Utility of a Smartphone Based System (cvrPhone) to Predict Short-term Arrhythmia Susceptibility

Figures

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  Figure 1. The smartphone-based repolarization alternans monitoring system. The Bluetooth-enabled ECG acquisition device is composed of three parts: An analog-to-digital (AD) converter, a microcontroller board, and a Bluetooth module. The AD converter amplifies and digitizes the signals from the ten electrodes on the torso, and the microcontroller transmits the signals to the smartphone through the Bluetooth module. Then, the smartphone calculates repolarization alternans indices for each lead in real-time.

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  Figure 2. Coronary artery occlusion induced temporal changes of the estimated repolarization alternans (ST-segment and T-wave) indices (n = 29 records; N = 17 animals): (A) alternans noise (µnoise), (B) alternans voltage, and (C) Kscore. Time zero indicates the balloon inflation moment. Each bar graph represents 10, 25, 50, 75 and 90 percentiles of the corresponding alternans index values beat-by-beat estimated for all animals for 1 minute time span. Asterisk indicates statistically significant increase after occlusion, compared to before occlusion (p < 0.0001 for the alternans noise, p < 0.0001 for the alternans voltage and p < 0.05 for the Kscore).

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  Figure 3. ECG signal (lead V3) displaying spontaneous transition to ventricular tachycardia after coronary artery occlusion.

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  Figure 4. Temporal changes of the repolarization alternans (ST-segment and T-wave) indices during myocardial infarction that led to spontaneous ventricular tachycardia/fibrillation (n = 4 records; 4 animals): (A) alternans noise (µnoise), (B) alternans voltage, and (C) Kscore. Time zero indicates the balloon inflation moment. Each bar graph represents 10, 25, 50, 75 and 90 percentiles of the corresponding alternans index estimated on a beat-by-beat basis for all animals, in 1 min time intervals. The asterisk indicates a statistically significant increase after occlusion compared to before occlusion (p < 0.05 for the alternans noise, p < 0.05 for the alternans voltage and p < 0.05 for the Kscore).

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  Figure 5. Sensitivity of the 12 lead ECG in detecting RA, that is P(any one in N leads is +| one of 12 leads is +). In the plot one observes the highest performing lead combinations of N leads, for any number of leads ranging from one to twelve. +: indicates positive.

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  Figure 6. Repolarization alternans (ST-segment and T-wave, RA) burden before and after coronary artery occlusion. RA positive, criteria were defined as: (i) alternans voltage is greater than 0.55 μV, and (ii) Kscore greater than 3. The RA burden is evaluated on a beat-by-beat basis as a percent of sequences that exhibited significant RA, and percentages of RA incidence are calculated before and after the occlusion separately, for each record. Each bar graph represents 10, 25, 50, 75 and 90 percentiles of alternans burden of all records. An asterisk indicates statistically significant (p < 0.05) difference between the two alternans percents before and after occlusion (n = 29 records; N = 17 animals).

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  Figure 7. Relationship of repolarization (ST-segment and T-wave) alternans vs ischemic index (A) during myocardial infarction and (B) preceding ventricular tachycardia/fibrillation. Alternans voltage (μV) versus ischemic index (upper panel), and Kscore versus ischemic index (lower panel). The color bars on the right side show time after coronary artery occlusion from 0 min to 5 min. The dashed line at each plot represents a data fitting line with a single-term exponential model. (D) PVS that was employed at baseline and after coronary artery occlusion, MI (N = 9), to assess the arrhythmogenic potential of RA. Although the Srank at baseline and after coronary artery occlusion was not statistically different, yet it trended towards a higher value after occlusion.