Monday, June 23, 2014

ECG Blog #93 (Basic Concepts-6) – Systematic Approach


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     This is my 6th installment of Basic ECG Concepts. Rather than specific cases — the goal of these Basic ECG Concepts is concise review of some less advanced topics that comprise the fundamentals of ECG interpretation. This material is excerpted with modification from my new introductory book to ECG Interpretation = “A 1st Book on ECGs-2014” and/or the expanded 1st-ECG-Book-ePub version (which is out in kindle-nook-kobo-ibooks). Your feedback on this series is WELCOME!
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NOTE: To enhance relevance — some advanced points have been added illustrating clinical application (with this more advanced material excerpted from our ECG-2014-ePub). In this way — We hope this post is of interest and value to ECG interpreters of any level.

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LINKS to Previous Basic ECG Concepts:
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     Regardless of the experience level of the interpreter — ECG interpretation should be systematic. The reason for this is simple — Findings will be missed unless the interpreter routinely follows an organized sequential Systematic Approach.
  • There are many valid systems for ECG interpretation. It matters not if the system you follow is the one we recommend. What counts is only that your system contains all essential components — and, that you regularly follow it with each and every ECG you interpret. Only in this way will you avoid overlooking potentially important findings.
  • ECGs can not be interpreted in a vacuum. One needs (at the very least) to know: i) The age of the patient; and ii) The reason why the ECG was ordered. Historical information may be brief. Examples include — “new-onset chest pain” — “heart failure exacerbation, but no chest pain” — “asymptomatic pre-employment physical examination”. The reason this minimal amount of clinical information is needed — is that an identical ECG pattern may be interpreted very differently depending on whether symptoms suggest an acute event versus a less worrisome scenario.

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     There should be 2 Steps to interpretation of any ECG (Figure-1):
  • Step 1 — is the initial overview of the entire tracing, which is known as Descriptive Analysis.
  • Step 2 — is formulation of the Clinical Impression.
     
The 1st STEP in the interpretation process (= Descriptive Analysis) — is easy!  The only thing one does is describe the findings that are seen on the tracing. We will momentarily present a Checklist structure to facilitate this task (below in Figure-2).
  • STEP 2 is the interesting and most clinically useful step — in which you interpret the ECG findings noted in Step 1 in light of the clinical situation. For Example — the identical shape and amount of ST segment elevation may be interpreted as the benign normal variant known as early repolarization IF seen in an asymptomatic young adult — but could be cause for concern (and possibly indicative of an early myocardial infarction) if seen in an older adult who presents with new-onset chest pain. Clinical correlation (as occurs in Step 2) — is an essential part of the interpretation process.
  • CAVEAT: One of the most common mistakes made by new and experienced interpreters alike — is failure to keep these 2 STEPS in the interpretation process that are shown in Figure-1 separate in your mind. Without doing so — there is far too much temptation to jump to conclusions from seemingly obvious findings that immediately catch your eye before you have systematically reviewed the entire tracing.

Figure-1: The process of ECG interpretation consists of 2 separate Steps. The KEY is not to begin Step 2 until you have completed your Descriptive Analysis of the entire tracing. Failure to follow this sequence will result in overlooking potentially important findings.


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The Systematic Approach: A Checklist for Descriptive Analysis
     The KEY to interpretation of any ECG is to utilize a Systematic Approach. The approach we suggest for interpreting each 12-lead ECG you encounter entails sequential systematic assessment of the 6 Parameters that we list below and summarize in Figure-2. The 6 Parameters to routinely assess during the 1st STEP of Descriptive Analysis are the following:
  • Rate.
  • Rhythm.
  • Intervals (PR/QRS/QT intervals).
  • Axis.
  • Hypertrophy (= Chamber Enlargement).
  • Ischemia/Infarction (Q-R-S-T Changes).
KEY Point: The purpose of having (and regularly using) a sequential systematic approach as a Checklist is simple: It prevents you from overlooking potentially important findings by reminding you what to look for.
  • The “good news” — is that there is NO need to memorize the details in our Systematic Approach. We reproduce it all later on in this Blog post in Figure-5 and Figure-6 — and, we constantly reinforce clinical application of this system in all of the posts on our ECG Blog.
  • Using the “system” does not slow you down. Admittedly — it may take longer initially to interpret tracings (as you are getting used to the system). That said, with surprisingly little practice — you’ll find routine use of a Systematic Approach on each and every tracing you interpret will: i) Speed Up your interpretations (because you will be organized — and therefore able to go through the checklist much faster); and ii) Increase Accuracy of your interpretations (because you will instantly become far less likely to overlook important findings).
  • NOTE: It does not matter if you decide to use our System (presented in Figure-2) — or some other system you prefer — or even a composite of multiple systems. What counts — is that YOU develop a sequential system for ECG Interpretation that YOU regularly use in the interpretation of each and every tracing that you encounter.

Figure-2: The Systematic Approach to ECG Interpretation. We integrate the 2 separate Steps listed in Figure-1 with checklist review of the 6 Parameters to routinely (systematically) assess during the Descriptive Analysis 1st STEP in interpretation. It is only after you have noted the ECG findings of Rate – Rhythm – Intervals – Axis – Hypertrophy and QRST Changes — that these ECG findings from Step 1 should be interpreted in light of the clinical situation (= STEP 2).


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What Happens When You Don’t Use a System?
     Consider the 12-lead ECG in Figure-3. The rhythm is sinus — as indicated by the upright P waves with fixed PR interval in lead II (red arrow).
  • Do the QS complexes in leads V1,V2,V3 (small black arrows) — indicate antero-septal infarction?
  • Does ST elevation in these same anterior leads — indicate that anteroseptal infarction may be acute?
  • Does ST-T wave depression in lead V6 (within the blue circle) and to a lesser extent in leads I, aVL and V5 — reflect ischemia or a reciprocal change?
  • Do Q waves in leads III and aVF (within the green rectangles) — indicate old inferior infarction?

Figure-3: 12-lead ECG showing sinus rhythm (red arrow in lead II) — and a number of ECG findings. These include: i) QS complexes in leads V1,V2,V3 (small black arrows); ii) J-point ST elevation in leads V1,V2 (above the red dotted baseline in these leads); iii) ST-T wave depression in lateral leads (especially in lead V6 — within the blue circle); and iv) Q waves in leads III and aVF (within the green rectangles). What is the clinical significance of these ECG changes?


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HINT: We intentionally chose the ECG in Figure-3 to illustrate the importance of using a sequential systematic approach. We admit that we deceptively labeled this ECG — in our best attempt to distract you to answer the questions we posed before performing systematic analysis.
  • Did you fall into the “trap”?


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ANSWERS and Interpretation of Figure-3: As should be done with every ECG you encounter — this tracing should be interpreted systematically by a sequential approach. We follow the 6-Parameter Checklist provided in Figure-2.
  • KEY Point: The ECG in Figure-3 illustrates why we place assessment of Intervals at an early point in our systematic approach. Criteria for Axis, Chamber Enlargement and Ischemia/Infarction all change when the QRS complex is widened by bundle branch block or IVCD (IntraVentricular Conduction Defect). We therefore proceed as follows:
  • Rate & Rhythm: The rhythm is regular at a rate just over 100/minute (the R-R interval is just under 3 large boxes in duration). The mechanism is sinus — as determined by the presence of an upright P wave in lead II (red arrow) with a constant PR interval.
  • Intervals: The PR interval is normal (not more than 1 large box in duration). However — the QRS complex is wide (clearly more than half a large box in duration). QRS morphology is consistent with complete LBBB (Left Bundle Branch Block) — in that there is a monophasic R wave in leads I and V6 and a predominantly negative QRS in lead V1.
COMMENT: The point to emphasize about our interpretation is that the patient has complete LBBB. Recognition of this conduction defect at an early point in the process (immediately after determining the Rate & Rhythm) — clues us in to how to assess the remarkable ECG findings that we highlighted above:
  • QS complexes in anterior leads — are common and expected with complete LBBB.
  • Secondary ST-T wave changes with this conduction defect are often oppositely directed to the major QRS deflection (especially in the 3 key leads = leads I,V1,V6). Therefore — the anterior ST elevation we see in V1,V2 and the ST-T depression we see in lateral leads are all expected findings with LBBB.
  • LBBB alters the direction of septal depolarization. Since the interventricular septum is the very first part of the ventricles to depolarize — this alteration in direction of septal activation affects Q wave formation when there is LBBB (since Q waves are the very first part of the QRS complex). Therefore — No conclusions can be drawn regarding possible prior inferior infarction from the Q waves we see in leads III and aVF of this tracing.
  • Exceptions exist when old and/or new infarction can be diagnosed despite the presence of LBBB. This is a more advanced topic. (See Section 05.24 in this 31-page pdf excerpted from our ECG-2014-ePub). None of those exceptions appear to be present in this case. All that can be said about this tracing is, “Sinus tachycardia; complete LBBB; most probably no acute changes — Strongly suggest clinical correlation”.
  • BOTTOM Line: Failure to use a Sequential Systematic Approach that assesses Intervals at an early point in the process for the ECG in Figure-3 — is likely to lead to a misunderstanding of the ECG findings and to misdiagnosis of this tracing.

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Our ECG “Crib Sheet”: Review of the Systematic Approach
     What then are the specific components of our Systematic Approach? Figure-4 and Figure-5 reproduce these components in our ECG Crib Sheet (which is excerpted from — A 1st Book on ECGs-2014).
  • We list key elements for each of the 6 Parameters in these next 2 Figures. More detail is (and/or will be) available in previous and in future Basic ECG Concept posts.
  • For More Advanced Interpreters: — We would ADD to Figure-5 assessment for left and right atrial abnormality (LAA and RAA) — as well as for RVH (Right Ventricular Hypertrophy) — to our comments for LVH/Chamber Enlargement. Specific criteria for RAA/LAA are covered in ECG Blog 75 — and, for RVH in ECG Blog 77.
  • KEY Point: With the exception of expanding Chamber Enlargement assessment to encompass RAA/LAA/RVH criteria — the checklist components for the ECG Crib Sheet in Figure-4 and Figure-5 are virtually the SAME for what we recommend for beginning — intermediate — and advanced ECG interpreters.

Figure-4: Part I of our ECG Crib Sheet — which includes assessment of the first 4 Parameters (Rate-Rhythm-Intervals-Axis). Remember that IF the QRS complex is wide — that the next step should be to determine WHY the QRS is wide (ie, ventricular rhythm vs bundle branch block, IVCD, WPW, or some other cause).


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FIGURE-4: The First 2 Parameters: Rate & Rhythm
    The first 2 parameters in the Descriptive Analysis part of our Systematic Approach are Rate and Rhythm. Look first at a long-lead rhythm strip IF there is one. If not — Look at Lead II:
  • Memory Aid: “Watch your Ps & Qs and the 3 Rs!” Once established that the patient is hemodynamically stable — the 5 essential parameters to assess in evaluation of any cardiac arrhythmia are readily recalled by use of this phrase.
NOTE: It does not matter in what sequence you assess the Ps, Qs & 3Rs — as long as you always assess them all. We often vary the sequence in which we address these 5 parameters — depending on whether atrial activity, QRS width or rhythm regularity are easy or more subtle to assess in the rhythm we are looking at. PEARL: By remembering to “Watch Ps, Qs and the 3Rs” — we have an easy way to ensure that we don’t overlook any of these 5 essential elements. We ask ourself the following questions:
  • Are there P waves? If so — Is the P upright in lead II?
  • Is the QRS complex wide or narrow?
  • What is the Rate?
  • Is the rhythm Regular?
  • If P waves are present — Are P waves Related to the QRS?
KEY Concept: In “real life” — Be sure to assess the patient first before getting “lost” in the details of the ECG. It should take no more than a few seconds — to determine IF the patient is hemodynamically “stable” (ie, alert and tolerating whatever the rhythm may be with adequate blood pressure and vital organ perfusion).
  • For example, IF the patient is “unstable” in a fast rhythm — then immediate treatment (ie, cardioversion) may be needed before you are able to become certain of the specific rhythm diagnosis. It is common in acute care to be less than 100% certain of the rhythm diagnosis at the time that you need to begin treating the patient.
  • Once you ensure that the patient is stable — Proceed with the Ps, Qs & 3Rs in the hope of determining a specific rhythm diagnosis.
NOTE: For those wanting more regarding the diagnostic process for assessing tachycardias in acute patients — We offer the following pdf downloads from ACLS-2013-ePub: Section 14.0 for regular SVTs — Sections 08.0,09.0 for regular WCTs — and ECG Blog #36 for irregular WCT rhythms.


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FIGURE-4: Parameter #3 = Intervals (PR – QRS – QT )
     There are 3 Intervals to routinely assess (discussed in detail in Basic ECG Concepts #2). As a memory aid — Remember the numbers “1” and “2” to recall the upper normal limits of the PR/QRS/QT intervals:
  • The PR Interval — should not be more than 1 large box in duration.
  • The QRS Complex — should not be more than 1/2 large box in duration.
  • The QT Interval — should not be more than 1/2 the R-R interval.
Clinical NOTES Regarding Intervals: Remember the following:
  • IF the PR interval is long (more than 1 large box) with Sinus Rhythm — then 1st-degree AV Block is present.
  • IF the QRS is wide — We need to determine WHY it is wide (usually either BBB/IVCD or a ventricular rhythm — occasionally due to WPW, hyperkalemia, or other metabolic disorder/drug overdose).
  • IF the QT is long — Think “Drugs/Lytes/CNS” as the cause (See Section 06.0 in ECG-2014-ePub for more detailed discussion). Be aware that it is more difficult to assess the QT interval if the rate is fast (over 100/minute) or if the QRS is wide (since BBB often prolongs the QT interval).

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FIGURE-4: Parameter #4 = AXIS Determination
The easiest way to classify Axis is the Quadrant Approach (discussed in detail in Basic ECG Concepts #3).
  • Normal Axis = between 0 to +90 degrees (positive in lead I and positive in lead aVF).
  • LAD (Left Axis Deviation) = between 0 to -90 degrees (positive in I; negative in aVF).
  • RAD (Right Axis Deviation) = between +90 to +180 degrees (negative in I; positive in aVF).
  • Indeterminate Axis = in the “northwest” quadrant (negative in I and negative in aVF).
NOTE: Precise calculation of Axis is rarely necessary. Clinically — It often suffices to simply determine the Quadrant within which the Axis lies.
  • IF you are within 20-to-30 degrees of the actual Axis — this is more than accurate enough for our purposes.
  • IF the QRS complex is isoelectric (equal parts positive and negative) in any one of the limb leads — then the Axis will usually be perpendicular to (~90 degrees away from) this lead.
Clinical Perspective: Realistically — The amount of clinical information that determination of Axis provides is limited. For purposes of “the basics” — Keep in mind the following generalities:
  • Slight LAD is not necessarily abnormal. On the other hand — marked LAD (as suggested by a positive QRS complex in lead I with a markedly negative QRS in aVF) — may indicate a conduction defect known as LAHB (Left Anterior HemiBlock). For more on ECG diagnosis of LAHB — See Figures 11-thru-15 in Basic ECG Concepts #3.
  • Slight RAD is not necessarily abnormal. However — marked RAD (as suggested by a markedly negative QRS in lead I with a positive QRS in aVF) — may suggest pulmonary disease or RVH (Right Ventricular Hypertrophy).
  • Patients with pulmonary disease are also prone to an indeterminate Axis.

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ECG “Crib Sheet”: Part II
     We reproduce the 2nd part of our ECG Crib Sheet below in Figure-5.

Figure-5: Part II of our ECG Crib Sheet — which includes assessment of the last 2 Parameters (Chamber Enlargement-QRST Changes) — as well as a reminder regarding STEP 2 (formation of one’s Clinical Impression) after completion of Descriptive Analysis. For More Advanced Interpreters — Add in assessment for RAA, LAA and RVH when evaluating for Chamber Enlargement.


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FIGURE-5:  Parameter #5 = Hypertrophy (Chamber Enlargement)
     For “the basics” — We limit assessment of Chamber Enlargement (Hypertrophy) to looking for LVH (discussed in detail in Basic ECG Concepts #5). The “magic numbers” are “35” and “12”.
  • Is the Sum of the deepest S wave in V1,V2 plus the tallest R wave in V5,V6 ≥35? If so — then voltage criteria for LVH are met (especially if ‘strain’ is present).
  • Is the R wave in lead aVL is ≥12 mm?
  • NOTE: You do not need for both criteria to be present to diagnose LVH. Satisfying either the 35 mm or 12 mm voltage criteria suffices.
  • KEY Point: The accuracy of the ECG for diagnosing LVH is much less — IF voltage for LVH is present but “strain” is not seen in at least one of the lateral leads.
  • For More Advanced Interpreters: — We cover ECG assessment for LAA/RAA in ECG Blog #75 — and for RVH in ECG Blog #77.

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FIGURE-5:  Parameter #6 = Assessing for Q-R-S-T Changes
     The components of the last (=6th) Parameter are best remembered by the memory aid = Q-R-S-T (to be discussed in detail in upcoming Basic ECG Concepts posts). For purposes of “the basics” — We don’t worry about lead aVR beyond our expectation that there may normally be a Q wave and/or T wave inversion in this lead. Instead — Focus your attention on the remaining 11 leads. Look at each lead for:
  • Q waves — small and narrow q waves may normally be seen in one or more of the lateral leads (leads I, aVL; V4,V5,V6). In contrast — larger and wider Q waves are more likely to indicate infarction. The larger and wider a Q wave is — the more likely it is that infarction has occurred at some point.
  • R Wave Progression — Does Transition (where the R wave becomes taller than the S wave is deep) occur normally (ie, between lead V2-to-V4?).
  • ST-T Wave Changes — See below.
DEFINING the ST Segment: More than any parameter — ST-T Wave Changes define if MI (Myocardial Infarction) has occurred — and, if so — whether the MI is likely to be acute.
  • The normal ST segment is isoelectric. It lies on the baseline — and, is neither “elevated” nor “depressed” (Figure-6).

Figure-6: Overview illustration of ST-T Wave Changes. ST segment deviation (either elevation or depression) — is judged with respect to the PR Segment Baseline (green arrow in Panel A). Alternatively — the TP baseline may be used. Panels B and C show several millimeters (little boxes) of ST Elevation (B) or ST Depression (C). Panel D shows the J-Point (defined as the point where the end of the QRS — joins the beginning of the ST segment). Note that there is at least 1mm of J-point ST elevation in Panel D.


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Assessing for ST-T Wave Changes: Attend to the following:
  • Is there ST elevation or depression?
  • What is the shape of any ST-T wave changes? (ie, upward concavity “smiley”-shape — or more worrisome coved = “frowny”-shape — See  Section 09.0 from ECG-2014-ePub or more detail regarding assessment of ST-T wave changes — with the part on Early Repolarization beginning in Section 09.14).
  • What part (location) of the heart affected? (discussed in detail in Basic ECG Concepts #4).

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FIGURE-7: Using the Systematic Approach
      Interpret the 12-lead ECG shown in Figure-7. Feel free to refer to Figure-4 and Figure-5 for review of specifics in your Descriptive Analysis (= the 1st Step in your interpretation).
  • QUESTION-1: How would the 2nd Step of your Interpretation (= your Clinical Impression) change — depending on whether the patient was: i) an asymptomatic young adult being seen for a pre-employment physical examination? — ii) an older adult presenting to the ED (Emergency Department) with worrisome new-onset chest pain? — or iii) a young adult with recent upper respiratory infection and new pleuritic and positional chest pain?
  • QUESTION-2: Even if this patient was older and having new chest pain — What ECG features make it less likely that the ST elevation seen in Figure-7 represents acute MI (Myocardial Infarction)?

Figure-7: Interpret this 12-lead ECG by the Systematic Approach. How might the clinical history change your Clinical Impression regarding this tracing?



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ANSWER to Figure-7: We begin our Systematic Approach with assessment of the 6 Parameters that comprise the 1st Step in interpretation = Descriptive Analysis. We then formulate our Clinical Impression — based on the history (See below).
  • Rate & Rhythm: The rhythm is fairly regular — and the QRS complex is narrow (not more than half a large box in duration). The upright P wave with fixed PR interval in lead II (red arrow) defines this as Sinus Rhythm. The R-R interval is ~5 large boxes. Therefore the rate = 300/5 ~60/minute.
  • Intervals: All 3 intervals are normal. That is — the PR interval is not more than 1 large box — the QRS is not more than half a large box — and, the QT is not more than half the R-R interval.
  • Axis: The Axis is normal (ie, within 0 to +90 degrees) — because the net QRS deflection in both lead I and lead aVF is positive. Since the net QRS deflection is nearly equally positive in leads I and aVF (perhaps slightly more positive in aVF) — the Axis lies within the range of +40-60 degrees. For “fine tuning” — We note that the QRS complex in lead aVL is isoelectric (equal parts positive and negative). This suggests the Axis is perpendicular to (ie, 90 degrees away from) lead aVL that lies at -30 degrees, or at +60 degrees. Bottom Line: These detailed calculations (in an attempt to fine tune Axis estimation) extend beyond-the-core of what is needed. The “quick answer” (and the one we would gladly accept) — is that the Axis in Figure-7 is “normal” and lies somewhere near the middle of the range between 0 and +90 degrees.
  • Hypertrophy: There would be voltage for LVH if this patient was over 35. No ‘strain’.
  • Q-R-S-T Changes: Small and narrow q waves are seen in leads V5,V6. Transition is normal (the R wave becomes taller than the S wave is deep between lead V2-to-V3). The most remarkable finding on this tracing relates to J-point concave up (ie, “smiley”-shape) ST elevation that is present in multiple leads — including leads I, II and V3-thru-V6. The amount of ST elevation in these leads is considerable — attaining at least 3mm in lead V5. There is no reciprocal ST depression.

KEY Clinical Point: The above Descriptive Analysis remains the same regardless of what the clinical history is. However, our Clinical Impression will change — depending on which of the 3 scenarios proposed in Question 1 is operative:
  • Scenario-1: IF this patient was an asymptomatic young adult being seen for a pre-employment physical examination — then the ST-T wave findings in Figure-7 would most probably be benign because: i) The patient is a young adult who is asymptomatic; ii) The q waves that are seen in leads V5,V6 are small and narrow (ie, they are most probably normal septal q waves that are commonly seen in one or more lateral leads); iii) ST elevation is “smiley” shape (which is common and often a benign finding when it occurs in otherwise healthy young adults); and iv) There is no reciprocal ST depression. The overall ECG picture is typical of the normal variant pattern known as Early Repolarization. No further follow-up would be needed.

  • Scenario-2: IF instead, this patient was an older adult presenting to the ED with worrisome new-onset chest pain — a different conclusion should be reached. It would still be unlikely that the ECG in Figure-7 represents an acute STEMI (ST Elevation Myocardial Infarction) because: i) The q waves in V5,V6 are small; ii) ST elevation is more diffuse than is usually seen with acute MI — and, the shape of the ST elevation looks benign (“smiley”-shape upward concavity); iii) There is no reciprocal ST depression; and iv) which is an Advanced Point — The QT interval looks short and R wave amplitude is preserved in the early chest leads. That said — there is ST elevation in Figure-7 — and in the absence of a prior tracing for comparison, one could not rule out the possibility of new acute ST elevation superimposed on baseline Early Repolarization. Clinical Correlation would be needed to know what to do!

  • Scenario-3: If this patient was a young adult with recent upper respiratory infection and new pleuritic and positional chest pain — then the diffuse ST elevation in multiple leads without reciprocal ST depression might represent acute Pericarditis. As an Advanced Point — there is PR depression (in aVF and V3-thru-V6) as well as PR elevation in lead aVR. That said — PR depression is a nonspecific change that may support the diagnosis of acute Pericarditis, but which may also be seen with acute MI and as a normal variant. BOTTOM Line: Depending on the clinical history and physical exam findings (ie, presence of a pericardial friction rub?) — the ECG in Figure-7 could be consistent with a diagnosis of acute Pericarditis (despite the lack of tachycardia). Clinical Correlation is needed.

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SUMMARY: We hope that this Basic ECG Concepts #6 has accomplished the following:
  • i) Emphasized the need for routine application of a sequential Systematic Approach to the interpretation of each and every ECG you encounter.
  • ii) Provided you with the essentials of the Approach we favor (contained in Figure-4 and Figure-5).
  • and iii) Illustrated how to use our Systematic Approach — both for assessment of the 6 Parameters (= Step 1) — as well as for interpreting the likely clinical significance of the ECG findings you recognize in Step 1 depending on the clinical scenario (= Step 2, which is formulation of the Clinical Impression).
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— For more information — GO TO —

  • Material and Figures #1, 2, and 4-thru-7 have been excerpted from our newest publication = “A 1st Book on ECGs-2014” and/or from the expanded 1st Book ePub version (available in kindle-kobo-nook-ibooks).
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  • More advanced material and Figure #3 have been excerpted from ECG-2014-Pocket Brain and/or from the expanded ECG-2014 ePub version (available in kindle-kobo-nook-ibooks).
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  • Please check out Free Download of our expanded GLOSSARY of ECG-related terms.
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