We present the case of an 18-year-old man, with a history of subarachnoid hemorrhage, who is found to have the spiked helmet sign on electrocardiogram during a hospital admission for severe respiratory infection. The spiked helmet sign is a poorly understood electrocardiographic finding that mimics other electrocardiographic pathologies, and is associated with critical illness and high mortality. (Level of Difficulty: Beginner.)

Spectral Doppler and plethysmographic waveforms vary significantly in the presence of circulatory assist devices. Understanding the effect these devices have on the waveforms and flow characteristics is necessary for the appropriate interpretation of duplex ultrasound and other noninvasive vascular studies. We review the different arterial waveforms that can be seen with circulatory assist devices.