QT Interval Basics – The Premier EKG Resource for Medical Professionals

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LECTURES:
1. QT Interval
2. Long QT Syndrome
3. Short QT Syndrome
4. Full ECG Course
5. The EKG Guy Lectures

QT interval: represents time from QRS complex onset to end of T wave

QT interval = [QRS complex] + [ST segment] + [T wave]
Cardiac event: ventricular depolarization + ventricular repolarization (note: all of ventricular systole)

QT interval duration: variable (age, sex, HR, electrolytes)

In general: normal QT interval <½ preceding RR interval
Best measured in II, V5, or V6 (use maximum interval)
If TU fusion: use maximum slope-intercept method to define end of T wave (include U wave if amplitude >1 mm)
Females > males
Inversely related to heart rate (↓ QT interval with ↑ heart rate; ↑ QT interval with ↓ heart rate)

QTc interval: attempts to “correct” for QT interval variation with heart rate

Improves detection of patients at ↑ risk of arrhythmias
Bazett’s formula: QTc = 𝑄𝑇/√𝑅𝑅
Normal (varies): males <440 ms; females <460 ms; >350 ms
QTc >500 ms: ↑ risk of torsades de pointes

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DID YOU KNOW?

Dr. Anthony Kashou (The EKG Guy) is a physician resident at the Mayo Clinic in Rochester, Minnesota. He is on a mission to transform ECG education and filling the gap exists around the world. Dr. Kashou has taught and developed curriculum for medical students, including 500+ lectures and 100+ hours of adult and pediatric ECG lessons.

At the Mayo Clinic, he pursues innovative ECG research and was awarded first place for his research at the Minnesota American College of Cardiology Conference 2018. His passion for medical education and innovation led to the development of EKG.MD, which provides a convenient and accessible forum to learn the fundamentals and foundations of ECG interpretation. He has also authored dozens of peer-reviewed articles for medical journals and textbooks, along with multiple ECG books for learners at all levels.

Dr. Kashou continues to lead and teach weekly ECG sessions and weekend seminars for residents, nurses, ECG interpreting technicians, and physician assistants at the Mayo Clinic. He has been asked and is currently developing an ECG board review course for cardiology fellows. He has an online following of over 275,000 individuals and is the founder of the largest, fastest growing ECG community in the world. His clinical research focuses on developing innovative ECG algorithms that can be integrated and implemented into clinical practice.

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