suMMARY Discrete delicate fibromuscular structures crossing the cavity of the left ventricle were identified on morphological examination in 329 (48%) of 686 hearts from patients of all ages with congenital heart disease, acquired heart disease, or normal hearts. These structures were also present in 151 (95%) of 159 hearts from animals of six species. Cross sectional echocardiographic findings compatible with these structures were obtined in 39 (21-7%) of 179 children reviewed retrospectively and in three of 800 (0-4%) adults studied prospectively. These structures appear to be a normal anatomical finding.Isolated examples of filaments of tissue crossing the cavity of the left ventricle were first reported in 1893 by Turner. '-3 In 1906 Keith and Flack noted that they were almost constantly present in both bovine and human hearts and they regarded them as being part of the left bundle branch distribution of the Purkinje conduction fibres.4 Although these structures are hardly mentioned in the standard textbooks of anatomy and cardiac pathology,56 the development of echocardiography appears to have reawakened interest in them.7-1 ' We made a quantitative morphological assessment of the prevalence of these structures as this would seem to be a prerequisite for an appraisal of their importance. For reasons that we will discuss later we have called these structures left ventricular bands. Patients and methodsWe reviewed 686 hearts in the collection of this hospital specifically for the presence of left ventricular bands. Six hundred and thirty six were from children below the age of 15. Of these, 581 had had congenital cardiac malformations and 55 had had normal hearts. The 50 other hearts were from adults who had previously had surgery for acquired cardiac disease. We also examined 159 hearts from six species of animals Accepted for publication 31 July 1984 (none of which was killed for the purpose of the study). Ventricular bands were identified as discrete fibromuscular structures crossing the left ventricular cavity and having no attachment to the atrioventricular valve (Fig. 1). They extended from a papillary muscle to the septum, from a papillary muscle to the free wall, between the papillary muscles, or from the septum to the free wall. They were either single or multiple and sometimes branched. Small multiple strands at the junction of the setpum with the free walls were disregarded as were small apical networks.In addition to the morphological study, we reviewed cross sectional echocardiograms from 800 adults and 179 children. Adult echocardiograms had been recorded on a Varian V3400 phased array system with a 2*2 MHz transducer.
The housing of the implantable cardioverter defibrillator (ICD) is being considered for a remote electrode to replace the conventional subcutaneous woven wire patch. It is not clear that the solid smooth and rigid metal surface of the ICD housing will provide the same performance as does the woven wire patch. We compared a solid titanium disk to a titanium woven wire patch for defibrillation performance in a canine model. The patch had a smaller outline area, a slightly smaller conductive perimeter, and slightly less of a small feature surface area than did the disk. The remote electrode (disk or patch) was inserted at the point of maximal apical cardiac impulse. A commercially available endocardial electrode was placed in the right ventricle (RV). Conventional biphasic shocks (140-microFrench capacitor and 65% tilt) were delivered between the RV and subcutaneous electrode. The patch had significantly lower resistances than did the disk (81.6 +/- 8.0 omega vs 90.0 +/- 11.6 omega P < 0.006). The patch also had significantly lower stored energy defibrillation thresholds than did the disk (8.0 +/- 2.6 J vs 9.3 +/- 3.3 J, P < 0.007). In spite of smaller values for every geometrical dimension, the woven wire patch out performed the solid disk for defibrillation with conventional biphasic waveforms. Since the ICD housing is typically smooth titanium, the use of waveforms better suited for the active can configuration may deserve a systematic evaluation.
We hypothesized that a long thin right ventricular (RV) electrode would have equivalent defibrillation threshold (DFT) performance to a short thick electrode with approximately the same surface area. This could lead to thinner transvenous lead systems, which would be easier to implant. A thin (5.1 French) lead was compared to a standard control (10.7 French). The thin lead had an 8-cm RV electrode length with a surface area of 4.26 cm2. The standard lead had a RV electrode length of 3.7 cm and a surface area of 4.12 cm2. A 140-mu French capacitor 65%/65% tilt biphasic defibrillation shock was delivered between the RV electrode and a 14-cm2 subcutaneous patch. DFTs were determined following 10 seconds of fibrillation in 11 dogs by a triple determination averaging technique. The thin lead had a lower resistance (77.1 +/- 27.4 omega vs 88.9 +/- 30.3 omega, P < 0.001) than did the thick lead. There was no significant difference in stored energy DFTs (9.9 +/- 2.5 vs 10.3 +/- 2.7, P = 0.098 2-sided, P = 0.049 1- sided). This was in spite of the fact that the long thin lead had a portion of its RV coil extending above the tricuspid valve and, thus, not contributing efficiently to the ventricular gradients in the small dog heart. We conclude that a long thin right ventricular electrode and a standard short thick electrode had equivalent defibrillation performance. This preliminary result should be confirmed in clinical studies as it could lead to significantly thinner transvenous lead systems.
Cycle periods in ECG during VF are correlated with periods of reentrant activation. The ECGs recorded from different locations on the thorax were contributed to from electrical activations within the heart in approximately inverse proportion of their distance from the recording sites. Similarity in cycle periods between ECGs recorded from two locations, therefore, can be used as an index of spatiotemporal similarity in the rate of activation. In the present study coherence was used, which is a mathematical function that measures the degree of similarity that two signals exhibit at specific cycle periods, to test if spatiotemporal similarity in cycle periods between pairs of orthogonal ECGs was correlated with defibrillation shock outcome. The authors estimated time-varying coherence from orthogonal ECGs during 10 seconds of electrically induced VF, which was terminated with a defibrillation shock with a 50% probability of successful outcome. Defibrillation shocks were delivered between a coil electrode placed at the right ventricular apex and a subdermal patch electrode. Time-varying coherencies between pairs of ECGs were estimated using an adaptive least mean square algorithm. Time-coherence surfaces were integrated within a frequency region centered at the dominant frequency. Data were collected from ten dogs during 206 (48%) successful and 221 (52%) unsuccessful trials. The results showed that coherencies between the sagittal-transverse pair were 10%-15% higher (P < 0.05) for successful than unsuccessful trials. The correlation between coherence and defibrillation outcome suggests that more defibrillation shocks occurred when the degree of spatial similarity in the rate of activations was higher terminated VF, than those that occurred at other times. These results are consistent with a hypothesis, recently proposed by others, that more uniform activation within regions of the heart that receive low potential gradients during shock may increase the probability of successful defibrillation.
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