Muscarinic inhibition of basal L-type calcium current in pacemaker cells from the rabbit atrioventricular node

Effects of acetylcholine (ACh) on the L-type calcium current were examined in isolated atrioventricular nodal cells that exhibited spontaneous contractions. ACh (0.1 to 10 microM) inhibited basal calcium current dose-dependently. This inhibition was eliminated by dialysis with 8Br cAMP or cAMP-dependent kinase inhibitory peptide. Both extracellular N-ethylmaleimide 50 microM and intracellular GDPssS 0.2 mM abolished the ACh effect. Dialysis with cGMP or NG-monomethyl-L-arginine did not significantly affect ACh inhibition of basal calcium current. Similarly, cGMP-dependent protein kinase inhibitor KT5823 (1 microM) and the type II phosphodiesterase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (30 microM) did not attenuate the ACh effect. Therefore, ACh inhibits the basal calcium current in the atrioventricular node mainly by suppressing cAMP synthesis through the inhibitory GTP-binding protein.     

Echophonocardiographic studies of the contribution of the atrioventricular valves to the first heart sound

The movements of the mitral, tricuspid and aortic valves have been recorded echocardiographically and related to the first heart sound (S1) in patients with various hemodynamic and conduction abnormalities. Closure of the mitral and tricuspid valves has been studied with respect to the corresponding atrioventricular pressure crossover and it is clear that both valves finish closing about 50 msec after pressure crossover. In order to clarify the relative contribution of tricuspid valve closure and aortic root events to the second high frequency component of S1, a new simultaneous dual echophonocardiographic technique was employed. This permitted the simultaneous registration of tricuspid and aortic valve movements and demonstrated that in certain circumstances the second high frequency component of S1, could be attributed to tricuspid closure, aortic root events being excluded from the genesis of this sound. These observations suggest that the two high frequency components of S1 are related to closure of the mitral and tricuspid valves. The results do not however, exclude a contribution to S1 of aortic root events, which may be of lower frequency vibrations.     

Preceding His-atrial interval as a determinant of atrioventricular nodal conduction time in the human and rabbit heart

This investigation shows that atrioventricular (A-V) nodal conduction time (A-H interval), both in the human and in the isolated rabbit heart, is determined mainly by the length of the preceding His-atrial (H-A) interval. The A-H intervals obtained during atrial extrasystolic stimulation at different basic rates, during Wenckebach cycles and during both transient and steady state responses to stepwise increases in stimulation frequency were plotted against the corresponding H-A intervals. The A-H intervals were found to have nearly the same duration provided they were preceded by the same H-A interval. The only important difference appeared in the short H-A interval range as a shortening of the A-H interval at faster basic rates. This facilitating effect of frequency, which was found in the majority of cases, is compatible with the similarly frequency-dependent shortening of the functional refractory period of the A-V node.     

Lipoxygenase activity in heart cells

Arachidonic acid (AA) metabolism via the lipoxygenase (LOX) pathway in rat hearts and in cultured rat cardiomyocytes was investigated using 1-[14C]AA. LOX activity was detected in the microsomal fraction, in the high speed supernatant prepared from rat hearts and in rat cardiomyocyte supernatant. LOX products from all fractions comigrated in thin layer chromatography as 12-hydroxyeicosatetraenoic acid (12-HETE) and 15-HETE. Enzyme linked immunosorbent assay for 12-HETE showed its formation by the microsomal fraction, the ammonium sulfate (AS) pellet, and by rat cardiomyocyte supernatant, while radioimmunoassay for 15-HETE showed its formation only by the AS pellet. The properties of LOX in each fraction are reported here.     

Cellular basis for the negative dromotropic effect of adenosine on rabbit single atrioventricular nodal cells

Detection and resolution of square patches of sinusoidal gratings were measured in central and peripheral vision (30 degrees horizontal temporal visual field) for high-contrast gratings as a function of the number of cycles in the stimulus. We determined performance in a forced-choice paradigm for a fixed number of stimulus cycles by arranging for stimulus diameter to vary inversely with spatial frequency. For both psychophysical tasks and for both target locations, the psychometric function relating performance to log spatial frequency shifted to higher frequencies without changing slope significantly as the number of cycles in the stimulus was increased. Thus the entire effect could be captured by an analysis of spatial acuity, which increased with increasing number of grating cycles over the range 0.5-6 cycles but remained constant over the range 6-14 cycles. In the central field, resolution acuity and detection acuity were equal regardless of the number of cycles in the stimulus. In the peripheral field, detection acuity exceeded resolution acuity and perceptual aliasing occurred for stimuli in the range 1-14 cycles. From this result we conclude that resolution acuity is sampling limited in the periphery, provided that the stimulus contains at least one full cycle of the grating. Essential features of the results could be accounted for by Fourier analysis of the stimulus.     

Experience with surgery of the heart valves

A review is given of a 15 year experience of valve replacement with Teflon cusps, pericardial cusps, Starr-Edwards, Key-Shiley, Wada-Cutter and Bj?rk-Shiley artificial valve prosthesis. The Bj?rk-Shiley tilting disc valves have shown the lowest gradient and blood trauma and excellent durability in more than 1 000 implantations during a 7 year period. Anticoagulation therapy is considered necessary with all types of artificial heart valves. Thrombo-embolism is negligible after aortic valve replacement (1 episode in 4 000 patient months) but still a problem in the mitral position (4 episodes in 1 000 patient months).     

The development of sinoatrial dysfunction in pacemaker patients with isolated atrioventricular block

The purpose of this paper is the assessment of sinus node competence over time in patients with isolated atrioventricular block (AV block). Patients implanted with AV synchronous pacemakers for isolated AV block between December 1993 and June 1995 were prospectively evaluated at predischarge, 6 weeks, and subsequent 6 months follow-up with respect to atrial rate monitors/24-hour Holter and modified exercise test. Patients unable to maintain AV synchronous pacing or complete a modified exercise test were excluded. Sinus node competency is interpreted as: (1) absence of atrial brady- or tachyarrhythmia, (2) ability to achieve a minimum heart rate of 100 beats/min with modified exercise test or during daily activities. There were 58 patients (22 women), mean age 71.0 +/- 13.8 with an average follow-up of 30.4 months (11-40). Three patients did not complete a modified exercise test, 4 patients were lost to follow-up, and 2 patients were unable to maintain AV synchronous pacing. Of the remaining 49 patients, 3 developed chronic or paroxysmal atrial fibrillation. No patient developed significant bradyarrhythmias. All patients achieved a heart rate of > or = 100 beats/min modified exercise test. In our group of patients with isolated AV block within a moderate follow-up period, development of sinoatrial dysfunction was rare (6%). A longer follow-up is required to delineate the natural history of sinoatrial dysfunction in patients with isolated AV block.     

The Fusus coli of the rabbit as a pacemaker area

Section of the rabbit's proximal colon orad to the fusus coli resulted in a marked reduction in both slow-wave frequency and differentiation of the two kinds of faeces produced. This indicates the existence of a pacemaker area and a mechanical role for the reversed oral-aboral gradient of the proximal colon.     

Acoustic classification of the state of artificial heart valves

Transthoracic acoustic signals from BSCC (Bj?rk-Shiley convexo-concave) mechanical heart valves implanted in human patients were processed to determine if the valves had separated outflow struts. For normal valves with intact outflow struts it is demonstrated that a time-windowed spectral analysis reveals the resonant frequency of the vibrating strut. The strut, which is set into vibration when the valve closes during each cardiac cycle, has a resonant frequency that varies among valves but usually is between 7000 and 8000 Hz. The signal processing technique is based on the hypothesis that the strut's resonant waveform has a smaller decay rate than interfering signals and noise generated upon closure by other mechanical components of the valve. A time window can be selected that optimizes the outflow strut's signal-to-interference ratio. It is shown that the absence of the resonant frequency in the 7000- to 8000-Hz interval is an indication that one of the strut's legs has separated from the valve's flange. This separation of one leg appears to precede the valve's failure that occurs if the other leg also separates from the flange, a state referred to as OSF (outlet strut failure). Acoustic data recorded from 18 clinical patients with implanted valves, that were later explanted and examined, formed the database for this study. Of the 18 valves 9 were SLS (single-leg separated) and 9 were intact (both legs of the outflow strut still attached to the valve's flange). The time-windowed spectral process correctly identified the states of all 18 valves.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro endothelialization of bioprosthetic heart valves

BACKGROUND AND AIMS OF THE STUDY: The main disadvantage of xenograft bioprosthetic heart valves is limited durability due to tissue degeneration. METHODS: To study possible alternatives to conventional bioprosthetic heart valves, glutaraldehyde preserved porcine aortic valve leaflets were precoated with fibronectin-heparin and acidic fibroblast growth factor (aFGF) to enhance cell proliferation. Furthermore, different methods of storage and preservation (1.0% benzoic acid, 1.0% sorbic acid, 0.05% and 0.5% dialdehyde starch) were compared to conventional preservation procedures. Valve leaflets were lined with adult human saphenous vein endothelial cells (1.0 x 10(4) AHSVEC/cm2). The different methods of preservation were compared to leaflets precoated additionally with 1.0 microgram/cm2 aFGF protein, derived from gene manipulated bacteria. Endothelial growth kinetics were studied and verified by an increase of activation following 3H-thymidine incorporation, while the maintained metabolic cell activity was demonstrated by prostacyclin (PGI2) release measurements. In subsequent experiments in vivo degeneration and mineralization were determined by subcutaneous implantation in rats for up to 40 days. RESULTS: Our results favored alternatively treated valve leaflets; endothelial cells grew to persistent monolayers in six to 12 days in contrast to conventional processed leaflets where no endothelial cell growth was possible. Atomic absorption spectroscopic assessment of subdermal valve implants showed significantly lower contents of calcium, magnesium and phosphate in alternatively treated leaflets. Furthermore, precoating of alternatively preserved valve leaflets with aFGF protein and endothelial cells improved in vitro and in vivo results significantly. CONCLUSIONS: Our study shows that endothelial cell growth as well as significantly reduced in vivo degeneration and mineralization of valve leaflets may be feasible if bioprosthetic heart valves are processed according to alternative, non-toxic conservation procedures and are precoated with angiogenic growth factor protein.     

Viability in human heart valves prepared for grafting

Oral administration of synthetic D-penicillamine to rats induces alterations of the renal mesangium, apparently without involvement of immune mechanisms. Alterations of mitochondria, especially enlargement, were seen in the proximal tubular epithelium. These results are discussed in the light of recent findings in "penicillamine" nephritis and diseased human kidneys in general.     

Preimplantation alteration of adenine nucleotides in cryopreserved heart valves

To assess the initial metabolic phase of cellular injury from cardiac valve processing, high-energy phosphate concentrations were analyzed in valve leaflets subsequent to critical processing steps. Using a porcine model, valves were processed in a manner identical to human homografts, with 58 randomly assigned to five groups representing distinct preparation phases. Group I (controls) sustained 40 minutes of warm ischemia concluded by liquid nitrogen immersion. Remaining groups similarly endured 40 minutes of ischemia, but were subsequently prepared according to stepwise design: II, warm ischemia + 24 hours of 4 degrees C ischemia; III, warm ischemia + 24 hours of 4 degrees C antibiotic disinfection; IV, warm ischemia + 24 hours at 4 degrees C (without antibiotics) + cryopreservation (-1 degrees C/min cryoprotected freezing); and V, warm ischemia+disinfection+cryopreservation. At each regimen's conclusion leaflet extracts were assayed by high-performance liquid chromatography for high-energy adenine nucleotides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate) and catabolites. A 47% and 86% decrease in cellular adenosine triphosphate level was observed in group III and group V leaflets, respectively. The level of total adenine nucleotides was maintained up to cryopreservation; thereafter a 74% decrease was noted. Catabolite analysis confirmed incomplete degradation of adenine nucleotides indicating cellular metabolic resilience throughout standard homograft preparation in valves previously exposed to 40 minutes of warm ischemia.     

Particle image velocimetry in the investigation of flow past artificial heart valves

Full-field measurement of instantaneous velocities in the flow field of artificial heart valves is vital as the flow is unsteady and turbulent. Particle image velocimetry (PIV) provides us the ability to do this as compared to other point measurement devices where the velocity is measured at a single point in space over time. In the development of a PIV system to investigate the flow field of artificial heart valves, many problems associated with the project arose and were subsequently resolved. Experience gained in the setting up of an environment conducive for PIV studies of artificial heart valves; from seed particle selection to refractive index matching, and the evolution of computer algorithms to satisfy the varied flow conditions in artificial heart valves are presented here. Velocity profiles and distributions are computed and drawn for a porcine tissue heart valve based on measurements with the PIV system developed.