Unstable intraventricular conduction disorders

Unstable bundle branch blocks may be tachycardia dependent, bradycardia dependent, or rate independent. When appearing at the "critical" rates or "critical" cycle lengths they may seem to be rate independent. Conversely, "true" rate-independent blocks may be reversible or irreversible. Determining if a rate-unrelated block may disappear can be difficult because irreversile bundle branch block seems to develop through a slow process in time during which rate-dependent, rate-independent, and even normal conduction alternate in successive electrocardiograms.     

Myocardial scintigraphy in the diagnosis of infarct in patients with disorders of intraventricular conduction]

Myocardial scintigraphy with pyrophosphate-99mTc-Sn was used as a diagnostic test in 23 patients with different disorders of rhythm and intracardia conduction who were admitted to the department of emergency cardiology of the All-Union Cardiological Scientific Center, Academy of Medical Sciences of the USSR with suspected acute myocardial infarction. Scintigrams were positive in 11 of 12 patients with acute myocardial infarction who were examined in periods of 6 hours of 10 days. One patient examined on the 13th day of the disease had negative scintigrams. In 6 of 11 patients with myocardial infarction not confirmed, the scintigrams were also negative, in 3 other patients positive scintigrams were due to a postinfarction aneurysm. The authors conclude that myocardial scintigraphy with pyrophosphate-99mTc-Sn is an adequate test in the diagnosis of acute myocardial infarction, especially in the examination of patients with disorders of intracardiac conduction.     

Effect of intravenous amiodarone in patients with intraventricular conduction disorders

Using His bundle recordings and stimulation techniques, theelectrical effects of amiodarone (5 mg/kg intravenously) wereassessed in 12 patients aged 34–80 years (mean 65) exhibitingin sinus rhythm, intraventricular conduction disturbances. Bundlebranch block was present in 10 patients: left bundle branchblock in three patients, right bundle branch block in three,bilateral bundle branch block in four. All the patients hada long H-V interval (65–80 ms; mean 71). As has been previouslyreported, amiodarone slowed the sinus rate, prolonged the QTinterval, increased the atrial effective refractory period anddepressed A-V nodal conduction. Despite the presence of advancedconduction disturbances within the His-Purkinje system, amiodaronedid not alter the H-V interval in 11 patients and increasedit in one by only 5 ms. Thus, clinically, the use of amiodaronein patients with bundle branch block should be safe.     

Significance of intraventricular conduction disorders observed in arrhythmogenic right ventricular dysplasia

Correlations between surface ECGs, epicardial mapping and histological data in 15 cases of arrhythmogenic right ventricular dysplasia (ARVD) provide information about the possible mechanism of intraventricular conduction defects in about one third of cases. Two cases in this series had complete right bundle branch block and 4 cases showed diffuse intraventricular conduction defects. The other cases had normal ECGs. The point of origin of the activation in 11 cases was situated in the left ventricle, even in 6 of the 9 cases with normal ECGs. The points of latest activation were located over the right ventricular free wall near the atrio-ventricular groove. However, in all cases but one, a normal right ventricular point of origin was observed, suggesting participation of the right bundle within a free wall showing delayed activation. This activation showed very irregular delayed propagation due to the zones of dysplasia. These results suggest that in ARVD, the mechanism of the conduction defects is not disease of the bundle branch itself but a distal block probably situated in the right ventricular wall. This hypothesis is supported by the histological appearances of the dysplastic zones.     

Septal displacements during intraventricular conduction disorders. Echocardiographical study]

We have analysed the echocardiograms of ten healthy subjects, sixty patients with disorders of intra-ventricular conduction, and ten who were treated by a temporary intracavitary pacemaker. There was found to be a pre-ejection displacement of the septum towards the posterior wall, beginning just after electrical depolarisation of the ventricle followed, in most cases, by 'paradoxical' displacement towards the anterior wall during systole. Such a displacement, producing a 'beaked' image on the echocardiogram, is only found when the ventricular complexes have the characteristics of complete left bundle branch block (LBBB), whether this is spontaneous LBBB or a functional LBBB produced by an intracavitary pacemaker. The results support the hypothesis that the posterior displacement of the septum in cases of LBBB is related to abnormal spread of excitation. Under these conditions, during the pre-ejection period the septal forces predominante over those of the free wall of the left ventricle. In a patient with LBBB who had failed to show this typical septal displacement in several investigations, the 'beak' of the septum could be observed only when the electrical axis deviated to the left, and when the QRS complex exceeded 0.14/s to 0.16/s, this condition being fulfilled because the LBBB was really complete at the time of the last investigation.