Introduction
Cardiovascular diseases are one of the most important leading causes of death worldwide such that, in Iran, 43% of all deaths are due to cardiovascular diseases [1] and is often associated with ischemic heart disease [2]. Annually, there are approximately 375.000-700.000 cases of cardiac arrest in Europe [3]. The result of a study in Rasht city, Iran showed that there have been 1565 cases of Cardiopulmonary Resuscitation (CPR) during 2016-2017, of which only 156 cases had long-term survival [4]. CPR is an emergency procedure for Return of Spontaneous Circulation (ROSC) in a person with cardiac arrest [5]. Improvements have been made in recent years to increase the chance of survival after CPR, but survival rates are still low [6, 7, 8]. Findings of a study by Van Jane et al. showed that 36.8% of patients had ROSC and more than half of those with successful initial CPR died before hospital discharge [14]. Based on previous studies on several factors as predictors of CPR outcome, there are different results in terms of severity and outcome of CPR [16]. Considering the impact of environmental and physical factors on the CPR outcome, this study aims to investigate the success rate of CPR and its related factors in patients referred to Dr. Heshmat Hospital in Rasht, Iran.
Methods
This retrospective cohort study was conducted on 1008 patients who had underwent CPR in Dr. Heshmat Hospital from April 2016 to March 2019. The information was collected by a form based on the Utstein pattern, divided into three sections: (a) Patient-related factors such as age, gender, cause of cardiac arrest, heart rhythm, (b) Event-related related factors such as the work shift when CPR was performed and location of cardiac arrest (out of hospital or in hospital), and (c) factors related to the time of actions such as the time from cardiac arrest to the arrival of resuscitation team, the time from cardiac arrest to electrical shock, the time from cardiac arrest to intubation, the time from cardiac arrest to the end of CPR, short-term and long-term outcomes of CPR, and brain function status until discharge from the hospital.
All data analyses were performed in SPSS v.16 software. The significance level in all tests was set at 0.05. Independent samples t-test and chi-square test were used to examine the relationship between CPR success rate and demographic/clinical variables. Multiple logistic regression analysis was applied for controlling the confronting variables to find the related factors. Findings of regression analysis were described by Odds Ratio (OR) at 95% Confidence Interval (CI). 
Results
Mean age of patients was 67.4±14.2 years of whom 565 (56.1%) were male. The most of cardiac arrests occurred in hospital (81.8%) with asystole rhythm (53.9%). The mean CPR duration was 39±21.3 minutes and the CPR success rate was 34.8%.
The CPR success rate in patients with asystole rhythm was lower than in other patients (P<0.001) and this rate in patients with in-hospital cardiac arrest was higher than in patients with out-of-hospital cardiac arrest (37.3% vs. 23.5%; P<0.001). The CPR success rate at night was lower than in other work shifts, although the difference was not statistically significant (P=0.091). The CPR success rates in the emergency department and CCU were lower than in ICU and other wards, although there was no statistically significant difference (P=0.113). Duration of CPR was shorter in patients with successful CPR (21.9±17.3 vs. 48.1±17.3; P<0.001).
According to the results in Table 1, the success of CPR decreased with the increase of age, although this association was not statistically significant (OR=0.99, 95% CI: 0.97–1.00, P=0.069).


Patients with in-hospital cardiac arrest were 1.8 times more likely to have successful CPR than patients with out-of-hospital cardiac arrest (OR=1.81, 95% CI: 1.02-3.22). Patients who had no asystole rhythm were 2.53 times more likely to have successful CPR than patients with asystole rhythm (OR=2.53, 95% CI: 1.75-3.66). Long CPR duration was associated with decreased CPR success rate (OR=0.89, 95% CI: 0.88–0.90). Compared to patients in CCU, those in emergency department (OR=1.62, 95% CI: 1.05-2.51) and other wards (OR=2.28, 95% CI: 1.12-4.62) were more likely to have successful CPR. Finally, the results showed that CPR outcome was not significantly related to patient’s gender and the work shift when CPR was performed
Discussion
The findings showed that chances of a successful CPR decreased with the increase of age, but it was not statistically significant. A study by Lima et al. showed that younger patients had ROSC earlier after a shorter period of CPR and the chance of survival was higher in them [5]. Since the results showed that patients with asystole rhythm had the lowest success rate of CPR and this rhythm occurs due to delay in initiation of treatment at the end of cardiac arrest, early treatment of patients with cardiac arrest caused by ventricular tachycardia rhythm or ventricular fibrillation can increase the chances of a successful CPR.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Guilan University of Medical Sciences (Code: IR.GUMS.REC.1398.036). 

Funding
This study was funded by the Deputy for Research and Technology of Guilan University of Medical Sciences, Rasht, Iran.

Authors' contributions
Conceptualization and study design: Sanaz Amini, Mohammad Taghi Moghaddamnia, Yasaman Borghei; Data collection: Yasaman Borghei; Data analysis: Saman Maroufizadeh; Writing the initial draft article and reviewing it critically: All authors; Final approval: All authors.

Conflicts of interest
The authors declare that they have no conflict of interest.

Acknowledgements
The authors would like to thank the Deputy for Research and Technology of Guilan University of Medical Sciences and the staff of Dr. Heshmat Hospital in Rasht for their support and cooperation in this study.


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