title: Description of the strength-interval relation with external noninvasive pacing.
abstract: The strength-interval relationship obtained by external pacing (EXP) was compared to curves obtained by endocardial pacing from a right ventricular site. There were 17 patients, age 45 +/- 17 years. Effective and functional ventricular refractory periods (ERP, FRP) were determined during a ventricular drive train of 8 stimuli at a cycle length 500 msec. Endocardial pacing threshold current averaged 0.5 +/- 0.3 mA (range 0.2-1.0 mA) and EXP threshold current averaged 64 +/- 14 mA (range 40-80 mA). At twice threshold, endocardial ventricular ERP was 235 +/- 32 msec and FRP was 262 +/- 29 msec. At 10 mA above threshold, EXP ventricular ERP was 276 +/- 29 msec and was significantly longer than endocardial ERP at twice threshold (P less than 0.001). EXP ventricular FRP shortened to 237 +/- 39 msec at twice threshold and was similar to endocardial ERP (P = 0.55). EXP ventricular FRP was significantly longer than endocardial ERP (280 +/- 29 vs 262 +/- 29 msec, P less than 0.001) at twice threshold. EXP strength-interval curves were similar to endocardial curves in 14 of 17 (82%) patients. We conclude, that at twice threshold, similar coupling intervals can be obtained with both endocardial and EXP. Therefore, EXP can provide critically coupled extrastimuli for programmed ventricular stimulation.
authors.affiliation: Cardiology Division, University Hospital, Pennsylvania State University, Hershey 17033.
authors.forename: J C
authors.initials: JC
authors.lastname: Luck
authors.forename: B P
authors.initials: BP
authors.lastname: Grubb
authors.forename: M L
authors.initials: ML
authors.lastname: Markel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004553:Electric Conductivity; D004558:Electric Stimulation; D004562:Electrocardiography; D004566:Electrodes; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction; D010138:Pacemaker, Artificial; D012032:Refractory Period, Electrophysiological; D013610:Tachycardia / Q000628:therapy*; D013997:Time Factors; D016276:Ventricular Function