Mr. M., a 62 year old with a history of stable angina pectoris, is admitted to a telemetry unit because of recent episodes of acute shortness of breath and near syncope. Mr. M’s cardiologist thinks the symptoms may be due to an arrhythmia or episodes of acute myocardial ischemia. The cardiologist explains that Mr. M. had a cardiac catheterization two weeks before which showed stenotic lesions in the left anterior descending (LAD) coronary artery which were too diffuse to treat with coronary angioplasty or stenting. The patient was offered coronary artery bypass surgery and was considering this option when his symptoms developed.

Nursing Implications: The goal of monitoring Mr. M. is to document any arrhythmias or acute myocardial ischemia episodes he might have and to correlate these EKG changes with his symptoms (Drew, 1991).

The best EKG lead for monitoring arrhythmias is lead V₁ because if Mr. M.’s symptoms are due to the development of a wide QRS complex tachycardia, there are criteria in the QRS configuration in lead V₁ that can be used to distinguish ventricular tachycardia from supraventricular tachycardia with aberrant conduction (Wellens, Frits & Lie, 1978; Drew & Scheinman, 1995).

The best EKG lead for monitoring for acute ischemia related to the LAD coronary artery is lead V₃ (Bush et. al., 1991; Drew & Tisdale, 1991; Mizutani et. al., 1990). Therefore, to detect both arrhythmias and acute ischemia, the ideal lead combination for Mr. M. would be V₁ and V₃. Unfortunately, the telemetry system in Mr. M.’s unit allows for monitoring only one precordial lead because there is only one chest lead (Figure 1).

Therefore, the nurse must chose between two bad options: (a) monitoring for arrhythmias while ignoring ischemia (V₁), or (b) monitoring for ischemia while ignoring arrhythmias (V₃). The nurse selects lead V₁.

Figure 1. Current cardiac monitors typically have patient cables with five lead wires which allows for monitoring any of the six limb leads (I, II, III, aVR, aVL, aVF), but only one precordial lead. While the chest (C) electrode can be placed in any of six precordial sites for monitoring (V₁ is illustrated here), it is impossible to monitor two precordial leads at the same time.

At 6:00 am, Mr. M. has an 11-beat burst of wide QRS complex tachycardia (Figure 2) which is diagnosed as supraventricular tachycardia (SVT) with an aberrant ventricular conduction because of the QRS configuration in lead V₁ (Figure 3). Mr. M. is unaware of any symptoms at this time and, therefore, the arrhythmia is not considered the cause of his symptoms. Moreover, nonsustained SVT is not life-threatening and doesn’t warrant immediate treatment.

Figure 2. Onset of wide QRS complex tachycardia recorded in lead V₁ shows a triphasic rsR' pattern, which favors the diagnosis of supraventricular tachycardia with aberrant ventricular conduction.

Figure 3. During a wide QRS complex tachycardia, an upright complex in V₁ is likely to be ventricular in origin if the configuration is a taller left peak or biphasic RS or QR pattern. A triphasic pattern is likely to be supraventricular tachycardia with right bundle branch block or aberrant ventricular conduction.

At 7:15 am, Mr. M.’s monitor alarm sounds and the rhythm strip shows a sustained wide QRS complex tachycardia at a rate of 188 beats per minute (Figure 4). Mr. M. is sitting in the bedside chair complaining of shortness of breath and "a feeling that I’m going to pass out." His blood pressure is palpable at 80 systolic. While Mr. M. does not lose consciousness, it is clear that the arrhythmia is ventricular tachycardia (VT) because of the QRS configuration in lead V₁. Moreover, it is imperative to immediately terminate the VT before it degenerates into ventricular fibrillation, causing a cardiac arrest. Mr. M. is assisted back to bed and a bolus of Lidocaine is successful in terminating the tachycardia.

Figure 4. Wide QRS complex tachycardia shows an upright QRS complex with a "taller left peak" pattern in lead V, which indicates a diagnosis of VT.

Nursing Implications: Monitoring lead V₁ proves valuable in this patient because it provides EKG criteria to make the important distinction between SVT and VT. Without these criteria, the nurse may have thought the sustained tachycardia (Figure 4) was SVT because the patient did not lose consciousness. A drug commonly used to terminate SVT is verapamil, a calcium channel blocker which is not efficacious in treating VT. Moreover, verapamil is contraindicated for patients with VT because it has negative inotropic effects and can cause sudden hemodynamic deterioration and cardiac arrest in patients with VT (Stewart, Bardy & Greene, 1986).

An EKG technician hands the nurse two standard 12-lead EKGs that were recorded at 7:03 am and 7:08 am, just prior to the sustained VT (Figures 5 & 6). The reason two EKGs were recorded was that the technician was training a new employee so the 1^st EKG was demonstrated by the technician and the 2^nd EKG was recorded by the new employee.

Figure 5. Standard 12-lead EKG showing Mr. M's normal ST segments recorded prior to an ischemic event.

The second EKG shows an ischemic event with striking ST segment elevation in leads V₃ – V₅ (Figure 6). Of interest, the ST segment in lead V₁ does not change during this time, which explains why the ST monitor alarm was not triggered during this ischemic episode. Moreover, the patient did not experience chest pain or other symptoms during this time, so his nurse was unaware of this ischemic event.

Figure 6. Standard 12-lead EKG recorded minutes later showing ST segment elevation, which is best visualized in leads V₃ - V₅. Mr. M's cardiac monitoring lead V₁ fails to detect this ischemic event. Another routinely used monitoring lead (Lead II) also fails to detect acute ischemia in this patient.

Mr. M.’s cardiologist is grateful for the inadvertent 12-lead EKG documentation of an ischemic event prior to the development of VT because it indicates that the trigger for malignant ventricular arrhythmias in Mr. M. is acute ischemia. Thus, the need for coronary bypass surgery is a high priority and surgery is scheduled for the next day. In addition, intravenous (IV) nitroglycerine is initiated with an order to "titrate up if further ischemic episodes occur."

Nursing Implications: The nurse realizes that the EKG documentation of this ischemic episode was a lucky accident. It would have been missed with routine cardiac monitoring of Leads V₁ or II. The dilemma the nurse faces now is how best to monitor Mr. M. for both arrhythmias and ischemia over the next 24 hours prior to surgery. Because Mr. M. has silent ischemia, the nurse cannot rely on chest pain symptoms to detect acute ischemic episodes. Moreover, without chest pain symptoms, the nurse will not be cued as to when to record a "stat" 12-lead EKG with an EKG cart to document further ischemic episodes. If monitoring is continued with Lead V₁, the titration of IV nitroglycerine will be based on guesswork rather than valid EKG data. However, if the monitoring lead is changed to Lead V₃, future episodes of wide QRS complex tachycardia will not contain the valuable QRS criteria to make the important distinction between VT and SVT. What is needed is a telemetry system that provides for monitoring of two precordial leads (e.g.: V1 and V3) so that both goals of monitoring (arrhythmias and ischemia) can be achieved in this patient.

Arrhythmia Monitoring:

• For diagnoses of bundle branch blocks, right versus left ventricular pacing rhythms, ventricular versus supraventricular tachycardia with aberrancy:

Lead V₁

• For diagnosis of atrial flutter:

Lead II, III, or aVF

Ischemia Monitoring: (Drew et. al., 1999)

• Acute anterior myocardial infarction (MI) or left anterior descending (LAD) artery interventions:

Lead V₂ or V₃ (ST elevation)

• Acute inferior MI or right coronary artery (RCA) interventions:

Lead II, III, or aVF(ST elevation)

Posterior infarction or left circumflex (LCX) artery interventions:

Lead V₂ or V₃(reciprocal ST depression)

• Ischemia related to increased myocardial O₂ demand (e.g., early post operative period, angina related to increased heart rate or development of a tachycardia):

Lead V₅(ST depression)

Bush, H.S., Ferguson, J.J., Angelini, P. and Willerson, J.T. (1991). Twelve-lead electrocardiographic evaluation of ischemia during percutaneous transluminal coronary angioplasty and its correlation with acute reocclusion. American Heart Journal, 121(6), 1591-1599.

Drew B.J. (1991). Bedside electrocardiographic monitoring: State of the art for the 1990s. American Journal of Critical Care, 20(6), 610-623.

Drew, B.J. and Tisdale, L.A, (1991). ST Segment monitoring for coronary artery reocclusion following thrombolytic therapy and coronary angioplasty: identification of optimal bedside monitoring leads. American Journal of Critical Care, 2(4), 280-292.

Drew, B.J. and Scheinman, M.M. (1995). ECG criteria to distinguish between aberrantly conducted supraventricular tachycardia and ventricular tachycardia: Practical aspects for the immediate care setting. PACE, 18, 2194-2208.

Drew, B.J., Krucoff, M.W. and the ST-Segment Monitoring Practice Guideline International Working Group (1999). Multilead ST-segment monitoring in patients with acute coronary syndromes: A consensus statement for healthcare professionals. American Journal of Critical Care, 8, 372-388.

Mizutani, M., Freedman, S.B., Barns, E., Ogasawara, S., Bailey, B.P. and Beinstein, L. (1990). ST Monitoring for myocardial Ischemia during and after coronary angioplasty. American Journal of Cardiology, 66(4), 389-393.

Stewart, R.B., Bardy, G.H. and Greene, L.H.(1986). Wide complex tachycardia: Misdiagnosis and outcomes after emergent therapy. Annals of Internal Medicine, 104, 766-771.

Wellens, J.J., Frits, W.H. and Lie, K.I. (1978). The value of the electrocardiogram in the differential diagnosis of a tachycardia with a widened QRS complex. The American Journal of Medicine, 64, 27-33.

"This document, prepared by Barbara J. Drew, RN, PhD, FAAN, is provided by GE Medical Systems, Inc., as an educational supplement on the value of monitoring a second precordial lead for patients in the telemetry unit. GE Medical Systems does not make any claims, direct or indirect, linking any of their products to the clinical conditions described in this document or their management."