Table 1.

Composition of Derivation and Validation Cohorts

	Derivation Cohort		Validation Cohort
	Included	Excluded	Included	Excluded
Initial single-chamber or dual-chamber ICD implantation for primary prevention of SCD, matched on HIC/SSN	23,405		42,903
Matching date of birth and sex	21,597	1,808	39,687	3,216
LVEF ≤40%	20,918	679	37,732	1,955
NYHA functional class I–III HF (excluding class IV)	20,206	712	36,498	1,234
No PCI or CABG within 3 months	19,070	1,136	33,552	2,946
No MI within 40 days	18,869	201	31,966	1,586
Fulfills remaining criteria for implantation*	17,991	878	27,893	4,073
Final cohort total	17,991		27,893

^*LVEF ≤ 35% and NYHA class II or III (at least 3 months); LVEF ≤ 30% and prior MI; and LVEF ≤ 40%, MI, nonsustained ventricular tachycardia, and ventricular tachycardia or ventricular fibrillation on electrophysiological study.

CABG = coronary artery bypass grafting; HF = heart failure; HIC = health insurance claim; ICD = implantable cardioverter-defibrillator; LVEF = left ventricular ejection fraction; MI = myocardial infarction; NYHA = New York Heart Association; PCI = percutaneous coronary intervention; SCD = sudden cardiac death; SSN = Social Security number.