According to Medscape, an online medical information site: “a heart rate of more than 160 beats per minute in infants and a respiratory rate of more than 60 per minute are associated with an increased mortality risk and often signal the development of septic shock.”
The May EM:RAP Pediatric Pearls podcast by Dr. Ilene Claudius, Dr. Sol Behar, Dr. James Salway and Dr. Liza Kearl offers prudent advice on differentiating respiratory from cardiac sources of pediatric tachycardia. Or pull up the PDF and have a fast read of the bullet points to keep your rate in check and your knowledge bounding.
Who Knew? Willem Einthoven, working in Leiden, the Netherlands, used the string galvanometer (the first practical electrocardiograph) he invented in 1901 which was more sensitive than previous 1870s inventions. He assigned the letters P, Q, R, S, and T to the waveform deflections. (Wikipedia)