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A quantitative study is a unique form of research that is used in the social sciences, particularly in the field of psychology (Heiman, 2001). Quantitative study employs systematic empirical investigation of social processes with the use of statistical, mathematical and computational techniques, which is allows the accruement of quantitative data. The objective of this type of research is to develop and employ mathematical models, theories and or hypothesis pertaining to a particular research of interest (Houser, 2009). One quantitative study that was of interest is Prevalence and Persistence of Depression in Patients w/ Implantable Cardioverter Defibrillator: A 2-year Longitudinal Study, which was written by Tsuyoshi Suzuki, Tsuyushi Shiga, Kazae Kuwahara, Sayaka Kobayashi, Shinichi Suzuki, Katsuji Nishimura, Atsushi Suzuki, Koichiro Ejima, Tetsuyuki Manaka, Morio Shoda, Jun Ishigooka, Hirushi Kasanuki, Nobuhisa Hagiwara (2010).

   In the field of medicine, a prevailing disease that continues to be an issue of great pertinence are diseases of the cardiovascular system, specifically cardiovascular arrhythmia (Marieb, 2005). There are patients who have arrhythmia and as a result of their condition, are forced to have an implantable cardioverter defibrillator in order to improve their survival in case they experience asystole due to sinus block, sinus arrest, or ventricular tachycardia. The heart normally works through two components; the electrical conduction, which in turn leads to mechanical action. If there is a change or a problem in the conduction of electricity through the cardiac conduction system, then the 4 chambers of the heart will have a problem in contraction, which in turn can be severely life threatening (Marieb, 2005). In cases where there is a block in the conduction system at the level of the ventricular level, the heart will not beat, and can lead to asystole. The implantation of cardioverter defibrillators in patients with these severe arrhythmic conditions can initiate an electric shock on said patients and thereby preventing or correcting asystole (Suzuki et al, 2010).


   The researchers do present an adequate rationale for conducting the study, which is primarily to see what is the depression level in ICD patients. The researchers indicate that in prior studies, ICD implantation improves the quality of life of most ICD patients. The researchers do present the fact that poor social support or ICD-specific problems such as frequent shocks and poor understanding of ICD therapy can increase anxiety and depressive symptoms and as a result reduce the quality of life for ICD patients. The researchers wanted to evaluate the prevalence and persistence of depression in ICD patients in a 2 year study period and by doing so , examining the effect of ICD shocks on depression over that particular 2 year period (Suzuki et al, 2010). This study is quite significant because depression is associated with heightened morbidity and mortality in patients with cardiovascular disease. The researchers want to see ICD therapy and depressive states because by doing so, medical providers can better treat ICD patients with depression either through cognitive behavioral therapy and/or through antidepressant medication (Suzuki et al, 2010). The prevalence of depression is reported to be one in five among outpatients with coronary artery disease and one in three among outpatients with heart failure; this is quite a significant and thus is a clear reason why ICD patients with high depression indices should be monitored closely. The literature review was quite comprehensive in presenting the statistics of depression in heart patients and allowed one to greatly have a better understanding of the phenomenon being researched.


   From reading the literature review, the researchers do not demonstrate any potential biases in the literature review because they actually are quite open minded in their presentation of information as well as point to the fact that they will be conducting a prospective observational study of 90 ICD patients. Considering that bias conflicts with the study, all possible care has been taken to ensure that bias is limited and minimized at all cost. The researchers do note the previous methods that were taken in previous studies, particularly the TOVA study (Triggers of Ventricular Arrhythmia), which is important in suggesting that moderate to severe depression is a predictor of appropriate shock in patients with coronary artery disease and ICD (Suzuki et al, 2010).


   Suzuki et al (2010) clearly state the purpose of the study, which is to evaluate the prevalence and the persistence of depression in ICD patients over a 2 year period and to examine the effect of ICD shocks on depression over that particular 2 year period. Researchers note that to date it is not known if depression persists over time in CD patients or if  ICD shocks do contribute to depression during long term therapy. This was the basis for the conduction of research as any unveiling of further information on this regard will be invaluable for the decisions regarding intervention with cognitive behavioral therapy or antidepressants for patients with depression (Suzuki et al, 2010). The purpose statement is clearly based on the argument developed in the literature review and it actually builds on the fact that depression is seen in 1 in 3 patients with coronary diseases, the study also plans to further increasing the current understanding of depression in patients with ICD , thereby providing much needed observational information on ways to combat ICD-associated depression.


   Suzuki et al (2010) was able to identify the variables of interest. In an experiment, the independent variable is the variable that is mixed or manipulated and the dependent variable is the response that is measured. In other terms, the independent variable is the cause and the dependent variable is the effect. For this particular study, the independent variable is ICD therapy and the dependent variable is the depression level in patients. This particulary study is quite unique from others in that it does not have a standard hypothesis, it does not have a alternative nondirectional or alternative directional hypothesis, rather, it is Inductive. This particular study is a prospective observational study of 90 ICD patients who were admitted to Tokyo Women’s Medical University Hospital over an 8-month period from April 2006 to November 2008. Yes the researchers provide a clear direction for their study, the aim is to evaluate the prevalence and persistence of depression in ICD patients over a 2 year period and to examine the effect of ICD shocks on depression (Suzuki et al, 2010). The hypothesis is testable and is stated with brevity and clarity.


   The sampling method was random and was conducted at the Tokyo Women’s Medical University. The patients that were being sampled were being hospitalized for new implantation of ICD or cardiac resychronizination therapy with defibrillator devices. Yes, the relevant demographic characteristics of the sample are identified: most of the particpants were male with the average age beign 57 years old, most of them were coming in for implantation of ICD, some were coming in because of Left Ventricular Fibrillation that needed to be resychronized. 24 percent of the patients had coronary artery disease, 23 percent had idiopathic dilated cardiomyopathy, 22 percent had hypertrophic cardiomyopathy, 4 percent had arrythmogenic right ventricular cardiomyopathy, 2 percent had unclassified cardiomyopathy, 3 percent had valvular heart disease, 12 percent had idiopathic ventricular fibrillation with long QT syndrome. The patients were randomly selected, and many of them did have cardiac-related disorders and all had ICDs that were implanted. The methods of sample selection used by the researchers did provide a good representation sample based on the population in Japan. There was no identifiable bias in selection of the sample as the patients were randomly selected.


   The particular quantitative research design used here was a true experimental design with emphasis on prospective observational analysis. True experimental design is considered by scientific researchers as the most accurate form of experimental research because there is an emphasis in analyzing data statistically and mathematically (Houser, 2009).  From analyzing the literature review, the research design is consistent with the purose and hypothesis presented in the introduction. The variables are clearly defined: the independent variable is ICD therapy and the dependent variable is the depression level in patients.


Considering the fact that this study was conducted in Japan, the results can generalizable for the Japanese population. However, if one were to conduct a similar research only on American patients in an American hospital, one would be able to do so since the independent and the dependent variables are clearly stated (Suzuki et al, 2010). Internal validity is the validity of inferences in scientific studies. Some of the threads to internal validity are ambiguous temporal precedence, confounding bias as well as selection bias as well as experimenter bias. For this particular study, the one threat to internal validity is experimenter bias. In the case that the reserachers put more emphasis in observing patients with ICD with higher indices of depression, can affect the results of patients with lower or medium level of depression. External validity is the validity of generalized inferences in scientific studies. Some of the threats to external validity would be pre-test effects as well as post-test effects (Houser, 2009). This comes to mind because the patients that were being observed were asked to take the Zung Self-Rating Depression Scale in the beginning of the study and then a second time 2 years later (Suzuki et al, 2010).


The type of measures that were use din the study was direct observation as well as behavioral measures and self-report tests , in particular the patients were asked to take the Zung Self-Rating Depression Scale. The Zung SDS is a short self-administered survey to quantify the dependent status of patients. There are some 20 items on the score that rate the rating affecting psychological and somatic symptom associated with depression. Scores between the 20-49 range is considered normal, scores between 50 to 59 is considered mildly depressed, scores between 60 to 69 is considered moderately depressed and scores above 70 is considered severely depressed (Suzuki et al, 2010). The realiability of the observational measures are reported to be reliable and have high validity (Suzuki et al, 2010).


To evaluate the effect of ICD therapy on depression, the frequencies of ICD therapy during the 2 year follow-up period in patients with and without depression at the 2 year time point were shown. Results showed that there was a significantly higher incidence of appropriate shocks in patients with depression at the 2 year follow-up than in those without depression (7/25 vs 4/65, P < 0.005), however no higher incidence of antitachycardial pacing. It was also observed that depression was indeed associated with increased numbers of shocks during the 2 year period (0 shocks, 16/25 vs 59/65; 1-9 shocks, 5/25 vs 5/65; >10 shocks, 4/25 vs 1/65; P 0.005). The type of descriptive statistics that were being analyzed were bivariate statistics, analyzing the effects of shocks to depression.


In the prospective observational study, the prevalence of depression at baseline and after 2 years was at 32% and 28%, respectively (Suzuki et al, 2010). It was noted that three quarters of the patients with depression were depressed at both the baseline and the 2 year time points. Meta analysis was conducted and showed that depression is quite common among patients with heart failure and much higher with patients with heart failure. Patients with higher forms of heart failure, ICD conditions have a severe form of depression as well. It is noted that patients with depression at the 2 year time point had experienced more ICD shocks during the 2 year follow-up than those without depression. The researchers also concluded that the occurrence of defibrillator shocks were independently associated with a significant reduction in mental well being and physical functioning in ICD patients (Suzuki et al, 2010). The researchers clearly restate the purpose of the research: The researchers want to see ICD therapy and depressive states because by doing so, medical providers can better treat ICD patients with depression either through cognitive behavioral therapy and/or through antidepressant medication (Suzuki et al, 2010). The researchers do not present the questions used, however. The implications of the findings allow the medical community to better understand how patients with coronary artery disease who have ICDs implanted are affected by depression. The results also show to us that the higher rates of depression on arrhythmic patients should be addressed by counseling to try to raise the quality of living in these patients.


The researchers did identify some limitations; there were several imitations inherent to the study, one limitation was the fact that most of the patients were hospitalized and were heterogenous. More than half of the patients had newly implanted ICDs and the fact that there was treatment bias, including pharmacotherapy. Another particular limitation was the fact that the number of participants was rather small; only 90 participants. Considering the fact that only 90 patients were used, the use of subgroup analysis was not feasible. Despite these limitations, the researchers note a meta-analysis that depression is quite common in patients with ICD as well as coronary artery disease. Depression is indeed associated with higher incidence of shock therapy (Suzuki et al, 2010).
 



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