Influence of ventricular conduction defects on ventricular repolarisation and coupling intervals of ventricular extrasystoles.

In all conduction disorders of the left ventricle the Q-T interval is prolonged in relation to the prolongation of the QRS duration, but the S-T interval (measured from the end of the S wave) is within normal limits. Right ventricular conduction defects are associated with prolongation of the Q-T interval, but the S-T interval in incomplete and complete right bundle branch block is subnormal. In the absence of a broad QRS, the Q-T and S-T intervals are not prolonged in left anterior hemiblock. However, an associated non-specific left intraventricular conduction defect or right bundle branch block does prolong the QRS and thus the Q-T interval. The S-T interval is normal or subnormal in the presence of right bundle branch block and left anterior hemiblock confirming that left anterior hemiblock does not effect the Q-T interval and repolarisation. In the presence of any conduction defect which prolongs the QRS duration, extrasystoles have longer coupling intervals. The coupling intervals are longer in the presence of left bundle branch block than right bundle branch block. It is postulated that this is due to the differences in the time of depolarisation and thus repolarisation of the left ventricle.     

Initial vector rates in differentiation between supraventricular extrasystoles with aberration and ventricular extrasystoles.

A computer method was constructed for analysing vector rates. Initial vector rates of QRS of ventricular extrasystoles (VES) and of aberrant supraventricular extrasystoles were compared. Bundle branch block (BBB) was used as a model for aberration. Spontaneous VES during heart catheterization and VES found by His-bundle recording represented the VES group. The VES were found to contain a longer average "activation time," i.e. the duration from the onset to the spatial amplitude maximum, than the BBB. The maximum amplitudes were similar. A method for calculating initial vector rate distribution was also developed. This showed a significantly higher proportion of fast rate components in BBB than in VES. The calculation of vector rate distribution gave advantages over the calculation of the mean initial vector rate, when considering electrocardiographic abnormalities such as preexcitation QRS or post-infarction Q waves. With a simple discriminatory analysis using initial vector rate distribution values, a 95% precision was obtained in differentiating between VES and BBB. It is concluded that a QRS from a supraventricular impulse focus with aberration has faster initial vector rates than a QRS from a ventricular focus and that this difference is useful in distinguishing between them.     

Vectorcardiographic study of aberrant conduction anterior displacement of QRS: another form of intraventricular block.

Aberrant ventricular conduction was induced in 44 subjects by introduction of atrial premature beats through a transvenous catheter-electrode. Multiple patterns of aberrant ventricular conduction were obtained in 32 patients and, in the whole group, 116 different configurations were recorded. Of these, 104 showed a classical pattern of mono- or biventricular conduction disturbance. The pattern frequencies were as follows: right bundle-branch block, 28; left anterior hemiblock combined with right bundle-branch block, 21; left anterior hemiblock, 17; left posterior hemiblock combined with right bundle-branch block, 12; left posterior hemiblock, 10; complete left bundle-branch block, 10; and incomplete left bundle-branch block, 6. The remaining 12 configurations could not be classified into the usual categories of intraventricular blocks. In 7 of them, the alterations only consisted of trivial modifications of the QRS contour. In the other 5 instances, aberrant conduction manifested itself by a conspicuous anterior displacement of the QRS loop, with increased duration of anterior forces. The latter observation is worthy of notice, as it indicates that, in the differential diagnosis of the vectorcardiographic pattern characterized by prominent anterior forces, conduction disturbances should be considered a possible aetiological factor in addition to right ventricular hypertrophy, and true posterior wall myocardial infarction.     

Prognostic significance of right ventricular extrasystoles

Extrasystoles (RVES) from the right ventricular outflow tract(RVOT) are a common arrhythmia in routine ECGs. METHODS: In this prospective study 56 consecutive patients with RVES(22 males, 34 females) were examined for morphological and/orfunctional right ventricular (RV) abnormalities by 12-lead,Holter, exercise ECGs, transthoracic echocardiography and signalaveraging. The follow-up time was 3.1–15.8 years (arithmeticmeanSD=7.21.6 years; median, 6.9 years). Patients with hyperthyroidism,structural cardiovascular and/or lung diseases were excluded. RESULTS: A total of 57.1% of the patients with RVES presented with echomorphologicabnormalities of the right ventricle (RV). In 26.8% the echomorphologicright ventricular abnormalities progressed in 33.3% of patientswith normal RVs at baseline (group I) and in 21.9% of thosewith abnormal RVs at baseline (group II). No significant differences were found between the 2 patientgroups in terms of age at onset, family history, ECG changes,late potentials and malignant right ventricular outflow tractarrhythmias on 24-h and exercise ECGs. While females predominatedin group I, males were numerous in group II (p=0.006). Sustainedventricular tachycardia, syncope or sudden death were absentthroughout the follow-up. CONCLUSION: Patients with RVES carry a good prognosis in terms of morbidityand mortality no matter whether echomorphologic abnormalitiesare present or not.     

Characteristics of ventricular extrasystoles and their prognostic importance: a reappraisal of their method of classification.

The concept of two different types of extrasystoles, parasystolic and coupled, depends upon two distinguishing characteristics of these beats. The characteristics of the parasystolic extrasystoles are the invariability of the ectopic cycle together with their independence from the basic rhythm. Coupled extrasystoles demonstrate a dependence upon the basic rhythm although they may express some degree of ectopic variability. The degree of variation of the interectopic interval or its common denominator measures the irregularity of the ectopic parasystolic rhythm. The variation of coupling intervals describes the dependence of the ectopic beat upon the basic rhythm. In a study of 719 electrocardiograms with ventricular extrasystoles, about one-third of the extrasystoles appeared intermediate between these types since they had both variable coupling intervals and variable interectopic intervals. Some of these had total variability of coupling intervals and of the interectopic intervals (random non-parasystolic coupling), and others had limited variation of coupling intervals when expressed in relationship to the total duration of electrical diastole (approximate non-parasystolic coupling). Both these ectopic types appeared to be associated with cardiac disease, and repetitive ventricular extrasystoles. Left bundle branch type extra-with fixed coupling. There were no obvious relationships between the contour and the type of coupling of ventricular extrasystoles. Left bundle branch type extrasystoles with vertical or right axis were the most frequent, particularly in normal subjects, but in the presence of cardiac disease there were more electrocardiograms with right bundle branch type extrasystoles. Extrasystoles in the presence of underlying conduction defects were usually of opposite configuration to this defect. The contour of uniform extrasystoles did not appear to predispose to serious ventricular arrhythmias but multiformity of extrasystoles was an important prognostic indicator. It is suggested that variability of contour and coupling are important signs of inhomogenous conduction and may precede the onset of severe ventricular arrhythmias. Random nonparasystolic coupling and marked multiformity indicate a more sinister arrhythmic state.