Transient entrainment and interruption of atrioventricular node tachycardia

The possibility of transiently entraining and interrupting the common type of atrioventricular (AV) node tachycardia (anterograde slow, retrograde fast AV node pathway) was studied using atrial and ventricular pacing in 18 patients with paroxysmal AV node tachycardia. Transient entrainment occurred in all patients. During atrial pacing, localized block in the AV node for one beat followed by anterograde conduction over the fast pathway was observed in three patients. During ventricular pacing, localized block for one beat followed by retrograde conduction over the slow pathway was not observed in any patient. Neither atrial nor ventricular fusion beats were observed during entrainment.These observations indicate in a way not previously shown that reentry involving two functionally dissociated pathways in the AV node is the underlying mechanism of paroxysmal AV node tachycardia. The inability to demonstrate atrial or ventricular fusion beats during entrainment suggests a true intranodal location of the reentrant circuit. Finally, the ability to transiently entrain intranodal tachycardia demonstrates that this electrophysiologic phenomenon is not exclusively limited to macroreentrant circuits

Ventricular arrhythmias initiated by programmed stimulation in four groups of patients with healed myocardial infarction

Programmed electrical stimulation of the heart was prospectively used in 160 patients with healed myocardial infarction to study the incidence and characteristics of ventricular arrhythmias induced. Thirty-five patients had neither documented nor suspected ventricular arrhythmias (Group A); 37 patients had documented nonsus-tained ventricular tachycardia (Group B); 31 patients had been resuscitated from ventricular fibrillation (Group C); and 57 patients had documented sustained mono-morphic ventricular tachycardia (Group D). No electrophysiologic differences were found between patients in Group A and Group B, but patients in both groups differed significantly from patients in Group C and Group D. In the last two groups, sustained monomorphic ventricular tachycardia was more frequently induced, the cycle length of the induced ventricular tachycardia was slower and a lesser number of premature stimuli was required for induction. No differences were found in the incidence, rate or mode of induction of nonsustained monomorphic ventricular tachycardia, but nonsustained polymorphic ventricular tachycardia and ventricular fibrillation were more frequently induced in Groups A and B.It is concluded that the substrate for sustained ventricular arrhythmia is present in at least 42% of patients after myocardial infarction. The electrophysiologic characteristics of the substrate for ventricular tachycardia seem to be the major determinant of the clinical occurrence of sustained ventricular arrhythmia. Changes in the electrophysiologic properties of the substrate of ventricular tachycardia, either spontaneously with time or induced by ischemia or antiarrhythmic drugs, can contribute to the clinical occurrence of sustained ventricular arrhythmias in patients with an old myocardial infarction

Ventricular fibrillation in six adults without overt heart disease

AbstractFindings are described in six patients with no clinical evidence of heart disease who had documented ventricular fibrillation (five patients) or ventricular flutter (one patient). The mean age of the six patients, all men, was 34 years (range 26 to 43). Cardiovascular collapse occurred in all and was followed by successful cardioversion. No patient had electrolyte or QT abnormalities. One patient had slight right ventricular enlargement on M-mode echocardiography, and another had a left ventricular pressure gradient at rest of 30 mm Hg with a normal two-dimensional echocardiogram. Holter electrocardiographic monitoring revealed incessant ventricular tachycardia in one patient and nonsustained ventricular tachycardia in three others. Exercise testing revealed nonsustained ventricular tachycardia in one patient.Ventricular fibrillation was induced at the time of programmed electrical stimulation in four of the six patients. Documented recurrence of ventricular fibrillation or ventricular flutter occurred in three patients, but in only one patient receiving antiarrhythmic drugs. Four patients were treated with amiodarone and one received an automatic implantable cardioverter-defibrillator. All patients are alive after a mean follow-up period of 78 months after the first documentation of their arrhythmia and 37 months after programmed electrical stimulation.Ventricular fibrillation can occur in the apparently structurally normal human heart. Antiarrhythmic treatment can provide effective control of this malignant arrhythmia

Out-of-Hospital Cardiac Arrest in the 1990s: A Population-Based Study in the Maastricht Area on Incidence, Characteristics and Survival

AbstractObjectives. We sought to describe the incidence, characteristics and survival of out-of-hospital sudden cardiac arrest (SCA) in the Maastricht area of The Netherlands.Background. Incidence and survival rates of out-of-hospital SCA in different communities are often based on the number of victims resuscitated by the emergency medical services. Our population-based study in the Maastricht area allows information on all victims of witnessed and unwitnessed SCA occurring outside the hospital.Methods. Incidence, patient characteristics and survival rates were determined by prospectively collecting information on all cases of SCA occurring in the age group 20 to 75 years between January 1, 1991 and December 31, 1994. Survival rates were related to the site of the event (at home vs. outside the home) and the presence or absence of a witness and rhythm at the time of the resuscitation attempt in out-of-hospital SCA.Results. Five hundred fifteen patients were included (72% men, 28% women). In 44% of men and 53% of women, SCA was most likely the first manifestation of heart disease. In patients known to have had a previous myocardial infarction (MI), the mean interval between the MI and SCA was 6.5 years, with >50% having a left ventricular ejection fraction >30%. The mean yearly incidence of SCA was 1 in 1,000 inhabitants. Of all deaths in the age groups studied, 18.5% were sudden. Nearly 80% of SCAs occurred at home. In 60% of all cases of SCA a witness was present. Cardiac resuscitation, which was attempted in 51% of all subjects, resulted overall in 32 (6%) of 515 patients being discharged alive from the hospital. Survival rates for witnessed SCA were 8% (16 of 208 subjects) at home and 18% (15 of 85 subjects) outside the home (95% confidence interval 1% to 18.8%).Conclusions. The majority of victims of SCA cannot be identified before the event. Sudden cardiac arrest usually occurs at home, and the survival of those with a witnessed SCA at home was low compared with that outside the home, indicating the necessity of optimizing out-of-hospital resuscitation, especially in the at-home situation