Jason Coult

Course of quantitative ventricular fibrillation waveform measure and outcome following out-of-hospital cardiac arrest

BACKGROUND Quantitative measures of the ventricular fibrillation waveform at the outset of resuscitation are associated with survival. However, little is known about the course of these measures during resuscitation and how this course is related to outcome. OBJECTIVE The purpose of this study was to determine how waveform measures change over the course of resuscitation and whether these changes might be used to guide resuscitation. METHODS We evaluated 390 persons treated by emergency providers following out-of-hospital ventricular fibrillation arrest. We assessed the ventricular fibrillation waveform using the amplitude spectrum area (AMSA) from the defibrillators continuous electrocardiogram measured before each of the first three shocks. We used logistic regression to evaluate the relationship of AMSA and the change in AMSA with favorable neurologic survival as determined by the Cerebral Performance Category at hospital discharge 1-2. RESULTS Of the 390 patients who received an initial shock, 273 required a second shock and 210 required a third shock. The mean (standard deviation) for AMSA was 9.64 (0.52) for the 873 total shock cycles. AMSA₁ measured before the first shock was strongly associated with favorable neurologic survival (odds ratio [OR] 3.40, 95% confidence interval [CI] [2.48, 4.66] for 1 SD change). We observed a similar relationship for second-shock AMSA₂ (OR 3.53, 95% CI [2.42, 5.14]) and third-shock AMSA₃ (OR 3.10, 95% CI [2.03, 4.73]). The median change in AMSA was 0.24 for ΔAMSA₁₋₂ and 0.21 for ΔAMSA₂₋₃. A positive median change in AMSA between shocks was associated with favorable neurologic survival (OR 1.44, 95% CI [1.16, 1.80] for ΔAMSA₁₋₂ and OR 1.31, 95% CI [1.01, 1.71] for ΔAMSA₂₋₃). CONCLUSION Given their prognostic and dynamic qualities, quantitative waveform measures may provide an effective real-time strategy to guide individual treatment and improve survival.

Cardiopulmonary resuscitation duty cycle in out-of-hospital cardiac arrest.

BACKGROUND Duty cycle is the portion of time spent in compression relative to total time of the compression-decompression cycle. Guidelines recommend a 50% duty cycle based largely on animal investigation. We undertook a descriptive evaluation of duty cycle in human resuscitation, and whether duty cycle correlates with other CPR measures. METHODS We calculated the duty cycle, compression depth, and compression rate during EMS resuscitation of 164 patients with out-of-hospital ventricular fibrillation cardiac arrest. We captured force recordings from a chest accelerometer to measure ten-second CPR epochs that preceded rhythm analysis. Duty cycle was calculated using two methods. Effective compression time (ECT) is the time from beginning to end of compression divided by total period for that compression-decompression cycle. Area duty cycle (ADC) is the ratio of area under the force curve divided by total area of one compression-decompression cycle. We evaluated the compression depth and compression rate according to duty cycle quartiles. RESULTS There were 369 ten-second epochs among 164 patients. The median duty cycle was 38.8% (SD=5.5%) using ECT and 32.2% (SD=4.3%) using ADC. A relatively shorter compression phase (lower duty cycle) was associated with greater compression depth (test for trend <0.05 for ECT and ADC) and slower compression rate (test for trend <0.05 for ADC). Sixty-one of 164 patients (37%) survived to hospital discharge. CONCLUSIONS Duty cycle was below the 50% recommended guideline, and was associated with compression depth and rate. These findings provider rationale to incorporate duty cycle into research aimed at understanding optimal CPR metrics.

Long-range attraction in aqueous colloidal suspensions

Long-range attractions in aqueous suspensions were observed between polymeric microspheres and also between microspheres and a gel bead. Attractive displacements were consistently seen even between like-charged entities, and they were observed over spans as large as 2 mm. Such behaviors are unexpected, and may reside in a long-range attraction mechanism.

Short ECG segments predict defibrillation outcome using quantitative waveform measures

AIM Quantitative waveform measures of the ventricular fibrillation (VF) electrocardiogram (ECG) predict defibrillation outcome. Calculation requires an ECG epoch without chest compression artifact. However, pauses in CPR can adversely affect survival. Thus the potential use of waveform measures is limited by the need to pause CPR. We sought to characterize the relationship between the length of the CPR-free epoch and the ability to predict outcome. METHODS We conducted a retrospective investigation using the CPR-free ECG prior to first shock among out-of-hospital VF cardiac arrest patients in a large metropolitan region (n=442). Amplitude Spectrum Area (AMSA) and Median Slope (MS) were calculated using ECG epochs ranging from 5s to 0.2s. The relative ability of the measures to predict return of organized rhythm (ROR) and neurologically-intact survival was evaluated at different epoch lengths by calculating the area under the receiver operating characteristic curve (AUC) using the 5-s epoch as the referent group. RESULTS Compared to the 5-s epoch, AMSA performance declined significantly only after reducing epoch length to 0.2s for ROR (AUC 0.77-0.74, p=0.03) and with epochs of ≤0.6s for neurologically-intact survival (AUC 0.72-0.70, p=0.04). MS performance declined significantly with epochs of ≤0.8s for ROR (AUC 0.78-0.77, p=0.04) and with epochs ≤1.6s for neurologically-intact survival (AUC 0.72-0.71, p=0.04). CONCLUSION Waveform measures predict defibrillation outcome using very brief ECG epochs, a quality that may enable their use in current resuscitation algorithms designed to limit CPR interruption.

Ventricular fibrillation waveform measures combined with prior shock outcome predict defibrillation success during cardiopulmonary resuscitation

AIM Amplitude Spectrum Area (AMSA) and Median Slope (MS) are ventricular fibrillation (VF) waveform measures that predict defibrillation shock success. Cardiopulmonary resuscitation (CPR) obscures electrocardiograms and must be paused for analysis. Studies suggest waveform measures better predict subsequent shock success when combined with prior shock success. We determined whether this relationship applies during CPR. METHODS AMSA and MS were calculated from 5-second pre-shock segments with and without CPR, and compared to logistic models combining each measure with prior return of organized rhythm (ROR). RESULTS VF segments from 692 patients were analyzed during CPR before 1372 shocks and without CPR before 1283 shocks. Combining waveform measures with prior ROR increased areas under receiver operating characteristic curves for AMSA/MS with CPR (0.66/0.68 to 0.73/0.74, p<0.001) and without CPR (0.71/0.72 to 0.76/0.76, p<0.001). CONCLUSIONS Prior ROR improves prediction of shock success during CPR, and may enable waveform measure calculation without chest compression pauses.

An accurate method for real-time chest compression detection from the impedance signal

OBJECTIVE Real-time feedback improves CPR performance. Chest compression data may be obtained from an accelerometer/force sensor, but the impedance signal would serve as a less costly, universally available alternative. The objective is to assess the performance of a method which detects the presence/absence of chest compressions and derives CPR quality metrics from the impedance signal in real-time at 1s intervals without any latency period. METHODS Defibrillator recordings from cardiac arrest cases were divided into derivation (N=119) and validation (N=105) datasets. With the force signal as reference, the presence/absence of chest compressions in the impedance signal was manually annotated (reference standard). The method classified the impedance signal at 1s intervals as Chest Compressions Present, Chest Compressions Absent or Indeterminate. Accuracy, sensitivity and specificity for chest compression detection were calculated for each case. Differences between method and reference standard chest compression fractions and rates were calculated on a minute-to-minute basis. RESULTS In the validation set, median accuracy was 0.99 (IQR 0.98, 0.99) with 2% of 1s intervals classified as Indeterminate. Median sensitivity and specificity were 0.99 (IQR 0.98, 1.0) and 0.98 (IQR 0.95, 1.0), respectively. Median chest compression fraction error was 0.00 (IQR -0.01, 0.00), and median chest compression rate error was 1.8 (IQR 0.6, 3.3) compressions per minute. CONCLUSION A real-time method detected chest compressions from the impedance signal with high sensitivity and specificity and accurately estimated chest compression fraction and rate. Future investigation should evaluate whether an impedance-based guidance system can provide an acceptable alternative to an accelerometer-based system.

Rhythm profiles and survival after out-of-hospital ventricular fibrillation cardiac arrest

OBJECTIVE Treatment: protocols for cardiac arrest rely upon rhythm analyses performed at two-minute intervals, neglecting possible rhythm changes during the intervening period of CPR. Our objective was to describe rhythm profiles (patterns of rhythm transitions during two-minute CPR cycles) following attempted defibrillation and to assess their relationship to survival. METHODS The study included out-of-hospital cardiac arrest cases presenting with ventricular fibrillation from 2011 to 2015. The rhythm sequence was annotated during two-minute CPR cycles after the first and second shocks of each case, and the rhythm profile of each sequence was classified. We calculated absolute survival differences among rhythm profiles with the same rhythm at the two-minute check. RESULTS Of 569 rhythm sequences after the first shock, 46% included a rhythm transition. Overall survival was 47%, and survival proportion varied by rhythm at the two-minute check: ventricular fibrillation (46%), organized (58%) and asystole (20%). Survival was similar between profiles which ended with an organized rhythm at the two-minute check. Likewise, survival was similar between profiles with asystole at the two-minute check. However, in patients with ventricular fibrillation at the two-minute check, survival was twice as high in those with a transient organized rhythm (69%) compared to constant ventricular fibrillation (32%) or transient asystole (28%). CONCLUSION Rhythm transitions are common after attempted defibrillation. Among patients with ventricular fibrillation at the subsequent two-minute check, transient organized rhythm during the preceding two-minute CPR cycle was associated with favorable survival, suggesting distinct physiologies that could serve as the basis for different treatment strategies.