INTRODUCTION

Unstable angina (UA) is an irregular type of angina pectoris1 and a type of acute coronary syndrome (ACS).2 Every year, in the U.S, more than one million people are hospitalized due to unstable angina and non–ST-segment elevation myocardial infarction (UA/NSTEMI),3 and incidence is increasing in many countries. The burden of UA is high, as the first-year treatment cost of patients ($12,058 per patient) is almost as high as that of myocardial infarction ($15,540 for each survivor and $17,532 for each death).4 Even with a high cost intervention, health outcomes and long term prognosis may not improve.
Previously, survival rates, complication rates, and functional parameters were used as indicators of the efficacy of coronary artery disease (CAD) treatment.5 Over the past years, however, the quality of life (QoL) of patients with chronic diseases such as cardiovascular disease has also become an important indicator of successful clinical practice.6 Recently, percutaneous coronary intervention (PCI) has emerged as a breakthrough method for treating and predicting the outcomes of patients with CAD. Given its superiority, PCI has become a frequently used revascularization strategy8 with some evidence comparing QoL between patients with CAD and those receiving this intervention.9-12QoL of patients with CAD may be evaluated using different instruments, including the Seattle angina questionnaire (SAQ)13 and the physical activity score,14 which are specific to coronary diseases. Others, such as the 36-item short form (SF-36),15 the Nottingham health profile (NHP)16, and the Swedish quality of life survey (SWED-QUAL)17 give a more generic assessment and allow comparisons with non-CAD populations. SAQ scores have been shown to predict 1-year mortality and ACS among outpatients with coronary disease, and might play a crucial part in stratifying the risk of such patients18. A previous study of 65 patients receiving PCI found that QoL measured with the SF-36 improved significantly over time in six out of the eight domains and all other domains showed an increase at 3-month follow-up. Moreover, all five domains of SAQ improved significantly; however, the angina stability score at 3-month follow-up was lower than the baseline value.19 A 2008 study comparing PCI and optimal medical therapy alone showed remarkable improvements in health outcomes during the follow-up period in the PCI group but these disappeared after 36 months.20
These studies suggest mixed results for PCI on quality of life in patients in developed countries, but little is known about this area of research in developing countries, including Vietnam. As Vietnam moves into the epidemiological transition and experiences a growing burden of non-communicable disease (NCD), research on the optimal treatments for conditions such as Angina, and rapid implementation of best practice from high-income countries, is essential to prepare the Vietnamese health system for better management of the growing epidemic of NCDs. This study aimed to compare QoL among patients with unstable angina after PCI and examine factors associated with QoL improvement after PCI. Our study adopts Lawton’s theoretical framework21(see Fig. 1 ), which is regarded as appropriately for explaining factors associated with patients’ QoL after myocardial infarction. On theoretical grounds, Lawton distinguishes four domains of QoL: ‘Behavioral competence’, which includes physical health, daily activities, cognitive functioning and social behaviour; ‘Objective environment’, including material possessions, social support, and network; ‘Domain-specific perceived QoL’, the degree of satisfaction with all important (life) domains, such as social functioning, leisure activities, living accommodation, and income; and ‘Psychological well-being’, the weighted evaluated level of a person’s competence and perceived quality in all domains of contemporary life. Lawton recommends a hierarchical reference with ‘behavioral competence’ and ‘perceived quality of life’ as central domains, ‘environment’ as a prerequisite or catalyst, and ‘psychological well-being’ as the ultimate outcome.22 These behavioral competencies are the aspects of functioning that are strongly influenced by illness. Given the scope of this study as well as the complex nature of the intervention delivered to our participants, this theoretical model for our study is adapted and presented as hereinafter.