Myocardial fibrosis predicts ventricular arrhythmias and sudden death after cardiac electronic device implantation

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Unrestricted educational grants

Background

Increasing evidence supports a link between myocardial fibrosis (MF) and ventricular arrhythmias. We sought to determine whether presence of MF on visual assessment (MFVA) and gray zone fibrosis (GZF) mass predicts SCD and ventricular fibrillation / sustained ventricular tachycardia after cardiac implantable electronic device (CIED) implantation.

Methods

In this prospective study, total fibrosis and GZF mass, quantified using cardiovascular magnetic resonance, was assessed in relation to the primary endpoint of sudden cardiac death (SCD) and the secondary, arrhythmic endpoint of SCD or ventricular arrhythmias after CIED implantation.

Results

Among 700 patients (age 68.0 ± 12.0yrs [mean ± SD]), 27 (3.85%) experienced a SCD and 121 (17.3%) met the arrhythmic endpoint over 6.93 yrs (median; interquartile range 5.82-9.32). MFVA predicted SCD (hazard ratio [HR]: HR:26.3 [95% confidence interval [CI] 3.70-3337]; negative predictive value: 100%). In competing risks analyses, MFVA also predicted the arrhythmic endpoint (subdistribution [sHR]: 19.9 [95% CI 6.40-61.9]; negative predictive value:98.6%). Compared with no MFVA, a GZF mass measured with the 5SD method (GZF5SD) > 17 g was associated with highest risk of SCD (HR: 44.6;95% CI 6.12-5685) and the arrhythmic endpoint (sHR: 30.3 [95% CI 9.60-95.8]). Adding GZF5SD mass to MFVA led to reclassification of 39% for SCD and 50.2% for the arrhythmic endpoint. In contrast, LVEF did not predict either endpoint.

Conclusions

In CIED recipients, MFVA excluded patients at risk of SCD and virtually excluded ventricular arrhythmias. Quantified GZF5SD mass added predictive value in relation to SCD and the arrhythmic endpoint.

Induction of chromosome changes by metal compounds in cultured CHO cells

The effect of 4 metal salts on the induction of chromosome aberrations and sister chromatid exchange (SCE) in cultured Chinese hamster ovary (CHO) cells was investigated. It was observed that CdCl2, NiCl2, CrO3 and HgCl2 were effective in causing various types of chromosome aberrations. The percentages of abnormalities increased with increasing doses of the metals used. These metal compounds also raised the SCE rates compared to 5-bromo-2'-deoxyuridine controls. The importance of rapid screening of potentially hazardous metals is described.

Rapidly activating hydrogen ion currents in perfused neurones of the snail, Lymnaea stagnalis

Cells from the circumoesophageal nerve ring of the pond snail Lymnaea stagnalis were internally perfused with solutions containing Cs aspartate, EGTA and pH buffers. Time-dependent, voltage-dependent 'residual' outward currents were observed at positive potentials. They were found to be carried largely by H+. The outward H+ currents were reduced by high internal pH, low external pH, external Cd2+ and 4-aminopyridine. External tetraethylammonium ions reduced the H+ currents but had a more effective blocking action on the K+ currents in these cells. All five agents reduced the maximum H+ conductance. In addition Cd2+, low external pH and high internal pH were found to shift the voltage dependence of the H+ current to more positive potentials. There was no significant difference between H+ currents recorded with the internal pCa2+ about 7 and those recorded with the internal pCa2+ near 5. It is likely that the H+ channel described here provides the basis for the increase in H+ permeability described by Thomas & Meech (1982) in depolarized Helix neurones. As judged by their sensitivity to different antagonists, H+ channels are unlike any other previously described channel. They are highly selective for protons and we suggest that their role in molluscan neurones is to compensate for the rapid intracellular acidification which is generated by trains of action potentials (Ahmed & Connor, 1980).

Appearance of calcium action potentials in crayfish slow muscle fibres under conditions of low intracellular pH

1. The intracellular pH (pHi) of crayfish slow flexor muscle fibres was measured using recessed-tip pH micro-electrodes. To study the electrophysiological effects of intracellular acidification, pHi was lowered to values between the normal 7 . 2 and 6 . 3 by removal of external NH4Cl after a 20--30 min exposure. 2. During intracellular acidification, the fibres became capable of generating all-or-none Ca action potentials, rather than the normal small graded responses; no change in resting potential or input resistance accompanied this change in excitability. 3. All-or-none spikes appeared at pHi = 6 . 4--6 . 5. The spikes disappeared when pHi was increased again following the addition of 10 mM-bicarbonate to the external solution. CO2-saturated saline, which decreased pHi to 6 . 4, also caused the appearance of all-or-none action potentials. 4. The appearance of action potentials was correlated with a decrease in delayed rectification as pHi fell, as indicated by the response to depolarizing current pulses and by constant-current I--V plots in solutions in which all Ca ions had been replaced by Co. 5. External tetraethylammonium (TEA), at concentrations which reproduced the pHi = 6 . 4 effects on the I--V relation, also caused the appearance of all-or-none action potentials. 6. It is concluded that low pHi in these fibres partially blocks (or causes a depolarizing shift in the voltage dependence of) the voltage-sensitive outward K current which normally shunts the inward Ca current and prevents the generation of action potentials.

Mechanisms of alkaline degradation of sucrose. Relative rates of alkaline degradation of some sucrose derivatives

An earlier study of the relative rates of degradation of several sucrose derivatives has been refined and extended. The results support a novel hypothesis to explain the unusual alkali-lability of sucrose (1). In this hypothesis the first and rate-determining step in the degradation is an SN1cB displacement effected at the C1 anomeric centre of the glucose moiety by an oxyanion derived from the C1' hydroxyl (10), to produce 1-(α-D-glucopyranosyl)fructose (11). The latter is then very rapidly degraded, mainly to lactic acid. The possibility of analogous competing displacements involving the 3' and 6' oxyanions remains for further investigation.

Blocking effects of barium and hydrogen ions on the potassium current during anomalous rectification in the starfish egg

1. The blocking effects of Ba+ and H+ on the inward K current during anomalous rectification of the giant egg membrane of the starfish, Mediaster aequalis, were studied using voltage clamp techniques. 2. External Ba2+ at a low concentration (10--100 micron) suppresses the inward K current; the extent of suppression, expressed as the ratio of currents with and without Ba2+, can be described by a conventional bimolecular adsorption isotherm, K/(K + [Ba2+]o), K being an apparent dissociation constant. 3. The dissociation constant, K, decreases as the membrane potential V becomes more negative and can be expressed by K(V) = K(0) exp (zmuFV/RT), where K(0) is the K at V = 0, z is the charge of the blocking ion, and mu is a parameter for the membrane potential dependence of Ba2+ blockage. The value of mu ranges between 0.64 and 0.68. 4. Upon a sudden change in membrane potential the change in the blocking effect of Ba2+ follows first order kinetics; the forward rate constant is membrane-potential-dependent whereas the backward constant is potential-independent. 5. The blocking effect of Ba2+ appears to be independent of the activation of K channels during anomalous rectification. 6. The blocking effect of Ba2+ depends on V alone, in contrast to the activation of the K channel during anomalous rectification which depends on V--VK. 7. In these respects, the effect of Ba2+ is equivalent to the introduction of inactivation into the anomalous rectification. 8. SI2+ and Ca2+ show small but observable blocking effects only at much higher concentrations (about 10--20 mM). 9. The inward K current is suppressed when the external pH is reduced below 6.0. The blocking effect of H+ shows no significant potential dependence. The concentration dependence suggests that three H+ ions simultaneously titrate the acidic groups of each channel (pK = 5.3--5.4). 10. The implications of these results are discussed in terms of molecular models of the potassium channel of anomalous rectification and possible mechanisms of K channel inactivation.

Electrophysiological properties of onion guard cells

Intracellular electrical recordings in onion (Allium cepa L.) guard cells show that they maintain a membrane potential difference (MPD), inside negative. The MPD of intact cells averaged -72±29 mV (n=45); MPD of cells partially digested with a cellulolytic enzyme, -39±7 mV (n=65). Evidence indicates that the guard cells have two electrically distinct compartments, presumably delimited by the plasmalemma and tonoplast. Epidermal cells in partially digested preparations also showed MPD that could be either positive (+15±7 mV; n=23) or negative (-15 ±8 mV; n=13). Guard cells exposed to light-dark cycles hyperpolarized in the light and depolarized in the dark. The largest observed voltage changes reached 52 mV during hyperpolarizations and 60 mV during depolarizations. The light responses saturated with roughly exponential kinetics, with the depolarizations exhibiting a slower second phase that might be related to the contracting movements of the guard cells. Initial rates of the responses averaged about 14 mV min(-1) in the dark and about 8 mV min(-1) in the light. The results can be interpreted as electrical correlates of fluctuations in intracellular potassium concentration, as light-induced changes in membrane permeability, or as the photoactivation of an electrogenic proton pump. The last possibility seems to be the simplest interpretation of the data that also provides us with a mechanism driving the ion fluxes associated with stomatal function.