuff inflation, and cardiac autonomic function, by measuring heart rate variability (HRV), and QT and QT(c) intervals on 24-hour Holter recordings, in 25 postmenopausal women with angina and normal coronary arteries and in 22 healthy postmenopausal women. Compared with controls, patients had a reproducible strikingly lower time to FIP (149 +/- 121 vs 295 +/- 158 seconds, p <0.001), whereas there were no differences between the 2 groups in HRV variables and mean 24-hour QT and QT(c) intervals. HRV indexes, and QT and QT(c) intervals also showed similar circadian patterns. Thus, our data show that postmenopausal women with angina and normal coronary arteries have an enhanced sensitivity to systemic painful stimuli, but no detectable impairment in cardiac autonomic function compared with a well-matched control group of postmenopausal healthy women.     

Treatment with enalapril modifies the pain perception pattern in hypertensive patients

The cardiovascular system shares numerous anatomic and functional pathways with the antinociceptive network. The aim of this study was to investigate whether angiotensin-converting enzyme (ACE) inhibitor treatment could affect hypertension-related hypalgesia. Twenty-five untreated hypertensive patients, together with a control group of 14 normotensive subjects, underwent dental pain perception evaluation by means of a pulpar test (graded increase of test current applied to healthy teeth). After the evaluation of the dental pain threshold (occurrence of pulp sensation) and tolerance (time when the subjects asked for the test to be stopped), all the subjects underwent a 24-hour ambulatory blood pressure monitoring. The hypertensive group then was treated with 20 mg/d enalapril, whereas the normotensive subjects remained without any treatment. After a time interval of 6+/-2 months, the dental pain sensitivity was retested in all the subjects, and ambulatory blood pressure was recorded during treatment in the hypertensive patients. At the first assessment, hypertensive patients showed a higher pain threshold than normotensive subjects (P<.001). On retesting of pain sensitivity in hypertensive patients, a significant decrease of both pain threshold and tolerance, leading to their normalization, was observed during treatment (P<.001 and P<.005, respectively), in the presence of reduced 24-hour and office blood pressure values. A slight, though significant, correlation was observed between variations in pain tolerance and baseline blood pressure changes occurring during treatment. During follow-up, the normotensive subjects did not show any significant pain perception or office blood pressure changes. Hypertension-related hypalgesia was confirmed. Mechanisms acting both through lowering of blood pressure and specific pharmacodynamic properties may account for the normalization of pain sensitivity observed in hypertensive patients during treatment with ACE inhibitors.     

Autonomic nervous activity at episodes of myocardial ischemia in patients with coronary artery disease by heart rate power spectral analysis

Heart rate power spectral analysis in 44 patients with coronary artery disease was obtained from 24-hour dynamic electrocardiogram. 195 episodes of transient myocardial ischemia that was defined as horizontal or down sloping depression of the ST segment of > or = 0.1 mV and lasted for > or = 2 minutes were studied. The area of low frequency components (LF, 0.02-0.10 Hz) representing predominontly sympathetic tone with some contribution from the parasympathetic tone and that of high frequency components (HF, 0.15-0.40 Hz) representing mainly parasympathetic tone and the value of LF/HF on 4 minute heart rate power spectral graph at the deepest depression of ST segment were compared with that before the episode of myocardial ischemia. The area of HF of fast rate myocardial ischemia occurring in night reduces significantly (P < 0.001), the value of LF/HF increases markedly (P < 0.05) and the area of LF increases slightly. The results suggest that there is a change of autonomic nervous activity during the episode of fast rate myocardial ischemia in night, parasympathetic nervous tone decreases markedly, there may be secondary increase of sympathetic nervous activity.     

Effects of amlodipine and nifedipine retard on autonomic nerve activity in hypertensive patients

1. The effects of 1,4-dihydropyridine calcium antagonists with different biological half-lives, amlodipine and nifedipine retard on 24 h blood pressure (BP), heart rate (HR) and autonomic nerve activity in patients with essential hypertension were compared. 2. Twenty patients (six men and 14 women; mean (+/- SEM) age 63 +/- 2 years) with essential hypertension were enrolled in the present study. Their ambulatory BP and electrocardiograms were monitored for 24 h at intervals of 30 min with a portable recorder after a 4 week drug-free period, after a 4 week treatment period with amlodipine (2.5 or 5 mg once daily) and after a 4 week treatment period with nifedipine retard (10 or 20 mg twice daily). The order of the three periods was randomized. Autonomic nerve activity was evaluated by power spectral analysis of HR variability, using the high frequency (HF) component as an index of parasympathetic activity and the ratio of the low frequency (LF) to the HF component as an index of sympathovagal balance. 3. Amlodipine and nifedipine retard significantly lowered the 24 h BP to a similar extent (amlodipine: -12.7 +/- 2.6/-5.6 +/- 1.4 mmHg, P < 0.01/P < 0.01; nifedipine retard: -15.1 +/- 2.1/-6.9 +/- 1.5 mmHg, P < 0.01/P < 0.01). Amlodipine did not change the 24 h average HR, while nifedipine retard significantly increased it (+3.3 +/- 1.2 b.p.m., P < 0.05). Amlodipine also did not change the HF component or the ratio of the LF to the HF component. However, nifedipine retard significantly decreased the HF component (P < 0.01) and increased the ratio of the LF to the HF component (P < 0.05). 4. These results suggest that nifedipine retard caused a decrease in parasympathetic activity and an increase in sympathetic activity with reflex tachycardia in these patients with essential hypertension, while amlodipine did not produce such effects on the autonomic nervous system.     

Prevalence of heart disease in older women in a nursing home

The prevalence of coronary artery disease (CAD) and the incidence of new coronary events are similar in older men and women. Independent risk factors for new coronary events in older women include age, prior CAD, cigarette smoking, hypertension, diabetes mellitus, high serum total cholesterol and triglycerides, and low serum high-density lipoprotein cholesterol. Older women have a higher prevalence of hypertension than older men. In older women with hypertension, echocardiographic left ventricular hypertrophy is a powerful independent predictor of new coronary events, atherothrombotic brain infarction, and congestive heart failure (CHF). Older women have a higher prevalence of rheumatic mitral stenosis and of mitral annular calcium than older men. Older women and men have a similar prevalence of valvular aortic stenosis, aortic regurgitation, mitral regurgitation, hypertrophic cardiomyopathy, and idiopathic dilated cardiomyopathy. The prevalence and incidence of CHF increase with age. The prevalence of normal left ventricular ejection fraction associated with CHF increases with age and is higher in older women than in older men. The prevalence of chronic atrial fibrillation increases with age and is similar in older men and women. Atrial fibrillation is an independent predictor of new coronary events and thromboembolic stroke in older women. Older women with unexplained syncope should have 24-hour ambulatory electrocardiograms to determine whether pauses > 3 seconds are present, requiring permanent pacemaker implantation.     

Expression of Pit-1 mRNA and activin/inhibin subunits in clinically nonfunctioning pituitary adenomas. In situ hybridization and immunohistochemical analysis

Autonomic nervous activity is involved in the onset of paroxysmal atrial fibrillation, but it is not clear how the sympathetic and parasympathetic nervous systems interact before the onset of atrial fibrillation. Twelve lone atrial fibrillation patients and 10 healthy volunteers were studied using 24-hour Holter electrocardiography monitoring. A total of 17 episodes were analyzed. Autonomic nervous activity was assessed based on the high frequency power (HF) spectrum (HF represents parasympathetic nervous activity) and the ratio to the low frequency power (LF) spectrum (L/H represents sympathetic nervous activity) of heart rate variability during sinus rhythm, and the 24-hour averaged autonomic indices were compared between atrial fibrillation patients and healthy volunteers. Comparative data were obtained 30, 20, 10, and 2 min before the onset of atrial fibrillation for each episode. There were no significant differences in the HF and L/H ratio between the patients and healthy volunteers. There were no significant differences in the HF values before the onset of paroxysmal atrial fibrillation, but the L/H ratio before the onset of atrial fibrillation at 30, 20 and 10 min was 1.03 +/- 0.42, 0.95 +/- 0.50, and 1.32 +/- 0.46, respectively, and just before the episode was 1.73 +/- 0.73, so the Spearman's rank correlation coefficient was 0.43. Basal autonomic nervous activity in patients with paroxysmal atrial fibrillation showed no changes compared with healthy volunteers. Sympathetic nervous activity increased progressively from about 30 min before the onset of atrial fibrillation, but parasympathetic nervous activity showed no significant changes. Therefore, a transient augmentation of sympathetic tone may be important in the onset of atrial fibrillation.     

Reproducibility of fat area measurements in young, non-obese subjects by computerized analysis of magnetic resonance images

OBJECTIVE: To assess reproducibility, expressed as both inter-observer variability and intra-observer variability, of fat area measurements on images obtained by magnetic resonance (MR); to compare variability between fat area measurements, calculated from a single image per body region and from the average fat area of three images, and to determine reproducibility of image acquisition at the abdominal level. SUBJECTS: Thirty young, non-obese subjects (reproducibility of image analysis) and nine young, non-obese subjects (reproducibility of image acquisition). METHODS: Three MR images at the level of the abdomen (in 30 subjects) and at the level of the hip and thigh (in 14 of them). Quantification of subcutaneous fat depots (abdomen, hip and thigh) and visceral fat depots using an image-analyzing computer program. Assessment of variability of image analysis for fat area measurements between two observers and within observers. Assessment of reproducibility of image acquisition at the abdominal level (in nine subjects). RESULTS: Subcutaneous fat areas in all body regions were quantified with coefficients of variation (CV) ranging from only 2.1%-4.9%. By contrast, visceral fat area measurements showed markedly higher CVs (range: 9.4%-17.6%). Moreover, relative variability was much larger in small visceral fat areas (CVs up to 25.6%). The majority of CVs, calculated for intra-observer variability and calculated from the average fat area measurements of three images, was lower than calculated for inter-observer variability and for one single image, respectively. In particular, for the visceral fat depot, this reduction in variability had practical consequences for the number of subjects required for a study. Variation of repeated image acquisition was in the same range as variation of repeated measurements on the same image. CONCLUSION: One image per body site is sufficient to obtain a reliable estimate of subcutaneous fat depots. For estimations of the visceral fat depot, the average area measurements of three images reduces variability and increases statistical power. The availability of one single experienced observer during a study adds to accuracy.     

Cerana--a new method for the restoration of teeth with prefabricated ceramic inlays

We studied the reproducibility of multifocal electroretinography by repeated measurements in normal subjects. We also analyzed the amplitude and implicit time of the waves. Nine healthy eyes including myopic cases (-4.1 D on average) of 9 normal males, aged 19 to 42 years, were the objects of study. We used a (Visual Evoked Response Imaging System III (VERIS III), by TOMEY Corp.) for multifocal electroretinography. Each eye was examined 4 times on different days. The stimulus elements consisted of 103 hexagons. The net recording time was 4 minutes. We used the coefficient of variation (standard deviation/average) of 4 measurements of response density as index of reproducibility. Poor fixation and blinking were important factors that affected the reproducibility. In all the 9 eyes, reproducibility of multifocal electroretinography, expressed as average of the coefficient of variation of all regions, was 22% on average. In 6 eyes with good fixation and without blinking, the reproducibility was 15% on average. In 6 eyes with good reproducibility, we analyzed three parameters of the focal response waves: all traces, quadrants and rings, as well as the amplitude and latency of the waves. These data served as controls. Our studies showed that the response density correlated closely with the amplitude and not with the latency in normal subjects.     

Correlation of SPECT and PET cardiac images by a surface matching registration technique

To study the potential role of sympathetic activity in the pathogenesis of arterial hypertension associated with autosomal dominant polycystic kidney disease (ADPKD) and to analyze its relationship with 24-hour blood pressure pattern, plasma catecholamines and 24-hour ambulatory blood pressure monitoring were evaluated in 30 ADPKD hypertensive patients (of which 17 without and 13 with renal failure) and in 50 essential hypertensives. The groups were matched for sex, body mass index, known duration of hypertension, and clinic blood pressure. Plasma catecholamines, determined in resting position, were higher in ADPKD patients without renal failure than in essential hypertensives. Nighttime diastolic blood pressure was higher and the percentage day-night difference in mean blood pressure was lower in hypertensives with ADPKD compared to patients with essential hypertension. Blood pressure was significantly correlated with plasma noradrenaline in ADPKD patients, independently of renal function. No significant differences were observed between ADPKD patients with and without renal failure, with respect to plasma catecholamines, 24-hour daytime and nighttime ambulatory blood pressures and the percentage day-night difference in mean blood pressure.     

Clinical applications of signal-averaged electrocardiography in patients after myocardial infarction

In conclusion, signal-averaged electrocardiography is a useful, noninvasive technique to identify patients after myocardial infarction at risk for future arrhythmic events, especially in conjunction to existing tools, such as 24 hour ambulatory monitoring, echocardiography, nucleotide angiography and coronary angiography. It has a limited positive predictive value, but has an excellent negative predictive value. The optimum time to do signal-averaged electrocardiograms after myocardial infarction is unclear, 6 to 14 days after myocardial infarction has the highest sensitivity. Time domain analysis remains the most common method used to record late potentials. The definition of late potential and the scoring of a high resolution electrocardiogram as normal and abnormal have not yet been resolved. The criteria proposed by the Task Force Committee of the European Society of Cardiology, the American Heart Association and the American College of Cardiology (see introduction) should be observed at present. Many studies on signal-averaging were done in the prethrombolytic era. In patients who have received thrombolytic therapy, the positive predictive value of signal-averaged electrocardiograms has decreased. There are other limitations in applying signal averaging technique. The faster the ventricular tachycardia is induced in electrophysiological studies, the shorter is the late potential. Thus, a faster tachycardia which causes sudden cardiac death may not be detected by late potentials. The management strategies for patients who have abnormal signal-averaged electrocardiograms after myocardial infarction have not be defined. One should note that any management strategy has to prove that it improves prognosis. More prospective, randomized clinical trials are required to address these issues.     

Myocardial color scan with 43K in ischemic heart disease

The value of myocardial scanning with 43K was assessed in 64 consecutive patients undergoing coronary arteriography, and in five young volunteers. Myocardial scans at rest detected only 16 of the 35 transmural infarcts documented on electrocardiograms, 11 of 11 anterior infarcts and five of 24 in other sites. Myocardial scans were obtained immediately after a graded exercise test in the five normal volunteers, in nine patients with normal coronary arteriograms and in 25 patients with atherosclerotic narrowing greater than 75% involving the left anterior descending artery, with or without disease of other coronary vessels. All patients with normal coronary arteriograms had normal myocardial scans. A regional perfusion deficit was observed after exercise in all six patients with single vessel disease, but in only 11 of the 19 patients with disease involving two or three vessels. Although the technique was specific, it lacked sensitivity, due mostly to poor resolution and the location of the disease.