Slide 1: Chief concern. Syncope. Brought to ED by EMS. History of present illness. 60-year-old female with a history of asthma with frequent inhaled beta agonist use. EKG. Strips obtained by EMS en route. What’s the rhythm?
Slide 2: Polymorphic ventricular tachycardia. Also known as torsades de pointes or twist of the points. She spontaneously reverts to normal sinus rhythm in the ED. What questions will you ask?
Slide 3: Past medical history. Syncope. Seizures. Hearing loss. Hearing loss is present in autosomal recessive LQTS (also known as Jervell and Lange-Nielsen syndrome). Detailed family history. Sudden cardiac death. Unexplained drowning or motor vehicle accident. Medication history. Some common culprits – antiarrhythmics, antimicrobials, bronchodilators, antipsychotics, methadone.
Slide 4: Back in sinus. What’s the QTc? QT, uncorrected, is approximately 640 ms. But, don’t forget the bradycardia and wide QRS! Corrected for heart rate (which is 48 bpm), QTc equals QT divided by RR raised to the 1/3 exponent. This is equal to 594 ms. Based on Fridericia formula. Adjusted for wide QRS, QTcc equals 574 ms. QTcc equals QTc minus the difference between the patient’s QRS and a normal QRS.
Slide 5: Who should get genetic testing? Schwartz score can be calculated. Table showing Schwartz score values based on findings. EKG findings. QTc duration (ms) (Bazett formula) greater than or equal to 480 ms is 3 points. QTc duration equal to 460 to 479 ms is 2 points. QTc duration equal to 450 to 459 ms (for males) is 1 point. QTc greater than or equal to 480 ms during 4th minute of recovery from exercise stress test is 1 point. Torsades de pointes is 2 points. T wave alternans is 1 point. Notched T wave in 3 leads is 1 point. Low heart rate for age is 0.5 points. Clinical history findings. Syncope with stress is 2 points. Syncope without distress is 1 point. Congenital deafness is 0.5 points. Family history findings. Family member or members with definite LQTS is 1 point. Unexplained sudden cardiac death in immediate family member less than 30 years old is 0.5 points. If a patient’s cumulative score adds up to greater than or equal to 3.5 points, there is an 80% likelihood of positive testing for congenital LQTS.
Slide 6: LQTS treatment. Arrhythmia risk proportional to QTc. Greater than or equal to 50% probability of first cardiac event before 40-years-old if QTc is greater than or equal to 500. Acute LQTS treatment. Undifferentiated prolonged QTc. Isoproterenol. Non-selective beta agonist. AV conduction plus increased heart rate equals decreased QTc. Don’t forget the magnesium (Mg 2+) and defibrillation (when indicated). Long-term therapy for LQTS. Recommend caution with exercise and sports. If prior exercise-induced syncope, avoid swimming and diving. Long-acting beta blockers, such as nadolol, for symptoms or QTc greater than 470 ms. Up-titrate dose as tolerated. Mechanism is prevent norepinephrine release to inhibit adrenergic surges. ICD referral for prior cardiac arrest or recurrent events. Patients can look up new medications at www.crediblemeds.org.
- Patel P, Borovskiy Y, Deo R. QTcc, a novel method for correcting QT interval for QRS duration, predicts all-cause mortality. J am Coll Cardiol. 2015 Mar, 65 (10 Supplement) A336. Link.
- Vandenberk B, Vandael E, Robyns T, et al. Which QT Correction Formulae to Use for QT Monitoring? [published correction appears in J Am Heart Assoc. 2018 Aug 21;7(16):e004252]. J Am Heart Assoc. 2016;5(6):e003264. Published 2016 Jun 17. PMID 27317349.
- Schwartz PJ, Crotti L. QTc behavior during exercise and genetic testing for the long-QT syndrome. Circulation. 2011;124(20):2181-2184. PMID 22083145.
- Waddell-Smith KE, Skinner JR; members of the CSANZ Genetics Council Writing Group. Update on the Diagnosis and Management of Familial Long QT Syndrome. Heart Lung Circ. 2016;25(8):769-776. PMID 27262388.
Tags: 12 Lead, cardiology, EKG, long QTc, LQTS, prolonged QT, QTc, Schwartz Score, torsades de pointes