Effect of Enalapril on Survival in Patients with Reduced Left Ventricular Ejection Fractions and Congestive Heart Failure

Abstract

Congestive heart failure affects many people globally. In the United State, many people are affected by the disease. Most patients with the condition have lower ejection fraction. These conditions predispose patients to frequent hospitalizations. Additionally, the disease has been associated with higher mortality among the victims. Angiotensin-converting enzyme (ACE) inhibitors are efficient in managing this condition. However, each drug has its effects. In this regard, the Studies of Left Ventricular Dysfunction (SOLVD) investigators (1991) sought to examine the effect of enalapril, an ACE inhibitor, on the survival and hospitalization of patients with congestive heart failure and lower ejection fraction. The article by the SOLVD investigators (1991) was published in the New England Journal of Medicine. The abstract, hypothesis, sample size, and research objectives will be analyzed. Additionally, the study design, literature review, and data collection will be critiqued. Furthermore, the paper discussed statistical analysis, tests, and rationale together with assumptions. This paper will also review the study procedure, discussion, and the conclusion of the study.

Effect of Enalapril on Survival in Patients with Reduced Left Ventricular Ejection Fractions and Congestive Heart Failure

Heart failure affects many people in the United States. According to the Studies of Left Ventricular Dysfunction (SOLVD) investigators (1991), approximately 2 million people had heart failure by 1991. Currently, Centers for Disease Control and Prevention (CDCP) (2016) estimate that 5.7 million individuals in the United States have heart failure. Therefore, the increasing prevalence of this disease requires proper pharmacologic therapy. The SOLVD investigators (1991) conducted a study to examine the effect of enalapril on survival and hospitalization among patients with congestive heart failure and lower ejection fraction. This paper analyzes the article written by the SOLVD investigators (1991) to determine its reliability in the application of treating patients with congestive heart failure and lower ejection fraction.

Abstract

The abstract clearly states the aim of the study and classifies enalapril as an angiotensin-converting enzyme (ACE) inhibitor. The authors do not articulate the study design but provide an idea that the study is randomized and placebo-controlled. Additionally, the authors clearly state the outcomes of the research and the conclusions. Therefore, the authors present the contents of the article briefly giving the reader a clear picture of the objectives, the process, and the outcome of the research.

Hypothesis and Research Objectives

The aim of the research study is evident from the abstract and the introduction. The investigators sought to examine two aspects, hospitalization and mortality. They also provide the population: patients with congestive heart failure and lower ejection fraction. The investigators further make it clear that the drug to be used in the study is enalapril. The hypothesis of the article is provided in the statistical analysis section: enalapril would reduce mortality and hospitalization. Therefore, the article orients the readers appropriately to what is expected throughout the study.

Sample Size and Sample Characteristics

In the methodology section, the investigators provide a systematic description of determining an appropriate sample. First, they considered 83 hospitals. The inclusion criteria involved patients with an ejection fraction of 0.35 or below. The exclusion criteria involved patients who were 80 years of age with various cardiovascular abnormalities. The investigators identified 39, 924 patients. However, most were excluded based on such reasons as lack of consent, cardiovascular problems, contraindication to the use of ACE inhibitors and other life-threatening diseases. The authors explain how they have excluded other patients in the “run-in period and stabilization,” randomization, and follow-up sections (Studies of Left Ventricular Dysfunction [SOLVD] Investigators, 1991, p.294). Finally, the authors explain logically how they have selected 2569 patients. The sample selection is appropriate for this kind of study since such an average sample ensures the reliability of the research findings and prevents biases in results (Kaplan, Chambers, & Glasgow, 2014).

Study Design

In the methodology section, the SOLVD investigators (1991) assert that the study is randomized, double-blind, and placebo-controlled. The authors provide a precise description of how they chose the samples and used the placebo and real treatment in different groups to achieve the aim of the study. The double-blind placebo-controlled study has proved efficient in the studies that aim to make comparisons (Tohen, et al., 2012). Therefore, the design is appropriate for analyzing the effect of enalapril on the survival and hospitalization of the patients with congestive heart failure and lower ejection fraction.

Literature Review

In the introduction, the SOLVD investigators (1991) refer to various published and unpublished works that are relevant to the study. However, the article does not have a separate heading that identifies the literature review. Nevertheless, the literature review is comprehensive and supports the aim of the study. For instance, the researchers provide research findings of the prevalence of heart failure and various studies conducted on heart failure. Furthermore, most literature is no more than 10 years older than the article ensuring that the research is relevant. However, the researchers risked using outdated information as they referred to the research done more than 3 decades before.

Data Collection

The article does not have an independent section that explains data collection. However, under the methods section, the investigators indicate that they measured the ejection fraction using radionuclide techniques, contrast angiography, and two-dimensional echocardiography. The data collected is, therefore, discrete and nominal, which is appropriate for comparison in the study. However, the documentation of the data is not explained. The authors only describe the summarized data of how various patients have been excluded and included in the study and the follow-up. Therefore, the reader of the article cannot clearly understand how the authors documented the data for monitoring. In spite of that, the data collection process is clearly explained.

Statistical Analysis, Tests, and Rationale

The authors indicate that they used a stratified log-rank statistic to compare life-table survival curves for all the patients in the two groups. This method was efficient since the log-rank test had proven useful in measuring survival distribution of two groups in clinical trials (Yu, 2012). Additionally, the authors used Kaplan-Meier method to construct life-table plots, which are also efficient in comparing survival of patients over time. Although the authors do not explain the level of measurement used, it is clear that they employed the ratio level of measurement during data analysis since they used the likelihood-ratio test (SOLVD, 1991). Additionally, one-sided and two-sided tests were utilized. The use of these two tests is significant since it is critical in measuring and comparing both variables and testing the hypothesis (Ludbrook, 2013). Therefore, the analysis was reliable since they employed all the tests in collaboration with the Safety and Data Monitoring Board, which reviewed the data after every 6 months.

Assumptions for Inference, Alpha, and Statistical Tables

The authors do not explain the assumptions for the inferences in the article. Additionally, they do not provide details on the assumptions of alpha. The authors do not also give details on the assumptions of the statistical tables that are provided in the results section. However, the lack of these assumptions in the article does not affect the understanding of the results; thus, the reader can still comprehend the purpose of the research.

Study Procedure

In the article, the authors first identified the problem of the high prevalence of congestive heart failure and increased hospitalization and mortality. They then devised a plan to identify the effectiveness of enalapril in reducing hospitalization and mortality. Then, the authors consulted the literature on the subject. Next, they sought approval from the institutional review boards, which was granted. The investigators obtained consent from the patients before the study and then carried out the study in conjunction with the Data Safety and Monitoring Board. This procedure involved all the necessary parties that were essential for achieving the goals of the research. Thus, the authors enhanced the reliability of the results and conclusions.

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Discussion and Conclusion

After the results, the authors provide a detailed discussion of the whole study. It is also the final part of the article as there is no conclusion section. The investigators ascertained that enalapril reduced mortality and hospitalization in the enalapril group. The authors also stated that the results were consistent with other studies done on ACE inhibitors. However, the researchers noted that enalapril predisposed the patients to increased serum creatinine levels and hypotension, which was important since healthcare providers needed to monitor these side effects. Since the cause of death among patients during the study varied, the authors recommended further research in the field, which would help reduce the mortality. At the time of releasing the study, the SOLVD investigators were still analyzing the effect of enalapril on asymptomatic patients with low ejection fraction. The procedure followed in the study, the collaboration, ethical standards observed, data collection, and analysis were efficient in analyzing the effect of enalapril on the survival and hospitalization of the patients. Thus, this study is reliable and appropriate for use in the healthcare settings.