Chapter 1

### Introduction

A novice in a busy electrophysiology (EP) laboratory will generally learn to recognize the common arrhythmias in a relatively short time. It requires considerably more seasoning to recognize the variants and unusual mechanisms, or to "hit the curve ball." It is hoped that the following commentary assists in providing structure and focus to the EP study and facilitates analysis of the case studies to follow.

### It Begins with the Electrocardiogram

The EP study is an extension of the electrocardiogram (ECG) with the addition of intracardiac recording and programmed electrical stimulation. Insightful interpretation of the ECG allows for prospectively considering additional catheters, stimulation sequences, or maneuvers appropriate for the postulated arrhythmia. This limits the diagnostic possibilities and avoids unnecessary steps (Fig. 1–1). The fundamentals of ECG interpretation of an arrhythmia include identification of P waves, determining the atrioventricular (AV) relationship, and analyzing the QRS morphology (Table 1–1). For confusing problems, it is useful to create a "written" list of all potential hypotheses and to plan for specific interventions that will test them. As data are accumulated during the EP study, the facts supporting or refuting the hypotheses can be tabulated. The hypotheses can be represented by schematic drawings for complicated scenarios. This method is illustrated at the end of this chapter.

###### Figure 1–1

Two-channel rhythm strip recorded from a patient scheduled for electrophysiology study for palpitations. The onset of the tachycardia occurs after the second QRS and the P wave is noted in the following diastole to be of different morphology than the probable initial sinus P wave. The identification of the P wave during tachycardia is facilitated by comparison with the last QRS in the strip that is not followed by a P wave. Careful measurement with calipers (a critical tool of the electrophysiologist) will illustrate that the onset of the tachycardia does not require PR prolongation. In addition, the cycle length varies and during this, the PR stays constant while the apparent RP varies. These findings are most compatible with an atrial tachycardia. Note that most junctional reentrant tachycardias would require some AV delay at the onset and such variable retrograde conduction would be unusual. This information provides a focused starting point to plan electrophysiology study.

Table 1–1ECG Rhythm Analysis

### Less Is Often Not More

There are those gifted, intuitive individuals who leap to the correct diagnosis and apparently bypass all the rational, systematic steps. Most of us, however, are better served by a consistent, methodical approach that does not cut corners. A sample protocol ...

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