Enhanced inositol trisphosphate response to alpha 1-adrenergic stimulation in cardiac myocytes exposed to hypoxia.

Myocardial ischemia elicits an enhanced responsivity to alpha 1-adrenergic stimulation and a reversible increase in alpha 1-adrenergic receptor number. In adult cardiac myocytes, alpha 1-adrenergic receptor number increases two- to threefold after 10 min of hypoxia, an increase similar to that seen during ischemia in vivo. To determine whether this increase in alpha 1-adrenergic receptor number leads to an enhanced synthesis of inositol trisphosphate, the intracellular second messenger for the alpha 1-adrenergic receptor, the mass of inositol trisphosphate was quantified by a novel procedure developed in our laboratory that circumvents problems associated with using labeled precursors. The peak increases in inositol trisphosphate levels of three- to fourfold were measured after 30 s of norepinephrine stimulation and exhibited a 50% effective concentration (EC50) of 7.9 x 10(-8) M. Hypoxia produced a marked leftward shift in the dose-response curve for the production of inositol trisphosphate in response to norepinephrine stimulation (EC50 = 1.2 x 10(-8) M). Hypoxia also induced a 100-fold reduction in the concentration of norepinephrine required to elicit a threshold increase in inositol trisphosphate (10(-9) M), compared with control normoxic myocytes (10(-7) M). Thus, hypoxia, which increases alpha 1-adrenergic receptor density, also leads to an enhanced production of inositol trisphosphate and could account for the enhanced alpha 1-adrenergic responsivity in the ischemic heart in vivo, which is known to facilitate arrhythmogenesis.

Mechanisms contributing to malignant dysrhythmias induced by ischemia in the cat.

Continuously recorded bipolar electrograms were obtained simultaneously from epi-, endo-, and mid-myocardial regions of the ischemic and normal zones of cat left ventricle in vivo after coronary occlusion, analyzed by computer, and compared to regional cyclic AMP levels. Regional cyclic AMP content was used as an index of the combined local effects of: (a) efferent sympathetic nerve discharge; (b) release of myocardial catecholamines due to ischemia; and (c) circulating catecholamines. Ischemia resulted in a progressive increase in pulse width and rise time and a decrease in rate of rise of voltage (dV/dt) of the local electrograms from ischemic zones reaching a maximum within 2.4+/-0.3 min (mean+/-SE) at the time of onset of severe ventricular dysrhythmias, all of which returned toward control before the cessation of the dysrhythmia (33.5+/-1.5 min after coronary occlusion). Increases in cyclic AMP in ischemic zones preceded corresponding increases in the frequency of premature ventricular complexes (PVCs). Propranolol inhibited the increases in cyclic AMP and reduced the frequency of PVCs in animals without ventricular fibrillation. In animals with ventricular fibrillation, cyclic AMP was significantly elevated in normal and ischemic zones compared to animals with PVCs only. Electrical induction of PVCs or ventricular fibrillation in ischemic and nonischemic hearts failed to increase cyclic AMP. The results suggest that the changes in regional adrenergic stimulation of the heart may contribute to perpetuation of ventricular dysrhythmia and the genesis of ventricular fibrillation early after the onset of myocardial ischemia.

Alpha adrenergic contributions to dysrhythmia during myocardial ischemia and reperfusion in cats.

Alpha compared to beta adrenergic contributions to dysrhythmias induced by left anterior descending coronary occlusion and by reperfusion were assessed in chloralose-anesthetized cats (n = 96). Alpha receptor blockade with either phentolamine or prazosin significantly reduced the number of premature ventricular complexes during coronary reperfusion (321 +/- 62-14 +/- 10 premature ventricular complexes, P less than 0.001), abolished early ventricular fibrillation (from 25% in controls to 0%), and prevented the increase in idioventricular rate seen with coronary reperfusion. However, beta-receptor blockade was without effect. Ventricular dysrhythmias induced by coronary occlusion alone (without reperfusion) were attenuated markedly by alpha-receptor blockade under conditions in which perfusion (measured with radiolabeled microspheres) within ischemic zones was not affected. Alternative sympatholytic interventions including pretreatment with 6-hydroxydopamine to deplete myocardial norepinephrine from 8.8 +/- 1.4 to 0.83 +/- 0.2 ng/mg protein and render the heart unresponsive to tyramine (120 microgram/kg) attenuated dysrhythmias induced by both coronary occlusion and reperfusion in a fashion identical to that seen with alpha-receptor blockade. Although efferent sympathetic activation induced by left stellate nerve stimulation increased idioventricular rate from 66 +/- 6 to 144+/- 7 beats/min (P less than 0.01) before coronary occlusion, this response was blocked by propranolol but not by phentolamine. In contrast, during reperfusion the increase in idioventricular rate induced by left stellate nerve stimulation (to 203 +/- 14) was not inhibited by propranolol but was abolished by phentolamine (79 +/- 10). Intracoronary methoxamine (0.1 microM) in animals depleted of myocardial catecholamines by 6-hydroxydopamine pretreatment did not affect idioventricular rate before coronary occlusion. However, early after coronary reperfusion, methoxamine increased idioventricular rate from 33 +/- 7 to 123 +/- 21 beats/min (P less than 0.01). Thus, enhanced alpha-adrenergic responsiveness occurs during myocardial ischemia and appears to be primary mediator of the electrophysiological derangements and resulting malignant dysrhythmias induced by catecholamines during myocardial ischemia and reperfusion.

Increased alpha-adrenergic receptors in ischemic cat myocardium. A potential mediator of electrophysiological derangements.

We have recently demonstrated enhanced alpha-adrenergic responsiveness assessed electrophysiologically in ischemic and reperfused myocardium. This study was performed to determine whether ischemia alters alpha 1-adrenergic receptor number (Bmax) of affinity (KD) based on [3H]prazosin binding. Within 30 min after occlusion, Bmax increased in ischemic regions to 207% of control to 27 +/- 2 fmol/mg protein, with the increase persisting (+ 141% of control) during early reperfusion (2 min), before returning to control base-line values (13 +/- 1.6) after 15 min of reperfusion. KD was not altered at any interval studied. Beta receptor number of ([3H]dihydroalprenolol) and Na+-K+ ATPase activity were comparable in control compared to ischemic myocardium although beta-receptor Bmax and KD in both regions decreased during early reperfusion. Thus, the enhanced alpha-adrenergic responsivity previously recognized with ischemia and reperfusion is correlated with an increase in alpha 1-adrenergic receptors.

Electrophysiologic effects of intracellular lysophosphoglycerides and their accumulation in cardiac lymph with myocardial ischemia in dogs.

Lysophosphatidylcholine (LPC) accumulates in ischemic tissue, and exogenous LPC (20-100 microM) induces electrophysiologic alterations in vitro. However, to determine whether compartmentalization is critical, intracellular pressure microinjection of LPC was performed with simultaneous recording of the transmembrane action potential. Intracellular LPC in concentrations as high as 500 microM (n = 18), calculated based on calibration of injectate volume and cellular volume, did not induce electrophysiologic alterations. The concentrations and efflux of phospholipids and lysophospholipids were assessed in lymph obtained from the supracardiac lymph vessel in anesthetized dogs to assess the extent of extracellular accumulation. Prior to ischemia, phosphatidylcholine (PC) was the major phospholipid in lymph (79 +/- 2%) with substantial quantities of sphingomyelin (11 +/- 2%) and LPC (6 +/- 1%). With ischemia, the concentration of LPC increased by 18%, and net efflux of LPC increased by 24% (P less than 0.01) with no net efflux of PC or other assayed phospholipids. The calculated concentration of LPC increased from 84 to 197 microM in lymph within the ischemic region, a concentration sufficient to induce electrophysiologic derangements.

Prophylaxis of early ventricular fibrillation by inhibition of acylcarnitine accumulation.

Hypoxia in isolated myocytes results in accumulation of long-chain acylcarnitines (LCA) in sarcolemma. Inhibition of carnitine acyltransferase I (CAT-I) with sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (POCA) prevents both the accumulation of LCA in the sarcolemma and the initial electrophysiologic derangements associated with hypoxia. Another amphiphilic metabolite, lysophosphatidylcholine (LPC), accumulates in the ischemic heart in vivo, in part because of inhibition of its catabolism by accumulating LCA. It induces electrophysiologic alterations in vitro analogous to early changes induced by ischemia in vivo. The present study was performed to determine whether POCA could prevent accumulation of both LCA and LPC induced by ischemia in vivo and if so, whether attenuation of early arrhythmogenesis would result. LAD coronary artery occlusions were induced for 5 min in chloralose-anesthetized cats. Coronary occlusion in untreated control animals elicited prompt, threefold increases of LCA (73 +/- 8 to 286 +/- 60 pmol/mg protein) and twofold increase of LPC (3.3 +/- 0.4 to 7.5 +/- 0.9 nmol/mg protein) selectively in the ischemic zone, associated with ventricular tachycardia (VT) or ventricular fibrillation (VF) occurring within the 5-min interval before acquisition of myocardial samples in 64% of the animals. POCA prevented the increase of both LCA and LPC. It also prevented the early occurrence of VT or VF (within 5 min of occlusion) in all animals studied. The antiarrhythmic effect of POCA was not attributable to favorable hemodynamic changes or to changes in myocardial perfusion measured with radiolabeled microspheres. Thus, inhibition of CAT-I effectively reduced the incidence of lethal arrhythmias induced early after the onset of ischemia. Accordingly, pharmacologic inhibition of this enzyme provides a promising approach for prophylaxis of sudden cardiac death, that typically occurs very soon after the onset of acute ischemia, in man.

Alpha adrenergic-mediated accumulation of calcium in reperfused myocardium.

Reperfusion of ischemic myocardium is associated with increases in total myocardial calcium (Ca+2), which may influence the ultimate extent of ischemic damage as well as the development of arrhythmias. Since reperfusion is also associated with enhanced alpha-adrenergic responsivity, this study was performed to determine the potential interactions between alpha-adrenergic receptors and myocardial calcium during reperfusion. Cats were subjected to 35 min of left anterior descending coronary artery occlusion and 10 min of reperfusion. Total myocardial calcium was measured by atomic absorption spectrometry. Intracellular calcium was calculated from measurements of extracellular space [( 3H]inulin). In control animals with reperfusion, total calcium increased from 0.32 +/- 0.03 to 0.65 +/- 0.05 mmol/100 g dry tissue (P less than 0.0001), while intracellular calcium increased from 0.15 +/- 0.03 to 0.40 +/- 0.05 mmol/100 g dry tissue (P less than 0.001). Pretreatment with the alpha-adrenergic blocking agents phentolamine or prazosin prevented the increase in total and intracellular calcium. Phentolamine and the aqueous soluble alpha 1-adrenergic antagonist BE-2254 administered as late as 2 min before reperfusion similarly attenuated the increase in tissue calcium. Although administration of BE-2254 2 min before reperfusion failed to block the reperfusion-induced increase in extracellular space, the increase in calculated intracellular calcium was prevented. beta-Adrenergic blockade with propranolol partially attenuated but did not prevent an increase in total tissue calcium. Labetalol, a combined alpha- and beta-adrenergic blocking agent completely blocked the increase in tissue calcium during reperfusion. Additional experiments performed after 70 min of ischemia with reperfusion demonstrated a 49% attenuation of the increase in tissue calcium with alpha-adrenergic blockade. Electron microscopy with pyroantimonate and x-ray microprobe analysis demonstrated a large increase in calcium precipitate in mitochondria after reperfusion in untreated animals. Though alpha-adrenergic blockade prevented the calcium deposition in mitochondria, other criteria of ischemia persisted. Thus, alpha-adrenergic blockade specifically prevents the increase in intracellular calcium during reperfusion in reversibly injured tissue, independent of alterations in extracellular space and tissue water.

Accumulation of lysophosphoglycerides with arrhythmogenic properties in ischemic myocardium.

Lysophosphoglycerides, products of membrane phospholipid catabolism known to influence membrane function in several systems, appeared in the effluents of anoxic isolated rabbit hearts perfused at low flow and accumulated in perfused hearts and myocardium rendered ischemic in situ. Comparable concentrations of lysophosphoglycerides bound to albumin markedly and reversibly altered action potentials of isolated canine Purkinje fibers in vitro. Changes induced included diminution of the maximum diastolic potential, peak dV/dt of phase zero, amplitude, and action potential duration--alterations resembling those seen in ischemic myocardium in vivo. These electrophysiological alterations are compatible with changes implicated in predisposing to dysrhythmia dependent on reentry, a phenomenon potentiated by the presence of zones of decreased conduction. Thus, accumulation of lysophosphoglycerides induced by ischemia may contribute to the genesis of malignant dysrhythmia early after its onset.

Neural dysfunction and metabolic imbalances in diabetic rats. Prevention by acetyl-L-carnitine.

The rationale for these experiments is that administration of L-carnitine and/or short-chain acylcarnitines attenuates myocardial dysfunction 1) in hearts from diabetic animals (in which L-carnitine levels are decreased); 2) induced by ischemia-reperfusion in hearts from nondiabetic animals; and 3) in nondiabetic humans with ischemic heart disease. The objective of these studies was to investigate whether imbalances in carnitine metabolism play a role in the pathogenesis of diabetic peripheral neuropathy. The major findings in rats with streptozotocin-induced diabetes of 4-6 weeks duration were that 24-h urinary carnitine excretion was increased approximately twofold and L-carnitine levels were decreased in plasma (46%) and sciatic nerve endoneurium (31%). These changes in carnitine levels/excretion were associated with decreased caudal nerve conduction velocity (10-15%) and sciatic nerve changes in Na(+)-K(+)-ATPase activity (decreased 50%), Mg(2+)-ATPase (decreased 65%), 1,2-diacyl-sn-glycerol (DAG) (decreased 40%), vascular albumin permeation (increased 60%), and blood flow (increased 65%). Treatment with acetyl-L-carnitine normalized plasma and endoneurial L-carnitine levels and prevented all of these metabolic and functional changes except the increased blood flow, which was unaffected, and the reduction in DAG, which decreased another 40%. In conclusion, these observations 1) demonstrate a link between imbalances in carnitine metabolism and several metabolic and functional abnormalities associated with diabetic polyneuropathy and 2) indicate that decreased sciatic nerve endoneurial ATPase activity (ouabain-sensitive and insensitive) in this model of diabetes is associated with decreased DAG.

Subcellular distribution of endogenous long chain acylcarnitines during hypoxia in adult canine myocytes.

OBJECTIVE: Previous studies from our laboratory showed a pronounced increase in the sarcolemmal accumulation of long chain acylcarnitines in isolated neonatal rat myocytes after a prolonged (60 minute) hypoxic interval. Because much shorter intervals of hypoxia are associated with electrophysiological alterations in adult cells, the present study was performed to assess the extent of sarcolemmal accumulation of long chain acylcarnitines during hypoxia in adult canine myocytes. METHODS: Cells were incubated (for 24 hours) with 3H-carnitine and the uniformity of incorporation into carnitine fractions was verified biochemically. Cells were exposed to hypoxia (PO2 < 15 mm Hg) for 10 or 20 minutes in the presence or absence of sodium 2-[5-(4-chlorphenyl)-pentyl]-oxirane-2-carboxylate (POCA; 10 microM), an inhibitor of carnitine acyltransferase I. Cells were processed for electron microscopical autoradiography with a technique to spatially fix endogenous long chain acylcarnitines with selective and complete removal of short chain and free carnitine. Grain distributions were analysed by the maximum likelihood method from digitised micrographs. RESULTS: Total mass of long chain acylcarnitines increased ninefold [42.3(3.3) to 374(42) pmol.mg-1 protein] by 10 minutes of hypoxia and 15-fold [to 632(36) nmol.mg-1 protein] by 20 minutes of hypoxia. Normoxic cells exhibited little long chain acylcarnitines in the sarcolemma, and modest amounts in mitochondria and cytoplasm. In hypoxic cells, content of long chain acylcarnitines in mitochondria and cytoplasm increased by a maximum of twofold. By contrast, long chain acylcarnitines increased 100-fold in the sarcolemma to 4.18 x 10(6) molecules.microns-3 after 10 minutes of hypoxia. The increase in long chain acylcarnitines with hypoxia was completely prevented by pretreatment with POCA. CONCLUSION: Hypoxia in adult ventricular myocytes induces a rapid and preferential increase in endogenous long chain acylcarnitines within the sarcolemma.

Increased lysophosphatidylcholine content induced by thrombin receptor stimulation in adult rabbit cardiac ventricular myocytes.

OBJECTIVE: The aims were (1) to determine whether thrombin, which is increased in the presence of coronary thrombosis, can directly stimulate the production of lysophosphatidylcholine, which has arrhythmogenic properties, in ventricular myocytes; (2) whether the effect is dependent upon extracellular [Ca2+]; and (3) whether it is mediated directly through stimulation of the thrombin receptor. METHODS: Lipids were extracted from isolated adult rabbit ventricular myocytes and lysophosphatidylcholine was isolated by HPLC and quantified using a recently developed radiometric assay employing 3H-acetic anhydride. RESULTS: Thrombin (0.05 U.ml-1) stimulation of ventricular myocytes resulted in a nearly sixfold increase in lysophosphatidylcholine levels [0.26(SEM 0.03) to 1.61(0.42) nmol.mg-1 protein] within 1 min. The increase in myocytic lysophosphatidylcholine content was prevented by preincubation of thrombin with the proteolytic site inhibitors phenyly-prolyl-arginyl-chloromethyl ketone (PPACK) and dansylarginine N-(3-ethyl-1,5-pentanediyl)amide. The increase in lysophosphatidylcholine content in response to thrombin was not present at an extracellular calcium concentration ([Ca2+)]o) = 500 microM, but was marked at a physiological level of [Ca2+]o = 1.8 mM. Stimulation of myocytes with the thrombin receptor activating peptide SFLLRNPNDKYEPF (100 microM for 1 min) resulted in a similar increase in lysophosphatidylcholine content [1.61(0.27) nmol.mg-1 protein]. CONCLUSIONS: The marked increase in lysophosphatidylcholine content in cardiac myocytes in response to thrombin has important implications as an arrhythmogenic mechanism during early myocardial ischaemia.

Phosphatidic acid increases in response to noradrenaline and endothelin-1 in adult rabbit ventricular myocytes.

OBJECTIVE: The aim was to assess whether noradrenaline and endothelin-1 can stimulate endogenous production of phosphatidic acid in adult ventricular myocytes. METHODS: After stimulation of rabbit ventricular myocytes with noradrenaline and endothelin-1, total lipids were extracted using the Bligh and Dyer procedure and separated by thin layer chromatography, and phosphatidic acid was quantified using photodensitometric analysis of visualised lipids with CuSO4/H3PO4. RESULTS: Noradrenaline (10(-5) M) elicited a rapid increase in phosphatidic acid at 2 min, followed by a decrease at 5 min. A second delayed and sustained increase in phosphatidic acid occurred at 10 min. The response to noradrenaline (10(-9) to 10(-5) M) was concentration dependent with a half maximum response (EC50) of 3.1 x 10(-8) M and the maximum effect at 10(-6) M. The increase in phosphatidic acid production in response to noradrenaline was abolished by an alpha 1 adrenergic receptor blocking agent (2-[beta-(4-hydroxyphenyl)-ethylaminomethyl]tetralone) but unaffected by the beta adrenergic blocking agent L-propranolol. An increase in phosphatidic acid was also elicited in rabbit ventricular myocytes in response to endothelin-1. The response was time and concentration dependent with the maximal increase at 12 min, EC50 5.3 x 10(-9) M, and maximum effect at 10(-6) M. Both noradrenalin and endothelin-1 stimulated phosphatidylbutanol production in the presence of butanol (100 mM), indicating that both agonists activate phospholipase D. CONCLUSIONS: Noradrenaline at physiological concentrations elicits both a rapid and a delayed increase in phosphatidic acid in adult rabbit ventricular myocytes. Endothelial-1, at physiological concentrations, also stimulates an increase in the mass of phosphatidic acid in myocytes, but the increase induced by endothelin-1 is monophasic, in contrast to the biphasic response seen during stimulation with noradrenaline. Activation of phospholipase D contributes to the increase in phosphatidic acid seen during stimulation of myocytes with either noradrenaline or endothelin-1. These are the first data to characterise endogenous production of phosphatidic acid in isolated adult ventricular myocytes.

Exacerbation of coronary occlusion induced ventricular arrhythmias by the vagolytic effect of procainamide.

The influence of the vagolytic effect of procainamide on the early ventricular arrhythmias induced by left anterior descending coronary (LAD) occlusion was studied in chloraloseanaesthetised cats. All control animals developed a ventricular arrhythmia (1119 +/- 166 PVCs per hour), with a consistent onset time, duration, and overall mortality due to ventricular fibrillation (ie 20%). In 18 animals pretreated with procainamide (0.5 mg.kg-1.min-1 for 50 min), there was no effect on the ventricular arrhythmia in terms of ectopic frequency (1020 +/- 180 PVCs per hour), time to onset of arrhythmia, duration of arrhythmia, and mortality incidence (ie 16.7%). However, subdividing the data according to whether or not vagal blockade had been produced by procainamide revealed that animals exhibiting complete vagal blockade demonstrated significantly more ectopic beats (1606 +/- 310 PVCs per hour) and 33% developed ventricular fibrillation. Treated animals without complete vagal blockade exhibited an ectopic frequency rate of 620 +/- 98 PVCs per hour and none of the animals developed ventricular fibrillation. The haemodynamic parameters were similar between both procainamide treated subgroups. These results suggest that an important factor in response of the ischaemic heart to the cardiac rhythm effects of procainamide is the degree of vagal blockade induced by this agent.

Mechanisms contributing to the arrhythmogenic influences of alpha 1-adrenergic stimulation in the ischemic heart.

The majority of deaths associated with ischemic heart disease occur suddenly because of disturbances in cardiac rhythm culminating in ventricular fibrillation. Past research has focused on elucidating the biochemical membrane mechanisms responsible for the adverse electrophysiologic alterations in the ischemic heart, with major emphasis on the influence of adrenergic neural factors. It has been demonstrated that both alpha 1-and beta-adrenergic mechanisms contribute to arrhythmogenesis in the ischemic heart. In the normal heart, alpha 1-adrenergic input has very little effect on electrophysiologic indices. However, during early ischemia and reperfusion, enhanced alpha 1-adrenergic responsivity associated with a twofold reversible increase in alpha 1-adrenergic receptors in vivo has been demonstrated. Likewise, in a variety of species, alpha 1-adrenergic inhibition with prazosin markedly decreases the incidence of malignant ventricular arrhythmias associated with either myocardial ischemia or subsequent reperfusion. One major manifestation of alpha 1-adrenergic receptor activation during reperfusion of ischemic myocardium is an increase in intracellular calcium ion (Ca2+). It has been demonstrated that reperfusion of ischemic myocardium increases intracellular Ca2+ in reversibly injured tissue, and that the gain in intracellular Ca2+ is prevented by alpha 1-adrenergic inhibition with hydroxyphenylethyl aminomethyl tetralone, even when administered just prior to reperfusion. Subsequently, it was demonstrated that the alpha 1-adrenergic-induced increase in mitochondrial Ca2+ contributes to the decline in mitochondrial function. These findings suggest that even single-dose intervention with alpha 1-adrenergic inhibitors may improve markedly the functional recovery and extent of ultimate necrosis in humans after coronary thrombolysis. To investigate the mechanisms responsible for the increase in alpha 1-adrenergic receptors during ischemia, we used isolated adult canine ventricular myocytes exposed to hypoxia. Thirty minutes of hypoxia at 25 degrees C or 10 minutes of hypoxia at 37 degrees C resulted in a threefold reversible increase in the density of surface alpha 1-adrenergic receptors and a threefold increase in the cellular content of long-chain acylcarnitines. Inhibition of carnitine acyltransferase I abolished not only the accumulation of long-chain acylcarnitines during hypoxia but also the increase in alpha 1-adrenergic receptors. Exposure of normoxic myocytes to exogenous long-chain acylcarnitines (1 mumol/liter) for 10 minutes also increased alpha 1-adrenergic receptor number. These findings indicate that the sarcolemmal accumulation of long-cha

Simultaneous computer mapping to facilitate intraoperative localization of accessory pathways in patients with Wolff-Parkinson-White syndrome.

Sixteen patients with the Wolff-Parkinson-White syndrome underwent simultaneous intraoperative computer mapping from multiple sites before surgical division of the accessory pathways. A 16-bipolar electrode band was positioned around the atrioventricular groove. Ventricular epicardial electrograms from single beats were recorded simultaneously during atrial pacing, resulting in maximal preexcitation, and atrial electrograms were recorded during orthodromic supraventricular tachycardia. Four-level transmural plunge needle electrodes were used concomitantly in 3 patients. Electrograms were processed separately using a guarded signal conditioner that isolates, amplifies, filters and analog-to-digitally converts synchronously at 2 kHz with 12-bit accuracy. Digital data were transmitted by fiber optics to a high-density digital recorder and processed with a computer having rapid interactive graphics. Results in the 16 patients revealed 20 distinct Kent bundles. Two patients had only nonsustained supraventricular tachycardia induced intraoperatively and 1 patient manifested intermittent anterograde ventricular preexcitation. Multiple pathways were identified in 4 patients. This simultaneous multiple electrode mapping procedure facilitates intraoperative mapping by requiring only a single beat for analysis of anterograde and retrograde activation times, decreases cardiac manipulation during mapping and obviates the need for cardiopulmonary bypass, and permits analysis of transmural activation patterns. This approach decreases markedly the time required for mapping and permits accurate study of nonsustained arrhythmias as well as rapid identification of multiple accessory pathways.

The surgical treatment of atrial fibrillation. III. Development of a definitive surgical procedure.

On the basis of the known electrophysiologic mechanisms of atrial fibrillation, multiple surgical procedures were designed and tested in dogs to determine the feasibility of developing a surgical cure for human atrial fibrillation. These experimental studies culminated in a surgical approach that effectively creates an electrical maze in the atrium. The atrial incisions prevent atrial reentry and allow sinus impulses to activate the entire atrial myocardium, thereby preserving atrial transport function postoperatively. Since September 1987, this surgical procedure has been applied in seven patients, five with paroxysmal atrial fibrillation of 2 to 9 years' duration and two with chronic atrial fibrillation of 3 and 10 years' duration. All seven patients have been cured of atrial fibrillation and none is receiving any postoperative antiarrhythmic medications.

The surgical treatment of atrial fibrillation. II. Intraoperative electrophysiologic mapping and description of the electrophysiologic basis of atrial flutter and atrial fibrillation.

Computerized mapping of atrial fibrillation was performed in animals and man. To study atrial fibrillation in a systematic manner, we developed a clinically relevant experimental model of atrial fibrillation. Chronic mitral regurgitation was created surgically in 25 dogs without opening the pericardium. After several months of chronic mitral regurgitation, the atria became enlarged and sustained atrial fibrillation could be induced by standard programmed electrical stimulation techniques. Computerized isochronous activation maps of the atria were recorded during atrial fibrillation from 208 bipolar electrodes simultaneously. In a parallel study, human atrial fibrillation was mapped with a separate 160-channel intraoperative mapping system in patients with paroxysmal atrial fibrillation who were undergoing surgical correction of the Wolff-Parkinson-White syndrome. The canine activation sequence maps demonstrated a spectrum of rhythm abnormalities ranging from simple atrial flutter to complex atrial fibrillation. They also showed that macroreentrant circuits within the atrial myocardium were responsible for the entire spectrum of arrhythmias. Atrial reentry was also documented during human atrial fibrillation. All patients had nonuniform conduction around regions of bidirectional block in both atria resulting in multiple discrete wave fronts. In addition, six patients had a single reentrant circuit in the right atrium in which bidirectional block of the activation wave front occurred along the sulcus terminals between the venae cavae. The left atrium in all patients demonstrated multiple wave fronts and conduction block, but left atrial reentry could not be detected. Both the experimental study and the clinical study demonstrated that multiple wave fronts, nonuniform conduction, bidirectional block, and large (macroreentrant) reentrant circuits occur during atrial fibrillation. The presence of macroreentrant circuits and the absence of either microreentrant circuits or evidence of atrial automaticity suggests that atrial fibrillation should be amenable to surgical ablation.

Computerized global electrophysiological mapping of the atrium in patients with Wolff-Parkinson-White syndrome.

The activation sequence of the human atrium has been inferred previously from a limited number of atrial electrograms recorded sequentially with a single-point mapping system. In 10 patients with Wolff-Parkinson-White (WPW) syndrome, three form-fitted, flexible templates containing a total of 156 bipolar electrodes were fixed to the epicardial surface of both atria. Data were recorded continuously from all 156 electrodes simultaneously during normal sinus rhythm, left atrial pacing, right atrial pacing, and reciprocating tachycardia. In all 10 patients, the site of the accessory pathway correlated with the results of the preoperative electrophysiological study and of the standard intraoperative band electrode mapping. The accessory pathway was located in the left free wall position in 8 patients, the right free wall position in 1 patient, and the posterior septal position in 1 patient. In 4 of the 8 patients with left free wall pathways, activation maps of retrograde atrial activation during reciprocating tachycardia demonstrated a broad base of initial atrial depolarization. This finding suggests that some accessory pathways may have a broad band of insertion on the atrium, and supports our practice of wide dissection of the entire anatomical space associated with each pathway to avoid recurrences of WPW syndrome. Simultaneous global atrial-activation mapping in patients with WPW syndrome provides a clearer understanding of atrial activation during reciprocating tachycardia.

Computerized global electrophysiological mapping of the atrium in a patient with multiple supraventricular tachyarrhythmias.

The first clinical experience and the potential benefit of intraoperative global atrial-activation mapping recorded from 156 electrodes simultaneously are demonstrated in a 14-year-old girl with an ectopic (automatic) right atrial tachycardia, junctional tachycardia, and atrial flutter secondary to a previous atriotomy. Cryoablation of the right atrial focus terminated the automatic tachycardia, and surgical interruption of the atrial flutter pathway temporarily terminated this arrhythmia. Persistence of the junctional tachycardia necessitated elective cryoablation of the bundle of His.

Computerized activation sequence mapping of the human atrial septum.

To delineate the propagation of electrical activation in the atrial septum, atrial epicardial and atrial septal maps were recorded intraoperatively using a 156-channel computerized mapping system in 12 patients during sinus rhythm (n = 10), supraventricular tachycardia associated with septal pathways in Wolff-Parkinson-White syndrome (n = 3), atrioventricular (AV) node reentrant tachycardia (n = 4), and atrial flutter (n = 5). The epicardial and septal data were recorded simultaneously from 156 atrial electrodes, digitized, analyzed, and displayed as isochronous maps on a two-dimensional diagram of the atria. During sinus rhythm, the activation wave fronts propagated most rapidly along the large muscle bundles of the atrial septum. During supraventricular tachycardia associated with Wolff-Parkinson-White syndrome, the earliest site of retrograde atrial activation usually corresponded to the position of atrial insertion of the septal pathways. However, the earliest site of activation during orthodromic supraventricular tachycardia was different from that during ventricular pacing in 1 patient with a posterior septal accessory pathway localized by the epicardial mapping study. The data document the rationale for dividing the ventricular end of the accessory pathways (ie, the endocardial technique) rather than the atrial end (ie, the epicardial technique) in patients with Wolff-Parkinson-White syndrome. During AV node reentrant tachycardia, atrial activation data suggested that atrial tissue lying outside the confines of the anatomical AV node is a necessary link in this common arrhythmia. Thus, these atrial septal maps explain why surgical dissection, or properly positioned small cryolesions placed in the region of the AV node, can ablate AV node reentrant tachycardia without altering normal AV node function. The maps recorded during atrial flutter suggest the importance of the atrial septum as one limb of a macroreentrant circuit responsible for the arrhythmia, and imply that atrial flutter is amenable to control by surgical techniques. These studies demonstrate the details of normal atrial septal activation, the importance of the atrial septum in a variety of different atrial arrhythmias, and the basis of and potential for surgical ablation of the most common types of supraventricular arrhythmias.