From the Guidelines
Yes, in an atrial paced EKG rhythm strip, the computer calculation of QTc can be falsely prolonged. This occurs because the computer algorithm may incorrectly measure the QT interval when pacing artifacts are present, as noted in the guidelines for electrocardiographic monitoring in hospital settings 1. The pacemaker spike can distort the beginning of the QRS complex, and the repolarization pattern is often altered by paced beats, leading to T-wave changes that affect QT measurement. Additionally, the computer may have difficulty distinguishing between the pacemaker spike and the true onset of ventricular depolarization.
When evaluating QTc in paced rhythms, manual measurement by a clinician is recommended for accuracy, as emphasized in the AHA/ACC/HRS recommendations for the standardization and interpretation of the electrocardiogram 1. The clinician should measure from the pacemaker spike to the end of the T wave, then apply the appropriate heart rate correction formula. This is particularly important when making clinical decisions about medications that may prolong QT intervals or when evaluating patients for conditions like Long QT Syndrome. Remember that paced rhythms inherently have a different ventricular activation sequence compared to intrinsic conduction, which affects repolarization and the QT interval independent of any measurement errors.
Some key considerations in QT interval measurement include:
- Recognizing the onset of the QRS complex and the end of the T wave
- Determining the appropriate lead(s) in which to measure the QT interval
- Adjusting the QT interval for increases in QRS duration, gender, and rate
- Using the lead showing the longest QT interval, usually V2 or V3, and considering measurements from adjacent leads if there are significant differences
- Visually validating QT-interval prolongation reported by a computer algorithm, as automated systems may not always provide accurate measurements.
It is essential to visually validate QT-interval prolongation reported by a computer algorithm, especially in the context of atrial paced EKG rhythm strips, to ensure accurate assessment and minimize the risk of false prolongation.
From the Research
Atrial Paced EKG Rhythm Strip and QTc Calculation
- In an atrial paced EKG rhythm strip, the computer calculation of QTc can be falsely prolonged due to the abnormal ventricular activation caused by the pacemaker 2.
- The QTc interval prolongation in pacemaker-dependent patients may not represent true repolarization abnormalities and is not associated with an increased risk of fatal arrhythmia 2.
- However, it is essential to consider the potential effects of medications that can prolong ventricular repolarization in these patients 3, 4, 5.
- The study by 2 found that receiving medications with known potential to prolong QTc in ventricular pacemaker patients can be considered a safe approach, but long-term follow-up data showed that these patients are at increased risk of developing heart failure and heart failure decompensation.
Factors Affecting QTc Interval Calculation
- The QTc interval calculation can be affected by various factors, including the type of EKG lead used, the presence of bundle branch blocks, and the patient's heart rate 6, 5.
- The use of automatic measurements for QTc interval calculation can also introduce errors, particularly if the algorithm used is not validated for pacemaker-dependent patients 6.
- Manual measurement of the QTc interval can be more accurate, but it requires expertise and can be time-consuming 6.
Clinical Implications
- Clinicians should be aware of the potential limitations of QTc interval calculation in atrial paced EKG rhythm strips and consider the clinical context when interpreting the results 3, 4, 5.
- Regular monitoring of EKG and electrolytes is necessary to prevent torsades de pointes, particularly in patients with risk factors for QTc interval prolongation 3, 4, 5.