Programmed deep septal pacing for the diagnosis of left bundle branch capture

BackgroundDuring permanent deep septal pacing, it is important to confirm left bundle branch (LBB) capture.ObjectiveThe effective refractory period (ERP) of the working myocardium is different than the ERP of the LBB; we hypothesized that it should be possible to differentiate LBB capture from septal myocardial capture using programmed extra-stimulus technique.MethodsIn consecutive patients undergoing pacemaker implantation who received pacing lead in a deep septal position programmed pacing was delivered from this lead. Responses to programmed pacing were categorized on the basis of QRS morphology of the extrastimuli as: myocardial (broader QRS, often slurred), selective (narrower QRS, preceded by an isoelectric interval) or non-diagnostic (unequivocal change).ResultsProgrammed deep septal pacing was performed 269 times in 143 patients; in every patient with the use of an 8-beat basic drive train of 600 ms and when possible also during supraventricular rhythm. Responses diagnostic for LBB capture were observed in 114 (79.7%) of patients. Selective LBB paced QRS was more often seen when premature beats were introduced during the intrinsic rhythm rather than after the basic drive train. The average septal-myocardial refractory period was significantly shorter than the LBB refractory period: 263.0±34.4 ms vs. 318.0±37.4 ms.ConclusionsA novel maneuver for the diagnosis of LBB capture during deep septal pacing, was formulated, assessed and found as diagnostically valuable. This method, based on the differences in refractoriness between LBB and the septal myocardium is unique in enabling the visualization of components of the usually fused, non-selective LBB paced QRS complex.Graphical abstract

Feline Hypertrophic Cardiomyopathy: The Consequence of Cardiomyocyte-Initiated and Macrophage-Driven Remodeling Processes?

vHypertrophic cardiomyopathy (HCM) is the most commonly diagnosed cardiac disease in cats. The complex pathophysiology of HCM is still far from clear, but myocardial remodeling is a key process, and cardiomyocyte disarray, interstitial fibrosis, leukocyte infiltration, and vascular dysplasia are described histopathologic features. The present study systematically investigated the pathological processes in HCM, with the aim to shed more light on its pathogenesis. Hearts from 18 HCM cases and 18 cats without cardiac disease (controls) were examined, using light and transmission electron microscopy, immunohistochemistry, and morphometric approaches to identify and quantify the morphological changes. Reverse transcription–quantitative polymerase chain reaction was applied to provide additional mechanistic data on remodeling processes. In HCM, the left and right ventricular free wall and septal myocardium exhibited a significantly reduced overall cellularity, accompanied by a significant increase in interstitial Iba1-positive cells with macrophage morphology. In addition, the myocardium of almost half of the diseased hearts exhibited areas where cardiomyocytes were replaced by cell-rich fibrous tissue with abundant small and medium-sized vessels. HCM hearts also showed significantly higher transcription levels for several inflammatory and profibrotic mediators. Our findings suggest that HCM is the consequence of cardiac remodeling processes that are the result of cardiomyocyte damage and to which macrophages contribute by maintaining an inflammatory and profibrotic environment.

Modified Septal Myectomy Using a Curved Knife for Left Ventricular Septal Hypertrophy

An 86-year-old woman presented with chest pain and discomfort. Echocardiography revealed severe aortic valve stenosis and asymmetric septal hypertrophy. Aortic valve replacement and myectomy were performed using a curved knife. The blade was U-shaped in cross-section, and was curved upward along the long axis. Hypertrophic septal myocardium was removed along the long axis of the left ventricle (LV), and a groove for blood flow was constructed. The patient was discharged uneventfully without recurrence of her chest discomfort. Our result suggested that a curved knife is a reasonable option for transaortic septal myectomy in patients with obstructive LV hypertrophy.

A Triaxial-Measurement Shear-Test Device for Soft Biological Tissues

A novel shear-test device for soft biological tissue, capable of applying simple shear deformations simultaneously in two orthogonal directions while measuring the resulting forces generated in three axes, is described. We validated the device using a synthetic gel, the properties of which were ascertained from independent tensile and rotational shear tests. Material parameters for the gel were fitted using neo-Hookean analytical solutions to the independent test data, and these matched the results from the device. Preliminary results obtained with rat septal myocardium are also presented to demonstrate the feasibility of the apparatus in determining the shear characteristics of living tissue. [S0148-0731(00)00205-3]

Lack of electrical interaction between proximal bundle branches and subjacent muscle

Microelectrode techniques were used to assess the importance of subthreshold electrotonic interactions between the canine proximal bundle branches and adjacent septal myocardium, and vice versa. Bundle branch action potential duration, maximal rising velocity of phase O, current threshold requirements for all-or-none depolarization, transmembrane voltage, and spontaneous frequency were not altered by adjacent septal muscle activation. Activation of the proximal bundle branches did not change the transmembrane voltage of immediately subjacent muscle cells; likewise, all-or-none activation of ventricular septal muscle did not effect a voltage change in the overlying proximal bundle branches. We conclude that a high ohmic resistance barrier between proximal bundle branch and subjacent muscle precludes significant electrotonic interactions between these neighboring structures.