Outcome of apparently unexplained cardiac arrest results from investigation and follow-up of the prospective cardiac arrest survivors with preserved ejection fraction registry
Sylvia Okoma, Mercer University College of Pharmacy
It has been stated that there are a number of identifiable causes of heart disease, which include the primary causes of coronary artery disease and cardiomyopathy, but there are also unidentifiable causes when the pathogenesis for cardiac arrest is not apparent. [1, 2]
It has also been noted that identified genetic conditions that cause sudden cardiac death include these inherited rhythm disorders: arrhythmogenic right ventricular cardiomyopathy (ARVC), Brugada Syndrome, catecholaminergic polymorphic ventricular tachycardia, and long QT syndrome (LQTS). 
|Title: Outcome of apparently unexplained cardiac arrest results from investigation and follow-up of the prospective cardiac arrest survivors with preserved ejection fraction registry |
|Design||Retrospective, cohort study; N = 200|
|Objective||To evaluate the diagnostic outcome of patients with unexplained cardiac arrest in the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER)|
|Study Groups||Patients were divided into two groups: one that had patients diagnosed based on a definite or probable diagnosis (n = 81), and the other group was undiagnosed based on unexplained cardiac arrest or only weak evidence of a diagnosis (n = 119, possible diagnosis and single inconclusive test)|
|Methods||Patients received a diagnosis and patients with unexplained cardiac arrests were monitored and evaluated in follow-up. Diagnoses were based on phenotypic evidence in 63 patients (78%), genetic evidence in 11 patients (13%) and both phenotypic and genetic evidence in seven patients (9%). In addition, 158 patients (79%) received some form of genetic testing, and 85 family members of 65 patients had clinical and genetic testing to determine if they were at risk of cardiac disease.|
|Duration||Between January 1, 2004 and December 1, 2013 and a minimum of a one year follow up period after initial assessment (the mean duration of follow-up was 3.15 +/- 2.34 years)|
|Primary Outcome Measure||Symptoms of cardiac events: the presence of syncope, palpitations, recurrent cardiac arrest or implantable cardioverter defibrillator (ICD) events|
|Baseline Characteristics||Definite/probable diagnosed||Undiagnosed/possible diagnosed
|Age (year +/- standard deviation)||47.9 +/- 14.6||49.0 +/- 14.5||0.674|
|Females (%)||35 (43%)||46 (39%)||0.559|
|ICD Implantation||79 (98%)||111 (93%)||0.207|
|Average heart rate||73.0 +/- 18.3||71.5 +/- 17.9||0.565|
|QTc||429.6 +/- 37.9||421.7 +/- 26.7||0.096|
|Left Ventricular Ejection Fraction (LVEF)||57.1 +/- 8.8||57.6 +/- 10.2||0.160|
|Results||There were 25 patients who experienced an appropriate ICD shock during the follow-up (16% with a median time of 2.22 years) and 25 patients who had antitachycardial pacing (ATP, 16% with a median time of 1.04 years). There were also 15 patients who experienced both a shock and ATP (10%). The overall rate of receiving an appropriate therapy (ATP or shock) in ICD recipients was 8.4% after one year and 18.1% after three years. There was a strong association between ICD shock and ATP (p <0.001) and patients who experienced ATP as the first detected event were more likely to experience a subsequent ICD shock (p = 0.03).
For patients with a diagnosis, comparisons were made between the underlying structural heart disease and those with the primary electric disease. There were 53 patients (65%) who had an underlying primary electric disease and 28 patients (35%) who had an underlying structural heart disease. The ICD groups at follow up had a trend toward increased ATP in patients with structural heart disease compared with electric disease (HR 2.73, 95% CI, 0.672 – 7.030, p = 0.077).
|Adverse Events||Common Adverse Events: presyncope (6%),|
|Serious Adverse Events: syncope (21%), palpitations (9%), chest pain (12%)|
|Percentage that Discontinued due to Adverse Events: two deaths (1%, one from ventricular tachycardia (VT) storm due to lead failure and inability to deliver high voltage therapy and the other from a malignancy that caused LQTS)|
|Study Author Conclusions||In this study it has been demonstrated that with the use of systematic advanced testing, a clinical diagnosis can be determined in about half of the patients who present with unexplained cardiac arrest. In the absence of a gold standard, the strength of diagnosis was used and a patient was only considered diagnosed if they met probable or definite strength. Since CASPER’s initiation in 2004, continued research has led to the acceptance of new mechanisms involved in cardiac arrest. In addition it is important to continual monitor patients with the primary electric diseases or latent structural causes because they are often dynamic and phenotypes may become more evident with continual testing or recording of events. Lastly, diagnosis was an important component of diagnosis that aided in risk stratification to determine those more likely to have a future cardiac event.|
The future reporting of unexplained cardiac arrest events should be more promising with large scale clinical trials that include patients with structural heart disease. Future studies should seek to determine if shock burden would be reduced by focusing on utilizing the ICD programming and intervention from recent deferred programming strategies instead of the early delivery of shocks previously used [3,4].
- Herman, Adam, Christopher Cheung, Brenda Gerull, et al. Outcome of apparently unexplained cardiac arrest results from investigation and follow-up of the prospective cardiac arrest survivors with preserved ejection fraction registry. Circ Arrhythm Electrophysiology (9):pp 1-9, Accessed 21 Jan 2016.
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