KCNQ1 p.D446E Variant as a Risk Allele for Arrhythmogenic Phenotypes: Electrophysiological Characterization Reveals a Complex Phenotype Affecting the Slow Delayed Rectifier Potassium Current (IKs) Voltage Dependence by Causing a Hyperpolarizing Shift and a Lack of Response to Protein Kinase A Activation

Genetic testing is crucial in inherited arrhythmogenic channelopathies; however, the clinical interpretation of genetic variants remains challenging. Incomplete penetrance, oligogenic, polygenic or multifactorial forms of channelopathies further complicate variant interpretation. We identified the KCNQ1/p.D446E variant in 2/63 patients with long QT syndrome, 30-fold more frequent than in public databases. We thus characterized the biophysical phenotypes of wildtype and mutant IKs co-expressing these alleles with the β-subunit minK in HEK293 cells. KCNQ1 p.446E homozygosity significantly shifted IKs voltage dependence to hyperpolarizing potentials in basal conditions (gain of function) but failed to shift voltage dependence to hyperpolarizing potentials (loss of function) in the presence of 8Br-cAMP, a protein kinase A activator. Basal IKs activation kinetics did not differ among genotypes, but in response to 8Br-cAMP, IKs 446 E/E (homozygous) activation kinetics were slower at the most positive potentials. Protein modeling predicted a slower transition of the 446E Kv7.1 tetrameric channel to the stabilized open state. In conclusion, biophysical and modelling evidence shows that the KCNQ1 p.D446E variant has complex functional consequences including both gain and loss of function, suggesting a contribution to the pathogenesis of arrhythmogenic phenotypes as a functional risk allele.

[Corrected QT interval and GRACE score relationship in patients with non-ST segment elevation myocardial infarction]

Background

The Global Registry of Acute Coronary Events (GRACE) prediction model stratifies patients with non-ST-segment elevation myocardial infarction (NSTEMI). Corrected QT interval (QTc) is not considered in this model.

Objective

To evaluate the relationship between the QTc interval and the GRACE score in patients with NSTEMI.

Materials and methods

An observational, retrospective study was carried between 2016 and 2019. We included patients with diagnosis of NSTEMI, QTc intervals were calculated with Bazett's formula, and they were classified into 2 groups: a normal QTc interval (<440 ms) and prolonged (≥440 ms). According to the GRACE score they were classified in three ranges: low risk (≤109 points), intermedium (110 - 139 points) and high (≥140 points), we determined if there were a correlation between QTc interval and the GRACE score.

Results

A total of 940 patients with a diagnosis of NSTEMI were admitted in our institution, 634 met the inclusion criteria, there were 390 patients with normal QTc interval and 244 with a prolonged QTc interval. Patients with prolonged QTc were older (65.5 vs 61, p=0.001) with a lower proportion of males (71.7% vs 82.8%, p=0.001). An association was found between the GRACE score and the QTC interval, subjects with a normal QTc had a greater proportion of low and intermediate risk than those with a prolonged QTc (p=0.001). Conclusions. In NSTEMI patients, a normal QTc interval (<440 ms) is associated with a GRACE risk score of low or intermediate risk.

Compound Heterozygous KCNQ1 Mutations Causing Recessive Romano-Ward Syndrome: Functional Characterization by Mutant Co-expression

Next Generation Sequencing has identified many KCNQ1 genetic variants associated with type 1 long QT or Romano-Ward syndrome, most frequently inherited in an autosomal dominant fashion, although recessive forms have been reported. Particularly in the case of missense variants, functional studies of mutants are of aid to establish variant pathogenicity and to understand the mechanistic basis of disease. Two compound heterozygous KCNQ1 mutations (p.A300T and p.P535T) were previously found in a child who suffered sudden death. To provide further insight into the clinical significance and basis for pathogenicity of these variants, different combinations of wildtype, A300T and P535T alleles were co-expressed with the accessory β-subunit minK in HEK293 cells, to analyze colocalization with the plasma membrane and some biophysical phenotypes of homo and heterotetrameric channels using the patch-clamp technique. A300T homotetrameric channels showed left-shifted activation V_1/2 as previously observed in Xenopus oocytes, decreased maximum conductance density, slow rise-time_300ms, and a characteristic use-dependent response. A300T slow rise-time_300ms and use-dependent response behaved as dominant biophysical traits for all allele combinations. The P535T variant significantly decreased maximum conductance density and Kv7.1-minK-plasma membrane colocalization. P535T/A300T heterotetrameric channels showed decreased colocalization with plasma membrane, slow rise-time_300ms and the A300T characteristic use-dependent response. While A300T left shifted activation voltage dependence behaved as a recessive trait when co-expressed with WT alleles, it was dominant when co-expressed with P535T alleles. Conclusions: The combination of P535T/A300T channel biophysical properties is compatible with recessive Romano Ward syndrome. Further analysis of other biophysical traits may identify other mechanisms involved in the pathophysiology of this disease.

KCNQ1 V141M and Short QT Syndrome: are we dealing with a different entity?

 

Short QT Syndrome (SQTS) is a highly malignant inherited primary electrical disease that is associated with ventricular arrhythmias and sudden cardiac death (SCD); despite this, some patients may present a different arrhythmic phenotype with supraventricular affection. One particular presentation can be notably separated from others. The V141M variant from the KCNQ1 gene frequently presents with fetal bradycardia, atrial fibrillation, sinus, and AV node dysfunction, but without a single reported event of ventricular arrhythmia.

To perform a literature review and pool analysis of SQTS cases, and compare patients with the V141M mutation in KCNQ1 to other SQTS cases to determine if we are dealing with a different electrical disorder.

We conducted a search in the Varsome, Mastermind, MEDLINE, PubMed, and ClinVar databases to identify SQTS patients and conduct a pooled analysis. Their age, gender, clinical presentation, ECG findings, genetic analysis, and follow-up assessment were collected for analysis. If the duration of the QT interval was not described, it was determined by direct measurements in published ECG. For the comparison between groups, SQTS patients, we separated into two main groups: Non-KCNQ1 V141M patients (Group 1) and positive KCNQ1 V141M mutation (Group 2). Categorical variables are expressed as percentages. The categorical variables were analyzed using chi-square or Fisher exact test when necessary.

We gathered 56 patients with a diagnosis of SQTS from 27 previous publications combined with one other case followed by the authors. A total of 13 (23.2%) patients presented with the V141M KCNQ1 mutation, the majority of KCNQ1 V141M patients were female (10 [77%]). Patients from group 1 had a significantly higher rate of familiar SCD (53.4% vs. 18.1%; P=0.04). Patients from the latter group have a significant history of SND when compared to the control group (36.3% vs. 0; P=0.001). The presence of SCD showed no significant difference between the two groups; nevertheless, the difference regarding ventricular arrhythmias is well represented (41.8% vs. 0; P=0.01). Both sinus and AV node dysfunction were present in almost all V141M patients when compared to the control group; a statistical significance was found (P = &gt;0.001 for both instances). On the same regard, almost all patients from de V141M group presented SVA (84.6% vs 28.5%; P=0.001), specifically atrial fibrillation was present in all but 2 patients from the V141M group, which was significant (84.6% vs 24.3%; P = &gt;0.001). Finally, fetal bradycardia was present in most of the members of this group, in contrast with the control group, with no patients with this characteristic (P = &gt;0.001).

SQTS is a phenotypically heterogeneous disease with many genetic subtypes; we propose a differentiation between the common known presentations of this syndrome and the more defined phenotype of the KCNQ1 V141M mutation.

First Mexican patient with SQTS

Funding Acknowledgement

Type of funding source: None

Diagnostic challenges of Brugada Syndrome in pediatric patients

Although most cases of Brugada syndrome have been described in adults, pediatric patients with the disease have been reported since the original article from Josep and Pedro Brugada. Herein is presented the case series of Brugada syndrome in pediatric population of the National Institute of Cardiology Ignacio Chavez. One boy and two adolescent males had palpitations as clinical presentation of the disease. Atrial arrhythmias were documented in two, in the third case there was a high clinical suspicion and quinidine abolished symptoms. The aim of this report is to highlight the importance of performing a detailed clinical history as well as the usefulness of high precordial leads for the diagnosis of this entity.

Idiopathic Lead Migration: Concept and Variants of an Uncommon Cause of Cardiac Implantable Electronic Device Dysfunction

OBJECTIVES

This cumulative case study was performed to properly address the possible mechanisms, forms, and consequences of "twiddler's," "reel," and "ratchet" syndromes.

BACKGROUND

Twiddler's, reel, and ratchet syndromes are rare entities responsible for lead displacement of cardiac implantable electronic devices (CIED).

METHODS

From 2007 to 2012, 1,472 CIED were implanted at our center. Eighty-nine cases were reviewed for failure of pacing circuit integrity. Only 9 met the inclusion criteria for idiopathic lead migration (ILM) and were grouped as ILM (twiddler) or ILM (reel). For a pooled analysis of cases, a review of the literature from 1990 to 2012 was performed, and the authors identified 78 cases from 64 publications.

RESULTS

The study population consisted of 87 cases (45 women; median age, 66 years; 46 with ILM [twiddler] and 41 with ILM [reel]). Migration affected only 1 lead in 65% of 46 devices with more than 1 lead. None of the previously reported risk factors-manual manipulation of the device, elderly age, obesity, oversized pocket, and psychiatric history-correlated with the risk of ILM.

CONCLUSIONS

Neither manual manipulation of the device nor the other traditional risk factors reported in the literature for ILM syndrome correlated with the risk of ILM.

[Cardiology in the Morgagni's anatomo pathological work]

In the XVIII century, under the influence of the "systematic spirit", characteristic of the Enlightenment age, pathological anatomy was systematized in the Morgagni's fundamental treatise De sedibus et causis morborum per anatomen indagatis, published as letters in 1761. Certain biographical data of the author are reported here as well as some his more important contributions to cardiology such as the Morgagni's, Adams', Stokes' syndrome. His points of view on sudden death and his observations on post-infarct myocardial rupture, are related also. In his global evaluation of these facts, the speculative approach always predominates. Indeed, in these anatomist's works, we find a good example of the application of epistemologic principles to the medical field.

Reuse of pacemakers: comparison of short and long-term performance

BACKGROUND

In developing economies, there are patients in whom pacemaker implantation is delayed because they cannot afford one. Reused devices have been a solution. To address concerns about safety, a cohort of consecutive patients implanted with a reused pacemaker was compared with a control group.

METHODS AND RESULTS

A cohort of 603 consecutive patients from 2000 to 2010 was studied in an ambispective noninferiority study. The study group patients (n=307) received resterilized pacemakers, and the control group patients (n=296) received a new pacemaker. A combined end point of 3 major outcomes-unexpected battery depletion, infection, and device dysfunction-was analyzed. A total of 85 pacemakers had to be explanted, 31 in the control group (10.5%) and 54 in the study group (17.6%; relative risk, 1.68; 95% confidence interval, 1.1-2.5; P=0.02). Forty-three reached the primary end point, 16 in the control group (5.5%) and 27 in the study group (7.2%; relative risk, 1.3; 95% confidence interval, 0.70-2.45; P=0.794). In terms of individual outcomes, 5 new pacemakers (1.7%) and 11 resterilized pacemakers (3.6%) had unexpected battery depletion (relative risk, 2.12; 95% confidence interval, 0.75-6; P=0.116); 3.7% new pacemakers and 3.2% reused pacemakers had a procedure-related infection (relative risk, 0.87; 95% confidence interval, 0.38-2.03; P=0.46); and 1 pacemaker in the study group malfunctioned.

CONCLUSIONS

Pacemaker reuse is feasible and safe and is a viable option for patient with bradyarrhythmias. Other than the expected shorter battery life, reuse of pacemaker generators is not inferior to the use of new devices.

Electrocardiographic manifestation of the middle fibers/septal fascicle block: a consensus report

There are fibers in the left ventricle (LV) (LV middle network) that in around one third of cases may be considered a true septal fascicle that arises from the common left bundle. Its presence and the evidence that there are 3 points of activation onset in the LV favor the quadrifascicular theory of the intraventricular activation of both ventricles. Since the 70s, different authors have suggested that the block of the left middle fibers (MS)/left septal fascicle may explain different electrocardiographic (ECG) patterns. The 2 hypothetically based criteria that are in some sense contradictory include: a) the lack of septal "q" wave due to first left and later posteriorly shifting of the horizontal plane loop and b) the presence of RS in lead V(2) (V(1)-V(2)) due to some anterior shifting of the horizontal plane vectorcardiogram loop. However, there are many evidence that the lack of septal q waves can be also explained by predivisional first-degree left bundle-branch block and that the RS pattern in the right precordial leads may be also explained by first-degree right bundle-branch block. The transient nature of these patterns favor the concept that some type of intraventricular conduction disturbance exists but a doubt remains about its location. Furthermore, the RS pattern could be explained by many different normal variants. To improve our understanding whether these patterns are due to MF/left septal fascicle block or other ventricular conduction disturbances (or both), it would be advisable: 1) To perform more histologic studies (heart transplant and necropsy) of the ventricular conduction system; 2) To repeat prior experimental studies using new methodology/technology to isolate the MF; and 3) To change the paradigm: do not try to demonstrate if the block of the fibers produces an ECG change but to study with new electroanatomical imaging techniques, if these ECG criteria previously described correlate or not with a delay of activation in the zone of the LV that receives the activation through these fibers or in other zones.

[Clinical predictors of ventricular arrhythmia storms in Chagas cardiomyopathy patients with implantable defibrillators]

OBJECTIVES

To define the predictive factors of electrical storm (ES) in patients with Chronic Chagas Heart Disease (CCh) with an implantable cardioverter defibrillator (ICD).

MATERIAL AND METHODS

We retrospectively studied 21 consecutive patients with CCh in whom an ICD was implanted between April 2005 and December 2008, with a mean follow up of 867 days. Patients were classified into two groups according to the presence of electrical storm episodes. We compared baseline characteristics, medical treatment and determinants of ventricular function. P values less than 0.05 were considered statistically significant.

RESULTS

Of the 21 patients with CCh there were eight women (37%), mean age 61 years and an EF of 30%. It was noted at least one episode of arrhythmic storm in 9 cases (incidence of 43%). The total number of episodes of arrhythmic storm was 13 and the number of ventricular arrhythmias in each episode of arrhythmic storm was 15.6 (range 3-61). A trigger was identified in only two cases (pulmonary infectious process and decompensation of chronic heart failure). After analyzing the possible predictors of arrhythmic storm was found that a greater percentage of subjects with this complication had an EF <35% (89% vs. 50%, p = 0.01) and NYHA functional class III (66% vs. 8.3%, p = 0.001). In contrast, a lower percentage of subjects with arrhythmic storm were under beta-blocker treatment (55% vs. 100%, p = 0.01).

CONCLUSIONS

In subjects with CCh with an ICD, the following variables are predictive of arrhythmic storm: EF <35%, NYHA functional class III-IV and absence of beta-blocker treatment.

Peripheral heart blocks associated with myocardial infarcts: clinical diagnosis based on experimental findings

Septal necrosis + peripheral left blocks. Because of an extensive septal necrosis, the manifestation of the initial ventricular activation forces decreases in the precordial leads. With left bifascicular block (LASB + LPSB), the first ventricular activation forces become more evident and the electrical signs of septal necrosis can be concealed. In the presence of a trifascicular block, manifestation of the first ventricular electromotive forces diminishes again and the electrical signs of septal necrosis become evident once more. Small Q waves are present in leads V₁ to V₄.

Extensive anterior necrosis + peripheral blocks. This necrosis is manifested by QS complexes from V₂ to V₆. An associated left bifascicular block reduces the electrical manifestation of dead tissue: QS complexes persist only in V₃ and V₄. In turn, a coexisting trifascicular block causes the presence of QS complexes from V₂ to V₅.

Posteroinferior necrosis + peripheral blocks. Electromotive forces of the ventricular activation shift upward, due to a posteroinferior necrosis and QS or QR complexes are recorded in leads aVF, II and III. An associated left bifascicular block displaces the main electromotive forces downward, posteriorly and to the left, due to a delay of the posteroinferior activation fronts. The ventricular complexes become positive and wider in all leads, reflecting the potential variations of the inferior portions of the left ventricle: aVF, II, III, sometimes V₅ and V₆. Consequently, the electrical signs of necrosis are reduced or abolished. Due to a trifascicular block, wide and slurred QS complexes are recorded in aVF, II, III and sometimes in V₅ and V₆.

Electrocardiographic characteristics of patients with Ebstein's anomaly before and after ablation of an accessory atrioventricular pathway

The abnormal development of the tricuspid valve in patients with Ebstein's anomaly results in several activation abnormalities including delayed intraatrial conduction, right bundle branch block (RBBB), and ventricular preexcitation. The aim of the present study was to define the ECG characteristics before and after ablation of an accessory A-V pathway (AP) in patients with Ebstein's anomaly.

METHODS

A series of 226 consecutive patients with Ebstein's anomaly was studied. Sixty-four patients (28%) had documented tachycardia. Thirty-three patients with recurrent tachycardia were found to have a single right-sided AP that was successfully ablated (study group). Thirty patients without tachycardia served as the control group.

RESULTS

Only 21 of 33 patients (62%) had a typical ECG pattern of preexcitation. In addition, none of the patients had an ECG pattern of RBBB during sinus rhythm. In contrast, 28 of 30 (93%) patients in the control group had RBBB (P < 0.001). Radiofrequency catheter ablation resulted in appearance of RBBB in 31 of 33 (94%) patients. The absence of RBBB in patients with Ebstein's anomaly and recurrent tachycardia had a 98% sensitivity and 92% specificity for the diagnosis of an AP. The positive predictive value was 91% (0.77, 0.97 CI 95%) and the negative predictive value was 98% (0.85, 0.99 CI 95%).

CONCLUSION

One-third of patients with Ebstein's anomaly and symptomatic tachyarrhythmias have minimal or absent ECG features of ventricular preexcitation. In these patients, the absence of RBBB pattern is a strong predictor of an AP.

[On the electrical manifestations of some heart diseases associated with ventricular preexcitation]

Electro-Vectorcardiographic curves, corresponding some heart diseases, must be analyzed in the light of the ventricular depolarization sequence, as well as on the heart's position and rotation. A more than 30-msec interval between the end of the initial slurring (delta) and the vertex of the R wave in the left unipolar leads or the main axis of the vectorcardiographic ventricular curves, allows us to infer the coexistence of left ventricular hypertrophy. On the other hand, segmental irregularities or distorsions of the electric curves suggest the presence of a limited myocardial zone unable to be activated. Extensive or multiple deformations of these curves are more suggestive of a diffuse myocardial damage. Sometimes signs of preexcitation, due to a pharmacological action, can also appear.

[On the ventricular arrhythmias in Chagasic chronic cardiomyopathy]

Some authors have shown a high prevalence of electric circuits localized in the epicardium in Chagasic cardiomyopathy. Other authors have found in these patients, during electric mapping, mid-diastolic potentials and earlier myocardial activation in epicardial regions than in the endocardium. In a previous study, we found electrocardiographic signs of subepicardial ischemia in 66% of seropositive Chagasic patients against 16% of seronegative Chagasic ones. In the case presented here, a Chagasic dilated cardiomyopathy, we found electrocardiographic signs of subepicardial injury in the left free ventricular wall, related with histological findings of lymphocytic inflammation in these regions. In contrast, the endocardium was completely free from inflammation foci.

Arrhythmic storm responsive to quinidine in a patient with Brugada syndrome and vasovagal syncope

A 37-year-old man with Brugada syndrome (BrS) and arrhythmic storm is described. One month after implantation of a cardioverter-defibrillator he presented with recurrent appropriate shocks for spontaneous ventricular fibrillation (VF). Because of this arrhythmic storm, quinidine therapy was initiated with total suppression of all spontaneous arrhythmias. He had remained free of arrhythmias for 22 months since quinidine initiation. Two episodes of VF occurred after the patient stopped taking the medication. The patient resumed quinidine and has been free of VF for the last 3 months. This response to quinidine in a patient with symptomatic BrS supports its role in the prophylaxis of arrhythmic events in BrS.

Familial vasovagal syncope

Vasovagal syncope (VVS) is a common clinical problem characterized by transient episodes of loss of consciousness due to abnormal autonomic activity. This paper describes two groups of monozygotic twins, from different families, affected by VVS and a family with several members with this condition. Their clinical characteristics, haemodynamic response to tilt, treatment, and outcome are described.

Dynamic electrocardiographic changes after aborted sudden death in a patient with Brugada syndrome and rate-dependent right bundle branch block

A 37-year-old man with Brugada syndrome and dynamic changes of the ST-segment morphology observed after an episode of aborted sudden death is described. On admission, after 3 syncopal episodes during nighttime, his electrocardiogram showed right bundle branch block (RBBB) with a J-point elevation of 0.6 mV in lead V 2 . Changes observed in the following days included a diminished J-point elevation and intermittent "saddle-back" type of morphology. During a previous 2-year follow-up, intermittent, complete, acceleration-dependent RBBB was documented. Right ventricular intracavitary tracings showed an RS pattern with a broad S wave in the unipolar electrogram; the time of onset of intrinsic deflection in this electrogram was 60 milliseconds. To our knowledge, this is the first report of an intracavitary demonstration of complete RBBB in Brugada syndrome.

[Surgical radiofrequency catheter ablation of accessory pathways in Ebstein's anomaly]

Thirteen patients with Ebstein anomaly and atrioventricular reentrant tachycardia and at least one accessory pathway were included in this study. One accessory pathway in 7 (53.8%) patients and multiple accessory pathways in 6 (46.1%) were found. Mahaim accessory pathway was observed in 5 (38.4%) patients. A total of 22 accessory pathways was found, 2 (9%) were concealed. In all (100%), the accessory pathways were located in the tricuspid ring. The most frequent regions were right lateral free wall with 11 (50%) and 5 right posteroseptal (22.7%). Ten patients underwent surgical radiofrequency catheter ablation and three subjected to surgical section. We obtained success in 100%. No complications were observed during the procedures. In conclusion, surgical ablation therapy in patients with accessory pathways and Ebstein's anomaly is safe and effective.

[Cardiac involvement in Kearns-Sayre syndrome]

The mitochondrial cytopathies or oxidative-phosphorylation diseases are a diverse group of disorders that result from the structural, biochemical, or genetic derangement of mitochondria. Because mitochondrial dysfunction can affect the most highly energy-dependent organs, cardiac involvement is frequent in these diseases. To identify the clinical features of Kearns-Sayre syndrome, an entity associated with this group of diseases, we evaluated cardiac structure and function in 5 patients with Kearns-Sayre syndrome and followed the clinical course of these patients for 5 years.

[Direct cryothermal ablation eliminates conduction of the slow pathway without inducing ectopic rhythms]

Radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia is based on the elimination of conduction of slow or fast intranodal pathway. To avoid potential atrioventricular (AV) block, a new technology has been developed, cryothermal ablation. We report a case of AV nodal reentrant tachycardia in whom direct cryoablation, without previous ice mapping, was successfully performed. Interestingly and as previously described, cryotherapy did not induce ectopic rhythms, the conventional surrogate during radiofrequency ablation.

[Trans-septal puncture for radiofrequency ablation of left accessory pathway]

We present the case of an 18-year-old male patient with diagnosis of Wolff Parkinson-White syndrome due to a left free wall accessory pathway. We performed an electrophysiology study and transseptal punction guided by transesophageal echocardiogram to via access to the left atrium. We performed successful radiofrequency ablation of the accessory pathway, observing disappearance of the delta wave on the first attempt. There were no complications. In follow-up a 10 months, the patient had no clinical nor electrocardiographic evidence of recurrence. Transseptal radiofrequency ablation is an alternative for treatment of some arrhythmias localized in the left side of the heart.

[Infrequent electrocardiographic changes during exercise stress test in a patient with Brugada's syndrome]

38 year old patient with a syncope history and family background of sudden death had an electrocardiogram compatible with the "Brugada Syndrome". When an exercise stress testing with Bruce protocol was done, we found that during the effort phase and at maximum effort, contrary to a ST segment normalization, a discreet increase of the ST segment elevation of 2 mm in V1 and V2 occurred. During recovery phase a decrease in the ST segment elevation was observed, at a normal level as before the test.

[ Segmental ostial ablation to interrupt electrical conduction in a single pulmonary vein for the prevention of idiopathic paroxysmal atrial fibrillation]

Several studies have shown the role of focal trigers in the pulmonary veins initiating episodes of atrial fibrillation. Radiofrequency catheter ablation of this foci is a curative therapy for paroxysmal atrial fibrillation. We report a case of idiopathic paroxysmal atrial fibrillation triggered by abnormal electrical activity in a single pulmonary vein. Mapping was performed during sinus rhythm with a 4F decapolar catheter (Spiral Supreme, Daig, St. Jude Medical) positioned near the ostium by a transseptal approach. Pulmonary vein potentials were only identified in the left superior pulmonary vein. Segmental ostial ablation (30 W) performed during left atrial pacing resulted in complete cesation of conduction in the pulmonary vein. There were no complications. The clinical response (suppression of the paroxysms of atrial fibrillation in a 9-month follow-up) observed in this patient imply that atrial fibrillation was triggered by this pulmonary vein. This case report illustrates several aspects of catheter-based ablation of pulmonary vein foci for the treatment of paroxysmal atrial fibrillation and demonstrates its efficacy.

[On the clinical value of electrocardiogram]

Emphasis is given to the clinical value of the electrocardiogram, a simple, quick and unexpensive method for heart exploration. It provides functional information and reliably reflects the metabolic and electrolytic characteristics of myocardial fibers. Such an information cannot generally be obtained by other more sophisticated and expensive methods. The localization and extension of myocardial infarction, the positional and structural changes observed during the evolution of chronic cor pulmonale of obstructive origin, some characteristics of atrial and ventricular arrhythmias, the site of preexcitation in WPW syndrome and troubles due to a dysfunction of the ionic channels because of metabolic or genic alterations, are particularly examined. 1. A good correlation exists between the anatomical site and electrocardiographic indication of the infarcted area. 2. In the obstructive chronic cor pulmonale, positional and structural changes of the heart are observed. The first ones correspond to a vertical heart, due to a descent of the diaphragm and an increase of lung volume. The structural changes are due to an enlargement of the right heart: dilatation and hypertrophy. 3. Ventricular arrhythmias habitually present the "jumping wave" phenomenon between both septal masses and the consecutive aberrance of the ventricular complexes. 4. In the WPW syndrome, the thoracic circle permits to infer the site of preexcitation by the orientation of the first fronts of anomalous ventricular activation. 5. Modifications in the Q-Tc interval reflect the variations of ionic intracellular concentrations in a more reliable way than the changes of plasmatic concentrations. The aforementioned evidences the great usefulness of the electrocardiogram in the clinical setting.

Radiofrequency ablation of atrioventricular accessory pathways associated with discordant atrioventricular connections

Discordant atrioventricular connections associated with Wolff-Parkinson-White syndrome increase the challenge of radiofrequency ablation. We report the results and techniques of radiofrequency ablation in three patients with discordant atrioventricular connections, including one patient having double outlet right ventricle with atrioventricular reentry tachycardias. There were two males and one female, aged 14 and 22 years old. We found four accessory pathways during our electrophysiological studies, with two of them manifest on the electrocardiogram, corresponding to left paraseptal and right midseptal regions. The electrophysiological study confirmed this localization, and showed two concealed accessory pathways in the right and left paraseptal regions. Radiofrequency ablation was successful in all cases without recurrence at a mean follow-up of 18.6 months. No complications were observed during the procedures. We conclude that radiofrequency ablation is feasible and effective in the ablation of accessory pathways in patients with discordant atrioventricular connections.

An experimental contribution to the concept of "jumping wave" phenomenon in the interventricular septum

OBJECTIVE

The purpose of this study was to evaluate the existence of a histologically bipartite interventricular septum and the electrical independence of both septal masses, as well as to understand the changes of septal activation fronts in the presence of bundle branch blocks.

METHODOLOGY

We examined the histological characteristics of both septal masses in 12 canine hearts. Furthermore, in another 11 anesthetized dog hearts, we analyzed morphological and chronological data of intraseptal records with normal activation and in the presence of proximal blocks.

RESULTS

A histological discontinuity between the two septal masses in canine hearts seems to exist. Analysis of intraseptal and intracavitary electrical records confirmed slow transmission of the activation fronts from one septal mass to the other when proximal blocks were present. Morphological and chronological changes of the intracavitary complexes agree with the "jumping wave" phenomenon theory.

CONCLUSIONS

These results support the validity of this approach to the activation of both septal masses and explain the chronological and morphological changes of the intracavitary records in the presence of ventricular blocks. In addition, this approach is a useful tool to detect the possible coexistence of dead septal tissue.

Common electrocardiographic artifacts mimicking arrhythmias in ambulatory monitoring

BACKGROUND

Ambulatory electrocardiographic monitoring is used in clinical practice as a means of detecting cardiac arrhythmias during daily activities. Current equipment provides analysis for the detection of arrhythmias, ST-segment deviation, and more sophisticated analyses (late potentials, Q-T behavior, and heart-rate variability). However, despite the system used, a number of artifacts could mislead diagnosis.

METHODS AND RESULTS

We prospectively searched for artifacts during ambulatory electrocardiography in patients referred for monitoring to our institution, a tertiary referral center. Patients were ambulatory at home, work, school, or within the hospital. We divided artifacts according to Krasnow and Bloomfield's classification (pseudoarrhythmia, nonarrhythmia), and we added a new category, artifacts in patients with pacemakers. Artifacts encountered mimicked sinus arrest, supraventricular arrhythmias, ventricular arrhythmias, and aberrancy. Examples of each one and diagnostic clues are provided to recognize these artifacts properly.

CONCLUSIONS

A substantial amount of invalid data (false-positive findings because of electrocardiographic artifacts) were identified during ambulatory electrocardiographic monitoring that can lead to inappropriate interpretation and may result in severe diagnostic errors.

Radiofrequency ablation of multiple accessory pathways

The aim of the study was to review the clinical and electrophysiological characteristics and results of radiofrequency catheter ablation in patients with multiple accessory pathways to compare them with those of patients with single accessory pathways. Electrophysiological study and radiofrequency catheter ablation were performed in 1010 consecutive cases with Wolff Parkinson White Syndrome. Presence of multiple accessory pathways was documented in 31 patients (3.1%); 30 had two, and 1 had three accessory pathways. Of the 63 accessory pathways, 42 were manifest and 21 concealed. Nine patients had Ebstein's anomaly associated with atrioventricular bypass tracts. The most common combination was right posteroseptal with right free wall bypass tracts (15 patients with 30 accessory pathways). Fifty-one of the sixty-three accessory pathways (81%) were ablated successfully without complications. The duration of the procedure was 100 +/- 58 min and the fluoroscopic time 40 +/- 17 min. A follow up of 5 +/- 3 years after ablation, demonstrated recurrences of six accessory pathways (9.5%). In conclusion, patients with multiple accessory pathways can be treated by radiofrequency ablation in only one session with a high success rate although slightly less than that in patients with a single accessory pathway (81% vs 93%, P<0.01).

[Ventricular tachycardia associated with isolated right ventricular dysfunction as indicator of arrhythmogenic dysplasia of the right ventricle]

We report the case of a 21 year-old patient with arrhythmogenic right ventricular dysplasia manifested by episodes of QRS tachycardia greater than 0.12 sec and isolated dysfunction of the right ventricle. The patient treated with amiodarone however, the tachycardia episodes persisted. The surface electrocardiogram showed left branch block with the axis down, which suggested a right ventricle origin, and was therefore considered an arrhythmogenic dysplasia. Echocardiography and cardioangiography showed alterations in the anatomy of the outflow tract of the right ventricle. A myocardial gammagraphy revealed no perfusion alterations. The endomyocardial biopsy showed perivascular fibrosis. An electrophysiology study was performed, stimulating the outflow tract of the right ventricle, which induced two types of ventricular tachycardias, one of them identical to that recorded clinical. The patient was treated with sotalol, and has been being free of ventricular tachycardia episodes for 18 months of follow-up. We consider that this entity should be studied in a systematic way in those patients with ventricular tachycardia originated in the outflow of the right ventricle and with primary cardiac illness.

[Radiofrequency ablation and simultaneous insertion of an Amplatzer device in a patient with atrial septal defect and nodal reentry tachycardia]

The association of AV nodal reentry tachycardia and interatrial septal defect has not been described previously. This article reports a 47-year-old woman with an atrial septal defect (ostium secundum) and history of palpitations without documental tachycardia through resting and ambulatory electrocardiography. Rapid atrial pacing under the influence of isoproterenol, during an electrophysiology study, elicited and AV nodal reentry tachycardia of the common type. Successful radiofrequency catheter ablation was performed targeting the slow pathway. Immediately an Amplatzer device was used for closure of the septal defect. Both procedures were successful and without complications. What makes this case unusual is that both interventional procedures were performed during the same session.

[The Einthoven's electrocardiograph after 100 years]

The initial studies about the "irritability" of animal tissues by iatrophysic and iatromechanic scientists are reviewed. These studies led to discover the so called animal electricity envisaged by Luigi Galvani in the XVIII century and demonstrated by Carlo Matteucci and his followers in the XIX. Beginning with the Galvani's "reoscopic" frog, which allowed to assess the electrical current in a qualitative sense, it was possible to arrive, at the beginnings of the XX century, to the string electrocardiograph presented by Willem Einthoven in 1901. This opened the way that led to fabrication of ever more sophisticated instruments until the present systems of endocardial mapping by magnetic technology or by multipolar catheters, which permit to quickly identify the site of origin or the spreading ways of a tachycardia for their ablation with radio-frequency. Intracardiac echocardiography is also employed to define the anatomy of right atrium, during intracardiac cartography, in order to establish the most adequate sites for ablation. On the other hand, a logic i.e. rational, method for the interpretation of results from the electrical exploration of the heart has been developed. This one was introduced by Frank N. Wilson in Ann Arbor and has been fittingly applied by Demetrio Sodi Pallares in Mexico. Important diagnostic advances and notable therapeutic inferences have been derived from these latter developments.

[Usefulness of superficial electrocardiogram in the diagnosis of narrow QRS tachycardias: correlation with intracavitary electrocardiograms]

INTRODUCTION AND OBJECTIVES

The electrocardiogram is an important tool to diagnose tachycardias. The sequence of analysis of the superficial electrocardiogram was evaluated for the diagnosis of supraventricular tachycardias with narrow QRS complexes (<= 110 ms) establishing correlation with intracavitary electrograms.

PATIENTS AND METHODS

Between November 1996-October 1998, 674 electrophysiological studies were revised. 173 cases were selected, during which supraventricular tachycardias were inducted. In each study, the superficial electrocardiographic leads were correlated with the intracavitary electrograms during tachyarrhythmias. The P waves were located with respect to the R waves, the R-T or T-R' intervals, and the T waves, and relations between atrioventricular and ventriculoatrial intervals were established with the P-R' and R-P intervals, respectively, in the electrocardiogram.

RESULTS

107 patients were female. Upon locating the P waves in the electrocardiogram, in each supraventricular tachycardia we observed: a) P waves coincided with the R waves: 30 typical nodal reentries; b) P waves between R and T waves: 95 orthodromic atrioventricular reentries, 27 nodal reentries, 1 atrial tachycardia; c) P waves between T and R' waves: 4 nodal reentries, 5 orthodromic atrioventricular reentries, 7 atrial tachycardias, and <Id) P waves over T waves: 3 orthodromic atrioventricular reentries, and 1 nodal reentry.

CONCLUSIONS

The sequence of analysis locating the P waves in the superficial electrocardiogram is an useful, rapid method, with adequate sensitivity or specificity, in the evaluation of the mechanisms that sustain more common supraventricular tachycardias, permitting the performance of differential diagnosis between some of them.

[Trans-surgical ablation of atrial flutter in patients treated with closure of atrial septal defect. Pilot project]

Atrial flutter is one of the most common arrhythmias in patients with atrial septal defect, after surgery 14% of patients can develop it and may be associated with high morbidity. In this study we performed prophylactic and therapeutic ablation of atrial flutter during atrial septal closure surgery drawing 4 lines; line 1, isthmus cavo-tricuspid, the area between the inferior vena cava and the tricuspid ring; line 2, the area between coronary sinus ostium and inferior vena cava; line 3, the area between tricuspid valve annulus and coronary sinus ostium; and line 4, the area between lateral atriotomy and atrial septal defect. Twenty-one patients were included, 6 (28.5%) patients had atrial flutter before surgery and 15 (71.4%) were in sinus rhythm. There were no new cases of atrial flutter, but at six months follow up 2 (33.3%) patients recidivated with atrial flutter. One patient developed high degree atrio-ventricular block and a pacemaker had to be implanted. Older age at the time of surgery and high systolic pulmonary pressure were significantly higher in those patients with atrial flutter before surgery and in patients with arrhythmias recurrence. Ablation of atrial flutter during atrial septal closure surgery can be a good option for the treatment and prevention of atrial arrhythmias, but more studies are still needed.

The rational approach to the electrical exploration of the heart

A rational approach is inevitable in any scientific activity. Such an approach is opposed not only to irrationality, at all inadmissible in scientific thinking, but also to empiric reasoning. Many years ago, Sodi Pallares introduced the rational method in the electrical exploration of the heart based on experimental findings obtained in his laboratory. This method has progressively been accepted and used with good results for diagnoses and has led to logical therapeutic inferences. To confirm the results from the logical interpretation of electrical tracings, we present some examples of its application in three fields: arrhythmias, myocardial infarction, and left ventricular hypertrophy. In the studied cases--two with tachycardia, one with a posterior infarct, and two with left ventricular hypertrophy--a very satisfactory correlation has been observed between the electrical exploration findings and those obtained through direct examination of the heart. It is desirable, and even profitable, to analyze in this way the electrical tracings to get as close as possible to reality, rejecting the stereotyped aspects of a simple routine exploration, which often induce errors and lead to some fallacious asseverations.

[Sudden death in intermittent Wolff Parkinson White syndrome]

Sudden death is a rare condition in asymptomatic patients with asymptomatic intermittent Wolff Parkinson syndrome (WPW); for this reason it is believed that these patients should not undergo to radiofrequency ablation. We report an asymptomatic 44 year old man who developed ventricular fibrillation with a pre-excited RR interval less than 200 msec during atrial fibrillation, as a first manifestation of WPW syndrome. The Holter monitoring showed intermittent pre-excitation at low heart rate (70 bpm). During the electrophysiological study a successfully radiofrequency catheter ablation of a right posteroseptal accessory pathway was performed. We concluded that intermittent pre-excitation may not be used to identify patients who are at risk of sudden death. Radiofrequency catheter ablation should be recommended in those patients with a very high success rate, and a low incidence of serious complications.

Radiofrequency catheter ablation for the treatment of supraventricular tachycardias in children and adolescents

We report our experience in radiofrequency catheter ablation between April, 1992 and December, 1998, in which we treated 287 patients less than 18 years of age (mean 14.3 +/- 3.1 years) with supraventricular tachycardia. Accessory, pathways were the arrhythmic substrate in 252 of the patients (87.8%), the patients having a total of 265 accessory pathways. Atrioventricular nodal re-entry was the cause of tachycardia in 26 patients (9.0%), while atrial flutter was detected in the remaining 9 patients (3.1%). We were able successfully to eliminate the accessory pathway in 236 patients (89%), but 25 patients had recurrent arrhythmias. Ablation proved successful in all cases of atrioventricular node re-entry tachycardia, the slow pathway being ablated in 25 patients, and the fast pathway in only one case. Recurrence of the arrhythmia occurred in three patients (11.5%). We performed a second ablation in these children, all then proving successful. The ablation was successful in all cases of atrial flutter, with one recurrence (11.1%). Overall, therefore, ablation was immediately successful in 271 patients (94.4%), with a recurrence of the arrhythmia in 29 cases (10.7%). The incidence of serious complications was 2.09%. There was one late death due to infective endocarditis, 3 patients suffered complete heart block, 1 had mild mitral regurgitation, and 1 patient developed an haematoma in the groin. We conclude that radiofrequency catheter ablation can now be considered a standard option for the management of paroxysmal supraventricular tachycardias in children and young adults.

On the electrocardiographic diagnosis of biventricular infarctions

To diagnose posterior and anterior biventricular infarctions it is necessary to record from right and left thoracic and high abdominal unipolar leads. These supplementary leads are dependable, can be repeated as many times as needed and show the evolution from signs of myocardial injury to those of dead tissue (Q waves of 0.04 sec or more). This electrocardiographic evolution increases the diagnostic value of the electrical exploration, since the injury current can be observed also in other conditions. The diagnosis of right ventricular infarction can be established even in the presence of RBBB. Signs of a dead zone in the free right ventricular wall are more frequently observed in posterior biventricular infarctions than in anterior ones. In these cases, the signs of subepicardial injury are more accentuated in the right thoracic unipolar leads than in V3, indicating anterior right ventricular involvement. These signs are also observed in experimental studies made in animals. This electrocardiographic exploration opens a wide field for the diagnosis of myocardial infarction, particularly in biventricular involvement, including old myocardial scars, and in discarding signs of pericarditis manifested only by the upward displacement of the ST segment. A review of the medical literature concerning diagnosis of biventricular infarctions is presented.