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(a) Progressive heart block in iNOS+/αMtTA+ mice. Shown are five nonconsecutive 10-second ECG recordings (lead II) from conscious iNOS+/αMtTA+ animals. P-R intervals are shown above each complex. Progressive P-R elongation with a dropped beat is consistent with Wenkebach periodicity. (b) Cardiac arrest in an iNOS+/αMtTA+ mouse. (c) Normal baseline ECG recordings from a littermate control mouse.
