Ernest W. Lau

The Bayesian Approach Improves the Electrocardiographic Diagnosis of Broad Complex Tachycardia

LAU, E.W., et al.: The Bayesian Approach Improves the Electrocardiographic Diagnosis of Brand 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.

Comparison of the performance of three diagnostic algorithms for regular broad complex tachycardia in practical application.

LAU, E.W., et al.: Comparison of the Performance of Three Diagnostic Algorithms for Regular Broad Complex Tachycardia in Practical Application. The authors previously proposed a Bayesian approach to the electrocardiographic diagnosis of regular broad complex tachycardia (BCT), which can be due to VT or supraventricular tachycardia with aberrant conduction (SVTAC). They also published an account comparing the theoretical merits in the design of two of the most commonly used diagnostic algorithms for the same purpose, those of Brugada et al. and Griffith et al. In this study, a direct head‐to‐head comparison was performed on the practical performances of the three algorithms in this study. A set of 111 ECGs showing regular BCT (77 VT, 34 SVTAC) whose diagnoses were confirmed by electrophysiological study was shown to five internists in general medicine at a district general hospital. The observers were asked to comment on whether the ECG criteria in the three algorithms tested were fulfilled or not, and a computer program then derived the corresponding diagnoses. The sensitivity and specificity for VT achieved by the Brugada algorithm were 92% and 44%, 92% and 44% by the Griffith algorithm, and 97% and 56% by the Bayesian algorithm. The Bayesian algorithm achieved a higher sensitivity and specificity than the other two algorithms, but the differences are not statistically significant (P = 0.6583 and P = 0.5334, respectively). The Brugada, Griffith, and Bayesian algorithms show comparable performances in terms of overall sensitivity and specificity when tested in practice. Of the three algorithms, the Griffith algorithm excels in simplicity and is the easiest to implement in practice. The Bayesian algorithm achieved slightly higher values for sensitivity and specificity than the Brugada and Griffith algorithms but may be more suitable for automated computer‐aided diagnosis of ECG due to its complexity.

Delayed Cardiac Perforation by Defibrillator Lead Placed in the Right Ventricular Outflow Tract Resulting in Massive Pericardial Effusion

A 76‐year‐old man received a dual‐chamber implantable cardioverter defibrillator (ICD), with the defibrillator lead positioned within the right ventricular outflow tract. The lead parameters at the time of implantation were satisfactory and the postprocedure chest X‐ray showed the leads were in place. The patient was cardioverted from atrial fibrillation during defibrillation threshold testing and commenced on anticoagulation immediately. One month post implantation, he experienced multiple ventricular tachycardia episodes all successfully treated with antitachycardia pacing and shocks by his ICD, but he fell and hit his chest against a hard surface during one of these attacks. He developed a massive pericardial effusion and computed tomography confirmed cardiac perforation by the defibrillator lead. Pericardiocentesis was performed and the defibrillator lead replaced with a different model positioned at the right ventricular apex. The patient made an uneventful recovery. The management and avoidance of delayed cardiac perforation by transvenous leads were discussed.

The reliable electrocardiographic diagnosis of regular broad complex tachycardia: a holy grail that will forever elude the clinician's grasp?

LAU, E.W., et al.: The Reliable Electrocardiographic Diagnosis of Regular Broad Complex Tachycardia: A Holy Grail That Will Forever Elude the Clinicians Grasp? The reliable and accurate diagnosis of regular broad complex tachycardia (BCT) by the ECG is a goal that has eluded clinicians and electrophysiologists alike for years. This article explores the reason for this by first giving an historical account on the development of the subject. Next, the electrophysiological mechanisms of ventricular tachycardia, supraventricular tachycardia with aberrant conduction, and preexcited tachycardia, the three main differential diagnoses for regular BCT, according to the latest knowledge from cellular and clinical electrophysiology study will be reviewed, together with considerations on how such understanding may help account for the manifestations of these tachycardias on the ECG and the difficulty in distinguishing between them. Finally, the use of electrophysiological study as the criterion standard for diagnosing regular BCT, as has been the case in most studies on the subject, will be critiqued in terms of the potential for misdiagnosis by the method and the use of any ECG diagnostic algorithms developed with its aid in the acute medical care setting.

Comparison of Two Diagnostic Algorithms for Regular Broad Complex Tachycardia by Decision Theory Analysis

LAU, E.W., et al.: 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 (SVTAC). 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.

Technologies for Prolonging Cardiac Implantable Electronic Device Longevity: TECHNOLOGIES FOR PROLONGING DEVICE LONGEVITY

Prolonged longevity of cardiac implantable electronic devices (CIEDs) is needed not only as a passive response to match the prolonging life expectancy of patient recipients, but will also actively prolong their life expectancy by avoiding/deferring the risks (and costs) associated with device replacement. CIEDs are still exclusively powered by nonrechargeable primary batteries, and energy exhaustion is the dominant and an inevitable cause of device replacement. The longevity of a CIED is thus determined by the attrition rate of its finite energy reserve. The energy available from a battery depends on its capacity (total amount of electric charge), chemistry (anode, cathode, and electrolyte), and internal architecture (stacked plate, folded plate, and spiral wound). The energy uses of a CIED vary and include a background current for running electronic circuitry, periodic radiofrequency telemetry, high‐voltage capacitor reformation, constant ventricular pacing, and sporadic shocks for the cardiac resynchronization therapy defibrillators. The energy use by a CIED is primarily determined by the patient recipients clinical needs, but the energy stored in the device battery is entirely under the manufacturers control. A larger battery capacity generally results in a longer‐lasting device, but improved battery chemistry and architecture may allow more space‐efficient designs. Armed with the necessary technical knowledge, healthcare professionals and purchasers will be empowered to make judicious selection on device models and maximize the utilization of all their energy‐saving features, to prolong device longevity for the benefits of their patients and healthcare systems.

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 QBS morphologies in V1 and V6 are absolutely typical of BBB, preexcited AF will he 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.

Temperature‐Sensitive Focal Atrial Tachycardia in the Left Atrium

Temperature‐Sensitive Focal Atrial Tachycardia. 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 elTects 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 arrhytbmia 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.

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 it some means can be found to quantify it.