Materials and methods
Setting and participants
This quasi-experimental study was conducted from July to October 2019 in three cardiac care units in Kowsar hospital, Shiraz, Iran. Using G-Power software and based on a previous study on success in smoking cessation, with P1 = 0.67, P2 = 0.37, α = 0.05, and power = 0.9, a 92-patient sample size was estimated. Therefore, considering the possibility of attrition, 100 patients were selected . The patients were divided into intervention and control groups with a 1:1 allocation (50 people per group) using permutation block randomization. The randomization sequence was generated by an independent researcher in the form of 25 blocks of size 4 using random allocation software. This sequence was put in numbered sealed envelopes. After selecting each eligible participant, the envelope was opened and according to its code, the person was assigned to the intervention or control group. The inclusion criteria included passing eight hours from angioplasty and having stable vital signs, being over 18 years old, having smoking history before being hospitalized, and having a cell phone and the ability to use texting service. The exclusion criteria were addiction to narcotics and consumption of other nicotine products other than cigarettes based on self-report, not filling out the questionnaires completely and the patients’ death.
During the investigation, two people from the intervention group and two people from the control group were excluded from the study because they did not refer to the hospital and did not complete the post-test. Furthermore, one person from the control group was omitted because of death and one person from the intervention group was unwilling to continue the intervention; finally, the data of 94 patients were analyzed.
In this study, the patients in both intervention and control groups received routine training of the unit from nurses. The routine training included emphasizing the importance of adherence to treatment regimen and controlling modifiable risk factors for CAD.
In the intervention group, a motivational text-messaging program for quitting smoking was applied too. In this way, from the second day after discharge, 32 motivational-educational SMS were sent to the patients. These SMS were designed based on Allen Carr's ideas about an easy way to stop smoking . To ensure the validity of SMS, we revised them according to the comments of 10 experts from community health nursing and medical-surgical nursing. Then they were edited in writing (Additional file 1). To improve patients’ attitudes towards smoking cessation and motivate them in this regards, these messages questioned people's common misconceptions about smoking and the potential risks of quitting. Moreover, according to Allen Carr's ideas, instead of a mere emphasis on threats and dangers of smoking, the benefits of quitting and how deleting cigarettes from life can return valuable assets like energy, joy, peace, health, and financial resources were highlighted . Every week, four messages were sent on certain days from 8 a.m. to 8 p.m. for 2 months. Patients sent the word "received" after receiving each message. In addition, every week, the researcher sent a message to check whether the patients were following the SMS.
Data collection tools were Persian versions of the smoking status questionnaire, success in quitting smoking and Smoking Abstinence Self-Efficacy Questionnaire (SASEQ). The pre-test was done when the hospitalized patients’ condition was stable after angioplasty. After the intervention was finished, the post-test questionnaires were completed when the patients referred to the outpatient clinic for their scheduled appointment.
The smoking status questionnaire was extracted from the smoking questionnaire related to the Multinational Monitoring of Trends and Determinants in Cardiovascular Disease (MONICA) project. This questionnaire has 13 questions to examine the smoking condition [22, 27]. Kazemzadeh et al. selected eight questions about active smoking from this tool and after translation, investigated its psychometric properties. Similarly, in the present study, these questions were used .
To investigate the self-efficacy of people for quitting smoking the SASEQ designed by Spek et al. was used. The questionnaire has six questions and the answers are based on 5-point Likert scale scored from "I surely won't smoke"  to "I'd surely smoke" (0). The obtained score would be a number between 0 to 24. A higher score shows higher self-efficacy in quitting smoking . Spek et al. in addition to factor analysis, signified the discriminant validity of the tool via its negative and weak relationship with the Edinburgh Depression Scale (r = − 0.145, p = 0.001). Furthermore, they confirmed its reliability by internal consistency (Cronbach’s alpha = 0.89) .
To investigate success in quitting cigarette smoking, the self –report 4-weeks quitting (SR4WQ) questionnaire was used [26, 30]. In this questionnaire, people were first asked about cigarette smoking during the past two weeks and if their answers were yes, four questions were asked about the reasons of return to smoking. People who stated that they have completely quit cigarette smoking were considered successful. Quitting smoking by 50% of the people indicates the success of the intervention.
Kazemzadeh et al. confirmed the content validity of Persian versions of three tools by offering them to 10 experts. Additionally, they confirmed the reliability of the smoking status questionnaire by test re-test (r = 0.86), the reliability of SR4WQ by Cronbach’s Alpha of 0.87 , and SASEQ reliability by Cronbach’s alpha of 0.94 .
Data were analyzed using SPSS software version 22. The research variables were described using descriptive statistics. To compare the two groups in terms of qualitative variables, the Chi-square test was used. Also, to compare the two groups regarding quantitative variables, the independent t-test was applied. For comparing inter-group self-efficacy, a paired t-test was employed. P < 0.05 was considered as the statistical significance level for all analyzes.