Scenario: The image below is a bedside monitor view from a 40-year-old female orthopedic patient admitted to the preoperative unit. She has no cardiac history and is spontaneously breathing and resting quietly. Of note, the nurse increased the gain of the electrocardiograph (ECG) signal (2x) to improve his visualization of the ECG waveforms and notices the varying QRS wave amplitude in V1 and he wonders if this variation is normal.

The cardiac rhythm is sinus tachycardia at 110/min. During inspiration, as seen in the respiratory waveform (bottom), the QRS amplitude is diminished in lead V1.

QRS amplitude variation during respiration are almost always present, yet most often they are so small they are difficult to detect. Because the heart is not fixed in the chest cavity, the precordial chest lead V1 becomes more distant from the heart during...

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