Methods
Study population
The present study is a cohort data analysis of patients who were
enrolled prospectively in the ACSIS from 2000 to 2016. Details of ACSIS
have been previously reported (6). In brief, this survey is conducted
biennially over a 2-month period among ACS patients admitted to coronary
care units and cardiology wards in all 27 public hospitals in Israel.
Patient management was at the discretion of the attending physicians.
The diagnosis of AMI and ST-segment elevation MI (STEMI) or non-
ST-segment elevation MI (NSTEMI), was made by the attending cardiologist
according to pre-specified survey criteria based on accepted guidelines.
In total 15,200 patients were enrolled in our study. The patients were
grouped according to the occurrence of ventricular arrhythmias during
the course of index AMI. Data included baseline demographics, medical
history, hospital course, procedures, complications, and outcome based
on hospital’s charts. Additional data regarding health status, adverse
events and medication adherence were collected from the patients via
follow-up calls and from outpatients’ medical records one month after
hospital discharge. Mortality rates were determined for all patients
from hospital and out-patient charts and by matching their
identification numbers with the Israeli National Population Register.
In- hospital, one year, and five-year all-cause mortality was assessed
for the absence of VTA, early VTA and late VTA according to the periods
of presentation.
Definitions and
endpoints
The diagnosis of VTA, sustained ventricular tachycardia or ventricular
fibrillation was based on electrocardiogram (ECG) or continuous monitor
strips. Sustained ventricular tachycardia was defined as a series of
abnormally shaped QRS complexes longer than 120 milliseconds, with a
rate 100-250 beats/minute, lasting longer than 30 seconds or requiring
electrical cardioversion due to hemodynamic collapse. Ventricular
fibrillation was defined as rapid, very irregular rhythm with
indiscernible P waves or QRS. Patients were classified into three
groups: no VTA; early VTA (≤48h of onset) and late VTA
(>48h of onset). Survey periods were divided to early
decade (2000-2006) vs. late decade (2008-2016). Primary endpoints were
30-day, 1-year and 5-year mortality rate. Secondary endpoints included
30-day major adverse cardiac events (MACE) (all-cause mortality rate,
re-infarction, stent thrombosis and urgent revascularization). Left
ventricular ejection fraction (LVEF) was graded according to
echocardiography performed at admission in each center.
Statistical methods
Demographic, clinical features and the use of in-hospital therapies were
reported for all study participants. Multiple logistic regression
adjustments for age, gender, diabetes mellitus, chronic renal failure
and heart failure and for survey periods was performed to assess the
adjusted odds ratio (OR) and 95% confidence interval (CI) of in and out
of hospital complications and 30-day, 1 and 5-year mortality rate
associated with VTA at any time during and after the admission for ACS.
The cumulative probability of all-cause mortality rate was graphically
displayed using the Kaplan–Meier method and compared using the log-rank
test. In order to evaluate the independent association of VTA with the
5-year all-cause mortality rate outcome, a Cox proportional hazards
model was constructed adjusting for survey period. We employed an
interaction-term analysis to examine whether the risk of 5-year
mortality rate associated with VTA was different in the early period as
compared with the late period. Statistical significance was accepted for
a 2-sided p<0.05. Statistical analysis was performed using the
R Statistical Package (R Foundation for Statistical Computing, Vienna,
Austria).