Epidemiology And Natural History

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Data on the prevalence of supraventricular tachyarrhythmias are extremely scarce. Electrocardiographic (ECG) screening studies of large populations (13,14) suggest a prevalence of the WPW pattern on ECG of 1 to 2 per 1000, but not all of these patients have clinical arrhythmia. In a study of the 50,000 residents of the Marshfield Epidemiologic Study Area (MESA) in Wisconsin, the prevalence of symptomatic PSVT was 2.25 per 1000, with an incidence of 35 per 100,000 person-years (15). In this study, PSVT occurred more frequently in women than in men, which is also reflected in series of patients undergoing catheter ablation. Interestingly, episodes of PSVT may occur more during the luteal than the follicular phase of the menstrual cycle in premenopausal women (16).

Notably, PSVT is frequently misdiagnosed as panic disorder. Two-thirds of patients with PSVT fulfill DMS-IV criteria for panic disorder (17). In these patients, the proper diagnosis may be delayed by failure to recognize overt pre-excitation on a baseline ECG, as well as reliance on Holter monitoring rather than event monitoring (see Chapter 2).

Natural history data are also lacking in these patients. Except for patients with WPW, the prognosis in most patients with SVT is generally believed to be excellent, with therapeutic measures aimed at improving symptoms. Supraventricular arrhythmias can occur in the presence or absence of structural heart disease. In the absence of WPW and significant structural heart disease, the risk of sudden cardiac death resulting from SVT is extremely low (18). Although mitral valve prolapse is frequently diagnosed in patients with PSVT, evidence of a particular association is lacking thus far (19).

In patients with WPW, the risk of sudden cardiac death is linked to extremely rapid rates during AF/atrial flutter with degeneration into VF. This risk relates to the

Fig. 7. Mechanism of AVRT in WPW. The left panel represents sinus rhythm. The QRS has a slurred upstroke (delta wave), caused by rapid activation (pre-excitation) of the ventricle over the accessory pathway. During orthodromic AVRT (middle panel), there is no delta wave, because ventricular activation occurs entirely over the normal AV node and His-Purkinje system, with retrograde conduction over the accessory pathway. In antidromic AVRT (right panel), the ventricle is activated entirely over the accessory pathway, with retrograde conduction up the AV node (or a second accessory pathway). Thus, the QRS is fully pre-excited and is wide and bizarre appearing, an exaggerated version of the delta wave during sinus rhythm. (Reproduced from Ganz LI, Friedman PL. Supraventricular tachycardia. N Engl J Med 1995;332:162-173. Copyright © 1995 Massachusetts Medical Society.)

anterograde refractory period of the accessory pathway. Because of this risk, EPS and radiofrequency catheter ablation (see Chapter 4) are typically recommended as initial therapy in symptomatic patients. The management of asymptomatic patients is frequently debated, as sudden cardiac death can rarely be the initial clinical presentation in patients with the WPW syndrome (20-22). The risk of sudden death in asymptomatic WPW patients is estimated to be about 1 per thousand patient-years; the risk of death during catheter ablation is estimated to be about 1 per thousand. Noninvasive indicators (such as intermittent pre-excitation in sinus rhythm (see Fig. 14), or sudden loss of pre-excitation during exercise test or with procainamide infusion) carry some prognostic information, but direct measurements of the accessory pathway anterograde refractory period during EPS and shortest R-R interval during pre-excited AF are more accurate. Yet the specificity of all of these measures, both noninvasive and invasive, is limited. When coupled with a low pretest probability of sudden death in asymptomatic WPW patients, the positive predictive value of these tests remains low (23). In addition, most patients with asymptomatic WPW at initial diagnosis remain asymptomatic during follow-up, and some of these patients lose their capacity for anterograde conduction (and thus risk of sudden death) over time (24,25). For all of these reasons, many electrophysiologists recommend no particular diagnostic testing or treatment for asymptomatic individuals unless they are engaged in high-risk professions, such as the transpor-

Psvt Wpw Syndrome

Fig. 8. ECG in the same patient as in Fig. 6, during PSVT. Note that the QRS complex is now normal, with a sharp upstroke, and no evidence of pre-excitation. Retrograde P waves, best seen in leads V4 - V6 (arrows), fall on the junction of the ST segment and T wave, considerably later than during typical AVNRT. The P waves are still closer to the previous QRS complex compared to the next QRS complex, so like AVNRT, orthodromic AVRT is typically a short RP tachycardia.

Fig. 8. ECG in the same patient as in Fig. 6, during PSVT. Note that the QRS complex is now normal, with a sharp upstroke, and no evidence of pre-excitation. Retrograde P waves, best seen in leads V4 - V6 (arrows), fall on the junction of the ST segment and T wave, considerably later than during typical AVNRT. The P waves are still closer to the previous QRS complex compared to the next QRS complex, so like AVNRT, orthodromic AVRT is typically a short RP tachycardia.

Avnrt Antidromic

Fig. 9. ECGs in a patient with WPW. (A) Sinus rhythm, with delta-wave polarity indicative of a left-free-wall pathway. (B) Antidromic AVRT. Note that the QRS morphology is wide and bizarre, an exaggeration of the delta wave seen during sinus rhythm. Retrograde atrial activation is via the AV node, and is not evident in this tracing.

Fig. 9. ECGs in a patient with WPW. (A) Sinus rhythm, with delta-wave polarity indicative of a left-free-wall pathway. (B) Antidromic AVRT. Note that the QRS morphology is wide and bizarre, an exaggeration of the delta wave seen during sinus rhythm. Retrograde atrial activation is via the AV node, and is not evident in this tracing.

Table 2

Differential Diagnosis of Supraventricular Tachycardia

Short RP

Long RP

Typical AVNRT AVRT

Atypical AVNRT PJRT

Ectopic (unifocal) atrial tachycardia Sinus tachycardia Inappropriate sinus tachycardia Sinus node reentrant tachycardia

Nonparoxysmal junctional tachycardia Junctional ectopic tachycardia*

AVNRT = Atrioventricular nodal reentrant tachycardia; AVRT = Atrioventricular reentrant tachycardia; PJRT = Permanent junctional reciprocating tachycardia.

* Only if 1:1 V:A conduction; if A-V dissociation, RP classification does not apply.

tation industry or elite athletes (26). Other electrophysiologists feel that because of the risk of sudden death, even asymptomatic patients should undergo diagnostic EPS, with catheter ablation if the accessory pathway has a short refractory period and a location that is approachable without posing a high risk of heart block (e.g., left free wall) (27).

Few data are available regarding the natural history of symptomatic PSVT after patients present initially. Among 113 patients with WPW, concealed accessory pathway, or AVNRT initially presenting in the precatheter ablation era, only 10.3% reported spontaneous disappearance of their tachycardia during a mean follow-up of 9 ± 1 yr. Rather, both the symptom score and frequency of episodes tended to increase over time. Moreover, 13.5% developed new tachyarrhythmias during follow-up, most commonly atrial fibrillation (AF). For patients with manifest WPW, 38.5% developed new AF during follow-up (28).

The diagnostic approach depends on the manner in which patients present. Patients presenting with palpitations, without documented tachycardia, should have a history and physical examination for signs and/or symptoms of structural heart disease and baseline ECG. In most cases, ambulatory event monitoring will be the most cost-effective means of documenting an arrhythmia (see Chapter 2). If WPW is present, documentation of tachycardia is useful, but probably not necessarily imperative if the history is convincing. Patients with a history of syncope and WPW should proceed directly to EPS.

Documentation of tachycardia is useful in differentiating among the types of SVT. Most commonly, if regular P waves are apparent, there is a 1:1 relationship between P waves and QRS complexes. If the ratio of P waves to QRS complexes is greater than one, the diagnosis is almost always atrial tachycardia. Rarely, AVNRT can present with 2:1 infranodal block. AVRT must have a 1:1 A-V relationship. In multifocal atrial tachycardia (MAT), the P-wave morphology is variable, and the ventricular rate is irregular. Tachycardias with a 1:1 A-V ratio may be divided by the relationship between the QRS complex and the next P wave; short RP tachycardias are much more common than long RP tachycardias (see Table 2).

The most common short RP tachycardias are AVNRT and AVRT. With AVNRT, atrial and ventricular activation are roughly simultaneous, so the P wave is frequently

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  • NICOLA
    What is 3 p waves before a Qrs wave?
    8 years ago

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