The effects of acute global ischemia on cytosolic calcium transients were studied in perfused rabbit hearts loaded with the fluorescent calcium indicator indo 1. Indo 1-loaded hearts were illuminated at 360 nm, and fluorescence was recorded simultaneously at 400 and 550 nm from the epicardial surface of the left ventricle. The F4m/F550 ratio was calculated by an analog circuit, which allowed cancellation of optical motion artifact. Resulting calcium transients demonstrated a rapid upstroke and slow decay similar to those recorded in isolated ventricular myocytes. Global ischemia rapidly suppressed contraction, but it produced a concurrent increase in the systolic and diastolic levels of the calcium transients, together with an increase in the duration of the peak. The effects of ischemia were reversed by reperfusion, inhibited by verapamil, and mimicked by perfusion of nonischemic hearts with acidified (C02-rich) solution. In addition to elevation of the calcium transients, ischemia caused a pattern of intracellular calcium alternans that was discernible after 2-3 minutes. The pattern of alternans was stable at a given epicardial site, but it could be out of phase at different sites. Similar nonuniformities were observed in contraction strength and in the duration of monophasic action potentials recorded immediately adjacent to the fiber-optic probe. Abnormalities in intracellular calcium may be a causal factor in the loss of electrical and mechanical synchrony in the acutely ischemic heart. (Circulation 1988;78:1047-1059 C essation of blood flow causes rapid changes in the electrical and mechanical activity of the heart. The resting potential of ischemic cells declines promptly, which inactivates sodium channels and slows conduction.' The duration of the action potential is modified to varying degrees so that recovery of excitability no longer occurs in the normal, orderly sequence. The combination of slowed conduction and nonuniform excitability leads to vulnerability of the ischemic heart to ventricular

To elucidate the role of cytosolic calcium, [Ca2+]1, in the physiology of the normal and ischemic heart, we have developed a method for recording [Ca2+]1 transients from the epicardial surface of the rabbit ventricle after arterial perfusion with the cell-permeant cytosolic calcium indicator indo-l AM. Hearts were illuminated at 360 nm, and fluorescence was recorded simultaneously at 400 and 550 nm. The F4N/F550 fluorescence ratio was calculated by an analog circuit that allowed cancelation of small movement artifacts that were present at single wavelengths. Clear [Ca2+] METHODSAlbino male New Zealand rabbits weighing between 1.8 and 2.2 kg were sacrificed by cervical fracture. The heart was rapidly excised and perfused with a saline solution at a constant aortic flow rate of 20-30 ml/min. The perfusate contained 115 mM NaCl, 4.7 mM KCI, 2.0 mM CaC12, 0.7 mM MgCl2, 28 mM NaHCO3, 0.5 mM NaH2PO4, 20 mM glucose, 10 units of insulin per liter, and 0.1% fetal calf serum adjusted to pH 7.4, equilibrated with 95% 02/5% C02, and heated to maintain epicardial temperature at 30'C + 1PC. Contractions of the left ventricle were measured with an intracavitary latex balloon that contained a fiber-optic pressure transducer (Camino Laboratories) or with an epicardial strain gauge that had the advantage of monitoring wall stress near the site at which fluorescence was measured. The left ventricle was vented by a small polyethylene catheter that drained thebesian vein flow. Some hearts were paced at 180/min by an epicardial plunge electrode.Fluorescence excitation was provided by a 100-W Hg vapor lamp. Illumination was filtered at 360 ± 5 nm and directed through a silica fiber-optic cable onto a circular region of epicardium 1 cm in diameter. Movement artifact was minimized by attachment of the fiber-optic cables to the heart using a plastic hub and rubber girdle. Fluorescence was collected by a ring of eight coaxial fiber-optic cables, divided by a beam splitter, and then filtered at 400 ± 12.5 nm and 550 ± 20 nm before reaching photomultiplier tubes (Hamamatsu). The above emission wavelengths were found to give clearer fluorescence transients than the in vitro fluorescence maxima of indo-1 (Ca2' bound = 405 nm; Ca2+ free = 480 nm). Our chosen emission wavelengths allow greater rejection of the noncalcium-dependent fluorescence of unhydrolyzed indo-1 AM (fluorescence maximum = 450 nm), which is retained in tissue after loading (9). Photomultiplier output at the two emission wavelengths was entered into an electronic ratio circuit and the fluorescence ratio, F4w/F550, was displayed on a strip-chart recorder.Indo-1 AM was solubilized in a mixture of dimethyl sulfoxide/pluronic F-127 (25%, wt/vol), 1 ml of which was added to 400 ml of Tyrodes solution containing 5% fetal calf serum. The final concentration of indo-1 AM was 2.5 AM.Perfusion with indo-1 AM continued for 30 min; this was followed by a 30-min washout. This method of indicator loading produced a 5-to 12-fold increase in fluorescence at Abbreviation: [Ca21],, ...

Continuation of oral anticoagulation therapy with an INR level of <2.5 does not impose increased risk of bleeding for device-related procedures, although precaution is necessary to avoid supratherapeutic anticoagulation levels.

Transvenous lead removal is highly successful, with few serious procedural complications. We propose a risk stratification scheme that may categorize patients as low, moderate, and high risk for lead extraction. Such a strategy may guide which extractions are best performed in the operating room.

The time courses of changes in pHI and cytosolic calcium were compared in isolated perfused rabbit hearts with the use of the calcium-sensitive fluorescent indicator indo-1 and the pH indicator 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Cell-permeant forms of these indicators were loaded into myocytes by arterial infusion or by direct infusion into the extravascular space. Indo-1 fluorescence was recorded from the epicardial surface of the left ventricle at an excitation wavelength of 360 nm and emission wavelengths of 400 and 550 nm. BCECF fluorescence was recorded at an excitation wavelength of 490 nm and an emission wavelength of 530 nm. Calibration procedures were developed for each indicator that allowed [Ca2"], and pHi to be quantified during ischemia. Global ischemia decreased contractility and caused a rapid increase in both the systolic and end-diastolic levels of the calcium transients.