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SCD most likely to strike when LVEF doesn't meet criteria for prophylactic ICD

March 9, 2006

Steve Stiles

Portland, OR - Left-ventricular systolic function was at least moderately reduced in only about half of those who experienced sudden cardiac death (SCD) over two years in a US community-based study [1]. Less than one third had severely reduced LVEF, by far the most common indication for a prophylactic implantable cardioverter defibrillator (ICD). None of the study patients were being protected by such a device.

"These findings . . . confirm the need to identify SCD risk predictors other than severe LV dysfunction in the general population," write Dr Eric C Stecker (Oregon Health and Science University, Portland) and colleagues in a report published online February 23, 2006 in the Journal of the American College of Cardiology and scheduled for the journal's March 21, 2006 issue.

In the group's analysis of SCD patients enrolled in the ongoing Oregon Sudden Unexpected Death Study who had evaluable pre-SCD LV systolic functional data, features associated with SCD in the setting of normal LVEF included younger age, female sex, and presence of a seizure disorder.

The study provides population-based data that unfortunately show that only a small proportion of sudden-death victims could have benefited from the current primary prevention ICD guidelines.

The Oregon study "provides population-based data that unfortunately show that only a small proportion of sudden-death victims could have benefited from the current primary-prevention ICD guidelines," observes Dr William J Groh (Krannert Institute of Cardiology, Indiana University, Indianapolis) [2]. In an accompanying editorial, he writes that in the absence of proven SCD risk predictors for persons without known LV dysfunction, "there are population-based approaches that can be applied to prevent sudden death." Groh notes that the rate of CAD-related SCD has apparently declined along with rates of "non-sudden coronary death" as ischemic heart disease therapy has improved.

"Early identification of coronary risk factors and primary- and secondary-prevention measures should continue to decrease the population vulnerable to sudden death," Groh writes. "As well, communities need to optimize their emergency response to the cardiac-arrest victim, thereby increasing the likelihood of survivability of the arrhythmias associated with sudden death."

In the Oregon study, 121 of the 714 persons stricken with SCD had undergone prior LV systolic functional assessment. The subgroup appeared to differ from the larger group only by being slightly older, according to the authors. About 30% of the subjects with LV systolic data had a severely depressed LVEF, defined as <35%. However, the group writes, "Even if all of the other risk predictors, such as history of resuscitated cardiac arrest, long-QT or Brugada syndromes, hypertrophic cardiomyopathy, and arrhythmogenic right-ventricular dysplasia, were taken into account, only 35% of SCD cases would have been identified as being at high risk for SCD."

After searching for possible indicators of elevated SCD risk in the setting of normal LV systolic function, the investigators found several candidates. Of note, a history of seizure disorder was observed only among patients with a normal LVEF.

Characteristics of SCD cases that underwent evaluation of LV function


Parameter

LVEF<35%, n=36

LVEF 36%-54%, n=27

LVEF >55%, n=58

p*

Age (mean years)

74

73

66

<0.01

Female (%)

25

30

47

0.03

Obstructive CAD (%)

75

89

50

<0.01

Dyslipidemia (%)

58

56

40

0.06

Seizure disorder (%)

0

0

14

<0.01

*Highest LVEF group vs either other group. SCD=sudden cardiac death

To download table as a slide, click on slide logo below

In his editorial, Groh described limitations of the study that may suggest reduced LVEF is even rarer among SCD victims than was estimated. It's not evident how many persons in the community were protected from SCD by ICDs. Moreover, Groh writes, "One would expect that patients having an indication that prompted a structural cardiac assessment would be more likely to have significant left ventricular dysfunction than those without such an indication." Thus, he concludes, it is likely that a lower proportion of the 593 persons without such an assessment would have an LVEF low enough to qualify for a primary-prevention ICD.





Sources

1.              Stecker EC, Catherine Vickers C, Waltz J, et al. Population-based analysis of sudden cardiac death with and without left ventricular systolic dysfunction. Two-year findings from the Oregon Sudden Unexpected Death Study. J Am Coll Cardiol 2006; 47:1161-1166.

2.              Groh WJ. Lessons From a Population. The limitations of left ventricular ejection fraction as the major determinant for primary prevention implantable cardioverter-defibrillators. J Am Coll Cardiol 2006; 47:1167-1168.