42 ZOLL AED PLUS Administrator’s Guide
waveform in defibrillation of presenting and recurrent ventricular fibrillation: A prospective
multicenter study,” was included with PMA application P160015. A summary of the study is presented
below:
Objectives: The study tested the hypothesis that shock success differs with initial and recurrent
episodes of ventricular fibrillation (VF).
Methods: From September 2008 to March 2010 out-of-hospital cardiac arrest patients with VF as the
initial rhythm at 9 study sites were defibrillated by paramedics using a rectilinear biphasic waveform.
Shock success was defined as termination of VF within 5 s post-shock. The study used generalized
estimating equation (GEE) analysis to assess the association between shock type (initial versus
defibrillation) and shock success.
Results: Ninety-four patients presented in VF. Mean age was 65.4 years, 78.7% were male, and 80.9%
were bystander-witnessed. VF recurred in 75 (79.8%). There were 338 shocks delivered for initial
(n = 90) or recurrent (n = 248) VF available for analysis. Initial shocks terminated VF in 79/90 (87.8%)
and subsequent shocks in 209/248 (84.3%). GEE odds ratio (OR) for shock type was 1.37 (95% CI
0.68–2.74). After adjusting for potential confounders, the OR for shock type remained insignificant
(1.33, 95% CI 0.60–2.53). The study observed no significant difference in ROSC (54.7% versus 52.6%,
absolute difference 2.1%, p = 0.87) or neurologically intact survival to hospital discharge (21.9% versus
33.3%, absolute difference 11.4%, p = 0.31) between those with and without VF recurrence.
Conclusions: Presenting VF was terminated with one shock in 87.8% of cases. The study observed no
significant difference in the frequency of shock success between initial versus recurrent VF. VF
recurred in the majority of patients and did not adversely affect shock success, ROSC, or survival.
ECG Analysis Algorithm Accuracy
Sensitivity and specificity are expressions of ECG analysis algorithm performance when compared to
ECG interpretation by a clinician or expert. Sensitivity refers to the algorithm’s ability to correctly
identify shockable rhythms (as a percentage of the total number of shockable rhythms); specificity
refers to the algorithm’s ability to correctly identify non-shockable rhythms (as a percentage of the total
number of non-shockable rhythms). The data in Table 11 and Table 12 summarizes the accuracy of the
ECG analysis algorithm as tested against ZOLL’s ECG Rhythm Database.
The algorithm sequence takes approximately 9 seconds and proceeds as follows:
• Divides the ECG rhythm into three-second segments.
• Filters and measures noise, artifact, and baseline wander.
• Measures baseline content (“waviness” at the correct frequencies — frequency domain analysis) of
signal.
• Measures QRS rate, width, and variability.
• Measures amplitude and temporal regularity (“auto-correlation”) of peaks and troughs.
• Determines if multiple 3 second segments are shockable then prompts the user to treat patient.
• Stops analyzing the ECG after detecting a shockable rhythm and theAED Plus unit is charged and
ready to deliver a shock.
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