European survey on efficacy and safety of duty-cycled radiofrequency ablation for atrial fibrillation.

AIMS: Duty-cycled radiofrequency ablation (RFA) has been used for atrial fibrillation (AF) for around 5 years, but large-scale data are scarce. The purpose of this survey was to report the outcome of the technique. METHODS AND RESULTS: A survey was conducted among 20 centres from seven European countries including 2748 patients (2128 with paroxysmal and 620 with persistent AF). In paroxysmal AF an overall success rate of 82% [median 80%, interquartile range (IQR) 74-90%], a first procedure success rate of 72% [median 74% (IQR 59-83%)], and a success of antiarrhythmic medication of 59% [median 60% (IQR 39-72%)] was reported. In persistent AF, success rates were significantly lower with 70% [median 74% (IQR 60-92%)]; P = 0.05) as well as the first procedure success rate of 58% [median 55% (IQR 47-81%)]; P = 0.001). The overall success rate was similar among higher and lower volume centres and were not dependent on the duration of experience with duty-cycled RFA (r = -0.08, P = 0.72). Complications were observed in 108 (3.9%) patients, including 31 (1.1%) with symptomatic transient ischaemic attack or stroke, which had the same incidence in paroxysmal and persistent AF (1.1 vs. 1.1%) and was unrelated to the case load (r = 0.24, P = 0.15), bridging anticoagulation to low molecular heparin, routine administration of heparin over the long sheath, whether a transoesophageal echocardiogram was performed in every patient or not and average procedure times. CONCLUSION: Duty-cycled RFA has a self-reported success and complication rate similar to conventional RFA. After technical modifications a prospective registry with controlled data monitoring should be conducted to assess outcome.

The Midlands Trial of Empirical Amiodarone versus Electrophysiology-guided Interventions and Implantable Cardioverter-defibrillators (MAVERIC): a multi-centre prospective randomised clinical trial on the secondary prevention of sudden cardiac death.

AIMS: MAVERIC was a randomised clinical trial designed to test the possibility of prospectively identifying patients who would benefit most from the implantable cardioverter-defibrillator (ICD) by electrophysiology (EP) study in the context of secondary prevention of sudden cardiac death (SCD) through comparing EP-guided interventions (anti-arrhythmic drugs, coronary revascularization, and ICD) against empirical amiodarone therapy. METHODS: Two hundred and fourteen survivors of sustained ventricular tachycardia (VT), ventricular fibrillation (VF) or SCD were randomized to either treatment strategy, pre-stratified for haemodynamic status at index event, and followed up for a median of 5 years. RESULTS: Of the 106 amiodarone arm patients, 89 (84%) received the drug and 5 (5%) received an ICD after crossing over. Of the 108 EP arm patients, 31 (29%) received an ICD, 46 (43%) received anti-arrhythmic drugs only (mainly amiodarone or sotalol) and 18 (17%) received coronary revascularization but no ICD. No significant differences in survival or arrhythmia recurrence existed between the two treatment arms after 6 years. However, ICD recipients had a lower mortality than non-ICD recipients, regardless of allocated treatment (hazard ratio=0.54, p=0.0391). CONCLUSIONS: Prospective selection of patients to receive the ICD by EP study did not improve survival compared with empirical amiodarone therapy among survivors of VT, VF or SCD, whereas ICD implantation improved survival regardless of allocated treatment. On this basis, routine EP study has no role in the management of such patients, who should be offered empirical ICD therapy according to the results of other secondary prevention ICD trials.

Visual illusions created by survival curves and the need to avoid potential misinterpretation.

Randomized clinical trials play an increasingly important role in guiding management decisions, and survival curves are the most popular means for summarizing and depicting the results of a clinical trial. However, survival curves may create certain "visual illusions" that can be misinterpreted by the unwary, with potentially adverse effects on patient care. The authors provide a brief outline of the theoretical background of survival curves and explain the origin of the most common visual illusions. Statisticians need to be aware of such potential for misinterpretation of clinical trial data in order to safeguard clinicians against drawing undue inferences and applying them to actual practice.

Comparison of two diagnostic algorithms for regular broad complex tachycardia by decision theory analysis.

Sensitivity and specificity are two inversely related properties of a diagnostic test and it is often practically infeasible to secure a high value for both simultaneously. Decision theory analysis shows that the utility of a diagnostic test depends not only on its sensitivity and specificity but also on the prevalence of the intended target disorder: when prevalence is low, a high specificity is more important than a high sensitivity, whereas when prevalence is high, a high sensitivity is more important than a high specificity. The significance of this principle is illustrated by two popular algorithms for the electrocardiographic diagnosis of regular broad complex tachycardia (BCT), of which the two main differential diagnoses are ventricular tachycardia (VT) and supraventricular tachycardia with aberrant conduction (SVTAG). Brugada et al. focused on criteria highly specific for VT and used them to build a four-step algorithm. In contrast, Griffith et al. first selected criteria highly sensitive for VT and then criteria highly specific for VT to build a simple two-step algorithm. It can be objectively demonstrated that the Griffith algorithm is more efficient and effective than the Brugada algorithm in terms of clinching the final diagnosis and improving overall diagnostic accuracy. The main reason for this is that VT is more common than SVTAC as the cause of regular BCT, and the Griffith algorithm adhered to the aforementioned principle governing the choice between sensitivity and specificity according to prevalence in its design. The Griffith algorithm also embodies an additional important principle, namely, it is easier and more efficient to choose alternatively between criteria highly specific and highly sensitive for the intended target disorder than concentrating on just one or the other in designing a multiple-step sequential diagnostic algorithm.

Effects of direct sympathetic and vagus nerve stimulation on the physiology of the whole heart--a novel model of isolated Langendorff perfused rabbit heart with intact dual autonomic innervation.

A novel isolated Langendorff perfused rabbit heart preparation with intact dual autonomic innervation is described. This preparation allows the study of the effects of direct sympathetic and vagus nerve stimulation on the physiology of the whole heart. These hearts (n = 10) had baseline heart rates of 146 +/- 2 beats x min(-1) which could be increased to 240 +/- 11 beats x min(-1) by sympathetic stimulation (15 Hz) and decreased to 74 +/- 11 beats x min(-1) by stimulation of the vagus nerve (right vagus, 7 Hz). This model has the advantage of isolated preparations, with the absence of influence from circulating hormones and haemodynamic reflexes, and also that of in vivo preparations where direct nerve stimulation is possible without the need to use pharmacological agents. Data are presented characterising the preparation with respect to the effects of autonomic nerve stimulation on intrinsic heart rate and atrioventricular conduction at different stimulation frequencies. We show that stimulation of the right and left vagus nerve have differential effects on heart rate and atrioventricular conduction.

Variability in the manifestation of pre-excited atrial fibrillation: its quantification, theoretical origin, and diagnostic potential.

BACKGROUND: Irregular broad complex tachycardia (BCT) may be due to atrial fibrillation (AF) occurring in the presence of ventricular pre-excitation (pre-excited AF) or bundle branch block (BBB-AF). While irregularity is a defining characteristic of AF, it is a common subjective impression that greater variability in manifestation exists for pre-excited AF than BBB-AF. This difference can potentially be exploited for distinguishing the two conditions if some means can be found to quantify it. METHODS: For each of 75 ECGs showing irregular BCT (41 pre-excited AF and 34 BBB-AF), a random sample of 10 distinct QRS complexes were selected for quantitative measurement of variability in manifestation, which included the standard deviation (SD) of the width, the SD of the axis, and the coefficient of variation (CV) of the amplitude of the QRS complex. RESULTS: Pre-excited AF showed statistically significantly greater values than BBB-AF with respect to these measures, and receiver-operating characteristic curves showed that these differences could be useful for their discrimination. For the SD of QRS width, a cut-off value of 8 ms appeared optimal (sensitivity 1.00 and specificity 0.79). For the SD of QRS axis, a cut-off value of 2.5 degrees appeared optimal (sensitivity 0.84 and specificity 0.56). For the CV of QRS amplitude, a cut-off value of 0.10 appeared optimal (sensitivity 0.82 and specificity 0.76). CONCLUSIONS: Pre-excited AF demonstrated greater variability than BBB-AF in manifestation. The measures of variability developed can potentially be useful for diagnosing irregular BCT in practice, especially in the context of automated computer-aided diagnosis.

The Bayesian approach improves the electrocardiographic diagnosis of broad complex tachycardia.

Despite numerous attempts at devising algorithms for diagnosing broad complex tachycardia (BCT) on the basis of the electrocardiogram (ECG), misdiagnosis is still common. The reason for this may lie with difficulty in implementing existent algorithms in practice, due to imperfect ascertainment of ECG features within them. An attempt was made to approach the problem afresh with the Bayesian inference by the construction of a diagnostic algorithm centered around the likelihood ratio (LR). Previously studied ECG features most effective in discriminating ventricular tachycardia (VT) from supraventricular tachycardia with aberrant conduction (SVTAC), according to their LR values, were selected for inclusion into a Bayesian diagnostic algorithm. A test set of 244 BCT ECGs was assembled and shown to three independent observers who were blinded to the diagnoses made at electrophysiological study. Their diagnostic accuracy by the Bayesian algorithm was compared against that by clinical judgement with the diagnoses from EPS as the criterial standard. Clinical judgement correctly diagnosed 35% of SVTAC, 85% of VT, and 47% of fascicular tachycardia. In comparison, by the Bayesian algorithm devised, 52% of SVTAC, 95% of VT, and 97% of fascicular tachycardia were correctly diagnosed. The Bayesian algorithm devised has proved to be superior to the clinical judgement of the observers who participated in this study, and theoretically will obviate the problem of imperfect ascertainment of ECG features. Hence, it holds the promise for being an effective tool for routine use in clinical practice.

Temperature-sensitive focal atrial tachycardia in the left atrium.

Temperature sensitivity has not been reported in focal atrial tachycardia. We describe a patient with a left atrial tachycardia whose tachycardia rate was affected by hot and cold drinks. The effects were still evident after autonomic blockade. The arrhythmia focus was located at the entrance of the left upper pulmonary vein. Radiofrequency ablation was carried out, which proved to be difficult, but it was successful after several applications of energy, suggesting an epicardial location of the arrhythmia focus. Sensitivity of atrial tachycardia rate to the temperature of food or drink ingested suggests a left atrial focus with a posterior and possibly epicardial location.

Electrocardiographic criteria for diagnosis of irregular broad complex tachycardia with a high sensitivity for preexcited atrial fibrillation.

AF may appear as an irregular broad complex tachycardia (BCT) if atrioventricular conduction occurs via an accessory pathway (preexcited AF) or if bundle branch block (BBB), preexistent or rate related, exists in the His-Purkinje system (BBB-AF). While BBB-AF is relatively benign, preexcited AF may herald sudden cardiac death. Hence it is important that the two conditions can be reliably distinguished. Yet, there is no preexistent algorithms for this purpose. Griffith et al. previously proposed a simple algorithm for a similar problem, that of distinguishing the two differential diagnoses for regular BCT: VT and SVT with BBB, on the basis that unless the QRS morphologies in V1 and V6 are absolutely typical of BBB, VT will be diagnosed. The authors propose an extrapolation of this principle to irregular BCT by stating that, unless the QRS morphologies in V1 and V6 are absolutely typical of BBB, preexcited AF will be diagnosed. Seventy-five ECGs showing irregular BCT (41 preexcited AF and 34 BBB-AF) were shown to two fellows in electrophysiology who were given no other information and were instructed to diagnose preexcited AF unless the QRS morphology pattern was typical of BBB. Observer 1 achieved a sensitivity of 100% (41/41) and a specificity of 79% (27/34), while observer 2 achieved a sensitivity of 100% and a specificity of 85% (29/34). By QRS morphology pattern, an average sensitivity of 100% and specificity of 82% were achieved for the diagnosis of irregular BCT. The algorithm is simple and easy to implement and recommended for clinical use.

Imaging of adenosine bolus transit following intravenous administration: insights into antiarrhythmic efficacy.

OBJECTIVE: To study the effects of the site of intravenous injection of adenosine and to assess the site of action of adenosine in the heart by correlating cardiac effects with bolus transit. METHODS: Ten patients undergoing routine technetium (Tc-99m) gated blood pool ventriculography consented to the coadministration of intravenous adenosine. The dose of adenosine required to produce heart block during sinus rhythm was determined following antecubital vein administration. This dose (6-18 mg) was mixed with Tc-99m and given first into the same antecubital vein (proximal injection) and then repeated into a hand vein (distal injection). The ECG was recorded and the transit of the bolus was imaged using a gamma camera. RESULTS: Heart block occurred in all 10 patients (second degree in seven, first degree in three) at (mean (SEM)) 17.5 (1.0) seconds after the proximal injection of adenosine. Distal injection produced heart block in six patients (second degree in two, first degree in four) at 21.9 (4.4) seconds (p < 0.01). In eight of 10 patients the electrophysiological effects were less with distal injection. The onset of heart block was close to the time of peak bolus Tc-99m activity in the left ventricle. Peak bolus activity was delayed (by about three seconds) and the duration of bolus activity in the left ventricle was increased with distal injection compared with proximal injection, at 17.2 (4.2) v 9.2 (3.1) seconds, p < 0.01. CONCLUSIONS: The lesser electrophysiological effects of adenosine following distal intravenous injections were associated with delay in transit time and dispersion of the bolus. The correlation of adenosine induced heart block with bolus activity in the left heart indicated dependence on coronary arterial delivery of adenosine to the atrioventricular node.

A new ECG sign of an accessory pathway in sinus rhythm: pseudo partial right bundle branch block.

It is clinically important to be able to detect the presence of an accessory pathway, as pre-excited atrial fibrillation is a well recognised cause of sudden cardiac death, for which there is a potential "cure" in the form of radiofrequency ablation of the pathway. The classic manifestations such as a shortened PR interval or delta waves may not always be present. In certain patients a pseudo partial right bundle block pattern-that is, an rSr' complex in lead V1- may be the sole manifestation of a left sided accessory pathway. An electrophysiological mechanism is proposed for this pattern and it is suggested that this pattern may be used as a new ECG sign for diagnosing an accessory pathway in sinus rhythm.

Non-uniform prolongation of intracellular Ca2+ transients recorded from the epicardial surface of isolated hearts from rabbits with heart failure.

OBJECTIVES: To study the time course of Ca2+ transients recorded from the left ventricular epicardial surface of isolated hearts from rabbits with heart failure and to correlate the results with mechanical function. METHODS: Heart failure was induced in the rabbit 8 weeks after coronary ligation (n = 17) with 13 controls. Echocardiography was used to assess in vivo left ventricular dysfunction. The fluorescent indicator Indo-1 was loaded into isolated Langendorff-perfused hearts and Ca2+ transients were recorded from 15 sites over the left ventricular epicardial surface using a single core light guide. The time course of the Ca2+ transients was analysed and the duration measured and correlated with in vitro mechanical function. RESULTS: Significant mechanical dysfunction was produced in this model of heart failure. The mean duration of the Ca2+ transients obtained from failing hearts was prolonged (156.2 +/- 3.2 ms) when compared to controls (124.9 +/- 2.6 ms, P < 0.001). Delayed relaxation as measured by the maximum rate of intraventricular pressure decay was significantly correlated with the prolonged Ca2+ transients (r = -0.63, P < 0.001). In addition, there was increased variation of the Ca2+ transient duration in the failing hearts. CONCLUSIONS: Coronary artery ligation-induced heart failure is associated with changes in the surviving myocardium which result in a non-uniform prolongation of Ca2+ transient duration. This suggests that there is a regional heterogeneity to the abnormal intracellular Ca2+ handling in heart failure.

When is it futile for ambulance personnel to initiate cardiopulmonary resuscitation?

OBJECTIVE: To determine whether patients with unexpected prehospital cardiac arrest could be identified in whom ambulance resuscitation attempts would be futile. DESIGN: Review of ambulance and hospital records; detailed review of automated external defibrillator rhythm strips of patients in whom no shock was advised. SETTING: Scottish Ambulance Service; all cardiopulmonary resuscitation attempts after cardiorespiratory arrest during 1988-94 included in the Heartstart Scotland database. SUBJECT: 414 cardiorespiratory arrest patients with no pulse or breathing on arrival of ambulance personnel, no bystander cardiopulmonary resuscitation performed, and more than 15 minutes from time of arrest to arrival of ambulance. Patients were stratified into those with "shockable" and "non-shockable" rhythms. MAIN OUTCOME MEASURES: Return of spontaneous circulation, or survival to reach hospital alive, or survival to discharge, or all three. RESULTS: No patient with a non-shockable rhythm who met the entry criteria for analysis survived a resuscitation attempt. Review of the defibrillator rhythm strips of these patients failed to find any case in which the tracing was deemed compatible with survival. CONCLUSION: On the basis that it would be inappropriate to initiate vigorous resuscitation in patients who can be identified as "dead" and beyond help an algorithm was prepared to guide ambulance personnel.