Ambulatory electrocardiography for diagnosis and treatment of cardiac arrhythmias

Pacing for drug-refractory or drug-intolerant hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a genetic disease with an autosomal-dominant inheritance for which negative inotropes are the most widely used initial therapies. Observational studies and small randomised trials have suggested symptomatic and functional benefits using pacing and several theories have been put forward to explain why. Pacing, although not the primary treatment for HCM, could be beneficial to patients with relative or absolute contraindications to surgery or alcohol ablation. Several randomised controlled trials comparing pacing to other therapeutic modalities have been conducted but no Cochrane-style systematic review has been done.

OBJECTIVES

To assess the effects of pacing in drug-refractory or drug-intolerant hypertrophic cardiomyopathy patients.

SEARCH METHODS

We searched the following on the 14/4/2010: CENTRAL (The Cochrane Library 2010, Issue 1), MEDLINE OVID (from 1950 onwards ), EMBASE OVID (from 1980 onwards ), Web of Science with Conference Proceedings (from 1970 onwards). No language restrictions were applied.

SELECTION CRITERIA

Randomised controlled trials of either parallel or crossover design that assess the beneficial and harmful effects of pacing for hypertrophic cardiomyopathy were included. When crossover studies were identified, we considered data only from the first phase.

DATA COLLECTION AND ANALYSIS

Data from included studies were extracted onto a pre-formed data extraction paper by two authors independently. Data was then entered into Review Manager 5.1 for analysis. Risk of bias was assessed using the guidance provided in the Cochrane Handbook. For dichotomous data, relative risk was calculated; and for continuous data, the mean differences were calculated. Where appropriate data were available, meta-analysis was performed. Where meta-analysis was not possible, a narrative synthesis was written. A QUROUM flow chart was provided to show the flow of papers.

MAIN RESULTS

Five studies (reported in 10 papers) were identified. However, three of the five studies provided un-usable data. Thus the data from only two studies (reported in seven papers) with 105 participants were included for this review. There was insufficient data to compare results on all-cause mortality, cost effectiveness, exercise capacity, Quality of life and Peak O2 consumption.When comparing active pacing versus placebo pacing on exercise capacity, one study showed that exercise time decreased from (13.1 ± 4.4) minutes to (12.6 ± 4.3) minutes in the placebo group and increased from (12.1 ± 5.6) minutes to (12.9 ± 4.2) minutes in the treatment group (MD 0.30; 95% CI -1.54 to 2.14). Statistically significant data from the same study showed that left ventricular outflow tract obstruction decreased from (71 ± 32) mm Hg to (52 ± 34) mm Hg in the placebo group and from (70 ± 24) mm Hg to (33 ± 27) mm Hg in the active pacing group (MD -19.00; 95% CI -32.29 to -5.71). This study was also able to show that New York Heart Association (NYHA) functional class decreased from (2.5 ± 0.5) to (2.2 ± 0.6) in the inactive pacing group and decreased from (2.6 ± 0.5) to (1.7 ± 0.7) in the placebo group (MD -0.50; 95% CI -0.78 to -0.22).When comparing active pacing versus trancoronary ablation of septal hypertrophy (TASH), data from one study showed that NYHA functional class decreased from (3.2 ± 0.7) to (1.5 ± 0.5) in the TASH group and decreased from (3.0 ± 0.1) to (1.9 ± 0.6) in the pacemaker group. This study also showed that LV wall thickness remained unchanged in the active pacing group compared to reduction from (22 ± 4) mm to (17 ± 3) mm in the TASH group (MD 0.60; 95% CI -5.65 to 6.85) and that LV outflow tract obstruction decreased from (80 ± 35.5) mm Hg in the TASH group to (49.3 ± 37.7) mm Hg in the pacemaker group.

AUTHORS' CONCLUSIONS

Trials published to date lack information on clinically relevant end-points. Existing data is derived from small trials at high risk of bias, which concentrate on physiological measures. Their results are inconclusive. Further large and high quality trials with more appropriate outcomes are warranted.

The clinical impact of long-term ECG recording. A retrospective study of 150 patients

One-hundred and fifty patients referred for long-term ECG (LECG) recording at a university hospital were monitored for 12 hours or more. The referring physicians' patient records were studied 12 months or more after monitoring in an attempt to establish if and how LECG had affected patient management. Seventeen patients were treated with permanent pacemakers and 13 with antiarrhythmic drugs as a direct result of LECG. Thirteen patients who experienced symptoms with concomitant cardiac arrhythmia at the time of recording were considered not to require treatment. In 17 patients who experienced symptoms without concomitant arrhythmia during monitoring, cardiac arrhythmia could be ruled out as the cause of the symptoms. In 9 more patients, LECG was considered to have contributed "valuable clinical information" (which could not be obtained by other diagnostic methods) to the referring physician. Thus, LECG was considered to have affected the referring physician's management of the patients in 69 cases (46%).

Ambulatory ECG recording in patients referred because of syncope or dizziness

Data are presented on patients referred for ambulatory ECG recording because of syncope or dizziness during a 2-year period. Of the 272 consecutive patients subjected to the recording, 107 (39.3%) had syncope or dizziness as the main indication for referral. Sixteen of these patients (14.9%) experienced the presenting symptom during the recording, and in 8 (50%) of these the simultaneous ECG finding was interpreted as causative. In patients who were symptom-free during the recording, sinus arrests exceeding 2.5 seconds seemed to be a valuable finding to support the cardiac aetiology of the syncopal symptoms, whereas the diagnostic value of second degree AV block with either Wenckebach or Mobitz II like patterns, as such, and of ventricular tachycardia remained mostly unsettled.

Optimum lead positioning for recording bipolar atrial electrocardiograms during sinus rhythm and atrial fibrillation

BACKGROUND

To date, Holter monitoring has been predominantly utilized in the investigation and monitoring of ventricular arrhythmias and myocardial ischemia. Whether currently employed lead configurations are optimal for recording atrial electrocardiograms (ECGs) is unknown.

HYPOTHESIS

This study was undertaken to determine which conventional and novel lead configurations are optimal for recording atrial electrical activity during sinus rhythm and atrial fibrillation.

METHODS

Recordings were performed on eight healthy volunteers in sinus rhythm and four patients in atrial fibrillation. Each subject had 10 ECGs of three bipolar and three augmented unipolar leads recorded during supine rest, while rising to upright, and during standing rest, yielding a total of 60 leads (30 bipolar leads). Each tracing was inspected by two observers, and parameters such as P-wave amplitude and duration, whether the P-wave onset was clearly seen, atrial fibrillatory-wave amplitude, and amplitude of noise during standing were scored.

RESULTS

Leads recording inferiorly and leftward orientated bipoles provided the best registration of sinus P waves. The P-wave amplitude in the standard bipolar C5 lead (0.12 +/- 0.02 mV) was, however, inferior to others such as recordings between C1 and C6 positions (P-wave amplitude 0.16 +/- 0.02 mV) or from below the right clavicle to the left upper quadrant of the abdomen (0.16 +/- 0.01 mV). Optimal recording of fibrillatory waves was from different leads, such as a bipole from below the left clavicle to a low C1 position (fibrillatory wave amplitude 0.27 +/- 0.03 mV).

CONCLUSION

When Holter recordings are performed for the investigation of atrial arrhythmias, nonstandard lead configurations provide superior recording of atrial electrical activity. We advocate the use of electrodes positioned from C1 to C6, from below the left clavicle to a low C1 position, and a vertically orientated lead from the manubium to the twelfth vertebra or the xiphisternum.

Use of ambulatory electrocardiography for the detection of paroxysmal atrial fibrillation in patients with stroke. Canadian Task Force on Preventive Health Care

BACKGROUND

Patients with stroke commonly undergo investigations to determine the underlying cause of stroke. These investigations often include ambulatory electrocardiography to detect paroxysmal atrial fibrillation. There is conflicting evidence in the literature regarding whether routine ambulatory electrocardiography should be performed in all or selected stroke patients. This paper reviews the available evidence on (1) the yield of ambulatory electrocardiography in detecting paroxysmal atrial fibrillation in patients with stroke or transient ischemic attack and (2) the effectiveness of anticoagulation in preventing recurrent stroke in patients with paroxysmal atrial fibrillation.

METHODS

A MEDLINE search for primary articles was performed, and the references were reviewed manually. In addition, citations were obtained from experts. The evidence was systematically reviewed using the evidence-based methodology of the Canadian Task Force on Preventive Health Care.

RESULTS

Ambulatory electrocardiography can detect atrial fibrillation not found on initial electrocardiogram in between 1% and 5% of people with stroke. Ambulatory electrocardiography is generally safe. The risk of recurrent stroke in the setting of paroxysmal atrial fibrillation is uncertain, but appears to be similar to that seen with chronic atrial fibrillation (about 12% per year). Therapy with warfarin may reduce this risk by about two-thirds as compared to placebo. The annual risk of major bleeding with warfarin therapy is between 1% and 3% but rates for individual patients depend on various specific risk factors.

INTERPRETATION

There is insufficient evidence to recommend for or against the use of ambulatory electrocardiography for the detection of paroxysmal atrial fibrillation in either selected or unselected patients with stroke (C Recommendation). There is fair evidence to recommend therapy with warfarin for patients with stroke and paroxysmal atrial fibrillation (B Recommendation).

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.

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)

Are 24 hours of ambulatory ECG monitoring necessary for a patient after infarction?

The Beta-Blocker Heart Attack Trial was a randomized clinical trial of propranolol versus placebo in 3837 patients after myocardial infarction. A 24 hour ambulatory ECG was obtained before therapy in 3290 patients 2 to 21 days after myocardial infarction. Sensitivity, specificity, positive and negative predictive values, and prevalence were calculated for four definitions of ventricular arrhythmia with either total or sudden death (death in less than 1 hour of observed symptoms) as an endpoint. These indexes were obtained using the first 1, 2, 4, 6, 12, and 24 hours plus a random hour, a random daytime hour, and a random nighttime hour of the 24-hour ECG of 1336 placebo patients. For both total death and sudden death, as the duration of monitoring increased, (1) prevalence increased, (2) sensitivity increased, (3) specificity decreased, (4) positive predictive value either changed very little or decreased, and (5) negative predictive value was high (greater than 90%) and increased slightly. None of the 3 random hours offered anything beyond the first hour. The Beta-Blocker Heart Attack Trial data, which were based on an average follow-up of 25 months, show that as the number of hours of ambulatory monitoring increase, the percentages of patients identified at risk or not at risk (the positive and negative predictive values) do not change much. Twenty-four hours of monitoring does not appear to be the optimal time duration for deciding whether to treat arrhythmias in patients after infarction.

The prognostic value of the duration of the ambulatory electrocardiogram after myocardial infarction

The purpose of this study was to examine the value of various durations of ambulatory ECG recording with regard to providing useful prognostic information. The authors explored a decision theoretic approach to determine the most useful period of monitoring for making a treatment decision based upon postulated benefit-to-risk ratios of antiarrhythmic therapies. They used data collected as part of the Beta-Blocker Heart Attack Trial (BHAT), a randomized clinical trial of propranolol versus placebo in 3,837 post-myocardial-infarction patients. In BHAT, 1,336 placebo-treated patients had a 24-hour ambulatory ECG that had at least 23 readable hours. Sensitivity and specificity were calculated for eight definitions of ventricular arrhythmia using either total mortality or sudden death (death within one hour of symptoms) as an endpoint. These indices were obtained using the first 1, 2, 4, 6, 12, and 24 hours plus a random hour, a random daytime hour, and a random nighttime hour of the 24-hour ECG of 1,336 placebo-treated patients. The study showed that in the case of high-risk, low-benefit therapies, no test is needed to make a treatment decision. No one should be treated. In the case of high-benefit, low-risk therapies, again, no test is required. Everyone should be treated. For therapies in the middle benefit-to-risk ratio range the most appropriate test for a treatment decision changes from the very specific to the most sensitive. Twenty-four hours of ambulatory monitoring is usually not necessary for a treatment decision, since four hours is likely to be sufficient.

Utility of ambulatory electrocardiography in detecting pacemaker dysfunction in the early postimplantation period

The value of ambulatory electrocardiography (AECG) in detecting pacemaker dysfunction before hospital discharge was assessed in 100 patients a mean of 1.2 days after pacemaker implantation. The incidence of permanent pacemaker dysfunction detected by AECG in the early postimplantation period, the frequency that pacemaker dysfunction detected by AECG was not detected by telemetric monitoring and the frequency that results of AECG led to pacemaker reprogramming before hospital discharge were determined. AECG detected at least 1 type of pacemaker dysfunction in 35% of patients and routine telemetry identified the abnormality in only 8% (p less than 0.001). Pacemaker dysfunction occurred in 42% of patients with dual-chamber devices and 27% of those with single-chamber devices (difference not significant). In the 35 patients who had pacemaker malfunction, a total of 50 instances of pacemaker dysfunction were detected. Failure of atrial capture occurred in 2% of patients, failure of atrial sensing in 9%, failure of atrial output in 1%, failure of ventricular capture in 8%, failure of ventricular sensing in 14%, failure of ventricular output due to myopotential inhibition in 11% and pacemaker-mediated tachycardia in 5%. The results of the AECG led to a clinical intervention in 22 patients (pacemaker reprogramming in 21 patients and lead repositioning in 1 patient) in whom no pacemaker dysfunction was suspected on the basis of telemetry or clinical symptoms. In conclusion, AECG provides additional benefit beyond that of routine telemetry monitoring in identifying pacemaker dysfunction in the early period after implantation.

Antiarrhythmic efficacy of Ethmozine (moricizine HCl) compared with disopyramide and propranolol

In the investigation of new antiarrhythmic drugs, comparative trials with clinically available antiarrhythmic agents provide a perspective from which to judge the new investigational agent. Two clinical investigations of moricizine HCl, each using a placebo-controlled, double-blind, crossover design, are summarized. In the first study, 18 patients with greater than or equal to 30 ventricular premature complexes (VPCs) per hour (mean 369 +/- 95) were given propranolol (120 mg daily) compared with moricizine HCl (816 +/- 103 mg daily). Propranolol suppressed 38% of VPCs in the study group, moricizine HCl, 81% of VPCs, and the combination of both drugs, 87%. Moricizine HCl was more effective than propranolol in suppressing VPCs at all individual levels greater than 70% (p less than 0.05, McNemar's test). The combination of moricizine HCl and propranolol was well tolerated. The second investigation used a placebo-controlled, double-blind, crossover design to compare the efficacy of disopyramide (600 mg daily) and moricizine HCl (800 mg daily) in 27 patients. Patients had greater than or equal to 40 VPCs/hr on a 24-hour ambulatory electrocardiogram. During moricizine HCl administration, the mean VPC frequency decreased from 524 to 151 VPCs/hr (71.2% reduction). In contrast, disopyramide reduced VPC frequency from 535 to 253 VPCs/hr (52.8% reduction) and demonstrated significantly greater side effects (p less than 0.05). Moricizine HCl was more effective than disopyramide in suppressing VPCs at all individual percent reduction levels greater than 70% (p less than 0.05, McNemar's test). Moricizine HCl was more effective in suppressing VPCs than either disopyramide or propranolol, with significantly fewer side effects.

[Thoracic epidural anesthesia for extracorporeal lithotripsy. Comparison of 4 anesthetic solutions]

Extracorporeal shock-wave lithotripsy (ESWL) is a new non-invasive procedure allowing disintegration of upper urinary tract calculi, usually carried out in epidural anaesthesia (EA). The patient strapped to a stretcher is immersed in a bath. At the bottom of the tube is the shock-wave generator. The release of shock waves (1,000 to 2,000 for each treatment) is triggered by the R-wave of the patient's ECG. Arrhythmias and extrasystoles (ES) may occur. In the investigational trial, the preferred anaesthesia was continuous lumbar EA with a large volume of 2% lidocaine extended to the level of T6. This study was conducted to assess continuous thoracic EA at the T12 interspace with a lesser dose (12 ml) of 2% lidocaine (XT, comparing it with single dose EA with the same volume of three other agents: bupivacaine 0.5% (Ma) and mixtures of 2% lidocaine-0.2+ tetracaine (XT), and 2% lidocaine-fentanyl 50 micrograms (XF), all with 1/200,000th adrenaline. Eighty patients (ASA class I or II) were assigned randomly to receive one of the four types of EA. All were monitored with Holter's method. The demographic distribution was similar for the four groups. Mean duration of the procedure was 32 +/- 15 min. Premedication was given only in 16 patients, very anxious. The results were excellent in 68 patients; 11 had to be supplemented with one or two doses of intravenous agents: diazepam and/or fentanyl: one failure was given an intravenous general anaesthesia. Mild hypotension occurred in four patients. 242 ES occurred in 48 patients (60%).(ABSTRACT TRUNCATED AT 250 WORDS)

Findings on ambulatory electrocardiographic monitoring in subjects older than 80 years

Twenty-four-hour electrocardiograms were recorded in 50 subjects (44 women, 6 men) older than 80 years without cardiovascular disease and with normal standard electrocardiographic responses. During waking and sleeping periods, the mean sinus rates were, respectively, 78 +/- 3 and 64 +/- 1 beats/min; heart rate ranged from 43 to 180 beats/min over 24 hours. Supraventricular tachycardia (SVT) was present in 28% of the subjects. Nocturnal sinus arrhythmia was only noted in 12% of the patients; it was accompanied by sinus pauses of 1.8 to 2 seconds, and 1 woman had a transient pattern compatible with atrioventricular dissociation. Supraventricular ectopic contractions (SVECs) were present in all cases. The frequency was less than 1 per hour in 25% and more than 20 per hour in 65%. Serious supraventricular tachyarrhythmias included an episode of ectopic atrial tachycardia (1 subject), a short run of atrial fibrillation (1 subject) and of flutter (1 subject), and several episodes of supraventricular tachycardia (2 subjects), all accompanied by more than 50 SVECs per hour. The number of ventricular premature contractions (VPCs) exceeded 10 per hour in 32% and were multifocal in 18%. There were couplets in 8% and a run of 6 VPCs in 1 subject (2%). In conclusion, sinus pause and atrioventricular block are unusual in people older than 80 years without apparent heart disease. In contrast, frequent SVECs and VPCs are more common. This study stresses the difficulty of evaluating the normality of the electrocardiogram with portable monitoring in the older population.

The changing base line of complex ventricular arrhythmias. A new consideration in assessing long-term antiarrhythmic drug therapy

Initial base-line electrocardiograms are used to assess the efficacy of treatment for ventricular arrhythmias. This approach assumes that in the absence of treatment the frequency of arrhythmia would remain constant. To test the validity of this assumption, we studied 26 clinically stable patients with symptomatic but not life-threatening ventricular arrhythmias, during two periods of placebo treatment separated by a mean of 17 months. As compared with the initial placebo period, there were significant reductions in ventricular premature depolarizations (50 per cent), pairs (65 per cent), and ventricular tachycardia (83 per cent) during the second period of placebo administration (P less than or equal to 0.05 for all comparisons). Over one third of the patients gave the appearance of receiving successful therapy during the second placebo period, even when the reported spontaneous variability of ventricular arrhythmia was taken into consideration. If unrecognized, these long-term spontaneous changes in the frequency of arrhythmia could result in continuation of unnecessary and potentially toxic therapy and lead to incorrect conclusions regarding the efficacy of antiarrhythmic drugs in clinical trials. We therefore recommend that the frequency of arrhythmia be reassessed annually in the absence of treatment in patients similar to those in our study. These recommendations should not be applied to patients with life-threatening ventricular arrhythmias.

Ventricular arrhythmias in severe heart failure: incidence, significance, and effectiveness of antiarrhythmic therapy

Forty-three patients receiving maximal medical therapy for severe chronic heart failure from dilated cardiomyopathies (28 ischemic, 15 idiopathic) and ventricular premature beats (VPBs) on the 12-lead ECG had baseline 24-hour ambulatory ECG monitoring. Complex VPBs (multiform, repetitive--couplets, R on T phenomenon) and asymptomatic, nonsustained ventricular tachycardia were present in 38 patients (88%) and 22 patients (51%), respectively. Twenty-three patients (group I) were placed on long-term antiarrhythmic therapy (20 patients received procainamide and the remaining quinidine). Twenty patients (group II) did not receive antiarrhythmic therapy. At baseline, no significant differences between the two groups were noted for age, functional class, type of cardiomyopathy, medical therapy for heart failure, cardiothoracic ratio, radionuclide ejection fraction, or rate and complexity of the ventricular arrhythmias on the 24-hour ambulatory ECG tracings. At a mean follow-up period of 16 months (range 1 to 37), there were 16 deaths, 10 (62%) of which were sudden and unexpected. No significant differences in the incidence of sudden death and overall mortality were noted between the two groups. Among patients with nonsustained ventricular tachycardia, those who died suddenly had a lower mean left ventricular ejection fraction (0.15 +/- 0.01) when compared to the survivors (0.23 +/- 0.02; p less than 0.01). It is concluded that patients with severe heart failure have a high mortality from both sudden and nonsudden cardiac death, incidence of complex VPBs is very high, sudden death is more common when the left ventricular function is severely compromised, and apparently, therapeutic plasma levels of conventional antiarrhythmic drugs do not protect this group of patients from dying.

Can cardiac death be predicted from an ambulatory 24-hour ECG?

For the prediction of cardiac death significant prognostic information can be derived from ambulatory 24-hr ECGs when they are recorded on indication in the cardiological outpatient-clinic. In both CHD and non-CHD patients, ventricular arrhythmias, supraventricular arrhythmias and conduction disturbances are all of importance in the assessment of prognosis. These conclusions are based on a review of all 123 cardiac deaths and 433 randomly selected survivors from a cohort of 5095 patients who underwent 24-hr ECG-recording on clinical indication and whose survival status was ascertained 18 months after the recording date.

Computer recognition of cardiac arrhythmias and statistical approaches to arrhythmia analysis

The recognition of marked spontaneous variability in the frequency of ventricular ectopy has required the analysis of various statistical approaches to define appropriate guidelines for determining that a therapeutic agent, rather than spontaneous variability alone, is the cause of an observed reduction in VPC frequency. Analysis of variance or linear regression techniques have been applied to ambulatory ECG data obtained on different patient population groups. When similar patient groups are studied with comparable assumptions, then either of these statistical techniques provides similar guidelines to detect spontaneous variation as the cause of ventricular ectopic reduction. A 75% minimal reduction in VPC frequency should be required when comparing one 24-hour ambulatory monitoring period with another. The impact of spontaneous variability of ventricular ectopy on clinical trial designs is discussed, as is the categorization of various ambulatory ECG monitoring recorders and analysis systems.

Methods for documenting antiarrhythmic efficacy

Methods of documenting the efficacy of antiarrhythmic drugs are controversial because of wide inter- and intrasubject variability of the arrhythmias treated. In patients with symptomatic arrhythmias, clinical benefit can be inferred when symptoms are reduced or abolished, but the response cannot be quantitated. Multiple ambulatory monitoring periods before and during treatment permit determination of reductions of arrhythmia to levels of statistical significance but are costly and time-consuming. Programmed electrophysiologic induction study may be helpful in determining efficacy of some antiarrhythmic agents because of its high specificity, but its use is limited because of a low sensitivity. Titrating patients with multiple dosing into accepted plasma level therapeutic ranges may be helpful for individual patient care but does not allow quantitation. Recently, a statistical model based on linear regression analysis with established 95 and 99% confidence intervals has been used to compare efficacy of quinidine and encainide with success. Wider application of this model is suggested for determining antiarrhythmic drug efficacy.

Recognition and management of supraventricular tachyarrhythmias

While the principles of drug management of supraventricular tachyarrhythmias have remained essentially unchanged, such treatment remains empirical in many patients. Recent advances in the understanding of electrophysiological mechanisms have not only rationalised treatment but dictated newer approaches to these and other arrhythmias.

Premature ventricular complexes in the absence of identifiable heart disease

To define the prevalence, frequency and characteristics of premature ventricular complexes (PVCs) in adults free of recognizable heart disease, we performed 24-hour ambulatory electrocardiography on 101 subjects (51 men and 50 women, mean age 48.8 years) in whom physical examination, chest x-ray, ECG, echocardiogram, maximal exercise stress test, right- and left-heart catheterization and coronary arteriography were normal. Thirty-nine subjects had at least 1 PVC/24 hours, but only four had more than 100 PVCs/24 hours and fewer than five had more than five PVCs in any given hour. The probability of having at least 1 PVC/24 hours increased with age (chi square = 11.789, p = 0.019). The number of PVCs/24 hours was also positively associated with age (4 = 0.33, p = 0.001). These was no consistent relationship between the presence or number of PVCs/24 hours and sex, blood pressure, weight, height, body mass index, serum potassium or calcium, cholesterol and triglyceride, hemoglobin, the ingestion of coffee, tea or alcohol, and cigarette smoking. Four subjects had multiform PVCs, two of whom had early PVCs.

Computer quantitated evaluation of cardiac arrhythmias

The identification of a cardiac arrhythmia depends on the interpretation of both the QRS complexes and the P waves. P wave detection is unreliable and hence automated diagnostic systems are often imperfect. An alternative is a system which detects QRS only and which classifies the QRS events; the physician then has a detailed quantitated QRS analysis to aid in diagnosis. The ATREC system has an analog QRS detector, which suppresses the P wave and the T wave frequencies and feeds a minicomputer (Mitra 15/35) with signals for the RR interval, the QRS duration, and polarity. The computer classifies these signals as either narrow or wide complexes. The narrow complexes are analyzed for irregular rhythm, bradycardia, pauses, transient or continuous tachycardia, and fibrillation. The wide complexes are classed by their coupling interval, bi- or trigeminy, doublets, or salvos, and the number per hour. The system gives a trend of the 16 beat mean, and the minimum and maximum heart rate. The data is presented on several displays.

Arrhythmias in patients with hypereosinophilia: a comparison of patients with and without Löffler's endomyocardial disease

About one third of patients with Löffler's endomyocardial disease have abnormal electrocardiograms and some develop arrhythmias and die suddenly. To assess the significance of these findings, continuous ambulatory ECG monitoring was performed for 48 hr on 6 patients with acute or chronic forms of Löffler's endomyocardial disease, and the types and frequencies of arrhythmias were compared with recordings from 6 other patients with equally high blood eosinophil counts who did not have clinically evident cardiac disease. It was hoped that this would show whether arrhythmias were related to high blood eosinophil counts, cardiac injury or other factors. Three of the patients with endomyocardial disease had multiple ventricular extrasystoles with episodes of ventricular arrhythmias and occasional supraventricular arrhythmias which had not been detected with conventional ECGs. These abnormalities did not occur in 2 of the patients with acute endomyocardial lesions who died, nor were they found in patients who did not have congestive cardiac failure or in the control patients. Rhythm disturbances appeared to be most closely related to the development of cardiac failure and they resolved after successful cardiac surgery. Multiple ventricular extrasystoles and arrhythmias occurring in these patients with Löffler's endomyocardial disease are probably due to metabolic changes in the heart associated with cardiac failure and mechanical changes related to valvular dysfunction rather than a direct effect of the eosinophils themselves on the heart.

Ambulatory ST segment monitoring. Problems, pitfalls, solutions, and clinical application

The introduction of frequency modulated recording systems for ambulatory electrocardiographic monitoring (Oxford Medilog mark 2 and Cardiodyne cassette recorders) prompted comparison with a conventional direct recording type of recorder (Oxford Medilog mark 1). The recordings obtained by the frequency modulated recorders were very much superior to those obtained by the direct recording type of recorder. The direct recording suffered from poor low frequency response, phase shift, and cable motions artefacts. Correction of these problems with careful attention to electrode application enabled stable graphs to be obtained over 24 hours. The clinical applications were explored by comparing the results of exercie tests with a computer assisted system with frequency modulated ambulatory monitoring in 30 patients. A range of ST deviations from pure ST depressions throughout 24 hours, pure ST elevation, and a combination of ST elevation and depression were seen, suggesting a spectrum of changes hitherto unsuspected in these patients. Painless ST changes were approximately twice as common as those associated with pain. These findings indicate a valuable role for ST segment monitoring in ischaemic heart disease, particularly with the availability of high fidelity modulated tracings which do not distort ST segments.

Cardiovascular complaints. Correlation with cardiac arrhythmias on 24-hour electrocardiographic monitoring

Long-term ambulatory electrocardiographic (Holter) monitoring is frequently used to evaluate patients with various cardiovascular complaints, including palpitations, dyspnea, discomfort in the chest, dizziness, and syncope. In the present study, 518 consecutive 24-hour electrocardiographic recordings were reviewed to determine correlations between cardiac diagnoses, presenting complaints, and specific electrocardiographic abnormalities. Two hundred seventy-four patients (53 percent) had significant arrhythmias; 212 (41 percent) had significant ventricular arrhythmias, and 106 (20 percent) significant atrial arrhythmias, including 44 patients (8 percent) with both. No presenting complaint or cardiovascular diagnosis correlated closely with any specific cardiac arrhythmia. Major arrhythmias, including supraventricular and ventricular tachycardias, often occurred asymptomatically (in 44/54 and 37/40 patients, respectively); however, among 371 patients with accurate historic logs, only 176 (47 percent) had long-term electrocardiographic studies in which their typical symptoms occurred during the monitoring period. Fifty (13 percent) of the 371 patients had concurrence of their presenting complaints with an arrhythmia, and 126 patients (34 percent) had their typical symptoms associated with a normal electrocardiogram, which was helpful in excluding an abnormality of rhythm or conduction as the primary cause for their complaints.

Studies on the clinical pharmacology of prazosin. II: The influence of indomethacin and of propranolol on the action and disposition of prazosin

1 The possibility of pharmacodynamic and pharmacokinetic interactions of prazosin with indomethacin and with propranolol have been studied in healthy subjects. 2 In four out of nine individuals indomethacin considerably attenuated prazosin-induced hypotension, but noradrenaline concentrations were unchanged from the day when blood pressure fell greatly. The effect of prazosin in the other five subjects was not influenced by indomethacin. 3 Indomethacin prevented the rise in plasma renin activity seen following administration of prazosin alone. 4 Propranolol did not prevent the syncope associated with the first dose of prazosin. 5 Propranolol affected neither the absorption nor elimination of prazosin. 6 It is concluded that in certain subjects indomethacin can largely prevent the hypotensive effect of parazosin, possible by increasing adrenergic receptor sensitivity. The theoretical possibility that propranolol could influence prazosin disposition or syncope was not substantiated.

Studies on the clinical pharmacology of prazosin. I: Cardiovascular, catecholamine and endocrine changes following a single dose

1 Cardiovascular, catecholamine and neuroendocrine changes were studied following administration of prazosin to ten normal subjects. In response to a fall in standing blood pressure from 87±5 (s.d.) mmHg to 49±20 (P < 0.01) heart rate (measured by continuous ECG monitoring) rose from 81±11 to 118±20 (P < 0.01). Five of the ten subjects sustained their tachycardia on standing and developed at most mild symptoms. In the other five, tachycardia suddenly gave way to bradycardia and they became syncopal.

2 In the supine position, when blood pressure was not significantly different from control, plasma noradrenaline concentration (nmol/l) was 2±0.5 compared with a control value of 1.2±0.3 (P < 0.01). In response to standing hypotension plasma noradrenaline was 4.2±2.7 compared with a standing control value of 1.9±0.4 (P < 0.02).

3 Four hours after taking prazosin five of the subjects stood for 30 min and blood was drawn for plasma renin activity (PRA). Blood pressure at this time was 15 mmHg below control (P < 0.02). PRA (ng ml^-1 h^-1) was 6.4±2.3 compared with time matched placebo control of 1.4±0.8 (P < 0.01).

4 At the same time as the PRA sampling, plasma cortisol was 15.6±2.6 μg/100 ml during hypotension and 8.2±3.9 following placebo (P < 0.01). Growth hormone was 1.4±0.3 ng/ml during hypotension and 1.0±0.2 following placebo (P < 0.01). Prolactin did not rise significantly during hypotension induced by prazosin.

5 Isoprenaline infusion produced the same change in heart rate during the time of maximum prazosin action as when given alone.

6 It is concluded that these observations are not in keeping with earlier reports that prazosin lowers blood pressure without producing a reflex increase in heart rate or renin release. Nor are these findings in keeping with current theories of the mechanism of action of prazosin which variously suggest that noradrenaline concentration should not increase, or that the heart is incapable of responding to an adrenergic stimulus in the presence of prazosin.

Surgery for life-threatening ventricular tachyarrhythmias

Among 203 left ventricular aneurysmectomies performed since 1970, the operative mortality rate was 18.7 percent. In 49 patients (24 percent), left ventricular aneurysmectomy was performed for refractory life-threatening ventricular arrhythmias. Eight additional patients had coronary bypass grafting without ventricular aneurysmectomy. One of these patients had bypass grafting followed later by ventricular aneurysmectomy. All 56 patients had underlying coronary artery disease. The operative mortality rate was 19.6 percent. In patients with a recent myocardial infarction, the rate was 60 percent, whereas it was 11 percent in patients with a remote myocardial infarction. Other high risk variables in these patients included coronary bypass grafting without myocardial resection, and an elevated left ventricular end-diastolic pressure. The late mortality rate was 17.9 percent, but only one of these deaths was sudden and unexpected. The 35 long-term survivors have been followed up for a mean of 40.7 months (range 7 to 92 months). Of these, 20 remain on antiarrhythmic medications for palpitation or documented ventricular premature complexes, whereas 15 are free of detectable rhythm disturbances and do not require antiarrhythmic agents. Only 4 of 35 (11 percent) have had recurrent documented ventricular tachycardia. Left ventricular aneurysmectomy may be performed for refractory ventricular tachyarrhythmias with an acceptable operative mortality, particularly if the patient has survived longer than 6 weeks after myocardial infarction. Although epicardial mapping techniques may be useful in localizing the reentrant pathway of the ventricular tachycardia, ventricular aneurysmectomy without mapping techniques produces a satisfactory clinical result in the vast majority of long-term survivors.

Unusual artifacts in electrocardiographic monitoring

Three unusual artifacts noted during Holter and telemetry monitoring, not previously described, are presented. Recognition of the artifacts prevented misinterpretation and wrong treatment. The clues to the identification of the artifacts and the need for avoiding wrong interpretation and inappropriate treatment are discussed. The cause of the telemetry artifact is discussed.

Atrial bigeminy with block associated with bradycardia and paroxysmal atrial fibrillation -- an important variant of the tachycardia-bradycardia syndrome

Serial 2-channel 24 h dynamic ECGs in 7 patients who were referred with the "tachy-brady" syndrome for consideration for permanent cardiac pacing revealed: 1. atrial premature beats (APBs) which were conducted to the ventricles normally or aberrantly; 2. intermittent atrial bigeminy with block towards the ventricles (this rhythm mimicked sinus bradycardia with ventricular rates of 38-45 beats/min and the ectopic P waves were visible on only one of the ECG channels); 3. paroxysms of atrial fibrillation initiated by closely coupled APBs. These findings suggested that both the ventricular bradycardia and the atrial fibrillation were caused by frequent APBs and that pacing therapy was unnecessary. Disopyramide was given to 5 patients resulting in suppression of the arrhythmia and relief of symptoms. In one patient there was spontaneous resolution and one patient refused treatment. This variant of the "tachy-brady" syndrome can be successfully treated by suppression of abnormal atrial impulse formation without recourse to pacemaker implantation.

Nocturnal vs diurnal cardiac arrhythmias in patients with chronic obstructive pulmonary disease

Continuous electrocardiograms were recorded from ten patients with chronic obstructive pulmonary disease. During 24 hours of recording, the patients breathed air; and for 24 hours, they breathed oxygen at 2 L/min by nasal cannula. Oxygenation, as monitored by ear oximetric studies and by periodic analysis of arterial blood, showed frequent nocturnal desaturation. Nine patients demonstrated arrhythmias during the monitoring period, and the frequency of premature ventricular contractions was significantly greater at night. Therapy with supplemental oxygen dramatically reduced the frequency of premature ventricular contractions in four patients, but the reduction in frequency of arrhythmias in the total group did not reach statistical significance. These results show that cardiac arrhythmias occur commonly at night during sleep in patients with chronic obstructive pulmonary disease. The data suggest that arterial desaturation may be responsible for some of these arrhythmias.

Effectiveness of increasing hours of continuous ambulatory electrocardiography in detecting maximal ventricular ectopy. Continuous 48 hour study of patients with coronary heart disease and normal subjects

The effectiveness of 1, 6, 12, 24, 36 and 48 hours of continuous ambulatory electrocardiographic examination in detecting maximal ventricular ectopy was studied in 67 patients with coronary heart disease (45 with myocardial infarction, 22 with angina pectoris) and 23 normal subjects. Two consecutive 24 hour Holter recording examinations provided 48 hours of continuous examination. Ventricular ectopy was detected in 87 percent of patients and 35 percent of normal subjects. Complex forms (multifocal or repetitive patterns) were found in 62 percent and high frequency ectopy (greater than 60/hour) in 30 percent of the patients with coronary heart disease. Examination of either the initial hour of study or an hour of dynamic activity frequently failed to reveal the maximal ventricular ectopy present, particularly with regard to complex types and high frequency. Continuous 6 and 12 hour examinations were less effective than the 24 hour examination, which detected the maximal grade of ventricular ectopy in 71 to 74 percent and the maximal frequency in 58 to 83 percent of patients with coronary heart disease. Detection of maximal complex types and high frequency of ventricular ectopy was one to three times greater with a continuous 24 hour examination than with studies of shorter duration. Patient-recorded diaries showed that 50 to 80 percent of patients were engaged in mild to moderate activity during ventricular ectopy and only 9 percent indicated symptoms during the hours of maximal ventricular ectopy.

Holter monitoring in patients with transient focal cerebral ischemia

The value of continuous long-term ECG monitoring in patients with transient generalized neurological symptoms is well established, but its value in transient focal neurological deficits is less clear. A patient is reported who had significant dysrhythmias and transient focal cerebral symptoms which did not clear after cardiac pacing. Nineteen other patients were monitored as part of their evaluation for transient focal cerebral symptoms and were found to have essentially no cerebrally significant dysrhythmias. This report suggests cardiac dysrhythmias rarely cause such symptoms.

Limitations of routine long-term electrocardiographic monitoring to assess ventricular ectopic frequency

Variations in the frequency of ventricular premature depolarizations (VPDs) were evaluated with three consecutive 24-hour long-term electrocardiography monitor recordings from 15 clinically stable patients with various cardiac disorders. Mean hourly VPD frequencies ranged from 37--1,801 per hour. Data were subjected to 4 and 5 factor nested analyses of variance. The extent of spontaneous variation in arrhythmia frequency that occurred in individual patients from day to day was 23%, between 8-hour periods within days was 29%, and from hour to hour was 48%. In addition, the variability between repeated three-day monitoring periods over time was quantified in five patients and found to be 37%. This analysis determined that to distinguish a reduction in VPD frequency attributable to therapeutic intervention rather than biologic or spontaneous variation alone required a greater than 83% reduction in VPD frequency if only two-24-hour monitoring periods were compared, and greater than 65% reduction if two 72-hour periods were compared. The limitations of routine 24-hour electrocardiographic monitoring must be considered in diagnostic and therapeutic decision-making.