Non-Invasive Detection of Mechanical Alternans Utilizing Photoplethysmography

Abstract

Background and Significance: Mechanical alternans (MA) is a biomarker associated with mortality and life-threatening arrhythmias in heart failure patients. Despite showing prognostic value, its use is limited by the requirement of measuring continuous blood pressure (BP), which is costly and impractical. Objective: To develop and test, for the first time, non-invasive MA surrogates based on photoplethysmography (PPG). Methods: Continuous BP and PPG were recorded during clinical procedures and tests in 35 patients. MA was induced either by ventricular pacing (Group A, N=19) or exercise (Group B, N=16). MA was categorized as sustained or intermittent if MA episodes were observed in at least 20 or between 12 to 20 consecutive beats, respectively. Eight features characterizing pulse morphology were derived from the PPG and MA surrogates were evaluated. Results: Sustained alternans was observed in 9 patients (47%) from Group A, whereas intermittent alternans was observed in 13 patients (68%) from Group A and in 10 patients (63%) from Group B. The PPG-based MA surrogate showing the highest accuracy, V'M, was based on the maximum of the first derivative of the PPG pulse. It detected both sustained and intermittent MA with 100% sensitivity and 100% specificity in Group A and intermittent MA with 100% sensitivity and 83% specificity in Group B. Furthermore, the magnitudes of MA and its PPG-based surrogate were linearly correlated (R 2 =0.83, p<0.001). Conclusion: MA can be accurately identified non-invasively through PPG analysis. This may have important clinical implications for risk stratification and remote monitoring.

Real Time Non-Invasive Hemodynamic Assessment of Ventricular Tachycardia

“…As an estimator of blood pressure, PPG has been limited by calibration requirements, and has been shown to perform well only in some patients [15], [16]. Interestingly, PPG had already been shown potential to detect hypotensive events during haemodialysis and labour [17], [18], but it was never been utilized to classify the hemodynamic response to VT. We have recently shown that PPG features can be used to detect mechanical (or pulsus) alternans [19], [20]. Combined with the present results, this suggests that although PPG may not be accurate in measuring ABP, it can be used to detect fast and sudden changes in ABP though the analysis of its pulsatile components.…”

“…Combining ICD detected electrograms or surface ECG for rates below the standard VT zone rate cut-offs would also enable more accurate arrhythmia classification for determining therapy delivery in certain cases for slower VTs which can represent as significant challenge. Furthermore, PPG could be used to indirectly estimate respiratory rate [21]- [23], heart rate variability [24], mechanical alternans [19], [20] and other physiological markers to monitor cardiac risk and modulate ICD therapy (e.g. by preventively using antitachycardia pacing to prevent VTs).…”

Pulse Arrival Time and Pulse Interval as Accurate Markers to Detect Mechanical Alternans

“…The results of this study indicate that although PAT may not provide accurate estimates of SBP (at least without calibration), it can accurately track rapid oscillations in SBP. An important implication is that MA can be detected by analyzing beat to beat variations in the pulse interval, which can be measured non-invasively with affordable technology such as for example photoplethysmography, providing a potential surrogate for MA as an independent predictor of cardiovascular mortality without the need of invasive recordings and expensive technology 3…”

"Association between photoplethysmography pulse upslope and cardiovascular events in over 170,000 UK Biobank participants"

“…breathing rate [6] or arterial stiffness, and then using these to predict outcomes [7]. In this study, we focused on the PPG upslope because we previously found that it was closely related to significant hemodynamic changes, such as mechanical alternans [8] and life-threatening ventricular tachycardia [9]. The main strength of this study is the large sample size, over 170 thousand participants, and the long follow-up for multiple outcomes.…”