Left Ventricular Diastolic Dyssynchrony in Post-Myocardial Infarction Patients: Does It Predict Future Left Ventricular Remodeling?

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Left ventricular (LV) remodeling is well-known complication after myocardial infarction (MI) and numerous studies have emphasized the clinical importance of ventricular remodeling.1)2)3)4) In these literatures, progressive LV dilatation and decreased LV ejection fraction were major determinants in future development of heart failure and long term survival. That is why early recognition of patients at risk for LV remodeling after MI has vital importance and identification of the predictive markers for developing ventricular remodeling is clinically meaningful.

While the clinical importance of LV mechanical dyssynchrony is mainly described in heart failure patients,5)6)7) its significance in patients with MI was less well established. Actually, ventricular dyssynchrony is not uncommon in post-MI patients even with narrow QRS complexes.8)9) Zhang et al.8) and Fahmy Elnoamany et al.9) noted LV systolic dyssynchrony early after MI in 69.8% and 77.5% of the patients and it was mainly determined by the initial infarct size. After that, various parameters from tissue Doppler imaging and speckle-tracking technique have been used for detecting regional contraction and relaxation abnormalities and LV systolic and diastolic dyssynchrony early after MI. Several studies demonstrated that LV systolic dyssynchrony in post-MI patients is closely related with future LV remodeling10)11)12)13) and poor prognosis.14)15) Mollema et al.10) showed that patients with more extensive LV dyssynchrony at baseline have larger LV end systolic volume after 6 months of follow up and increased risk of LV remodeling. Similar results were showed by Zhang et al.11) that LV systolic dyssynchrony increased with worsening LV ejection fraction in the remodeling group. On the other hand, information on the role of LV diastolic dyssynchrony in post-MI patients is limited and only a few studies examined the clinical implication. In earlier studies, the prevalence of diastolic dyssynchrony was not significantly different in post-MI patients compared with control group.8)9) In a study from Zhang et al.,11) both standard deviation (SD) of time to peak myocardial contraction represents LV systolic dyssynchrony and SD of time to peak early relaxation (Te-SD) represents LV diastolic dyssynchrony at baseline were significantly higher in patients who experienced LV remodeling after 1 year with the marginal statistical significance of Te-SD (p = 0.048). However, in multivariate analysis to identify independent predictor of 1 year LV remodeling, Te-SD did not predict LV remodeling.

In the article published in this issue of the Journal of Cardiovascular Ultrasound titled "Diastolic dyssynchrony in acute ST segment elevation myocardial infarction and relationship with functional recovery of left ventricle,"16) the authors investigated the incidence and clinical impact of LV diastolic dyssynchrony after ST-segment elevation MI (STEMI). Substantial number of patients (58% of STEMI patients) presented diastolic dyssynchrony. One of the interesting finding of this study is that diastolic dyssynchrony was positively correlated with change in ejection fraction and the patients who have baseline diastolic dyssynchrony less frequently experienced adverse LV remodeling. But diastolic dyssynchrony per se was not an independent predictor of LV remodeling or improving ejection fraction. The authors explained the inverse relationship between baseline diastolic dyssynchrony and 6-month LV remodeling with stunned myocardium in peri-infarct zone which can be improved after successful revascularization. Because diastolic function can be affected by myocardial ischemia earlier than systolic function, diastolic dyssynchrony might come from stunned but viable myocardium. In other words, more prominent diastolic dyssynchrony may represent more viable myocardium. But the exact mechanism or clinical meaning is uncertain until now.

An almost certain thing relevant with previous studies is that there is no definite correlation between systolic dyssynchrony and diastolic dyssynchrony. While systolic dyssynchrony is seriously affected by infarct size and predicts adverse LV remodeling, diastolic dyssynchrony is considered distinct phenomena from systolic dyssynchrony which has different underlying mechanism and determinant. In a previous study,17) there was no significant correlation between the systolic and diastolic dyssynchrony indexes and the determinants of LV diastolic dyssynchrony are different from those of systolic dyssynchrony in asymptomatic hypertensive patients. Similar findings were reported in patients with diastolic heart failure.18)

The time is not yet ripe for defining the impact of LV diastolic dyssynchrony on LV remodeling after MI. A better understanding of pathophysiologic mechanism of LV diastolic dyssynchrony in post-MI patients might be helpful to clarifying the clinical significance.