Unusual signals in a halo catheter: what is the mechanism?

In this "featured arrhythmia" article we present a set of unusual intracardiac electrode tracings that were recorded in a patient with typical clockwise flutter but a very dilated right atrium. The potential mechanism underlying this phenomenon is discussed with reference to the current literature

Truths and Lies from the Polysomnography ECG Recording: An Electrophysiologist Perspective

Polysomnography remains the gold standard for diagnosis of Sleep Apnea (SA) and evaluation of the apnea/hypopnea index (AHI) which is used as the primary index of SA severity. The electrocardiogram (typically a single lead) obtained during the polysomnographic study is usually used to report the association between SA and cardiac rhythm disturbances. These findings help in guiding medical decisions but they could also represent a source for confusion. Electrophysiologists are frequently consulted to determine whether interventions need to be taken. We present 2 cases where the ECG during a polysomnography study required the intervention of an electrophysiologist to help with management

Multifactorial QT interval prolongation

Acquired long QT interval has been widely reported to be a consequence of drug therapy and electrolyte disturbances. We describe two cases of multifactorial acquired QT interval prolongation and torsades de pointes. In the first case, the drugs venlafaxine, amiodarone and domperidone may have contributed to QT interval prolongation in a patient with hypokalemia and hypomagnesaemia. In the second case, QT interval prolongation occurred in a patient taking quetiapine and citalopram, and whose use of hydrocholorothiazide and history of chronic alcohol abuse likely contributed by rendering the patient hypokalemic. These cases highlight the potential risks associated with polypharmacy and demonstrate that though torsades de pointes is an uncommon arrhythmia, the combination of multiple factors known to prolong QT interval may precipitate this life-threatening arrhythmia. (Cardiol J 2010; 17, 2: 184-188

Interatrial block in patients with obstructive sleep apnea

Background: Obstructive sleep apnea (OSA) is a common disorder that affects 5% of the adult North American population. It is associated with atrial arrhythmias and stroke. The mechanisms of this association remain unclear. The aim to the study was to identify the factors associated with interatrial block (IAB) among patients with OSA. Methods: Patients referred for polysomnography were studied. Sleep apnea severity (apnea-hypopnea index [AHI]) was measured in each subject. 12-lead ECGs were scanned and amplified (× 10); P-wave duration and dispersion were measured using a semi-automatic caliper. IAB was defined as a P-wave duration &#8805; 120 ms. Results: Data from 180 consecutive patients was examined. Moderate-severe OSA (mean AHI = 56.2 &#177; 27.9) was present in 144 (OSA group). The remaining 36 had mild or no OSA (mean AHI = 5.6 &#177; 3.6) and were used as controls. Age distribution between the groups did not differ and there were more males in the OSA group (69.4% vs 47.2%, p = 0.01). Obesity (78.5% vs 39.4%, p < 0.001) and hypertension (51.4% vs 27.8%, p < 0.01) were more prevalent in the OSA group. IAB was more prevalent in patients with moderate-severe OSA (34.7% OSA vs 0% controls, p 30 were independent predictors of maximum P-wave duration (p = 0.001 and p < 0.001, respectively). P-wave dispersion was significantly higher in the severe OSA group (14.6 &#177; 7.5 for OSA, 8.9 &#177; 3.1 controls, p < 0.001). Conclusions: Older age and moderate-severe OSA are predictors of IAB. P-wave dispersion is increased in patients with moderate-severe OSA. This may partly explain the high prevalence of atrial arrhythmias in patients with OSA. (Cardiol J 2011; 18, 2: 171-175

Regional Dominant Frequency: A New Tool for Wave Break Identification During Atrial Fibrillation

Cardiac mapping systems are based on the time/frequency feature analyses of intracardiac electrograms recorded from individual bipolar/unipolar electrodes. Signals from each electrode are processed independently. Such approaches fail to investigate the interrelationship between simultaneously recorded channels of any given mapping catheter during atrial fibrillation (AF). We introduce a novel signal processing technique that reflects regional dominant frequency (RDF) components. We show that RDF can be used to identify and characterize variation and disorganization in wavefront propagation- wave breaks. The intracardiac electrograms from the left atrium of 15 patients were exported to MATLAB and custom software employed to estimate RDF and wave break rate (WBR). We observed a heterogeneous distribution of both RDF and WBR; the two measures were weakly correlated (0.3; p &lt; 0.001). We identified locations of AF or atrial tachycardia (ATach) termination and later compared offline with RDF and WBR maps. We inspected our novel metrics for associations with AF termination sites. Areas associated with AF termination demonstrated high RDF and low WBR (↑RDF,↓WBR). These sites were present in 14 of 15 patients (mean 2.6 ± 1.2 sites per patient; range, 1–4 sites), 43% situated within the pulmonary veins. In nine patients where AF terminated to sinus rhythm (6) or ATach (3), post-hoc analysis demonstrated all ↑RDF,↓WBR sites were ablated and correlated with AF termination sites. The proposed RDF signal processing tools can be used to identify and quantify wave break, and the combined use of these two novel metrics can aid characterization of AF. Further prospective studies are warranted

The signal averaged P wave : a non-invasive marker of atrial electrophysiological substrate

The technological advances made over the last century have afforded the clinician an array of sophisticated tests to aid the diagnostic process. Much of the knowledge gained on the pathophysiology of cardiac disease has been from invasive assessment, often in animals, but also in human subjects. Application of this knowledge to patient care is limited by the need for invasive studies that present some risk of harm to the patient. Non-invasive assessment reduces risk of harm significantly whilst providing information equivalent to invasive assessment. The best example of this is the insight delivered by technological advances in imaging of the heart. Ultrasound echocardiography, radio-isotope imaging, computerised tomography and magnetic resonance imaging have all excelled expectations in delivering accurate anatomic and functional information non-invasively. Assessment of electrophysiologic function began non-invasively with the recording of surface potentials by Augustus D Waller1 and the development of the electrocardiogram (ECG) by William Einthoven2 (who was later awarded the Nobel Prize in 1924 for his endeavours). Recognition of pathology from the surface ECG was hypothesis generating. In order to explore the heart's electrical system further electrophysiological assessment was made invasively to supplement the information obtained from the surface ECG. This information proved favourable and when combined with pacing stimulus protocols provided the clinician with detailed information on conduction properties that could be measured in a reproducible and reliable way to reflect the impact of drugs or disease in detail that the surface ECG could not. Moreover, the invasively measured properties could be linked with changes at the cellular level and thus the effect of changes in ion channel density, for example, on electrophysiologic properties could be predicted. It would obviously be beneficial to somehow gather the information non-invasively, but this has proved more challenging. Firstly, much of the information obtained invasively is the product of pacing protocols that cannot be reproduced non-invasively. Secondly, the detailed assessment of cardiac electrophysiology from surface electrograms is hampered by multiple factors pertaining to the intervening tissue, i.e. body habitus and electrical interference (noise). Given these factors the expectations of non-invasive assessment of cardiac electrophysiology must be limited and cannot be compared to imaging. The utility of non-invasive tests must be in the 'broad stokes' rather than the fine detail. However it is not beyond expectations to provide useful insights that may be employed in the investigation of disease trends and or the impact of intervention. The trade off for lack of detailed information is the safety, low cost and general applicability to a large patient population. The difficulty in gathering further information from the surface ECG has been alluded to briefly above. Digital techniques are used to overcome some of the difficulties such as amplification and noise reduction. Digital applications are then often used to analyse the data gathered. It is useful to be familiar with some of the concepts involved in digital signal processing as it pertains to cardiac signals and thus a brief outline is presented in appendix 1. This thesis begins with a detailed review of the surface P wave in health and disease, and a review of atrial fibrillation (AF) - the most common arrhythmia encountered in clinical practice