TEORÍAS LITERARIAS PARA EL ANÁLISIS DE TEXTOS
3.3 El valor de la Literatura infantil y juvenil
There was a strong association between the NYHA functional class of subjects and both the primary end point (all-cause death) and secondary end point (clinical decompensation and re admission). The need for hospital re-admission also showed a significant relationship with
all-90
cause death in this study. The NYHA classification independently predicted outcome in subjects with HF. However, there was no significant relationship between reduced HRV parameters (SDNN and LF:High Freq. ratio) with all-cause death in this study using the Kaplan-Meier survival curve. Ponikowski et al., (26) reported NYHA functional class as an independent predictor of mortality in subjects with heart failure secondary to DCM and IHD. It was further noted that the HRV parameters (SDNN, SDANN and LF) were also predictors of death using the Kaplan-Meier survival analysis. This revealed 1-year survival probability in patients with SDNN < 100 ms as 78% when compared with 95% in those with SDNN > 100 ms. Differences in our findings may be suggested by the different cut-off value (higher threshold of classifying subjects into reduced HRV) employed in this study and also by the difference in the duration of study. Binder et al.,(21) noted in a study that reduced HRV (SDANN values of < 55 ms) in patients awaiting cardiac transplantation had a twenty-fold increased risk of death. Boveda et al.,(164) and Boskovic et al.,(163) reported in different studies that reduced HRV is an independent predictors for all-cause mortality in HF secondary to MI/IHD and DCM. Yi et al.,(135) noted that reduced HRV is related to disease severity and it can be used independently to predict the risk of clinical decompensation.
Perhaps, the aetiology of HF also contributes to the difference in the findings in this study to that of others. This suggests that the level of autonomic nervous system disturbance is less in heart failure secondary to hypertension than heart failure from MI/IHD and DCM.
Assessing the probability of survival in relation with the prolonged QT dispersion, using Kaplan-Meier survival curve did not show any significant association. This finding was earlier noted by Fei et al.,(14) in a study of QT dispersion and RR variations on 12-lead ECGs in patients with HF secondary to idiopathic dilated cardiomyopathy. He observed that prolonged QT dispersion in idiopathic dilated cardiomyopathy was not significantly related to cardiac size or function and does
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not predict death. On the contrary, Spargias et al.,(109) documented that prolonged QT dispersion remained an independent predictor of long-term, all-cause mortality risk in patients with acute myocardial infarction and clinical evidence of heart failure. However the author was quick to mention that the population studied was large and were at increased risk of death from the outset, and this, combined with the long follow-up, led to a large number of subjects reaching the end-points. In this study, the difference in our observation may be due to the size of study population, aetiology of HF, chronicity of the diseases state and the length of follow up time employed.
Galinier et al.,(15) although reported that prolonged QT dispersion can bean independent predictor of arrhythmic events and sudden death in subjects with DCM, he could not sustain the fact in subjects with IHD.
92 CONCLUSION
QT dispersion is prolonged and HRV is reduced in subjects with heart failure secondary to hypertension. The HRV time-domian parameter (SDNN) can be used to deduce the rate of readmission in subjects, however this same parameter did not show any relationship with the rate of clinical decompensation or death. The HRV frequency-domain parameter and prolonged QT dispersion did not show any relationship with the outcome measures (clinical decompensation, readmission and death).
There is also a strong relationship between NYHA functional classification (severity of diseases) and all the outcome measures.The NYHA class of subjects and re-admission rate are independent predictors of death in the study population. The Probability of survival of subjects in relation with prolonged QT dispersion and reduced HRV did not show any association using Kaplan-meier survival curve indices.
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RECOMMENDATIONS
Based on the findings in this study, the following recommendations are made:
A larger study with a much longer period of follow up should be done to further elucidate the relationship between increased QT dispersion and reduced HRV and morbidity/mortality in subjects with heart failure secondary to hypertension.
A 24 hour ambulatory ECG/ Holter study may be appropriate for further study, since this will enable full estimation of all the parameters of HRV.
94
LIMITATIONS OF THE STUDY
The effect of drugs used for treatment of heart failure in subjects on the QT dispersion and HRV remained difficult to determine as their influence could not be fully ascertained.
It was difficult to differentiate the actual cause of death, and thus separate death due to an arrhythmic event from that from progressive pump failure.
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