Occurrence of Digital Photoplethysmography Waveforms in Patients with Lower-Extremity Critical-Limb Ischemia

Purpose Digital photoplethysmography (PPG) has been proposed as an alternative to Doppler technology for measuring ankle pressures and ankle-brachial indices (ABIs). However, in patients with critical-limb ischemia (CLI), digital waveforms may not be detectable, which would negate digital pressure measurement and ABI calculation. In this study we evaluated the presence of digital PPG waveforms in patients with lower-extremity CLI (ABI < 0.40). Methods From January through December 2007, vascular laboratory patients who had a lower-extremity physiological study, including an ankle waveform, PPG waveform analysis of their great toe, and an ABI of =0.40, were prospectively entered into a database. ABIs and waveforms were obtained in the standard fashion. Patients with incomplete waveform data and CLI follow-up examinations were excluded from the analysis. Subjects were separated into 2 groups: those with digital PPG waveforms (group 1) and those with flatline digital waveforms (group 2). Each group was evaluated for audible posterior tibial (PT) and dorsalis pedis (DP) Doppler signals. Results A total of 160 extremities (140 patients) with CLI were identified during the study period; 45 patients and 53 extremities were excluded. There were 41% (44/107) group 1 and 59% (63/107) group 2 extremities. In group 2 extremities, 67% (42/63) had flatline ankle waveforms, 40% (25/63) had absent PT and DP Doppler signals, and 60% (38/63) had one or more audible PT or DP signals. Conclusions Less than one half of the extremities with CLI had digital PPG waveforms. However, 60% of those limbs with flatline digital waveforms had one or more audible pedal Doppler signal, requiring a more detailed noninvasive evaluation with a Doppler ABI endpoint. Automated digital PPG devices may be inadequate for ABI evaluation of patients with CLI.