Assessment of myocardial scarring improves risk stratification in patients evaluated for cardiac defibrillator implantation

Objective

We hypothesized that an assessment of myocardial scarring by cardiac magnetic resonance (CMR) would improve risk stratification.

Background

Current sudden cardiac death (SCD) risk stratification emphasizes left-ventricular ejection fraction (LVEF), however the majority of patients suffering SCD have a preserved LVEF and many with poor LVEF do not benefit from ICD prophylaxis.

Methods

One hundred thirty-seven patients undergoing evaluation for possible ICD placement were prospectively enrolled and underwent CMR assessment of LVEF and scar. A comprehensive medical history including CAD risk factors, heart failure functional class (NYHA), and medications at the time of CMR was obtained in all patients. A total of 105 (77%) patients underwent EPS within a median of 0 days (IQR 0, 3.5) of CMR. No patient experienced a change in clinical status in the time between CMR and EPS. 103 patients (75%) had an ICD placed, generally during the initial evaluation, 2 days (IQR 1, 7) after enrollment.

Results

During a median follow-up of 24 months, 39 patients experienced the prespecified primary endpoint of death or appropriate ICD discharge for sustained ventricular tachyarrhythmia. Whereas the rate of adverse events steadily increased with decreasing LVEF, a sharp step-up was observed for scar size >5% of LV mass (HR=5.2 [95% CI, 2.0-13.3]). On multivariable Cox proportional hazards analysis, including LVEF and electrophysiological-study results, scar size (as continuous variable or dichotomized at 5%) was an independent predictor of adverse outcome. Among patients with LVEF >30%, those with significant scarring (>5%) had higher risk than those with minimal-or-no (less than or equal to 5%) scarring (HR=6.3 [1.4-28.0]). Those with LVEF >30% and significant scarring had similar risk to patients with LVEF less than or equal to 30% (p=0.56). (Figure 1) Among patients with LVEF less than or equal to 30%, those with significant scarring again had higher risk than those with minimal-or-no scarring (HR=3.9 [1.2-13.1]). Those with LVEF less than or equal to 30% and minimal scarring had similar risk to patients with LVEF >30% (p=0.71). (Figure 2)

Figure 1

Figure 2

Conclusions

Myocardial scarring detected by CMR is an independent predictor of adverse outcome in patients being considered for ICD placement. In patients with preserved LVEF, significant scarring (>5% LV) identifies a high-risk cohort similar in risk to those with LVEF less than or equal to 30%. Conversely, in patients with LVEF less than or equal to 30%, minimal-or-no scarring identifies a low-risk cohort similar to those with preserved LVEF.