Spontaneous variability in the frequency of ventricular premature complexes over prolonged intervals and implications for antiarrhythmic treatment

Screening for dilated cardiomyopathy in dogs

BACKGROUND

Dilated cardiomyopathy (DCM) is the most common cardiac disease in large breed dogs. The disease can start with arrhythmias or with systolic dysfunction of the myocardium.

OBJECTIVE

To describe screening methods for DCM in various breeds and provide a new, modified staging system.

RECOMMENDATIONS

Screening for occult DCM should start at three years of age and use Holter monitoring in Boxers and Dobermans and might be useful also in other breeds. Single ventricular premature complexes (VPCs) can be detected in many healthy dogs, but healthy animals typically have <50 VPCs in 24 h and demonstrate minimal complexity most often occurring only as single ectopic beats. In general, >100 VPCs in 24 h was recommended as the cut-off value for establishing a diagnosis of DCM. However, there are breed-specific recommendations related to Holter recording diagnosis of DCM in Dobermans and Boxers. Yearly screening over the life of a dog is recommended, as a one-time screening is not sufficient to rule out the future development of DCM. Several echocardiographic methods such as M-mode derived measurements, the measurement of the left ventricular (LV) volume by Simpson's method of discs (SMOD), and E-point to septal separation (EPSS) are recommended for screening purposes. The value of additional tests such as cardiac biomarkers (troponin I and N-terminal pro-B-type natriuretic peptide) as well as a 5-min resting electrocardiogram (ECG) or newer echocardiographic methods such as strain measurements is discussed.

CONCLUSION

This review suggests some guidelines for screening for DCM in various breeds.

Heart rhythm during episodes of collapse in boxers with frequent or complex ventricular ectopy

OBJECTIVES

To describe heart rhythm during collapse events in boxer dogs using ambulatory electrocardiogram and determine the predictive value of frequent or complex ventricular ectopy for collapse associated with ventricular tachycardia.

MATERIALS AND METHODS

A total of 659 ambulatory electrocardiogram recordings from 429 boxer dogs were identified from a database in the UK. Summary statistics described the frequency and complexity of ventricular ectopy during all recordings, recordings in which collapse occurred and associated boxer demographics. Positive predictive values were calculated to investigate whether frequent ventricular ectopy was useful to predict heart rhythm during episodes of collapse.

RESULTS

Of the 659 ambulatory electrocardiogram recordings, 250 recordings showed <50 single ventricular beats (Group 1), and frequent (≥50) or complex ventricular ectopy were observed in 409 recordings (Group 2). A total of 90 collapse events were observed in 72 ambulatory electrocardiograms from 68 dogs, comprising 30 dogs in Group 1 and 38 dogs in Group 2. In both groups, sinus rhythm was the most frequent collapse rhythm, followed by neurally mediated collapse and then ventricular tachycardia. The proportion of dogs that displayed ventricular tachycardia-associated episodic collapse given that they had frequent (≥50) or complex ventricular ectopy in the study population was 0.11 [95% confidence interval = 0.01 to 0.21].

CLINICAL SIGNIFICANCE

These results challenge the preconception that UK boxer dogs with collapse will have ventricular tachycardia and, consequently, the authors recommend definitive diagnosis of the cause of episodic collapse to guide selection of therapeutic drugs.

Comparison of single- versus seven-day Holter analysis for the identification of dilated cardiomyopathy predictive criteria in apparently healthy Doberman Pinscher dogs

INTRODUCTION

The primary objective of this study was to test whether seven-day Holter recording improves the sensitivity of detecting dilated cardiomyopathy (DCM) predictive criteria (DCM_p) compared with 24-h Holter recording in asymptomatic Doberman Pinscher (DP) dogs.

ANIMALS

Twenty-eight asymptomatic DP dogs with normal echocardiographic examinations.

METHODS

Dogs with normal echocardiographic examinations underwent seven-day Holter monitoring. The presence of ≥50 ventricular premature complexes and or ≥ one couplet/one triplet/one episode of ventricular tachycardia per 24-h period was considered positive for DCM_p.

RESULTS

Five dogs were positive on the first day, and an additional six dogs tested positive from day two to seven of the Holter recording. The number of dogs positive for DCM_p detected by four days was significantly different (p = 0.031) compared with the first-day Holter recording.

CONCLUSIONS

Seven-day Holter recording detected significantly more dogs with DCM_p compared with the first-day Holter recording. Follow-up studies are warranted to evaluate the long-term accuracy of multiple-day Holter analysis in predicting the development of DCM in DP dogs.

Ventricular arrhythmias in the Chagas disease are not random phenomena: Long-term monitoring in Chagas arrhythmias

BACKGROUND

Variability of ventricular arrhythmias among days in patients with Chagas disease is not detected by 24 hours of Holter monitoring.

OBJECTIVE

To analyze whether ventricular arrhythmias are a random phenomenon or have a reproducible behavior in patients with Chagas cardiomyopathy.

METHOD

Holter monitoring was recorded in 16 subjects with a mean age of 52 ± 8 years. They were clinically stable and had ventricular couplets, isolated premature ventricular contractions (PVCs), and nonsustained ventricular tachycardia (NSVT). The recordings occurred for 7 days. Hurst exponent (HE) evaluated randomness and predictability index (PI) and repeated analysis of variance (ANOVA) assessed reproducibility.

RESULTS

The HE was significantly greater than 0.5 in all 16 patients, which confirms the nonrandomness of arrhythmias in this Chagas sample. The PI for ventricular couplets and isolated PVCs was, on average, 38% and 54%, respectively. ANOVA with repeated measurement showed significant differences in the daily frequency of ventricular couplets (n = 15, P ≤ .05), isolated PVC (n = 12, P ≤ .05), and NSVT (n = 7, P ≤ .05).

CONCLUSION

Ventricular arrhythmias in Chagas cardiomyopathy are not random. Dissimilarities in arrhythmias frequency make unlikely that 24 hours of Holter recording can capture this variability.

Outcomes of untreated frequent premature ventricular complexes with normal left ventricular function

Objective

The natural history of frequent premature ventricular complexes (PVCs) in association with preserved left ventricular ejection fraction (LVEF) is uncertain. The optimal management of this population is thus undefined. We studied the outcomes of untreated patients with frequent PVCs and preserved LVEF.

Methods

This cohort study prospectively evaluated consecutive patients from 2012 to 2017, with asymptomatic or minimally symptomatic frequent idiopathic PVCs (≥5% PVCs in 24 hours; normal LVEF; no cause identified on comprehensive evaluation). No suppressive therapy (ablation or antiarrhythmic drugs) were used and patients were followed with serial ambulatory ECG monitoring and echocardiography. The primary arrhythmic outcome was reduction in PVC burden to <1% on serial ambulatory monitoring. The primary echocardiographic outcome was a reduction of LVEF to <50%.

Results

One hundred patients met inclusion criteria (mean age 51.8 years, 57% female) with a median PVC burden of 18.4%. Reduction to <1% PVCs occurred in 44 of 100 patients (44.0%) at a median of 15.4 months (range 2.6 to 64.3). Recurrence was uncommon (4/44, 9.1%). Four patients (4.3%) with a persistently elevated PVC burden developed left ventricular dysfunction (LVEF <50%) during the follow-up period at a range of 53–71 months. The initial PVC burden did not predict subsequent resolution (HR 1.00(0.97, 1.03); p=0.86).

Conclusions

A strategy of active surveillance is appropriate for the majority of patients with frequent idiopathic PVCs in association with preserved LVEF, owing to the low risk of developing left ventricular systolic dysfunction and the high rate of spontaneous resolution.

Prognostic significance of frequent premature ventricular complex early after implantation among patients with implantable cardioverter defibrillator

BACKGROUND

Premature ventricular complex (PVC) was mainly studied by 24-hour Holter in previous studies. However, the value of long-term Home Monitoring of PVC burden early after ICD implantation is unknown.

METHODS

The data of 416 patients with ICD were analyzed. The percentage of days with frequent PVC (≥10/h) within 30th-90th days was calculated as the continuous frequent PVC (CfPVC) percentage. ROC curve of CfPVC percentages was plotted. Kaplan-Meier survival and Cox regression were used to assess the cumulative risks.

RESULTS

Based on ROC curves, the cut-off value for the CfPVC percentage was 40%. According to Kaplan-Meier analysis and multivariate Cox regression analysis, CfPVC percentage ≥40% was an independent predictor of higher incidences of VAEs, appropriate ATP, appropriate shocks, and cardiac death.

CONCLUSION

A long-term continuous burden of frequent PVC with CfPVC percentage ≥40% can be a predictor of future VAEs, appropriate ATP, appropriate shocks and cardiac death in ICD recipients.

European Society of Veterinary Cardiology screening guidelines for dilated cardiomyopathy in Doberman Pinschers

BACKGROUND

Dilated cardiomyopathy (DCM) is the most common cardiac disease in large breed dogs and is inherited in Doberman Pinschers with a high prevalence (58%).

OBJECTIVE

The European Society for Veterinary Cardiology convened a task force to formulate screening guidelines for DCM in Dobermans.

RECOMMENDATIONS

Screening for occult DCM in Dobermans should start at three years of age and use both Holter monitoring and echocardiography. Yearly screening over the life of the dog is recommended, as a one-time screening is not sufficient to rule out future development of DCM. The preferred echocardiographic method is the measurement of the left ventricular volume by Simpson's method of discs (SMOD). Less than 50 single ventricular premature complexes (VPCs) in 24 h are considered to be normal in Dobermans, although detection of any number of VPCs is cause for concern. Greater than 300 VPCs in 24 h or two subsequent recordings within a year showing between 50 and 300 VPCs in 24 h is considered diagnostic of occult DCM in Dobermans regardless of the concurrent echocardiographic findings. The guidelines also provide recommendations concerning ancillary tests, that are not included in the standard screening protocol, but which may have some utility when recommended tests are not available or financially untenable on an annual basis. These tests include assay of cardiac biomarkers (Troponin I and N-Terminal pro-B-type Natriuretic Peptide) as well as a 5-min resting electrocardiogram (ECG).

CONCLUSION

The current guidelines should help to establish an early diagnosis of DCM in Dobermans.

Slow [Na]i Changes and Positive Feedback Between Membrane Potential and [Ca]i Underlie Intermittent Early Afterdepolarizations and Arrhythmias

BACKGROUND

Most cardiac arrhythmias occur intermittently. As a cellular precursor of lethal cardiac arrhythmias, early afterdepolarizations (EADs) during action potentials(APs) have been extensively investigated, and mechanisms for the occurrence of EADs on a beat-to-beat basis have been proposed. However, no previous study explains slow fluctuations in EADs, which may underlie intermittency of EAD trains and consequent arrhythmias. We hypothesize that the feedback of intracellular calcium and sodium concentrations ([Na](i) and [Ca](i)) that influence membrane voltage (V) can explain EAD intermittency.

METHODS AND RESULTS

AP recordings in rabbit ventricular myocytes revealed intermittent EADs, with slow fluctuations between runs of APs with EADs present or absent. We then used dynamical systems analysis and detailed mathematical models of rabbit ventricular myocytes that replicate the observed behavior and investigated the underlying mechanism. We found that a dominance of inward Na-Ca exchanger current (I(NCX)) over Ca-dependent inactivation of L-type Ca current (I(CaL)) forms a positive feedback between [Ca](i) and V, thus resulting in 2 stable AP states, with and without EADs (ie, bistability). Slow changes in [Na](i) determine the transition between these 2 states, forming a bistable on-off switch of EADs. Tissue simulations showed that this bistable switch of cellular EADs provided both a trigger and a functional substrate for intermittent arrhythmias in homogeneous tissues.

CONCLUSIONS

Our study demonstrates that the interaction among V, [Ca](i), and [Na](i) causes slow on-off switching (or bistability) of AP duration in cardiac myocytes and EAD-mediated arrhythmias and suggests a novel possible mechanism for intermittency of cardiac arrhythmias.

Ventricular arrhythmias are not a short-term reproducible phenomenon--why long recording monitoring is necessary

BACKGROUND

The variability of ventricular arrhythmias (VA) among different days of the week is not well detected by one-day Holter monitoring.

AIMS

To evaluate whether there are differences in VA distribution pattern during long recording period.

METHODS

The EKG was recorded for 14 h per day during 7 days by Holter system in 34 consecutive pat ventricular couplets and non-sustained ventricular tachycardia (NSVT) recording from patients provided graphic data. We applied the Hurst method (H Coefficient) which evaluates whether a repetitive phenomenon is random or not. When the H is >0.5 and <1 means it is not random and implies a long-term memory effect. Considering the arrhythmic variability, the data were also analyzed by repetitive ANOVA comparing incidence of arrhythmias among the days.

RESULTS

Isolated PVCs and ventricular couplets during 98 h recording provided graphic of the occurrence. A trend of increasing and decreasing of arrhythmias was observed which looks erratic. The H coefficient, however, was significantly >0.5 for all patients. Repeated ANOVA showed statistic difference among days in 31 patients with isolated PVCs; in 26 with ventricular couplets and 19 with NSVT when analyzed per hour during week days (p < 0.05).

CONCLUSION

PVCs, ventricular couplets and NSVT are not a random phenomenon. Our data suggest the occurrence of ventricular arrhythmias had no similarity among the days, making unlikely that a single Holter recording for 24h may capture this phenomenon.

Which factors predict the behavior of ventricular extrasystoles in athletes over time?

Spontaneous behavior of ventricular extrasystoles (VE) was analysed. From a database containing 578 athletes with VE, 84 males and 11 females (29.9 ± 18.1 years) having ≥ 100 VE or repetitive VE [ventricular couplets (VC) or ventricular tachycardias (VT)] at first 24-hour Holter electrocardiographic monitoring (24-h-HM) (baseline) and at least 1-year of follow-up (3.1 ± 2.2 years) over the past 10 years were selected. The baseline was compared with the last 24-h-HM to establish DVE (VE reduction of at least 98%/24 h in the absence of VC or VT). SDVE was calculated as standard deviation of the number of VE on serial 24-h-HMs. DVE and SDVE were considered as dependent variables. Independent variables were: age, sex, type of sport, symptoms, baseline VE rate (BVE), baseline VC and VT, VE morphology, VE behavior during the baseline training session, disqualification from competitive sports, echocardiographic abnormalities. DVE occurred in 32 athletes (34%). SDVE varied from 0 to 12,658 VE/24 h (1916 ± 2649.9). Disappearance of VE during the baseline training session (DVET) correlated to DVE (P = 0.0319). BVE directly correlated to SDVE (P = 0.0008). Athletes' VE are highly variable over time, their variability depending on BVE, and they not infrequently tend to disappear. The only useful variable for predicting DVE is DVET.

Evaluation of ventricular arrhythmias in early clinical pharmacology trials and potential consequences for later development

This white paper, prepared by members of the Cardiac Safety Research Consortium, discusses several important issues regarding the evaluation of ventricular arrhythmias in early clinical pharmacology trials and their potential consequences for later clinical drug development. Ventricular arrhythmias are infrequent but potentially important medical events whose occurrence in early clinical pharmacology trials can dramatically increase safety concerns. Given the increasing concern with all potential safety signals and the resultant more extensive electrocardiographic monitoring of subjects participating in early phase trials, an important question must be addressed: Are relatively more frequent observations of ventricular arrhythmias related simply to more extensive monitoring, or are they genuinely related to the drug under development? The discussions in this paper provide current thinking and suggestions for addressing this question.

Evaluation of spontaneous variability in the frequency of ventricular arrhythmias in Boxers with arrhythmogenic right ventricular cardiomyopathy

OBJECTIVE

To evaluate spontaneous variability in the frequency of ventricular arrhythmias and assess the influence of day of ECG recording and day of week on arrhythmia frequency in Boxers affected with arrhythmogenic right ventricular cardiomyopathy (ARVC).

DESIGN

Prospective study.

ANIMALS

10 Boxers with ARVC with prior ambulatory ECG recordings that included > or = 500 ventricular premature complexes/24 h.

PROCEDURE

Consecutive 24-hour ambulatory ECG recordings were obtained during a 7-day period in each dog. The number of ventricular premature complexes and grade of the arrhythmia were obtained from each recording. For each dog, the number of ventricular premature complexes for each recording was evaluated to identify any differences relative to the day of recording (recording 1 to 7) and day of the week (Monday through Sunday).

RESULTS

Spontaneous variability accounted for as much as 80% of the change in frequency of ventricular premature complexes in dogs with frequent arrhythmias; this value was almost 100% in dogs with less frequent arrhythmias. Grade of arrhythmia was less variable but was also inversely related to frequency of arrhythmia. No significant differences in frequency values were identified among days of recording or among days of the week.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes of < or = 80% in the frequency of ventricular arrhythmias may be within the limit of spontaneous variability in dogs with ARVC. This degree of variability should be considered in evaluations of ambulatory ECG recordings, particularly in the assessment of the efficacy of antiarrhythmic drugs.

Comparison of the effects of four antiarrhythmic treatments for familial ventricular arrhythmias in Boxers

OBJECTIVE

To evaluate the effect of 4 antiarrhythmic treatment protocols on number of ventricular premature complexes (VPC), severity of arrhythmia, heart rate (HR), and number of syncopal episodes in Boxers with ventricular tachyarrhythmias.

DESIGN

Randomized controlled clinical trial.

ANIMALS

49 Boxers.

PROCEDURE

Dogs with > 500 VPC/24 h via 24-hour ambulatory ECG (AECG) were treated with atenolol (n = 11), procainamide (11), sotalol (16), or mexiletine and atenolol (11) for 21 to 28 days. Results of pre- and posttreatment AECG were compared with regard to number of VPC/24 h; maximum, mean, and minimum HR; severity of arrhythmia; and occurrence of syncope.

RESULTS

Significant differences between pre- and posttreatment number of VPC, severity of arrhythmia, HR variables, or occurrence of syncope were not observed in dogs treated with atenolol or procainamide. Significant reductions in number of VPC, severity of arrythmia, and maximum and mean HR were observed in dogs treated with mexiletine-atenolol or sotalol; occurrence of syncope was not significantly different between these 2 treatment groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment with sotalol or mexiletine-atenolol was well tolerated and efficacious. Treatment with procainamide or atenolol was not effective.

Pharmacokinetics of pirmenol enantiomers and pharmacodynamics of pirmenol racemate in patients with premature ventricular contractions

The pharmacokinetics and pharmacodynamics of pirmenol were investigated in 12 patients with premature ventricular contractions (PVCs) after oral administration of racemic pirmenol, 100 mg and 200 mg every 12 hours. Holter monitoring was performed and serial blood samples were collected after the seventh doses. Plasma concentrations of pirmenol enantiomer were determined using a stereospecific liquid chromatographic assay. Clearance of total (-)-pirmenol was 20% higher than that of total (+)-pirmenol, and the difference in unbound clearance was 45% between enantiomers. Total pirmenol showed a smaller difference because of stereoselective protein binding, with 25% (100-mg dose) or 27% (200-mg dose) higher fraction unbound for (+)-pirmenol than for (-)-pirmenol. Distribution volume was similar for both enantiomers. Dose-dependent clearance was observed for unbound pirmenol enantiomers, as both enantiomers showed 20% lower unbound clearance at the higher dose. Antiarrhythmic effect (% reduction in PVCs from baseline) was correlated with plasma concentrations of pirmenol using a sigmoid maximum drug effect model, and patients showed a large variability in their antiarrhythmic response to plasma concentrations of pirmenol. The median value for minimum effective plasma concentration of racemic pirmenol was 1.5 micrograms/mL.

Long-term temporal patterns of ventricular tachyarrhythmias

BACKGROUND

Technological limitations have precluded investigation of long-term temporal patterns of ventricular tachyarrhythmia recurrences. Newer implantable cardioverter-defibrillators permit such analyses by accurately recording the time and date of tachycardia detections during long-term follow-up. This study tests the hypothesis that ventricular tachycardia occurrences are randomly distributed over time in individual patients.

METHODS AND RESULTS

The time and date of 727 episodes of ventricular tachyarrhythmias were recorded from the data logs of 31 patients with implantable cardioverter-defibrillators followed for a median of 177 days (range, 7 to 782 days). All patients had three or more ventricular tachycardia detections and no detections from causes other than ventricular arrhythmias. In 28 of 31 patients, the distribution of the interdetection time intervals during follow-up differed significantly (all P < .01) from an exponential model distribution of interdetection intervals that assumed that detections were equally likely to occur at any time during follow-up (random). The Kolmogorov-Smirnov goodness-of-fit test was used to compare sample and model distributions. In each patient, the nonrandom distributions resulted from a preponderance of interdetection time intervals that were shorter than predicted by the random model, resulting in a temporal clustering of arrhythmic events. The interdetection interval was < or = 1 hour and < or = 91 hours for 55% and 78% of all intervals, respectively. When only those episodes receiving shock or antitachycardia pacing therapy were analyzed, 25 of 29 patients still manifested nonrandom distributions (all P < .01). When only episodes with tachycardia rates > 240 beats per minute were analyzed, 11 of 13 patients manifested non-random distributions (all P < .01).

CONCLUSIONS

Ventricular tachycardia detections and delivered antitachycardia therapies by implantable cardioverter-defibrillators are nonrandomly distributed throughout long-term follow-up in the majority of patients. The temporal clustering of these arrhythmic events may allow preemptive antiarrhythmic therapy and should be considered in the design of therapy based on suppression of spontaneous ventricular arrhythmias to statistically derived end points.

Usefulness of Holter monitoring in predicting efficacy of amiodarone therapy for sustained ventricular tachycardia associated with coronary artery disease

The ability of Holter monitoring to predict clinical events during amiodarone therapy was evaluated in 83 patients with coronary artery disease and inducible monomorphic ventricular tachycardia. Sixty-four patients (77%) had significant ventricular ectopy activity (> or = 10 ventricular premature complexes [VPCs]/hour) at baseline, and 19 (23%) did not; patients were similar in age (63 and 65 years, respectively; p = 0.24) and ejection fraction (31 and 32%, respectively; p = 0.75). Over a mean of 23 +/- 17 months, there was no difference in arrhythmia recurrence (33 and 26%; p = 0.89) or sudden death (16 and 20%; p = 0.94) in patients with and without significant ectopy, respectively. In patients with significant ectopy, amiodarone decreased VPC frequency from baseline to 2 weeks, but not from 2 to 6 weeks. Forty-two patients had > 85% reduction in ectopy at 2 weeks; 20 patients did not. However, this reduction of simple VPCs did not predict a decrease in arrhythmic recurrence (29 vs 40%; p = 0.59) nor sudden death (25 vs 11%; p = 0.56) in patients with and without VPC suppression, respectively. Forty-five patients had Holter monitoring at 6 weeks. Twenty-one patients (47%) had > 95% suppression of ectopy, and 24 did not. Neither the recurrence (38 vs 38%; p = 0.54) nor sudden death (33 vs 13%; p = 0.45) rate was predicted by the degree of VPC suppression. Amiodarone is a powerful suppressant of VPCs, but Holter suppression of this ectopic activity is not predictive of clinical outcome.

Variation in late potentials and the reproducibility of their measurement

The usefulness of a test depends on its reproducibility. This determines how closely the test result indicates the actual pathophysiologic state, how well it will predict that state in the future, and if interventions or further pathologic changes are reflected by the test. There is a variation in the parameters of the signal-averaged ECG, more so with spectral than with time domain measurements. These must be accounted for when estimating risk. If one presumes that risk is proportional to the extent of abnormality, then the variation in measurements simply means that only borderline cases can potentially be miscategorized. More important, the lack of reproducibility of measurements made from the signal-averaged ECG indicates that changes noted in an individual after an intervention, such as a surgical intervention, must be viewed with a jaundiced eye. Group changes are perhaps meaningful, and indicate a physiologic effect, but clinical decisions cannot be made unless the changes observed in an individual patient exceed the confidence limits of expected variation. There has been debate as to the usefulness of measurements made from the signal-averaged ECG in predicting antiarrhythmic drug effects (the effect of drugs is discussed elsewhere in this symposium). Here an analogy must be made to the suppression of asymptomatic ventricular ectopy. First, we cannot make a statement that there has been a drug effect unless the parameter measured changes beyond the confidence limits of normal variation or reproducibility. Second, we cannot translate a change in a measurement into a change in risk for arrhythmic events without subjecting that hypothesized relationship to a long-term placebo-controlled clinical trial, albeit acute electrophysiologic trials correlating changes in the signal-averaged ECG to ventricular tachycardia induction provide some insight. And perhaps the relationship must be tested independently for each drug assessed. In the same regard, there is much excitement about the benefits of thrombolytic therapy, but when diagnosing benefit to the individual patient we have to remember the lack of reproducibility of the measurements and also keep in mind that an improved signal-averaged ECG cannot be translated into an improved prognosis without long-term controlled studies. In summarizing the variation and reproducibility of measurements made from the signal-averaged ECG we avoided providing more than a sense of the extent of variation expected because precise confidence intervals depend on the particular techniques used to make the measurements.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of premature ventricular counts in long term ECG following myocardial infarction

Frequent and recurrent ventricular premature beats (VPB's) are considered to be associated with a higher risk of sudden cardiac death, particularly for survivors of myocardial infarction (MI). The distribution of VPB's has a large probability mass at zero, and a very heavy right hand tail. In this research, we fitted a model to VPB for patients for which VPB was present. The model was fitted on the basis of a relatively large data set on MI survivors in Israel. The model was fitted by a method which is based on the generalized linear model. This method, which was introduced by Zeger and Liang, is designed for longitudinal data and uses the quasi-likelihood concept. No specific assumptions are required on the shape of the distribution of the dependent variable. The results indicate that the model fits the data quite well but underestimates the very extreme high values. This research demonstrates the applicability of generalized linear models for longitudinal non-Gaussian data. Such data often arise in medical studies. The study also points out the distributional properties of VPB counts. In particular, it shows their associations with simple clinical and epidemiological variables, and with certain time periods during the day.

Reproducibility of the signal-averaged electrocardiogram

Variation in measurements made from signal-averaged electrocardiograms was examined. Averaging 200 beats in 18 normal subjects, pairs of high-frequency QRS and low-amplitude signal durations correlated at immediate, short-term, and long-term intervals. The percent high-frequency (60 Hz to 120 Hz) voltages in the late potential region had modest correlations. However, 95% confidence intervals of differences in paired measurements were as much as 7% for high-frequency QRS, 20% for a low-amplitude signal, and 53% for percent high-frequency, similar at all time intervals. With electrocardiograms averaged to 0.3 microV noise, high-frequency QRS and low-amplitude signals prolonged, but variation was similar to that of 200 beat pairs. In contrast, low noise reduced percent high-frequency and lessened variation to 29%. Therefore variation in signal-averaged electrocardiographic measurements was considerable (high-frequency voltage greater than durations). Noise did not appreciably influence variation in durations but was critical to consistent voltage measurements in the frequency domain.

Spontaneous variability of ventricular arrhythmias in patients with chronic heart failure

Spontaneous variability of ventricular arrhythmia in patients with chronic heart failure is not well described. We measured this variability in 23 consecutive patients with chronic heart failure who were prospectively enrolled in the placebo limb of a trial concerned with treatment of heart failure. Patients underwent from one to three periods of ambulatory monitoring separated by 1 to 3 months while they were not receiving antiarrhythmic drug treatment. The variability in frequency of premature ventricular complexes (PVCs) was determined at interrecording intervals of 1, 2, and 3 months. The percentage reductions in total PVCs required to exceed the 95% confidence limits of spontaneous variability at these intervals were 91%, 90%, and 97%, respectively. Corresponding values for repetitive beats (beats in couplets and beats in ventricular tachycardia events) were 98%, 80%, and 97% and for ventricular tachycardia events 98%, 83%, and 98%, respectively. The percentage increases in total PVCs, repetitive beats, and ventricular tachycardia events required to identify aggravation of arrhythmia in this study population were 1301%, 4050%, and 6147%, respectively, at 1-month intervals and 2950%, 2868%, and 5938%, respectively, at 3-month intervals. The percentage reductions required to show a true drug effect at 2- and 3-month intervals were 63% and 84% for patients with an ejection fraction less than 0.22 and 89% and 98% for those with an ejection fraction greater than or equal to 0.22 (p less than 0.05 for both). Ventricular arrhythmia would have been missed in 6 (26%) of the 23 patients if only one screening ambulatory recording was available. Thus marked variability in PVCs occurs in patients with chronic heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-myocardial infarction mortality in patients with ventricular premature depolarizations. Canadian Amiodarone Myocardial Infarction Arrhythmia Trial Pilot Study

BACKGROUND

Among survivors of acute myocardial infarction, frequent and repetitive ventricular premature depolarizations (VPDs) detected on ambulatory monitoring contribute independently to the risk of all-cause mortality and sudden death. Apart from the beta-blockers, no antiarrhythmic drug has been reliably demonstrated to reduce mortality among patients with VPDs. A pilot study was undertaken to gather data to aid in the design of a multicenter trial of amiodarone for the reduction of mortality from cardiac arrhythmias in such patients.

METHODS AND RESULTS

Seventy-seven patients with acute myocardial infarction within the previous 6-30 days and 10 or more VPDs/hr or one or more runs of ventricular tachycardia on 24-hour electrocardiographic recording were randomized in a double-blind fashion in a 2:1 amiodarone-to-placebo ratio. The loading dose was 10 mg/kg/day for 3 weeks. The maintenance dose was 300-400 mg/day with reductions at 4-month intervals in response to VPD suppression, excessive plasma levels, or toxicity. VPD suppression at 1 week and 2 weeks was 63% and 85%, respectively, on amiodarone and 17% and 27%, respectively, on placebo. Apart from thyroid-stimulating hormone elevation and skin reactions, no side effects occurred more frequently with amiodarone. The study drug was stopped for side effects or noncompliance in 35% of amiodarone patients and 34% of placebo patients. Patients were followed for a maximum of 2 years (mean, 20 months). Arrhythmic death or resuscitated ventricular fibrillation occurred in two of 48 amiodarone patients (6%) and four of 29 placebo patients (14%), whereas the rates of all-cause mortality were five of 48 (10%) and six of 29 (21%), respectively.

CONCLUSIONS

Amiodarone, in moderate loading and maintenance dosages with adjustments in response to plasma levels, VPD suppression, and side effects, results in effective VPD suppression and acceptable levels of toxicity.

Evaluation of antiarrhythmic drug effects with simultaneous analysis of single ventricular premature contractions, couplets and salvos

To improve the clinical value of ambulatory Holter electrocardiographic (ECG) monitoring as a tool of antiarrhythmic therapy control, a new statistical model was developed. In a patient group at increased risk of sudden cardiac death, the spontaneous variability of ventricular arrhythmias was assessed, with simultaneous consideration of single ventricular premature complexes, couplets and salvos. The study included 100 patients who suffered from coronary heart disease or idiopathic dilated cardiomyopathy and for whom greater than 30 ventricular premature complexes/h and couplets had been demonstrated on the last Holter ECG before the study. Between 3 and 12 Holter recordings were made for each patient in a drug-free state; the mean follow-up period was 260 days (maximum 1,403). The mean hourly values of the ectopic events (EE) were assessed separately for ventricular premature complexes, couplets and salvos. The spontaneous variability (SV) was calculated for single ventricular premature complexes, couplets and salvos as SV = log (EEday 2 + 0.01/EEday 1 + 0.01) and linked in one, two and three dimensions. Compared with the consideration of only one type of arrhythmia (one-dimensional model), the simultaneous use of two or three types of arrhythmia (two- or three-dimensional model) resulted in considerably lower reduction and aggravation rates as sufficient proof of drug effects. With control intervals up to 1 week, the one-dimensional model yielded reduction rates for ventricular premature complexes, couplets and salvos of -63%, -90% and -95%, respectively. In contrast, with the three-dimensional model, the rates were -28%, -72% and -88%. The corresponding aggravation values were +370, +1,114% and +2,189% versus +38%, +256% and +747%.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous variability in ventricular ectopic activity during chronic antiarrhythmic therapy

Previous determinations of variability in frequency of ventricular arrhythmias have been based on repeated recordings obtained in the absence of therapy. We evaluate variability during "effective" treatment with antiarrhythmic drugs. Variability in the percent suppression of premature ventricular complexes (PVCs) was determined in 55 patients with chronic arrhythmias who underwent multiple ambulatory electrocardiographic recordings during evaluation of chronic therapy with antiarrhythmic drugs initially determined to be effective, which was defined as 70% or more reduction in total PVC frequency or 90% or more reduction in repetitive forms. During chronic therapy, total PVCs were suppressed by 92%, averaged after a logarithmic transformation step, and repetitive beats were suppressed by 88%. Variability in suppression was substantial. The one-sided 95% confidence intervals required a fall in suppression of total PVCs to 40% or less to exceed limits of spontaneous variability and of repetitive PVCs to 66% or less. Suppression declined at least once during therapy to less than 60% for total PVCs in 24 of 55 patients (44%) and to less than 80% for repetitive PVCs in 13 of 33 patients (39%); nine patients (16%) showed increases in PVC frequency at least once to levels above pretreatment baseline. Seven subgroups were analyzed for their effects on variability and loss of suppression: age, gender, disease etiology, cardiac function, baseline PVC frequency, use of beta-blockers, and class of antiarrhythmic drug. Differences in confidence bounds and loss of suppression were found to be determined in a complex way by subgroup differences in variability and in initial levels of PVC suppression. Variability was greater for patient subgroups with greater PVC frequency, beta-blocker therapy, and non-coronary artery disease. However, clinical loss of suppression was more common only in more elderly patients and those with worse cardiac function. In summary, substantial variability in arrhythmia frequency occurs during effective antiarrhythmic therapy, and the 95% confidence limits of spontaneous variability are broad and determined in a complex way. Careful consideration should be given before concluding on the basis of a single Holter test that changes (increases) in arrhythmia frequency, especially in certain subgroups, are caused by treatment failure.

Efficacy of oral mexiletine therapy at a 12-h dosage interval

The antiarrhythmic effectiveness and safety of 12-h oral administration of mexiletine were evaluated in adult outpatients with a baseline hourly rate of PVCs of 30 or higher who had initially shown at least a 50 percent reduction of this rate when treated with mexiletine at an 8-h dosage interval. Doses were titrated on the basis of 24-h Holter monitoring for both 8- and 12-h intervals. Seventeen of 26 patients showed PVC reductions after 8-h treatment. Fifteen of these 17 patients reached the goal reduction of greater than or equal to 50 percent in the hourly PCV rate with 12-h dosing. Hour-by-hour analysis disclosed a consistent degree of PVC suppression throughout both 8- and 12-h dose intervals. No increase in the incidence of adverse effects was associated with conversion to the 12-h regimen.

Natural history of potentially lethal ventricular arrhythmias in patients treated with long-term antiarrhythmic drug therapy

To examine the natural history of long-term anti-arrhythmic therapy in patients with benign and potentially lethal ventricular premature complexes (VPCs), 28 patients with initial efficacy with moricizine (greater than 75% suppression of baseline mean VPCs/hr and greater than 90% suppression of repetitive VPCs) were prospectively followed for 1 to 56 (mean +/- standard deviation 25 +/- 17) months. Patients were examined during baseline placebo, anti-arrhythmic drug therapy and intermittent pulsed-placebo reexamination periods. The mean VPCs of all patients at baseline entry were 233 +/- 47 VPCs/hr, and after moricizine therapy 14 +/- 4 VPCs/hr. Follow-up demonstrated that antiarrhythmic efficacy decreased to 75% at 12 months and to 62% at 24 months. Loss of antiarrhythmic drug efficacy most commonly occurred as a "transient" event (10 patients [36%]), and efficacy was spontaneously reestablished without a change in antiarrhythmic therapy. In contrast, increased dose titration of moricizine was necessary to reestablish antiarrhythmic suppression efficacy in 4 patients (14%), and 4 patients (14%) lost antiarrhythmic drug responsiveness during follow-up. Spontaneous decrease in baseline VPCs resulted in discontinuation of antiarrhythmic therapy in 3 patients, and increase in baseline VPCs was associated with a loss of antiarrhythmic response in 2 patients. Late proarrhythmic effects (2 patients, 7%), delayed side effects necessitating drug withdrawal (6 patients, 21%) and medical events (4 patients, 14%) occurred during 56 months of follow-up. Individual serum moricizine levels remained in the therapeutic range throughout the study and did not correlate with changes in antiarrhythmic efficacy.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous variability and circadian distribution of ectopic activity in patients with malignant ventricular arrhythmia

Day to day variability of ventricular ectopic activity was analyzed in 45 patients with a history of malignant ventricular tachyarrhythmias who underwent two successive 24 h periods of ambulatory electrocardiographic (ECG) monitoring in the absence of antiarrhythmic drugs; 26 were male and 19 female, with a mean age of 56 years (range 15 to 76). The total number of single ventricular premature beats, couplets and ventricular tachycardia beats and runs on days 1 and 2 demonstrated a consistent overall correlation (r = 0.76 to 0.84). Individual variability was evaluated by regression analysis with determination of 95% confidence limits. The minimal decrease in arrhythmia density necessary to distinguish true drug effect from spontaneous variability was 64% for single ventricular premature beats, 83% for couplets, 90% for ventricular tachycardia runs and 93% for ventricular tachycardia beats. To meet the criteria for arrhythmia aggravation, the arrhythmia density had to increase by 400, 877, 1,500 and 2,400%, respectively. Multivariate analysis disclosed an inverse relation between day to day arrhythmia variability and baseline arrhythmia density and age. Variability was more pronounced in patients with coronary artery disease but was not influenced by the type of presenting arrhythmia or left ventricular function. The diurnal distribution of arrhythmias and heart rate followed a distinct circadian pattern. These data indicate that, despite good group reproducibility, spontaneous arrhythmia variability in individuals is substantial, necessitating standards to define both drug effect and arrhythmia aggravation.

Spontaneous variability of simple and complex ventricular premature contractions during long time intervals in patients with severe organic heart disease

Calculations of the spontaneous variability of ventricular arrhythmias are usually based upon the results of Holter electrocardiograms recorded either successively or separated by a short time interval. Only recently was it shown that the variability of ventricular premature contractions increases with longer intervals. This study was undertaken to investigate the variability of simple and complex ventricular arrhythmias over long periods to derive efficacy criteria for long-term antiarrhythmic therapy. In a prospective study, the influence of the length of the time interval on spontaneous variability was investigated in 100 patients with coronary artery disease or idiopathic dilated cardiomyopathy and untreated ventricular arrhythmia Lown grade IV. Patient follow-up was carried out for 260 +/- 387 days. In each of the 498 ambulatory Holter tapes, the mean hourly arrhythmia count (AC) of ventricular premature contractions, couplets, and salvos was verified. The variability of arrhythmia counts between two Holter electrocardiograms was defined as the logarithm of the ratio of (ACday 2 + 0.01) to (ACday 1 + 0.01). The 95% intervals for these ratios were calculated as +/- 2 SD, considering the fact that all mean values did not differ significantly from zero. The lower limit of these intervals refers to the reduction that is required for assuming drug efficacy, whereas the upper limit refers to an aggravation. The 95% intervals were calculated for each of four ranges of control intervals (0-6, 7-89, 90-364, and greater than or equal to 365 days). They increased significantly with longer control intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in spontaneous variability of ventricular ectopic activity as a function of time in patients with chronic arrhythmias

Previous determinations of spontaneous variability in ventricular arrhythmia have often been based on measurements from consecutive days in small patient populations, whereas clinical determinations of drug efficacy typically compare measurements at intervals of 1 week and longer to baseline. We, therefore, sought to determine whether spontaneous arrhythmia variability changes as a function of time during periods ranging from 1 day to 1 year or longer. The percent reduction in the frequency of total premature ventricular complexes (PVCs) and repetitive ventricular beats required to show true drug effect rather than spontaneous variability in PVCs was determined in 47 consecutive patients with chronic ventricular arrhythmias who underwent multiple ambulatory monitor recordings while off active drug treatment (during placebo therapy). The variability in PVC rate was determined during the intervals of 1 day, 1 week, 2 weeks, 3 weeks, 4 weeks, and 1 year or longer. The percent reductions in total PVCs required to exceed the 95% confidence limits of spontaneous variability at these intervals were 55%, 85%, 86%, 93%, 96%, and 96%, respectively. Corresponding values for repetitive beats were 75%, 95%, 92%, 95%, 94%, and 98%, respectively. The percent increase in total PVCs and repetitive beats required to establish "arrhythmia aggravation" caused by an antiarrhythmic drug with a 95% confidence limit also was calculated for this study population and was 124% and 303%, respectively, at 1-day intervals and 2,269% and 4,091%, respectively, at 1-year (or longer) intervals for the 24-hour monitor recordings. Variability was not substantially affected by underlying heart disease or ejection fraction. PVC rate showed a modest negative correlation with variability (r = 0.3). Thus, variability is substantially greater at 1 week, the usual time for clinical assessment of antiarrhythmic drug efficacy, than at 1 day (p less than 0.01). Suppression of more than 85% of total PVCs and more than 95% of repetitive beats appears to be necessary after 1-2 weeks to be confident of a true drug effect. Even greater variability is observed after 1 month and up to 1 year so that reductions of up to 95% in total PVCs and 98% in repetitive beats may represent spontaneous change.(ABSTRACT TRUNCATED AT 400 WORDS)