Chapter 5 Convolutional Neural Networks
5.1. Convolutional Layers
The association of reduced values of SDNN and SDANN with increased severity of heart failure in this study is similar to earlier findings by Zuanetti et al 66
,
as well as by La Rovere et al 67.Nearly all the frequency domain measures were reduced in the present study, confirming earlier findings from other studies 50, 72. In addition, the Total Power, VLF Power and LF Power showed significant correlation with the ejection fraction, corroborating the results from previous studies 68,69,70,71. These specific frequency domain measures have prognostic value for predicting outcomes following heart failure from myocardial infarction.
Patients with CHF are not a homogenous group. Some studies have shown that HRV values are significantly lower in specific heart failure types87. This finding was noted with ischemic heart disease compared with dilated cardiomyopathy, and is thought to be related to an increased risk of ischaemic episodes and MI in patients with CHF due to ischaemic heart disease88, 89. Other studies however did not confirm the relationship of SDNN with CHF etiology90, 91. It is important to note that the majority of studies of HRV in heart failure have been carried out on Caucasian patients with heart failure secondary to ischemic heart disease.
This study did not compare HRV values between heart failure patients with differing etiology. This was because by far the predominant cause of heart failure among the cases was hypertensive heart disease. Further studies would be required to ascertain the influence of race on HRV measures, as well as if there are differences in HRV parameters unique to CHF resulting from hypertensive heart disease.
Though many studies have been carried out to demonstrate the prognostic value of HRV in CHF in the identification of patients who are at risk of death, including both total and sudden cardiac mortality, the present study was limited in its scope. It sought only to obtain and compare HRV measures between CHF patients and normal controls, and thus cannot be used to predict outcomes in heart failure.
CLINICAL IMPLICATION OF STUDY
The finding from this study shows that HRV measures are reduced in Nigerian patients with heart failure. The degree of reduction of HRV is known to reflect the severity of autonomic dysfunction and, with it, poor outcomes following heart failure. Though 24-Hour Holter ECG monitoring has not yet become part of the routine for the work up of patients with CHF, severely ill patients, particularly those with arrhythmias and marked systolic dysfunction, may require assessment of HRV, as these patients have been shown to benefit from device therapies, particularly automatic implantable cardioverter defibrillators.
CONCLUSION
HRV measures are depressed in black African patients with CHF compared with healthy subjects. This noted reduction is obtainable even after adjusting for age differences between CHF cases and healthy controls. Reduction in HRV measures (both time and frequency domain measures) is more prominent with increasing severity of heart failure as measured by declining ejection fraction. Though 24-Hour Holter ECG monitoring has not yet become part of the routine for the work up of patients with CHF, severely ill patients, particularly those with arrhythmias and marked systolic dysfunction, may require assessment of HRV, as this class of patients have been shown to benefit from implantable cardiac device therapies.
LIMITATIONS OF THE STUDY
Patients included in our study were not representative of the whole population of patients with CHF, since it was a hospital-based study, and might not reflect findings in the larger community. Hence a multi-centered or community-based study would be desirable.
There was a noticeable age difference between the cases and the controls, reflecting on one hand the older age of patients presenting with heart failure, but more immediately, the logistic difficulty of getting age-matched normal healthy elderly control subjects –not on hospital admission- to wear the Holter device for the full 24 hours of monitoring required for the study.
A major limitation of this study is the use of medications which affect HRV.
Many of the CHF patients were not newly diagnosed, and thus were already on pharmacological therapy such as beta blockers, ACE inhibitors and digitalis, which have proven effects on HRV. The specific effect of individual agents on the overall HRV results was difficult to assess.
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