Background-The INTRINSIC RV (Inhibition of Unnecessary RV Pacing with AVSH in ICDs) study tested the hypothesis that dual-chamber rate-responsive (DDDR) with atrioventricular search hysteresis (AVSH) 60-130 programming is not inferior to single-chamber (VVI)-40 programming in an implantable cardioverter defibrillator with respect to all-cause mortality and heart failure hospitalizations using an equivalence margin of 5%. Methods and Results-At 108 centers, 1530 patients with an implantable cardioverter defibrillator indication received a VITALITY AVT (Guidant Corporation, St. Paul, Minn) implantable cardioverter defibrillator programmed consistently to DDDR AVSH 60-130 for the first week. Of those, 988 patients with Ͻ20% right ventricular pacing at 1 week were randomized to DDDR AVSH 60-130 or to VVI-40 programming. Among those randomized, 502 were assigned to DDDR AVSH and 486 to VVI. Groups were similar with regard to coronary disease (68%), gender (21% female), and New York Heart Association functional class ϾI (79%). A total of 32 patients (6.4%) in the DDDR AVSH arm and 46 patients (9.5%) in the VVI arm died or were hospitalized for heart failure during a mean follow-up of 10.4 months (relative riskϭ0.67, Pϭ0.072 in favor of DDDR AVSH). DDDR AVSH was not inferior to VVI programming (PϽ0.001). All-cause mortality was not significantly different between the DDDR AVSH arm (3.6%) and the VVI arm
Although morphologic findings in many of the cardiac arrhythmias of acute and chronic disease have been elusive, the correlates of heart block (particularly atrioventricular block) are abundant. Pathologic features of sinoatrial, atrioventricular, and bundle-branch block are reviewed. Lev and Lenegre diseases (idiopathic bilateral bundle-branch fibrosis) are also reviewed.
Normal anatomic and histologic features of the atrioventricular junction (transitional cell zone, atrioventricular node, penetrating portion of bundle) and the bifurcation of the penetrating portion into bundle branches are reviewed. Terminal ventricular Purkinje fibers are also discussed.
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