相同基因型而不同表现型的PRKAG2基因突变一家系报道

目的 位于7号染色体上的腺苷一磷酸激活的蛋白激酶γ^2调节亚单位基因（PRKAG2基因）调节代谢通路。报道一个具有PRKAG2基因突变而临床表现型不同的家系。方法 使用DNA直接测序法,对一个具有多种形式心律失常的患者家系（13例患者）进行PRKAG2外显子及外显子和内含子拼接部位序列筛查寻找基因突变。结果 心电图显示患者家系存在窦性心动过缓、短PR间期、完全性右束支传导阻滞、房室传导阻滞和房性心动过速。其中3例患者在年轻时发生猝死,没有1例有预激综合征（预激）表现,只有1例有心肌肥厚。DNA测序结果显示,该家系所有患者皆有一个PRKAG2错义突变（R302Q）。这个基因突变以前曾描述并与预激和左室肥厚有关。结论 PRKAG2基因突变不仅导致预激而且与多种临床表现型有关。完全性右束支传导阻滞、窦性心动过缓、短PR间期应该高度怀疑有PRKAG2基因突变的可能。     

Prehospital brady-asystolic cardiac arrest.

Of 133 persons with spontaneous cardiac arrest attended by paramedics within 10 minutes, 100 (75%) had ventricular fibrillation as the initial rhythm and 33 (25%) had extreme bradycardia or asystole. The latter group of arrhythmias was characterized by sinus arrest or severe sinus bradycardia (90%) and complete A-V block (10%). Junctional escape rhythm was also absent or markedly retarded. Despite cardiopulmonary resuscitation and the administration of epinephrine, atropine, isoproterenol, and sodium bicarbonate, recovery of the sinus and junctional tissues was infrequent. Ventricular fibrillation developed in 11 cases (33%). One patient lived 12 days, but all others were dead on arrival or died in the emergency room. Among the 13 coronary causes of death proved at autopsy, 10 (77%) were due to a fresh thrombus and seven (54%) to an occluded proximal right coronary artery, suggesting a causal relation to this type of arrest.     

Acute treatment with verapamil of paroxysmal supraventricular tachycardia and atrial flutter in paediatric age (author's transl)]

43 patients, 3 days to 12 years old, presented 68 paroxysms of supraventricular tachycardia and 2 crises of atrial flutter. 6 patients had a WPW syndrome and only 7 had an associated cardiac disease; the remaining had no other complaint but the arrhythmia. Verapamil, administered in the dose of 0.125-0.25 mg/Kg intravenously, interrupted critically the tachycardia in virtually all cases. The flutter was converted to atrial fibrillation with a slower ventricular rate. No adverse effects were observed but in two cases: one had a cardiac arrest promptly relieved and another a ventricular bradycardia corrected by atropine. Both cases had received an overdose of the drugs.     

Tachycardia-bradycardia syndrome (so-called "sick sinus syndrome"). Pathology, mechanisms and treatment

The tachycardia-bradycardia syndrome consists of paroxysmal atrial fibrillation, flutter or tachycardia followed by sinoatrial block or sinus arrest resulting in Stokes-Adams attacks. Detailed histologie findings of the conduction system of 2 patients with this entity correlated well with the clinical observation of cardiac rhythm disturbances in the sinus node, atria and atrioventricular (A-V) junction. Eight other patients with the syndrome were studied clinically. The mechanisms (as revealed by the electrocardiogram) producing the bradycardia phase include depression of pacemaker function (arrest) or of conduction (exit block) of the sinus impulse, or both, plus depression of A-V junctional impulse formation. Proper therapy usually requires electrical pacing in conjunction with administration of digitalis or propranolol, or both. Our findings suggest that the term “sick sinus syndrome” is an inaccurate and inappropriate synonym for the tachycardia-bradycardia syndrome.     

Atrial fibrillation in the Wolff-Parkinson-White syndrome.

Atrial fibrillation in patients with Wolff-Parkinson-White (WPW) syndrome may lead to syncope, ventricular fibrillation, and sudden death. In a follow-up study of 241 patients with WPW syndrome in a relatively unselected population, 26 patients had documented atrial fibrillation (11%). These patients were followed up after 1-37 years (median 11 years; mean 15 years). During this period, 2 of 26 died suddenly. These 2 patients had the shortest RR interval during spontaneous atrial fibrillation (less than or equal to 220 msec), greater than or equal to 1 episodes of syncope, and a persistent delta wave in all available electrocardiograms. In comparison, sudden or tachycardia-related death was seen in 4 of the 241 patients. This difference is not statistically significant. Thus, atrial fibrillation of 26 patients with WPW syndrome was surprisingly well tolerated in our follow-up study with only 2 sudden deaths.     

Cardiac rhythm disturbances early after orthotopic heart transplantation: prevalence and clinical importance of the observed abnormalities

To precisely define the incidence, type and consequences of cardiac arrhythmias early after heart transplantation, 25 cardiac transplant recipients were monitored continuously for 728 days from the day of surgery to discharge or death. A subset of 15 patients had sinus node function studies with overdrive suppression performed weekly at the time of endomyocardial biopsy. Results revealed sinus bradycardia in 10 patients (40%) and junctional bradycardia in 6 (24%). Supraventricular tachycardia in the form of atrial tachycardia, atrial fibrillation and atrial flutter occurred in 11 patients (44%). Ventricular tachycardia occurred in 15 patients (60%) and was nonsustained in all. Cardiac pacing for 1,403 h was used in nine patients with a pulse rate less than 50 beats/min; seven recovered and permanent pacing was instituted in two. In the subgroup that had sinus node function studies, seven patients were identified with clinical bradyarrhythmia; each had abnormal sinus node recovery time (greater than 1,400 ms) and abnormal corrected sinus node recovery time (greater than 525 ms) in at least one study. These seven patients also had a significantly prolonged ischemic time (236 +/- 26 versus 159 +/- 68 min, p less than 0.01). In conclusion, cardiac arrhythmias, particularly ventricular tachycardia and bradyarrhythmia, occur more commonly early after orthotopic heart transplantation than has previously been reported. Sinus node dysfunction due to prolonged organ ischemic time, antiarrhythmic drug use or surgical trauma, alone or in combination, may contribute to these arrhythmias.     

Ventricular fibrillation as a primary manifestation of Wolff–Parkinson–White syndrome

Wolff–Parkinson–White syndrome (WPW) is defined as a condition involving an accessory pathway associated with symptoms. A typical ECG pattern of a pre-excitation shows a short PQ interval, presence of delta wave and a broad QRS complex on surface ECG. The underlying mechanism involves an accessory pathway, which enables conduction of a depolarization wave from atria to ventricles bypassing the AV node and predisposes to arrhythmias and sudden cardiac death. The most common arrhythmia in patients with WPW syndrome is atrioventricular reentrant tachycardia. However, it is not present in all patients with pre-excitation [1], [2], [3], [4]. Up to 1/3 of patients with AVRT experience atrial fibrillation, which may be conducted to ventricular myocardium via the accessory pathway and lead to a life-threatening ventricular fibrillation. The most effective treatment of the WPW syndrome is a radiofrequency catheter ablation [2], [5], [6], [7], [8]. This paper describes a case of a 40-year-old woman after a cardiopulmonary resuscitation for ventricular fibrillation, which was a primary manifestation of the WPW syndrome. It focuses on pathophysiology, clinical pattern and treatment possibilities of patients with WPW syndrome.     

Prediction of a fatal atrial fibrillation in patients with asymptomatic Wolff-Parkinson-White pattern

Paroxysmal atrial fibrillation (PAF) in patients with manifest WPW syndrome can be a life-threatening arrhythmia by deterioration into ventricular fibrillation. In patients with asymptomatic WPW pattern, the first PAF may lead to ventricular fibrillation or sudden death. Therefore, the purpose of this study was to predict a fatal PAF in patients with asymptomatic WPW pattern. The patient population was divided into two groups: (1) 145 patients with manifest WPW syndrome, excluding intermittent ones (32 with an episode of PAF, 49 with AV reciprocating tachycardia alone, and 64 without any episode of paroxysmal tachyarrhythmia), and (2) mixed group of patients with and without WPW syndrome (36 with an episode of PAF and 66 without PAF). The results were as follows: (1) (a) out of 32 patients with WPW syndrome and PAF, 8 patients were observed to have both the shortest preexcited R-R interval of less than 200 msec during PAF and the shortest antegrade effective refractory period of the accessory pathway (ERP-AP) of less than 250 msec, 7 of whom had dizziness or syncope during PAF and 2 died suddenly during the follow-up period; (b) 21 (32.8%) out of 64 patients with asymptomatic WPW pattern showed the shortest antegrade ERP-AP less than 250 msec; (2) patients with PAF had a higher tendency to develop repetitive atrial firing (RAF), as well as fragmented atrial activity (FAA), which were induced using programmed atrial stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bezold-Jarisch-Like Reflex During Radiofrequency Ablation of the Pulmonary Vein Tissues in Patients with Paroxysmal Focal Atrial Fibrillation

Pulmonary Vein Ablation-Induced Bradycardia. Introduction: Information is lacking about the occurrence of radiation-related proarrhythmic events during application of radiofrequency (RF) energy at (he pulmonary veins in patients with paroxysmal focal atrial fibrillation. The purpose of this study was to assess the theoretical risk of reflex bradycardia and hypotension response during RF ablation of these regions rich in endocardial nerve terminals.
Methods and Results: Among the 40 consecutive patients (29 men, 11 women; mean age 65 ± 12 years) with clinically documented frequent attacks of paroxysmal atrial fibrillation who underwent superior pulmonary vein ablation for left local atrial fibrillation, 6 patients (15%) developed bradycardia-hypotension syndrome during energy delivery. A single atrial fibrillation trigger focus in the left or right superior pulmonary vein was found in 3 and 1 patients, respectively. Two patients had two trigger foci originating from the orifice or proximal part of both superior pulmonary veins. After RF current was applied for a period of 14 ± 10 seconds, 2 patients developed functional rhythm and sinus bradycardia, another 2 patients had profound sinus bradycardia, I patient had two episodes of sudden onset of complete AV block with resultant 9.5-second a systole, and I patient showed profound sinus bradycardia, transient AV block, and an K-second asystole due to sinus arrest. Blood pressure fell when any substantial bradyarrhythmias occurred. All 6 patients were free of rhythm disturbances during The postablation follow-up period (mean 8 ± 2 months).
Conclusion: RF catheter ablation of the pulmonary vein tissues could evoke a variety of profound bradycardia-hypotension responses. The Bezold-Jarisch-like reflex might be the underlying mechanism.     

Arrhythmic profiles evaluated by Holter's technique in sick sinus syndrome

OBJECTIVES: The aim of this study was to evaluate in a group of patients with sick sinus syndrome: 1) Characteristics of arrhythmia on Holter monitoring. 2) Value of Holter monitoring to select patients for pacemaker implantation. SETTING: Department of Cardiology in a Central Hospital. METHODS: In 40 patients (27 men and 13 women, aged 37 to 83 years) Holter monitoring during a 24-hour period was performed. According to the arrhythmia profiles four groups of patients were considered: group A--with severe sinus bradycardia; group B--with sinus bradycardia associated to sinoatrial exit block or to sinus pauses; group C--characterized by the bradycardia-tachycardia syndrome and group D--defined by the finding of atrial fibrillation with a slow ventricular response. Symptoms and the presence of structural heart disease were evaluated. RESULTS: In this patients population, 24 patients had coronary artery disease and/or hypertensive heart disease. A severe sinus bradycardia was found in 14 patients (group A) and in other 11 patients it was accompanied by sinoatrial exist block of sinus pauses (group B); 12 patients had the bradycardia-tachycardia syndrome (group C) and periods of atrial fibrillation with a slow ventricular response were found in 3 other patients (Group D). Nonspecific clinical pattern was observed in this population. CONCLUSIONS: Holter monitoring was important to the diagnosis of sick sinus syndrome and for posterior definitive pacemaker implantation. Coronary artery disease and/or hypertensive heart disease were the main pathologies found in this study, being the severe sinus bradycardia and the bradycardia-tachycardia syndrome the principal manifestations of the sick sinus syndrome.     

Susceptibility to atrial fibrillation and ventricular tachyarrhythmia in the Wolff-Parkinson-White syndrome: role of the accessory pathway

Clinical and electrophysiologic characteristics associated with spontaneous and inducible atrial fibrillation and ventricular tachyarrhythmia were assessed in 20 consecutive patients with Wolff-Parkinson-White (WPW) syndrome undergoing surgical division (n = 12) or transcatheter electrical ablation (n = 8) of accessory pathways. Patients with spontaneous atrial fibrillation were characterized by the trend (not significant) of a shorter antegrade accessory pathway effective refractory period (256 +/- 26 vs 303 +/- 109 msec). However, patients with and without spontaneous atrial fibrillation did not differ with respect to prevalence of structural heart disease (3 of 11 vs 2 of 9), intra-atrial conduction time (34 +/- 10 vs 32 +/- 10 msec), or interatrial conduction time (86 +/- 21 vs 88 +/- 17 msec). Thus, atrial and accessory pathway electrophysiologic properties (per se) were not clear determinants of susceptibility to atrial fibrillation. Among the 20 patients, 10 to 35 beats of nonsustained ventricular tachycardia (seven patients) or ventricular fibrillation (three patients) were induced at electrophysiologic study with one to three programmed extrastimuli. Clinically, a ventricular arrhythmia (ventricular fibrillation during atrial fibrillation) had occurred in only one of these patients. The discordance of these observations was significant (p less than 0.01). Patients with and without inducible ventricular arrhythmias were not distinguished by clinical factors or by electrophysiologic properties of the accessory pathway or ventricles. Accessory pathway conduction was completely or partially eliminated by ablation procedures in 14 of 20 patients. During a mean follow-up of 27 months, atrial fibrillation recurred in two patients with failed ablation procedures and in one patient with left atrial enlargement (despite accessory pathway division) (p = 0.019 vs pre-ablation). Ventricular arrhythmias remained inducible in two patients in whom accessory pathway ablation failed (p = 0.01 vs initial study). However, spontaneous ventricular tachyarrhythmias did not occur during follow-up. We conclude that susceptibility to spontaneous or inducible atrial fibrillation and ventricular tachyarrhythmia in patients with WPW syndrome and no organic heart disease depends primarily on the existence of a functional accessory pathway. These susceptibilities are eliminated by interruption of accessory pathway conduction. Ventricular tachyarrhythmias remain infrequent spontaneous events in the WPW syndrome. Their more frequent induction at electrophysiologic study is not predictive of clinical occurrence.     

Usefulness of invasive and non-invasive electrophysiologic studies in the selection of antiarrhythmic drugs for the patients with paroxysmal supraventricular tachyarrhythmia

A comparison of the effects of several antiarrhythmic agents was made in a study of 70 patients - 15 with manifest Wolff-Parkinson-White (WPW) syndrome, 17 with concealed WPW syndrome, 18 with AV nodal re-entrant tachycardia, 14 with paroxysmal atrial fibrillation and 6 with paroxysmal atrial flutter - employing intracardiac stimulation and esophageal pacing. For the termination of paroxysmal supraventricular tachycardia, intravenous administration of verapamil or aprindine was more effective than that of disopyramide or procainamide. In AV nodal re-entrant tachycardia, verapamil was the most effective for termination. In the manifest WPW syndrome, disopyramide or aprindine was indicated especially for patients with the accessory pathways of the short antegrade refractory period, because these drugs lengthened the refractory period of the accessory pathways. For the purpose of converting atrial fibrillation or flutter to the sinus rhythm, type IA drugs such as disopyramide were indicated. However, verapamil was effective for slowing down the ventricular rate in atrial fibrillation or flutter except in cases of manifest WPW syndrome. A 6-month follow-up study showed that oral administration of verapamil was also useful for putting a stop to the attacks in 24 out of 32 patients with paroxysmal supraventricular tachycardia, while oral disopyramide prevented the recurrence of atrial fibrillation in only 4 of 10 patients.     

Risk of sudden death after successful accessory atrioventricular pathway ablation in resuscitated patients with Wolff-Parkinson-White syndrome

INTRODUCTION: Cardiac arrest in patients with Wolff-Parkinson-White (WPW) syndrome can be due to ventricular fibrillation mediated by fast conduction over the accessory pathway during atrial fibrillation. However, if primary ventricular fibrillation is the reason for resuscitation, placement of an implantable cardioverter defibrillator (ICD) would be indicated. The aim of this study was to test the hypothesis that in resuscitated patients with WPW syndrome, recurrences can be prevented by sole ablation of their accessory pathways. METHODS AND RESULTS: We performed a long-term follow-up study of 48 resuscitated patients with WPW syndrome who underwent successful accessory pathway ablation as their sole primary treatment. Cardiac arrest had occurred either spontaneously in 32 patients (group A) or after intravenous administration of antiarrhythmic drugs in 16 patients (group B) and was never associated with an acute myocardial infarction or other concomitant factors. All patients had normal left ventricular function at echocardiography. A total of 56 accessory AV pathways were ablated successfully with radiofrequency current (n = 55) or during surgery (n = 1) and were located at the left free wall (n = 35), right free wall (n = 8), or septal-paraseptal region (n = 13). Follow-up 5.0+/-1.9 years after ablation (range 0.2 to 7.9) was obtained in all 48 patients. All of the patients were alive, and none had a life-threatening arrhythmia or syncope after successful ablation of their accessory pathways. CONCLUSION: In resuscitated patients with WPW syndrome who have normal left ventricular function at echocardiography and no ECG abnormalities suggesting additional electrical disease, ablation of their overt accessory pathways prevented cardiac arrest recurrences; therefore, ICD placement is generally not indicated.     

Intracorporeal cardiac pacemakers for refractory tachycardia (excluding atrial disease). Apropos of 18 cases]

The treatment of paroxysmal tachycardia by the use of permanent pacing to prevent or terminate attacks is discussed. The series comprises 18 patients with follow-up periods ranging from 1 to 12 years. In 6 cases the indication for pacing was atrial tachy-arrythmias favourised by bradycardia (5 of whom had vagally- induced atrial arrythmias). The atrial pacemaker successfully prevented attacks in 4 out of 6 cases. Three cases of chronic reciprocating tachycardia were successfully treated by simultaneous atrial and ventricular pacing or using sequential pacing with a very short P-R interval. Eight cases of paroxysmal orthodromic reciprocating tachycardia in the WPW syndrome were paced: in 5 cases pacing was employed to terminate attacks by atrial (3 cases) or ventricular (2 cases) stimulation, in the other 3 cases pacing was used to prevent the bradycardia which favourised the initiation of tachycardia. Good results were obtained in all 8 cases. Ventricular stimulation was used to terminate attacks in one patient with refractory ventricular tachycardia but the patient had a sudden death probably caused by the pacemaker. The place of these different pacing techniques with respect to medical treatment and specialised arrhythmia surgery is discussed.     

Improvement of symptoms in patients with sick sinus syndrome by spontaneous development of stable atrial fibrillation.

Fifty-six patients with symptomatic chronic sinus bradycardia because of sick sinus syndrome (SSS) were followed for periods from one month to 11 years (average 3-2 years). Eleven developed stable atrial fibrillation persisting for 8 to 61 months; 52 had permanent demand pacemakers implanted before atrial fibrillation commenced. In the 11 patients with atrial fibrillation, 10 had adequate ventricular rate, 8 with rates greater than 100 beats/min requiring digoxin for rate control. The 8 patients with atrial fibrillation with pacemakers remained asymptomatic for 13 to 18 months without requiring reimplantation; battery failure occurred in 2 whose rapid ventricular rates were controlled by digoxin. In the other 6 patients with pacemakers who developed atrial fibrillation, adequate ventricular rates persisted resulting in overdrive suppression. No patient had systemic embolisation. The previous duration of symptomatic sinus bradycardia was longer in patients developing atrial fibrillation (average 5-5 years) compared (P less than 0-01) with patients without atrial fibrillation (1-9 years). Further, premature atrial contractions occurred in all 11 patients before atrial fibrillation in contrast to only 21 of the 45 patients without atrial fibrillation. It is concluded that occurrence of atrial fibrillation in SSS with symptomatic sinus bradycardia provides a natural cure of symptoms caused by bradycardia. These data indicate that permanent ventricular pacing may not be necessary if persistent atrial fibrillation develops in SSS.     

Assessment and follow-up of pediatric survivors of sudden cardiac death

In the young patient resuscitated from sudden cardiac arrest, the risks of recurrence are uncertain and so are the criteria defining therapeutic efficacy for the presumed cause of the initial event. In this study, we analyzed the outcome of 15 consecutive young patients, who were resuscitated from pulseless ventricular tachycardia or ventricular fibrillation and who were evaluated by comprehensive hemodynamic and electrophysiological testing. Patients were 11.2 +/- 2.7 (mean +/- SD) years old at the time of their event, and each was known to have some form of heart disease before sudden cardiac arrest. Ventricular tachycardia or fibrillation was inducible by programmed electrical stimulation in eight patients. Accessory atrioventricular connections, with antegrade effective refractory periods less than 220 msec, were identified in three patients. Sustained atrial flutter was the only arrhythmia inducible in two patients, and no arrhythmias were inducible in two other patients. Surgical or electrophysiological-guided medical therapy resulted in noninducibility of the ventricular arrhythmias in six patients. Surgical division of the accessory atrioventricular connections was performed in three patients, and arrhythmias were not inducible after operation. The four patients with atrial flutter or without defined arrhythmia were treated with an empiric therapy. During 37 +/- 14 months of follow-up, the nine patients with documented noninducibility of a defined cause of sudden cardiac arrest were free of recurrent events. In contrast, during 18 +/- 10 months of follow-up, two of the six patients with empiric therapy or persistent inducibility of ventricular tachycardia died suddenly, and three others had recurrence of ventricular tachycardia or fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ventricular fibrillation in the Wolff-Parkinson-White syndrome

Ventricular fibrillation (VF) is a well-known but rare complication of the Wolff-Parkinson-White syndrome (WPW). Clinical and electrophysiological data of 23 patients with spontaneous VF were compared with data from 100 consecutive patients with WPW without VF but with symptomatic supraventricular tachycardia. The 23 patients were collected in a multicentre retrospective study in seven European centres. VF occurred in only one patient who was receiving antiarrhythmic drugs, and was the first manifestation of the syndrome in six. No significant differences were found between those with VF and without VF in age, complaints of palpitations, syncope, and presence of structural heart disease. The retrograde effective refractory period of the accessory pathway, the atrial refractory period and the fastest atrial pacing rate with 1:1 anterograde conduction over the accessory pathway were similar in both groups. Significant differences were found for sex, permanent pre-excitation on the electrocardiogram, type of documented supraventricular tachyarrhythmias, shortest RR interval less than or equal to 220 ms during spontaneous atrial fibrillation (AF), inducibility of supraventricular tachycardias, ventricular effective refractory period less than or equal to 190 ms, mean shortest RR interval during induced AF less than or equal to 180 ms and presence of multiple accessory pathways.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prevalence of Supraventricular Tachyarrhythmias in a Cohort of 115 Patients with Brugada Syndrome

Background : The Brugada syndrome is characterized by ST segment elevation in leads V₁ to V₃ and a right bundle branch block like pattern. It is associated with an increased risk of syncope and sudden cardiac death. Initial reports in small numbers of patients suggest an association between supraventricular tachycardias and Brugada syndrome with a prevalence varying between 13% and 40%. Objective : Aim of this study was to evaluate the prevalence of AV nodal reentrant tachycardia, AV reentry tachycardia, and/or atrial fibrillation in a large cohort of patients diagnosed as Brugada syndrome. Methods and Results : From three different European centers 115 consecutive patients with a Brugada syndrome were evaluated noninvasively and invasively (mean age 45 ± 12 years, n = 82 men, n = 33 women). Nineteen of 115 patients (17%) had a history of previous cardiac arrest. Syncope was reported by 58 patients (50%), 33 patients had a positive family history of sudden cardiac death (29%). Supraventricular tachycardias were documented in 26 of the patients (23%): Eight patients (7%) had AV‐nodal reentrant tachycardias and two patients had AV‐reentry tachycardias; atrial tachycardias were documented in three patients, and another 13 patients (11%) suffered from atrial fibrillation/atrial flutter. Additionally, atrial fibrillation was inducible by programmed atrial stimulation in nine patients (8%). Conclusions : Supraventricular tachycardias occur in 23% of patients with Brugada syndrome. Documentation of atrial fibrillation especially in the young or supraventricular tachycardias associated with syncope should give reason to screen for Brugada syndrome.     

Sudden death in the Wolff-Parkinson-White syndrome

Clinical electrophysiologic studies in patients with Wolff-Parkinson-White syndrome (WPW) suffering from ventricular fibrillation have shown a high prevalence of short anterograde refractory period of the accessory pathway (less than or equal to 250 ms), short preexcited RR intervals during atrial fibrillation (less than or equal to 250 ms), and multiple accessory pathways. Unfortunately the specificity of these findings is low, as they are present in almost 50% of patients with WPW without a history of ventricular fibrillation, and in 17% of patients with asymptomatic WPW. Pharmacologic and exercise testing detect a population of WPW with a low probability of having a short anterograde refractory period of the accessory pathway, but don't rule-out the ability of these patients to develop very short RR intervals during atrial fibrillation. Natural history studies show that sudden death in WPW occurs with an incidence less than or equal to 1:1,000 per year. The low predictive value of electrophysiologic and noninvasive studies for sudden death, makes then a poor means for screening patients at risk. Some clinical factors, such as the frequency of tachycardias and/or the detection of episodes of atrial flutter or fibrillation are markers of higher sudden death risk, and indications for aggressive electrophysiologic evaluation.     

Update on sick sinus syndrome, a cardiac disorder of aging

Sick sinus syndrome (SSS) is usually a disease of the elderly produced by idiopathic degeneration of the sinoatrial node. Its initial manifestations range from asymptomatic to nonspecific and include palpitations, fatigue, confusion, and even syncope and sudden death. Electrocardiographic evidence of SSS includes inappropriate sinus bradycardia, sinus pause or arrest, or sinus exit block. These bradyarrhythmias may alternate with tachyarrhythmias, especially atrial fibrillation, to create the tachycardia-bradycardia syndrome. The diagnosis of SSS may be established by electrocardiography or ambulatory monitoring in the majority of cases. Medications such as digoxin, beta-blockers, and calcium blockers may initiate or worsen the manifestations of SSS. Permanent pacing is indicated for symptomatic bradyarrhythmias. Progression of SSS is mostly dependent on the presence and severity of associated coronary or hypertensive heart disease.