QT interval prolongation is associated with all-cause mortality (1,2). American Heart Association/American College of Cardiology (AHA/ACC) recommends considering QTc interval above 99th percentile as abnormally prolonged, to prevent Torsade de Pointes (TdP).
This is a retrospective chart review of 291 EKG’s (162 unique), from patients visiting our facility at Valley Baptist Medical Center (Harlingen) from January 2016 to March 2020. All EKG’s were read, the measured QT interval was corrected for heart rate using the Bazett formula. Simple descriptive statistics were created with all variables considered: patient age, gender, interpreting physician, report/ documentation of long QT, presence of U-wave falsely prolonging QT, and death. Correlation analysis was done, with linear mixed models to assess prolongation to account for repeated measures on some patients.
The average age of patients was 65.7 years (SD=17.2, range:18-98) and 70.3% was male gender. EKGs were reviewed by a cardiologist or ER doctor 59.99%, 40.06% respectively. 4 EKG’s (1.3%) were not reviewed by a physician. The 90th and 99th percentile QTc (milliseconds) was 517 and 588.1 respectively. U-wave was included in the measurement of QT interval 1.7% times, contributed to false reporting of QTc above the 99th percentile once. Using the 90th percentile cutoff, cardiologist documented prolonged QT (57.1%, 12/21) more often than an ER doctor (45.45%, 5/11) [p-value= 0.529]. Of the reported deaths (12/162), arrhythmia-related deaths (80%) are more likely associated with QTc above 50th percentile i.e., 475 ms than non-arrhythmia related death (14.7%) [p-value= 0.022]. QT prolongation was not documented in any death summary.
The observed trend is for cardiologists less likely to make an error than ER doctors, though not statistically significant. Based on the results of the study, this problem is likely not acted upon and may be associated with increased mortality (more likely arrhythmia-related death). Long QT duration is a common problem and these results suggest further studies needed.
1) Charlotte Gibbs, Jacob Thalamus, Doris Tove Kristoffersen, Martin Veel Svendsen, Øystein L Holla, Kristian Heldal, Kristina H Haugaa, Jan Hysing, QT prolongation predicts short-term mortality independent of comorbidity, EP Europace, Volume 21, Issue 8, August 2019, Pages 1254–1260.
2) de Bruyne MC, Hoes AW, Kors JA, Hofman A, van Bemmel JH, Grobbee DE. Prolonged QT interval predicts cardiac and all-cause mortality in the elderly. The Rotterdam Study. Eur Heart J. 1999 Feb;20(4):278-84.
Supraja Thunuguntla, Rizwan Mohammed, Charles Mild. "Disparity in Physician Recognition of QT interval duration and associated Mortality" UTRGV SOM Publications and Presentations (April, 2020).
American College of Physicians Texas Chapter