Thrombolytic therapy preserves vagal activity early after acute myocardial infarction

Application of HRV-CD for estimation of life expectancy in various clinical disorders

BACKGROUND

Low heart rate variability (HRV) was found in various medical conditions including heart failure and acute myocardial infarction. Decreased HRV in these conditions predicted poor prognosis.

METHODS

HRV was estimated in 133 unselected inpatients with relevant clinical bedside conditions by non-linear analysis derived from chaos theory, which calculates the correlation dimension (CD) of the cardiac electrophysiologic system (HRV-CD).

RESULTS

Mean HRV-CD in the entire group was 3.75+/-0.45. Heart failure, coronary artery disease, cardiac arrhythmia, low serum potassium, renal dysfunction, and diabetes mellitus were significantly associated with reduced HRV-CD compared to their counterparts [3.6 vs. 3.9 (P<.001), 3.65 vs. 3.87 (P=.005), 3.58 vs. 3.8 (P=.01), 3.38 vs. 3.81 (P=.02), 3.59 vs. 3.8 (P=.04), and 3.66 vs. 3.82 (P=.04), respectively]. Stepwise logistic regression showed heart failure to be the condition most significantly associated with low HRV-CD (odds ratio 4.2, 95% confidence interval 1.90-9.28, P<.001). In the entire group, decreased HRV-CD (< or =3.75 vs. >3.75) was associated with lower survival (P=.01). Mortality of diabetic patients with HRV-CD < or =3.75 exceeded the mortality in patients with HRV-CD >3.75 (P=.02). Heart failure, renal dysfunction or age over 70 combined with HRV-CD < or =3.75 also appeared to be associated with augmented mortality.

CONCLUSIONS

Diminished HRV-CD is associated with heart failure, coronary artery disease, cardiac arrhythmia, renal dysfunction, diabetes mellitus and low serum potassium. Among the latter, heart failure is most significantly associated with decreased HRV-CD. Decreased HRV-CD values, especially in diabetics, are also associated with lower survival.

Heart rate variability in myocardial infarction and heart failure

The need to refine the identification of patients who might benefit from implantation of an implantable cardioverter defibrillator has been risen by the results of many clinical trials on ICD therapy. Traditional parameters such as left ventricular ejection fraction and the presence of non-sustained ventricular tachycardia were not strong enough to achieve this goal with reasonable cost-effectiveness. Heart rate variability (HRV) is one of the most popular parameters used to assess the autonomic tone. HRV has been reported as a strong predictor of cardiovascular mortality. Currently, three different categories of methods in HRV analysis are being used; the time domain, frequency domain, and non-linear dynamic analysis. Both time domain and frequency domain analyses of HRV have been investigated extensively regarding their use as a prognostic marker for cardiovascular mortality. The non-linear dynamic analysis is the latest tool that has shown to have an even higher predictive value than any of the traditional parameters. However, standardized and supporting evidence on this new technique is still lacking. In this article, the current role of HRV in the prediction of cardiovascular mortality in myocardial infarction and heart failure patients has been reviewed.

Ventricular arrhythmias: antiadrenergic therapy for the patient with coronary artery disease

Patients who have had a recent myocardial infarction (MI) are at high risk of ventricular arrhythmias that often cause sudden cardiac death. It is believed that sympathetic overactivity in the peri-infarction period may alter the electrophysiology and structure of the myocardium, thus placing these patients at risk of developing rhythm disturbances. A number of pharmacologic and nonpharmacologic therapies have been shown to reduce the risk of post-MI mortality, including sudden cardiac death. beta-Adrenergic blockers are recommended for all post-MI patients without contraindications because of overwhelming clinical evidence of their benefit in reducing mortality in this patient population. Recent clinical trials of implantable cardioverter defibrillators have provided compelling support that they are effective in both the primary and secondary prevention of sudden cardiac death. In addition, several studies have shown that combination therapy with beta-blockers and implantable cardioverter defibrillators have synergistic effects that optimize the benefits of both therapies.