Intracardiac Stimulation Research Articles

Downregulation of FKBP5 Promotes Atrial Arrhythmogenesis.

Atrial fibrillation (AF), the most common arrhythmia, is associated with the downregulation of FKBP5 (encoding FKBP5 [FK506 binding protein 5]). However, the function of FKBP5 in the heart remains unknown. Here, we elucidate the consequences of cardiomyocyte-restricted loss of FKBP5 on cardiac function and AF development and study the underlying mechanisms. Right atrial samples from patients with AF were used to assess the protein levels of FKBP5. A cardiomyocyte-specific FKBP5 knockdown mouse model was established by crossbreeding Fkbp5flox/flox mice with Myh6MerCreMer/+ mice. Cardiac function and AF inducibility were assessed by echocardiography and programmed intracardiac stimulation. Histology, optical mapping, cellular electrophysiology, and biochemistry were employed to elucidate the proarrhythmic mechanisms due to loss of cardiomyocyte FKBP5. FKBP5 protein levels were lower in the atrial lysates of patients with paroxysmal AF or long-lasting persistent (chronic) AF. Cardiomyocyte-specific knockdown mice exhibited increased AF inducibility and duration compared with control mice. Enhanced AF susceptibility in cardiomyocyte-specific knockdown mice was associated with the development of action potential alternans and spontaneous Ca2+ waves, and increased protein levels and activity of the NCX1 (Na+/Ca2+-exchanger 1), mimicking the cellular phenotype of chronic AF patients. FKBP5-deficiency enhanced transcription of Slc8a1 (encoding NCX1) via transcription factor hypoxia-inducible factor 1α. In vitro studies revealed that FKBP5 negatively modulated the protein levels of hypoxia-inducible factor 1α by competitively interacting with heat-shock protein 90. Injections of the heat-shock protein 90 inhibitor 17-AAG normalized protein levels of hypoxia-inducible factor 1α and NCX1 and reduced AF susceptibility in cardiomyocyte-specific knockdown mice. Furthermore, the atrial cardiomyocyte-selective knockdown of FKBP5 was sufficient to enhance AF arrhythmogenesis. This is the first study to demonstrate a role for the FKBP5-deficiency in atrial arrhythmogenesis and to establish FKBP5 as a negative regulator of hypoxia-inducible factor 1α in cardiomyocytes. Our results identify a potential molecular mechanism for the proarrhythmic NCX1 upregulation in chronic AF patients.

PO-455617-2 UNRAVELLING THE ARRHYTHMOGENIC MECHANISMS OF SHORT QT SYNDROME TYPE 3 IN AN ANIMAL MODEL OF KIR2.1M301K GAIN-OF-FUNCTION MUTATION

Short QT Syndrome Type 3 (SQTS3) is an extremely rare, highly arrhythmogenic disease caused by gain-of-function mutations in the KCNJ2 gene coding the inward rectifier potassium channel Kir2.1. We investigated arrhythmogenic mechanisms associated with the mutation Kir2.1M301K in a patient presenting an extremely abbreviated QT interval, paroxysmal atrial fibrillation, and ventricular fibrillation inducibility. To study mechanisms of life-threatening arrhythmias produced by Kir2.1M301K. We tested the hypothesis that, in addition to abolishing IK1 rectification, Kir2.1M301K produces functional defects in Kir2.1 partner proteins, predisposing patients to an arrhythmogenic phenotype. We used intravenous cardiac-specific adeno-associated virus-mediated gene transfer to generate mice expressing wild-type (WT) and M301K mutant channel. We characterized the mice using molecular and cellular biology techniques, electrocardiograms (ECGs), intracardiac stimulation and patch-clamping. We confirmed Kir2.1WT or Kir2.1M301K gene expression specifically in the mouse heart. On ECG, the corrected QT (QTc) interval of Kir2.1M301K mice was significantly shorter than Kir2.1WT mice (p<0.0001), and the QRS complex was prolonged (p<0.01). On intracardiac stimulation, 7 out of 8 Kir2.1M301K mice had inducible ventricular tachycardia/fibrillation of >500ms duration, while none of 10 Kir2.1WT mice were inducible (p=0.0009). Compared with Kir2.1WT, the current/voltage relation of Kir2.1M301K cardiomyocytes showed increased outward IK1 at voltages positive to -80 mV (p<0.0001) with no inward-going rectification. However, inward IK1 was reduced at voltages negative to -80 mV (p=0.006). Unexpectedly, Kir2.1M301K cardiomyocytes had a reduced INa density (p<0.0001) with voltage shifted activation and inactivation. Membrane fractionation and western blot analysis revealed that, while 100% of NaV1.5 channels reached the membrane in Kir2.1WT cardiomyocytes, only 77% did in Kir2.1M301K cardiomyocytes. The Kir2.1M301K mouse recapitulates the arrhythmogenic phenotype of the SQTS3 patient. Kir2.1M301K mutation produces both Kir2.1 and NaV1.5 dysfunction, confirming the reciprocal modulation of these channels in macromolecular complexes. This is the first demonstration that a KCNJ2 gain-of-function mutation modifies NaV1.5 current, thus producing severe arrhythmias by both shortening QT interval and reducing ventricular excitability.

Atrial-specific reduction of Kir2.1 channel pore diameter in addition to loss of inward-going rectification underlies inducible atrial fibrillation in a mouse model of short QT syndrome type 3

Abstract Introduction Short QT Syndrome Type 3 (SQTS3) is an extremely rare arrhythmogenic disease caused by gain-of-function mutations in the KCNJ2 gene coding the inward rectifier potassium channel Kir2.1. We investigated arrhythmogenic mechanisms associated with a de-novo mutation (E299V) in Kir2.1 in an 11-year-old boy presenting an extremely abbreviated QT interval, paroxysmal atrial fibrillation, and mild left ventricular dysfunction. Amino acid E299 in the Kir2.1 sequence is necessary for polyamine binding induced inward rectification. Purpose Test the hypothesis that Kir2.1E299V induces reduced conductance and lack of rectification that causes electrical defects in atrial cardiomyocytes, predisposing patients to atrial arrhythmias. Methods We used intravenous adeno-associated virus-mediated gene transfer to generate mice expressing wild-type (WT) and the E299V mutant protein. We used ECG, intracardiac stimulation, patch-clamp, molecular biology and computational modelling to characterize the models and study arrhythmia mechanisms in the atria and ventricles. Results We confirmed WT or mutant Kir2.1 gene expression specifically in the mouse heart. On ECG, the corrected QT (QTc) interval of Kir2.1E299V mice was significantly shorter than Kir2.1WT mice (p&amp;lt;0.0001). The PR interval in Kir2.1E299V was also significantly shorter than WT mice (p&amp;lt;0.0001). On intracardiac stimulation, the largest proportion of arrhythmic events occurred in the atria, as 7 out of 9 Kir2.1E299V mice presented &amp;gt;1 second atrial flutter/fibrillation, while only 2 out of 10 Kir2.1WT mice showed this type of arrhythmia (p=0.023). On patch clamping, both atrial and ventricular cardiomyocytes expressing Kir2.1E299V had extremely abbreviated action potential durations (APD90) at all frequencies studied (p&amp;lt;0.0001). The current/voltage relation of ventricular Kir2.1E299V cardiomyocytes revealed an absence of inward-going rectification and increased IK1 at voltages positive to −80 mV compared to Kir2.1WT cardiomyocytes (p&amp;lt;0.0001). In contrast, while in the atrial Kir2.1E299V cardiomyocytes the outward IK1 was increased at voltages positive to −80 mV with loss of rectification, IK1 was significantly reduced at voltages negative to −80 mV (p&amp;lt;0.0001), suggesting a loss of function leading to atrial arrhythmia inducibility. A higher proportion of Kir2.2 at atrial level and atomic in-silico 3D simulations suggested that the mutation impaired polyamine block of the Kir2.1E299V-Kir2.2 channel while reducing the pore diameter. Conclusions This first in-vivo mouse model of cardiac-specific SQTS3 recapitulates the electrophysiological phenotype of a patient with the Kir2.1E299V mutation. The mutation results in a Kir2.1 gain-of-function mediated by and absence of rectification. The predominant arrhythmias induced in these SQTS3 mice were supraventricular likely due to the combined lack of inward rectification and atrial-specific reduced pore diameter of the Kir2.1E299V-Kir2.2 channel. Funding Acknowledgement Type of funding sources: Private company. Main funding source(s): La Caixa FoundationLa Maratό TV3 Foundation

Abstract P356: Dual Dysfunction Of Kir2.1 Underlies Conduction And Excitation-contraction Coupling Defects Promoting Arrhythmias In A Mouse Model Of Andersen-tawil Syndrome Type 1

Background: Andersen-Tawil syndrome type 1 (ATS1), caused by trafficking deficient mutations in the gene KCNJ2 coding the inward rectifier K + channel Kir2.1, is associated with life-threatening arrhythmias, which in some patients resemble catecholaminergic polymorphic ventricular tachycardia (CPVT), but the mechanisms are poorly understood. We tested the hypothesis that dysfunction of two different populations of mutant Kir2.1 channels, one at the sarcolemma, and the other at the sarcoplasmic reticulum (SR) membrane, directly alters conduction and intracellular calcium dynamics, respectively, to promote the ATS1 phenotype and arrhythmias that resemble CPVT. Methods: We generated a new mouse model of ATS1 by a single i.v. injection of cardiac specific adeno-associated viral (AAV) transduction with Kir2.1 Δ314-315 . In-vivo and cellular, structural and functional analyses of the model were carried out by electrocardiogram (ECG), magnetic resonance imaging (MRI), intracardiac stimulation, patch-clamping, membrane fractionation, western blot, immunolocalization and live calcium imaging. Results: Our mouse model carrying mutant Kir2.1 Δ314-315 recapitulated the ATS1 phenotype without modifying ventricular function. On ECG, Kir2.1 Δ314-315 mice had prolonged PR, QRS and QT intervals and occasional U waves. They showed significantly slower conduction velocities than wildtype mice in response to flecaidine-induced Na + -channel blockade, additional QT prolongation in response to isoproterenol, and increased vulnerability to cardiac fibrillation. Cardiomyocytes from Kir2.1 Δ314-315 mice had significantly reduced inward rectifier K + and Na + inward currents, depolarized resting membrane potential and prolonged action potential duration. Immunolocalization in wildtype cardiomyocytes and skeletal muscle cells revealed a novel SR microdomain of functional Kir2.1 channels contributing to intracellular Ca 2+ homeostasis. Kir2.1 Δ314-315 cardiomyocytes showed defects in SR Kir2.1 localization and function, which contributed to abnormal spontaneous Ca 2+ release events. Conclusions: Cardiac-specific AAV transduction with Kir2.1 Δ314-315 in mice recapitulates the ATS1 phenotype by disrupting localization and function of Kir2.1 channels at the SR, and the Kir2.1-Na V 1.5 channelosome at the sarcolemma. These results reveal a novel dual mechanism of arrhythmogenesis in ATS1 involving defects in Kir2.1 channel trafficking and function at two different microdomains. They also provide the first demonstration at the molecular level of the mechanism underlying the overlap between ATS1 and CPVT associated with defects in intracellular calcium homeostasis.

Abstract 14836: Dual Dysfunction of Kir2.1 at the Sarcolemma and the Sarcoplasmic Reticulum Underlies Arrhythmogenesis in a Mouse Model of the Andersen-Tawil Syndrome Type 1

Introduction: Andersen-Tawil syndrome type 1 (ATS1) is associated with fatal cardiac arrhythmias. However, the underlying mechanisms are poorly understood. Hypothesis: Cardiac-specific expression of trafficking deficient Kir2.1 channels in mice in-vivo recapitulates the cardiac electrical phenotype of ATS1 and investigate the underlying mechanisms. Methods: We generated a new mouse model of ATS1 by a single i.v. injection of cardiac specific adeno-associated viral (AAV) transduction with Kir2.1 Δ314-315 , which recapitulated the ATS1 ECG phenotype without modifying ventricular function. The animal and cellular, structural and functional analyses were carried out by ECG, intracardiac stimulation, patch-clamping, membrane fractionation, western blot, immunolocalization and live calcium imaging. Results: AAV-Kir2.1 Δ314-315 mice were significantly more sensitive to flecainide than control, increasing the PR and QRS intervals over time. Kir2.1 Δ314-315 mice had increased vulnerability to cardiac fibrillation. Patch-clamping in ventricular cardiomyocytes from Kir2.1 Δ314-315 mice demonstrated significantly reduced I K1 and I Na , depolarized resting membrane potential and prolonged action potential. Immunolocalization in control mice revealed two bands of Kir2.1 staining, one colocalizing with Na V 1.5 and AP1 near the Z disk, the other near the H zone. Membrane fractionation and western blot experiments demonstrated two distinct levels of Kir2.1 protein expression, one at the sarcolemmal fraction together with Na V 1.5 and the other at the sarcoplasmi creticulum (SR). Kir2.1 Δ314-315 cardiomyocytes showed disruption of the Kir2.1-Nav1.5 channelosome at the sarcolemma, indicating dysfunctional trafficking o fboth channels. In addition, the SR Kir2.1 was disrupted and calcium transient dynamics were altered, resulting in frequent abnormal spontaneous calcium release events, and revealing an excitation-contraction coupling defect. Conclusions: Cardiac-specific AAV transduction with Kir2.1 Δ314-315 in mice recapitulates the ATS1 phenotype by disrupting localization and function of Kir2.1at the SR, and the Kir2.1-Na V 1.5 channelosome at the sarcolemma, revealing anovel dual mechanism of arrhythmogenesis.

Macrophages facilitate post myocardial infarction arrhythmias: roles of gap junction and KCa3.1.

Effective therapeutic targets against post-myocardial infarction (MI) arrhythmias remain to be discovered. We aimed to investigate the role of macrophages in post-MI arrhythmias.Methods: Mononuclear cell accumulation, macrophage polarization from M0 to M1 subset, and gap junction formation were analyzed in MI patients and MI mice by flow cytometry, immunofluorescence and patch clamping. Differentially expressed genes were identified by RNA sequencing. Macrophages and cardiomyocytes were cocultured in vitro, and the effects of gap junction and KCa3.1 on electrophysiological properties were assessed by patch clamping. The effects of KCa3.1 inhibition on post-MI arrhythmias were assessed by intracardiac stimulation and ambulatory electrocardiograms in vivo.Results: Percentage of pro-inflammatory mononuclear cells were significantly elevated in patients with post-MI arrhythmias compared with MI patients without arrhythmias and healthy controls (p<0.001). Macrophages formed gap junction with cardiomyocytes in MI border zones of MI patient and mice, and pro-inflammatory macrophages were significantly increased 3 days post-MI (p<0.001). RNA sequencing identified Kcnn4 as the most differentially expressed gene encoding ion channel, and the upregulation is mainly attributed to macrophage accumulation and polarization into pro-inflammatory subset. In vitro coculture experiments demonstrated that connection with M0 macrophages via gap junction slightly shortened the action potential durations (APDs) of cardiomyocytes. However, the APD90 of cardiomyocytes connected with M1 macrophages were significantly prolonged (p<0.001), which were effectively attenuated by gap junction inhibition (p=0.002), KCa3.1 inhibition (p=0.008), KCa3.1 silencing (p<0.001) and store-operated Ca2+ channel inhibition (p=0.005). In vivo results demonstrated that KCa3.1 inhibition significantly decreased the QTc durations (p=0.031), intracardiac stimulation-induced ventricular arrhythmia durations (p=0.050) and incidence of premature ventricular contractions (p=0.030) in MI mice.Conclusion: Macrophage polarization leads to APD heterogeneity and post-MI arrhythmias via gap junction and KCa3.1 activation. The results provide evidences of a novel mechanism of post-MI heterogeneous repolarization and arrhythmias, rendering macrophages and KCa3.1 to be potential therapeutic targets.

Abstract 118: NLRP3 Inflammasome Mediates the Obesity-induced Pathogenesis of Atrial Fibrillation

Background: Obesity increases the risk of atrial fibrillation (AF), the most common cardiac arrhythmia; but it is unknown what molecular pathway(s) underlying obesity promotes AF pathophysiology. ‘NACHT, LRR &amp; PYD Domains-containing Protein 3’ (NLRP3) inflammasome can activate Caspase-1 (Casp1) and mediate inflammatory response associated with obesity. Prior studies revealed that NLRP3 activity is enhanced in atrial tissues of AF patients, and our preliminary studies demonstrated a positive correlation between obesity and NLRP3 activation. Thus, we hypothesized that diet-induced obesity promotes AF pathogenesis via activation of the NLRP3 inflammasome. Methods and Results: Wildtype (WT) and NLRP3 knockout (KO) mice were fed high fat diet (HFD, 60% kcal) or normal chow (NC, as control) for 10 weeks to establish the obese but non-diabetic phenotype. At 10 weeks, WT+HFD and KO+HFD mice showed a significant increase in body weight, compared to WT+NC and KO+NC mice (P&lt;0.001). Echocardiography showed ventricular function were similar among all groups at 10 weeks. Western blotting revealed increased levels of mature Casp1 in atria of WT+HFD mice (P&lt;0.05 vs WT+NC mice), suggesting activity of NLRP3 is enhanced by HFD. Programmed intracardiac stimulation was performed to assess the inducibility of AF. While only 3 of 14 (21.3%) WT+NC mice showed AF evoked by atrial pacing, 7 of 8 (87.5%) WT+HFD mice developed pacing-induced AF (P&lt;0.05). Atrial effective refractory period (AERP) was reduced in WT+HFD mice (P&lt;0.05 vs WT+NC), suggesting that HFD promotes an electrical remodeling substrate for AF development. In contrast, AF incidence was reduced to 33.3% (3 of 9; P&lt;0.05 vs WT+HFD) and AERP was normalized in KO+HFD mice, suggesting NLRP3 is required for AF development in obese mice. Compared to WT+NC mice, Ca 2+ sparks were increased in atrial myocytes of WT+HFD mice (4.5±0.6 vs 6.4±0.7 sparks/100μm/s, P&lt;0.05), which was normalized in KO+HFD mice (4.4 ±0.4 sparks/100μm/s, P&lt;0.05). Conclusion: Our data suggests that obesity promotes NLRP3 activation and inhibition of NLRP3 can prevent the development of substrate for AF development. Our study potentially establishes a mechanistic link between obesity-induced inflammatory signaling and AF pathogenesis.

Impaired local regulation of ryanodine receptor type-2 by protein phosphatase 1 promotes atrial fibrillation

Purpose: Atrial fibrillation (AF) is the most common cardiac arrhythmia with a growing prevalence yet current pharmaceutical treatments are ineffective. Previous studies suggest that protein phosphatase 1 (PP1) is dysregulated globally in AF patients but its local regulation on key Ca2+-handling proteins such as ryanodine receptor type-2 (RyR2) is not known. In this study we hypothesize that decreased PP1 regulation of RyR2 promotes AF through increasing Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of RyR2. Methods: To study the local regulation of RyR2 by PP1, we used spinophilin knockout mice (KO), since PP1 targets RyR2 via spinophilin. The interaction between RyR2 and PP1 was measured using co-immunoprecipitation while RyR2 phosphorylation level was quantified using Western blot. RyR2 activity was determined by measuring 1) single RyR2 channel activity in a lipid bilayer system and 2) Ca2+ sparks frequency in atrial myocytes loaded with Fluo4-AM. Baseline cardiac characteristics were determined using echocardiography and histological staining while AF inducibility was assessed by intracardiac electrophysiology study. Results: The interaction of PP1 with RyR2 was reduced by 55% in the KO hearts compared to WT (P<0.001). RyR2 phosphorylation at Serine 2814 was increased by 43% in the KO atria (P<0.05 vs. WT) while unchanged at Serine 2808. Single RyR2 channels isolated from KO hearts had a higher open probability (0.10±0.02) compared to that from WT (0.02±0.01; P<0.01). Ca2+ spark frequency normalized to sarcoplasmic reticulum (SR) Ca2+ content was increased in atrial myocytes isolated from KO mice (1.72±0.26 a.u.) compared to WT (0.77±0.20 a.u.; P<0.05). Furthermore, this increase was rescued by CaMKII-inhibitor KN93 but not by protein kinase A (PKA) inhibitor H89. End diastolic diameter of hearts from KO mice was 10% smaller than that from WT (P<0.01) but both the heart weight to body weight ratio and ejection fraction were unchanged. Also, there was no difference in fibrosis between KO and WT heart based on histological sections stained with Masson's trichome. However, when subjected to intracardiac electrical stimulation, KO mice had a higher incidence of pacing-induced AF (100%) compared to WT (33%; P<0.01). Conclusions: PP1 regulates RyR2 by counteracting CaMKII but not PKA phosphorylation of RyR2. Spinophilin deficiency leads to decreased PP1 regulation of RyR2 which may promote AF. This regulation may represent a novel therapeutic target for treating AF.

Abstract 1076: Conditional Fkbp12.6 Overexpression In Mouse Cardiac Myocytes Protects From Triggered Ventricular Arrhythmia Through Specific Alteration In Ec Coupling

In cardiac myocytes, Ca2+ release from the sarcoplasmic reticulum (SR) into the cytoplasm via the ryanodine receptor (RyR2) activates cell contraction. During diastole, RyR2 are closed and prevent Ca2+ efflux from the SR. One of the major regulators of RyR2 function is FKBP12.6. Binding of FKBP12.6 stabilizes RyR2 in the closed formation in diastole and contributes to synchronized RyR2 opening in systole. Beta-adrenergic stimulation dissociates FKBP12.6 from RyR2, leading to diastolic Ca2+ leak that can trigger ventricular tachycardias (VT). We tested the hypothesis whether FKBP12.6 overexpression in the myocardium can reduce the susceptibility to VT in stress conditions. We developed a mouse model with conditional cardiac specific overexpression of FKBP12.6 using the Tet-Off system. Transgenic (TG) mice and controls (CT) were examined by echocardiography, PV-catheterization, ECG, and underwent intracardiac stimulation to trigger VT before and after pre-treatment with isoproterenol. In isolated cardiac myocytes, SR Ca2+ load, Ca2+ sparks and Ca2+ transient were measured using confocal microscopy, and L-type Ca2+ current was determined by the patch-clamp technique. Echocardiography, PV-catheterization and ECG recording did not reveal differences between Tg (n=11) and CT (n=13) mice. Burst pacing (figure 1) could induce TV in 4 of 24 controls and in 0 of 14 TG mice (n.s.). Following pre-treatment with isoproterenol, TV could be induced in 10 of 23 controls, but only in 1 of 14 TG animals (figure 2, p&lt;0.05). In isolated myocytes, decreased Ca2+ spark frequency, increased Ca2+ spark size, unchanged SR Ca2+ load and decreased Ca2+ transient were observed in TG cells (n=19) as compared to controls (n=48, p&lt;0.05). L-type Ca2+ channel current was found to be decreased in Tg myocytes (n=29 vs n=32, p&lt;0.01). We conclude that myocardial FKBP12.6 overexpression has a protective effect against VT induced by rapid pacing after pretreatment with catecholamines. This antiarrhythmic effect is probably, at least in part, linked to decreased diastolic SR Ca2+ leak. Our results support the hypothesis that increased FKBP12.6 binding to RyR2 might represent a potential therapeutical target in the prevention and treatment of ventricular arrhythmias.

Chronic Cardiac Neurostimulation for Ventricular Rate Control During Atrial Fibrillation

The inferior interatrial ganglionated parasympathetic plexus (IIGP) almost exclusively innervates the atrioventricular node. Acute intracardiac stimulation of this plexus with electrode catheters has been shown to decrease the ventricular rate during atrial fibrillation (AF) in humans. The present study reports on the 6 months stimulation effects of a permanent neurostimulation lead which has been implanted transvenously into this IIGP in dogs. In 5 dogs a DDD-pacemaker was implanted and AF induced by rapid pacing. During 6 months intermittent high frequency stimulation of the IIGPP was performed over a second implantable stimulator to assess chronic neurostimulation efficacy. From 1 to 6 months a continuous decrease of the voltage at which atrioventricular block III° could be elicited was observed. At implant/6 months a 1.8/2.5-fold prolongation of the RR interval during AF was achieved at 1 V/1 ms. Dynamic modulations of the magnitude of the negative dromotropic effect could be obtained by varying stimulus frequency, voltage and duration. Selective chronic cardiac neurostimulation for ventricular rate control during AF can be achieved in animals. The results obtained so far justify human studies.

Absence of an impact of emotional distress on the perception of intracardiac shock discharges.

The pain of transvenous cardioversion shocks in awake patients is an important clinical problem. It is unknown whether psychological factors modulate any observed variation in pain perception. Thirty-seven patients with chronic atrial fibrillation (AF; mean age 61.9 years, 29 men, 8 women) were consecutively included in the study. Pain perception of a low energy test shock (60V, 0.1J) during internal cardioversion was assessed immediately following the stimulus. Before treatment anxiety, depression, somatization were evaluated. The intracardiac shock was perceived as hypalgesic in 15 (41%) patients, as normalgesic in 10 (27%), and as hyperalgesic in 10 (32%) patients. Pain threshold was significantly lower in patients in which AF was accidentally diagnosed (p < 0.029). Age, sex, and the level of education were equally distributed over the three pain groups. The hyperalgesic pain threshold was not associated with anxiety, depression, or the patients' tendency to amplify benign bodily sensations. This study discloses a wide range of perceived pain intensity caused by a homogenous intracardiac stimulation. Anxiety and depression do not amplify perception of intracardiac shocks. Sensory gating mechanisms may play a more important role in the level of intracardiac shock perception than distressing affective factors.

Presynaptic inhibitory actions of lignocaine in canine isolated, blood-perfused atrial preparations.

1. Cardiac effects of lignocaine on sinoatrial nodal pacemaker activity and atrial contractility were investigated in five canine isolated, blood-perfused right atria that were perfused with heparinized blood from support dogs. The effects of lignocaine on responses to intracardiac nerve stimulation and administered acetylcholine and noradrenaline were also examined. 2. Lignocaine was injected into the support dog intravenously or administered selectively to the sinus node artery of the isolated atrium. At doses that did not produce significant depressor action (0.3, 1.0 and 3.0 mg/kg), lignocaine produced no significant changes in heart rate. A large dose of 10 mg/kg lignocaine caused significant depressor effects and slight bradycardia. Direct administration of lignocaine (0.3, 1.0, 3.0, 10.0 and 30.0 mumol) into the sinus node artery of the isolated atrium consistently caused slight negative chronotropic and rather marked negative inotropic effects. 3. After treatment with a relatively large dose of lignocaine, electrical stimulation-induced negative chronotropic and inotropic responses were significantly inhibited in a dose-related manner, but positive chronotropic and inotropic responses were slightly depressed only at an extremely high dose of lignocaine (10.0 mumol). 4. Noradrenaline-induced positive chronotropic and inotropic effects were not modified by any doses of lignocaine used (0.3, 1.0, 3.0 and 10.0 mumol). Acetylcholine-induced negative chronotropic and inotropic effects were slightly, but significantly, depressed by 10 mumol lignocaine. 5. These results suggest that a relatively large dose of lignocaine has a dominant presynaptic inhibitory action, particularly on the parasympathetic component.

Abnormal cardiac pain perception in syndrome X

Objectives. The purpose of this study was to determine whether a diminished cardiac pain threshold contributes to chest pain in patients with syndrome X.Background. There have been some reports of an altered pain perception in syndrome X.Methods. Intracardiac catheter manipulation was performed in four groups of patients (syndrome X [group 1, 36 patients]; mitral valve disease and normal coronary arteries [group 2, 36 patients]; mitral valve disease and coronary artery disease [group 3, 36 patients]; and heart transplant recipients with normal coronary arteries [group 4, 36 patients]). Coronary flow was measured in patients with syndrome X and in transplant recipients by use of an intracoronary Doppler catheter positioned in the left anterior descending coronary artery at intracardiac catheter manipulation. Coronary flow reserve in response to papverine was also measured in patients with syndrome X and in transplant recipients.Results. Intracardiac stimulation produced typical anginal chest pain in 34 group 1 (syndrome X) patients (94%). However, chest was produced only in five patients (14%) in group 2, seven patients (19%) in group 3 and no patients in group 4. There were no significant changes in coronary blood flow velocity associated with chest pain in group 1 patients. Coronary flow reserve in response to a hyperemic dose of intracoronary papaverine was significantly lower in the syndrome X group. There was no significant difference in the prevalence with which the stimulation tests produced chest in patients with syndrome X with an impaired coronary flow reserve or a positive radionuclide scan.Conclusions. The results of our study suggest that abnormal cardiac pain perception is a fundamental abnormality in syndrome X.

Value of oesophageal pacing in evaluation of atrial arrhythmias.

The study of 'atrial vulnerability' is often clinically indicated but it requires the use of invasive intracardiac stimulation. The purpose of the study was to assess the use of oesophageal pacing in the evaluation of atrial tachyarrhythmias (ATA). Fifty-five patients with documented ATA (group I) and 60 without (group II) were studied. The protocol of oesophageal pacing consisted of atrial pacing up to the second-degree AV block and programmed stimulation in the control state and after isoproterenol infusion. ATA was induced in 47 group I patients (85%) either in the control state (n = 27) or during isoproterenol infusion (n = 20) and in three group II patients (5%). There was no other electrophysiological abnormality. The presence of underlying heart disease did not precipitate ATA in group II. In conclusion, because of its good sensitivity (85%) and specificity (95%) transoesophageal pacing could be used to evaluate atrial arrhythmias.

Electrophysiologic effects of sotalol on the immature mammalian heart.

Sotalol is a beta-blocker with class III antiarrhythmic properties that has recently been used in children for the treatment of supraventricular and ventricular arrhythmias. However, little is known about its electrophysiologic effects on the immature heart. Using intracardiac electrocardiographic recordings and stimulation techniques, 15 canine neonates (8-15 days) and 15 adult mongrel dogs were studied with cumulative doses of sotalol (0.5, 1, 2, and 4 mg/kg plus an additional dose of 8 mg/kg for neonates). Heart rate decreased significantly in the two groups, but more in adult dogs (-43% in adult dogs versus -25% in neonates, p less than 0.05). There was no significant change for QRS duration and His-Purkinje system conduction time interval. QT and atrioventricular nodal conduction time intervals increased in adult dogs and neonates. Sinus node recovery time increased significantly in the two groups, but more in adult dogs. Refractory periods of the atrioventricular (AV) node increased significantly in neonates. Atrial flutter was no longer inducible in 12 of 15 neonates after the 2 mg/kg dose. Atrial effective refractory period increased significantly more in neonates (96%, p less than 0.001) than in adult dogs (58%, p less than 0.001). Ventricular effective refractory periods increased significantly both in neonates (46%) and adult dogs (50%), in a similar way. In conclusion, sotalol has greater electrophysiologic effects on the immature heart at the atrial level when compared to the adult, and similar effects on the refractory period of AV node and ventricle.

Successful intracardiac electrical conversion of atrial flutter in patients with complex congenital heart disease.

Sixteen patients presenting on 21 occasions with atrial flutter in association with complex congenital heart disease were treated by intracardiac stimulation techniques combined with activation mapping. Nineteen episodes of atrial flutter were successfully converted to sinus rhythm. In the remaining two episodes atrial fibrillation was induced with spontaneous conversion to sinus rhythm within 12 hours in one episode and immediate DC cardioversion to sinus rhythm in the other. Intracardiac stimulation techniques were highly successful in this group and allowed reliable conversion to sinus rhythm without general anaesthesia and high energy cardioversion. In patients with atrial flutter associated with congenital heart disease intracardiac stimulation techniques should be tried first.

Transesophageal versus intracardiac atrial stimulation in assessing anterograde conduction properties of the accessory pathway in Wolff-Parkinson-White syndrome

Electrophysiologic intracardiac and noninvasive transesophageal testing, used to evaluate parameters of anterograde conduction across the accessory pathway, the refractory period and shortest atrial cycle length with 1:1 conduction over the pathway, were compared to assess the reliability of the noninvasive technique in identifying patients with Wolff-Parkinson-White syndrome, at risk of rapid ventricular response during atrial fibrillation when this arrhythmia is not inducible. Sixteen patients with Wolff-Parkinson-White syndrome were submitted both to invasive and transesophageal atrial stimulation. We evaluated both the functional and effective refractory periods of the accessory pathway, using the same drive cycle length, and the shortest cycle length with 1:1 atrioventricular conduction over the accessory pathway. There were no differences between the parameters obtained by intracardiac atrial stimulation and by transesophageal atrial stimulation. The two approaches correlated well: mean functional refractory periods of the accessory pathway were 285 ± 42 msec and 289 ± 32 msec, respectively (NS, r = 0.88); mean effective refractory periods of the accessory pathway were 267 ± 41 msec and 271 ± 32 msec, respectively (NS, r = 0.89); mean shortest cycle lengths with 1:1 conduction over the accessory pathway were 255 ± 48 msec and 255 ± 44 msec, respectively (NS, r = 0.94). These data demonstrate the reliability of transesophageal atrial stimulation in estimating the parameters for anterograde conduction across and accessory pathway. These results, and the already documented ability of transesophageal atrial stimulation to induce atrial fibrillation, suggest this noninvasive technique should be taken as a first approach in screening patients with Wolff-Parkinson-White syndrome. When sustained atrial fibrillation is not inducible by transesophageal stimulation, very short parameters obtained by both continuous and programmed pacing can identify patients at risk, thus avoiding intracardiac stimulation. On the other hand, long refractory periods are less useful because of their well-known limits as risk factors. In this case, intracardiac induction of atrial fibrillation is needed, even using alternating current.

Electropharmacodynamics of N-Acetylprocainamide in the Immature Mammalian Heart - Evidence for a Prominent Class III Effect in the Newborn

The electrophysiologic effects of N-acetylprocainamide (NAPA), a metabolite of procainamide reported to exert significant Class III antiarrhythmic effects in the adult heart, were evaluated in 12 neonatal mongrel canines (ages 7-14 days). Following transvascular placement of quadripolar electrical catheters in the right atrium and ventricle, and a tripolar catheter in the region of the His bundle, electrophysiologic assessments were made of sinus and AV nodal function and atrial and ventricular refractoriness utilizing intracardiac stimulation and recording techniques following cumulative intravenous doses of 20 and 40 mg/kg of NAPA (serum concentrations 13.1 +/- 1.9 and 25.6 +/- 3.4 micrograms/ml). NAPA resulted in an overall increase in sinus cycle length of 18%. No changes were observed in the paced cycle length resulting in AV nodal Wenckebach. Consistent with NAPA's reported Class III action, NAPA increased the effective and functional refractory periods of the ventricle by 35 and 34%, respectively (p less than 0.001). Even larger increases were observed in atrial refractoriness (effective 75%, functional 57%, p less than 0.001). In separate experiments (n = 6), the effects of intravenous NAPA (40 mg/kg) on the duration of the monophasic action potential recorded from the neonatal atrium and ventricle were determined. NAPA increased APD90 of the atrium by approximately 50% and that of the ventricle by 60%, thus confirming a significant effect on myocardial repolarization in the neonate.

Electrophysiologic effects of intravenous propranolol in the intact immature mammalian heart.

Using intracardiac electrogram recording and stimulation techniques, 13 neonatal puppies (3-15 days) and 9 adult dogs were studied following cumulative doses of intravenous propranolol. Although propranolol caused a dose-dependent increase in the sinus cycle length in both groups, the increase was significantly less in the neonates than in the adults. In both groups the pacing interval resulting in atrioventricular (AV) nodal Wenckebach was increased significantly by propranolol; however, the increase was again less in the neonates than in the adults. There were comparable dose-dependent increases in atrial and ventricular refractoriness in both neonate and adult groups.

Acute increase in right atrial pressure by intracardiac stimulation releases atrial natriuretic peptide.

We studied the effect of an increase in heart rate and/or in right atrial pressure (RAP) on the release of atrial natriuretic peptide (ANP) in 18 patients. In group 1 (n = 6), right ventricular stimulation (100, 120, 140 and 150 bpm) was used to increase RAP by asynchronous contraction of the right atrium and ventricle. Mean RAP increased from 3.9 +/- 0.2 to 8.3 +/- 0.6 mmHg (mean +/- SEM). Median ANP levels increased from 120 to 440 pg ml-1 (P less than 0.05). In group 2 (n = 6), right atrial stimulation below 140 bpm did not have any effect on ANP or RAP, but at a rate above 140 bpm RAP increased from 5.8 +/- 0.5 to 7.5 +/- 0.5 mmHg and ANP from 226 to 396 pg ml-1 (P less than 0.05). In group 3 (n = 6), RAP or ANP were not influenced by continuous right atrial stimulation at 110 bpm. Plasma cyclic GMP levels paralleled the changes in plasma ANP. Thus, an acute increment of RAP results in a release of ANP, but acceleration of heart rate alone has no effect on ANP secretion.