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Kate Martin CNE April 2009. Beyond Arrhythmias ST & QT Segment Monitoring. Monitoring Practice International Guidelines. Chest pain that prompts a visit to the emergency department, Post cardiac surgery Patients at risk for postoperative cardiac complications after non-cardiac surgery.
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Kate Martin CNE April 2009 Beyond ArrhythmiasST & QT Segment Monitoring
Monitoring Practice International Guidelines • Chest pain that prompts a visit to the emergency department, • Post cardiac surgery • Patients at risk for postoperative cardiac complications after non-cardiac surgery.
Angina • Although chest pain is a real-time indicator of ischemia, up to 80% to 90% of ischemia is "silent" or "concealed”
Diagnostic Testing • 12-lead (ECG), measurement of serum markers of injury, and cardiac catheterization, provide only a static "snapshot" of the dynamic process of ongoing ischemia.
Diagnostic Relevance • Although the accuracy of continuous ST monitoring has improved with technology the diagnostic relevance of ST changes remains dependant on several factors • ST segment changes may be an indication for a 12 lead EKG
Establishing ST Monitoring • On Admission • Ensure skin is properly prepped • Ensure leads are in proper position • Record a baseline ST strip
Choosing Your Leads • Just like with a 12 lead EKG, lead placement should be accurate. • The Phillips monitor can monitor ST segments on up to six leads on a telemetry unit and all 12 leads on a hardwire monitor • Choose the leads which monitor the area of the heart most at risk
Anterior Leads Leads I & V1-4 • LAD • LM
Lateral Leads • Leads avR, avL, & V5-6 • Circumflex
Inferior Leads Leads II, III, & avF • RCA • Circumflex
Posterior Leads Leads I & V1-4 • Mirror Image • Posterior Artery
The J Point The ST segment begins at the point where the QRS ends (J-point). Diagnostic criteria of ST segment changes have been defined to be measured at 60 ms after the J-point (1.5 small squares/.06sec)
Metabolic Abnormalities Producing ST Changes Hypokalemia • ST depression Hyperkalemia • Peaked T waves Hypermagnesemia • ST depression Hyperthyroidism • ST elevation with T wave inversion in inferior leads
Medications Producing ST Changes • Digitalis • ST depression • Shortened QT interval • Amiodarone • Lengthened QT interval
Other Factors Producing ST Changes • Pericarditis • ST elevation • Hypothermia • ST depression • Pulmonary Infarction • Depressed ST segments and inverted T waves in V 1 – 3
Effect of Arrhythmias • Bundle Branch Blocks • ST segment shifts • Paced Rhythm • ST segments non diagnostic
Response to change in ST Segment • Is patient experiencing angina symptoms? • Follow ACS protocol • Is patient hemodynamically unstable • Stabilize
Pharmacology and the QT Interval A number of drugs are known to prolong the QT interval and include all of the antiarrhythmics
Importance of QT monitoring • QT prolongation can indicate a risk of severe arrhythmias, torsades de pointes, and sudden cardiac death.
What is a QTc? • The QT has an inverse relationship to HR. • QT = QTc at a HR of 60 bpm only • Heart rate corrected QT interval is abbreviated as QTc • Normal QTc is < 460 ms
QT Measurement Limitations “Cannot Analyze QT” INOP message: Flat T, Atrial Fib/Flutter Prominent U Waves Highly variable QRS-T waveforms over 10 minutes duration Clinical Verification: Widened QRS (Paced rhythm, bigeminal rhythm) High heart rates > 150 due to P waves being too close to T waves.
Sources Leeper, B. Continuous ST-segment monitoring. AACN Clinical Issues 2003. 14(2): 145-154. American Association Of Critical Care Nurses St Segment Monitoring Practice Alert Critical Care Nurse. 2005; Clinical Usefulness of the EASI 12-Lead Continuous Electrocardiographic Monitoring System; Mary Jahrsdoerfer, RN, MHA.,Karen Giuliano, RN, PhD., Dean Stephens, RN, MS