Slide 1: What’s the EKG finding? 65yo female with history of CKD. Chief complaint: vomiting and weakness.
Slide 2: Prolonged QTc Interval! The longer the QTc interval, the higher the risk of torsades de pointes (most pronounced when QTc >500ms). Our patient’s QTc is 555mms! (Think back to our March 8th, 2018 post!)
Slide 3: Bazett Formula: QTc = (QT/sqrt(RR)). Ëyeball” Test: If the QT is less than 1/2 the RR interval it is likely normal. A “normal” automated EKG report should never replace clinical acumen. What electrolyte abnormality might this patient be experiencing?
Slide 4: Hypocalcemia common causes: renal disease (think of our patient), medications (inhibit bone resorption), electrolyte disturbances (hypoMg, hypoPhos), sepsis, vitamin D deficiency, blood transfusions (citrate binds calcium)
Slide 5: Medical management of hypocalcemia: Prolonged QTc with or without symptoms due to hypoCa is an indication for IV calcium repletion! 1. Triage: consider transferring to a telemetry unit if acute change or high risk of further QTc prolongation. 2. Replete: start with IV calcium gluconate & monitor frequently (q4-6 hours), also replete Mg and K. 3. Treat: address the underlying cause (also consider other causes of QTc prolongation – Mg, meds, drugs, etc). Medications are more likely than hypocalcemia to cause polymorphic VT.
Slide 6: Cardiac action potentials. Low Ca primarily affects QT by prolonging phase 2 of the cardiac cycle, and therefore the effective refractory period which is reflected in the length of the ST segment of the EKG – ST prolongs, T-waves unchanged
- Bazett HC. An analysis of the time-relations of electrocardiograms. Heart 1920;7:353-70.