Electrophysiologic Manifestations in So-called "Sick sinus Syndrome"

Lien, Wen-Pin; Lee, Ying-Shiung; Chang, Fu-Zen; Chen, Jin-Jer

doi:10.1253/jcj.42.195

Cited by 8 publications

(1 citation statement)

References 26 publications

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“…Overdrive pacing is commonly used clinically or experimentally while obtaining intracavitary ECGs to unmask sinus node dysfunction and AV conduction abnormalities (20,23). Hearts were paced at cycle lengths of 150, 120, and 100 ms, and the PR interval was measured.…”

Section: Enhanced M 2 R-mediated Sinus Bradycardia and Av Block In G␣ I2mentioning

confidence: 99%

Endogenous RGS proteins modulate SA and AV nodal functions in isolated heart: implications for sick sinus syndrome and AV block

Fu¹,

Huang²,

Piao³

et al. 2007

American Journal of Physiology-Heart and Circulatory Physiology

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G protein-coupled receptors play a pivotal role in regulating cardiac automaticity. Their function is controlled by regulator of G protein signaling (RGS) proteins acting as GTPase-activating proteins for Galpha subunits to suppress Galpha(i) and Galpha(q) signaling. Using knock-in mice in which Galpha(i2)-RGS binding and negative regulation are disrupted by a genomic Galpha(i2)G184S (GS) point mutation, we recently (Fu Y, Huang X, Zhong H, Mortensen RM, D'Alecy LG, Neubig RR. Circ Res 98: 659-666, 2006) showed that endogenous RGS proteins suppress muscarinic receptor-mediated bradycardia. To determine whether this was due to direct regulation of cardiac pacemakers or to alterations in the central nervous system or vascular responses, we examined isolated, perfused hearts. Isoproterenol-stimulated beating rates of heterozygote (+/GS) and homozygote (GS/GS) hearts were significantly more sensitive to inhibition by carbachol than were those of wild type (+/+). Even greater effects were seen in the absence of isoproterenol; the potency of muscarinic-mediated bradycardia was enhanced fivefold in GS/GS and twofold in +/GS hearts compared with +/+. A(1)-adenosine receptor-mediated bradycardia was unaffected. In addition to effects on the sinoatrial node, +/GS and GS/GS hearts show significantly increased carbachol-induced third-degree atrioventricular (AV) block. Atrial pacing studies demonstrated an increased PR interval and AV effective refractory period in GS/GS hearts compared with +/+. Thus loss of the inhibitory action of endogenous RGS proteins on Galpha(i2) potentiates muscarinic inhibition of cardiac automaticity and conduction. The severe carbachol-induced sinus bradycardia in Galpha(i2)G184S mice suggests a possible role for alterations of Galpha(i2) or RGS proteins in sick sinus syndrome and pathological AV block.

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Section: Enhanced M 2 R-mediated Sinus Bradycardia and Av Block In G␣ I2mentioning

confidence: 99%