Beat-to-beat corrected QT analysis detects corrected QT prolongation in 50 consecutive telemetry-monitored patients.

BACKGROUND: The American Heart Association/American College of Cardiology Foundation recommends monitoring for corrected QT (QTc) prolongation. The incidence of QTc prolongation in the general public is unknown. Episodic measurements may miss patients at risk.

OBJECTIVE: The purpose of this study was to determine the incidence of QTc prolongation in hospitalized telemetry patients when beat-to-beat monitoring, confirmed by manual calculation, was used for detection.

METHODS: After institutional review board approval was obtained, waveforms of telemetry-monitored patients were analyzed consecutively until 50 patients with prolonged QTc were identified (QTc >470 milliseconds in men and >480 milliseconds in women). Prolongation was confirmed by manual calculation. Incidence was calculated. Clinical risk factors and the outcomes of torsades de pointe or sudden death were explored.

RESULTS: Telemetry waveforms were evaluated for 192 444 minutes (3207.4 hours) of recordings, yielding 8,076,653 QTc measurements. In 50 consecutive patients (24 [48%] men), 100% had verified episode(s) of QTc prolongation. Home medications that could result in QTc prolongation were identified in 9 patients (18%). Hospital medications with risk of QTc prolongation were administered to 31 patients (62%). Sixteen patients (32%) were not on a QTc-prolonging medication. Corrected QT prolongation risk factors in the history were found in 2 patients (4%) and hypomagnesemia or hypokalemia was seen in 6 patients (12%). Twelve-lead electrocardiogram detected prolonged QTc in 13 of 45 patients (26%). Prolongation of QTc was detected by standard of care manual analysis in 4 patients (8%). No patient experienced torsades de pointe or sudden death.

CONCLUSION: With beat-to-beat analysis, QTc prolongation was detected in 100% of 50 consecutive patients where standard of care (nursing manual analysis or 12-lead electrocardiogram) would have detected 28%. Hospital medications were more likely to contribute to QTc prolongation than home medications.

IMPLICATIONS FOR PRACTICE: More specific definitions for determining proarrhythmic risk are needed as automated technology improves the capture rate of QTc prolongation events.