Atypical reentrant circuits (often seen post-operatively or post-ablation) and the influence of antiarrhythmic drugs can alter these classic findings, resulting in atypical flutter waves ( waveform 6). The electrocardiographic and electrophysiologic features of atrial flutter are discussed in detail separately. (See "Electrocardiographic and electrophysiologic features of atrial flutter".) P wave morphology The P wave morphology provides insight into the site of origin of atrial activity, and therefore the mechanism of the tachycardia. The P wave should be evaluated in as many leads as possible, ideally all 12 leads of a surface ECG, although in some situations a single-lead ECG strip may be all that is available for review. https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 12/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate The P wave morphology can be classified into one of three general categories: Similar to sinus rhythm Retrograde Abnormal Similar to sinus rhythm The most reliable way to determine if the P wave in a narrow complex tachycardia is consistent with an origin from the sinus node is to compare the P wave during the tachycardia to that from the same patient during sinus rhythm. Although sinus P wave morphology can vary slightly with changes in heart rates, the P wave during the tachycardia should be nearly identical to that seen on the baseline ECG in all 12 leads. If a baseline ECG is not available, characteristics of the P wave can still suggest origin from the region of the sinus node. A sinus P wave is usually upright in leads I, aVL, and the inferior leads II, III, and aVF, and negative in lead aVR. These features indicate that atrial activity is proceeding in a right-to-left and superior-to-inferior direction. (See "ECG tutorial: Basic principles of ECG analysis", section on 'P wave'.) At atrial rates greater than approximately 140 bpm or in the presence of first degree AV block, the P wave tends to merge into the preceding T or U wave, making P wave identification difficult ( waveform 7). In such cases, slowing of the ventricular response using the Valsalva maneuver, carotid sinus massage, or adenosine may allow for better analysis of the P waves. If P wave morphology is consistent with origination from the sinus node, the differential diagnosis of the tachycardia includes: ST(see "Sinus tachycardia: Evaluation and management", section on 'Definition and ECG features') Inappropriate ST (IST) (see "Sinus tachycardia: Evaluation and management", section on 'Inappropriate sinus tachycardia') Sinoatrial nodal reentrant tachycardia (SANRT) ( waveform 8) (see "Sinoatrial nodal reentrant tachycardia (SANRT)") AT, usually originating near the sinus node (see "Focal atrial tachycardia", section on 'Electrocardiographic features') P wave morphology alone is not sufficient to distinguish these arrhythmias from one another. In persons with a P wave morphology that is consistent with origination from the sinus node, additional ECG features that assist in the diagnosis include: Atrial rate In ST and IST, the rate typically ranges from 100 to 180 bpm. Faster atrial rates suggest an AT. https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 13/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Onset/offset pattern ST and IST have smooth, gradual changes in rate. Both SANRT and AT have an abrupt onset and offset, although the rate in AT can vary significantly with autonomic tone. Relationship between atrial and ventricular activity In ST and IST, there is usually a 1:1 relationship between atrial and ventricular activity. The response to vagal maneuvers or adenosine With ST or IST, there is a gradual slowing of the atrial and ventricular rates, followed by a gradual resumption of the previous rate. In contrast, SNRT can terminate abruptly with these maneuvers. Abnormal P waves Any P wave that does not have the characteristics of a sinus P wave is considered an abnormal P wave. Abnormal P waves that are due to retrograde conduction from the ventricle to the atrium are a specific subset of abnormal P waves. (See 'Retrograde P waves' below.) Abnormal P waves that are not retrograde are most consistent with AT, although some patients with AVRT have abnormal P waves. Retrograde P waves P waves that are due to retrograde conduction from the ventricle to the atrium are a specific subset of abnormal P waves. These P waves have a characteristic morphology and suggest certain diagnoses, specifically: AVNRT AVRT Junctional ectopic tachycardia Nonparoxysmal junctional tachycardia The most common retrograde P wave morphology is associated with atrial activation that originates from the AV node and proceeds in an inferior-to-superior direction. Thus, the defining trait of a retrograde P wave is that it is negative in the inferior leads II, III, and aVF. Due to the central location of the AV node, atrial activation proceeds simultaneously leftward and rightward, so the P wave morphology in leads I, aVL, and aVR varies among patients, but it is often relatively narrow. In addition, because the AV node is posteriorly located, the activation is usually posterior-to-anterior, producing a narrow but positive P wave in lead V1. Retrograde P waves due to conduction via an accessory pathway can have a variety of morphologies, depending upon the site of the pathway. However, they are still usually negative in the inferior leads. (See "Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis".) https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 14/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Because retrograde P waves are often associated with a short RP interval, they can blend with the terminal portion of the QRS. If a baseline ECG during sinus rhythm is available for comparison, a pseudo S wave in the inferior leads or a pseudo R' in V1 that is not present during sinus rhythm is often a retrograde P wave ( figure 3) [7,8,13]. (See 'RP relationship' below.) RP relationship In patients with a retrograde P wave, the temporal relationship between the P wave and the R wave divides narrow complex tachycardias into two categories: short RP and long RP tachycardias. The RP interval is defined as the interval from the onset of the QRS to the onset of the P wave. Short RP tachycardias tend to be paroxysmal, while long RP tachycardias can be paroxysmal or incessant. Short RP tachycardias If the RP interval is less than one-half of the RR interval, the tachycardia is considered a short RP tachycardia. The differential diagnosis of a short RP tachycardia is generated by considering the P wave morphology. Abnormal P wave The combination of abnormal P waves and a short RP interval is most often seen in the setting of an AT with AV nodal conduction delay. (See 'Abnormal P waves' above.) Retrograde P wave The combination of retrograde P waves and a short RP interval is typical of the "common" form of AVNRT and of AVRT utilizing an accessory pathway. (See 'Retrograde P waves' above.) In the "common" form of AVNRT (which accounts for 90 percent of AVNRT) [14], reentry occurs in the AV node and perinodal tissues. Antegrade conduction occurs down the slow pathway and retrograde conduction up the fast pathway ( figure 4 and figure 5). This slow-fast pattern gives rise to retrograde P waves that may be inapparent if obscured by the QRS complex ( figure 3). (See "Atrioventricular nodal reentrant tachycardia".) AVRT utilizing an accessory pathway can be either orthodromic or antidromic. Orthodromic AVRT is more common, and in this form of the arrhythmia, antegrade conduction occurs through the AV node, producing a narrow QRS complex, and retrograde conduction to the atrium occurs over an AV bypass tract ( figure 6). (See "Atrioventricular reentrant tachycardia (AVRT) associated with an accessory pathway".) In contrast, during antidromic AVRT, antegrade conduction occurs through the AV bypass tract and retrograde conduction occurs through the AV node or a second accessory pathway. This pattern of activation results in a wide QRS complex (thus, antidromic AVRT is not a narrow QRS complex tachycardia). (See "Wide QRS complex tachycardias: Approach to the diagnosis".) https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 15/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Long RP tachycardias If the RP interval is more than one-half of the RR interval, the tachycardia is considered a long RP tachycardia. As with short RP tachycardias, the differential diagnosis is generated by combining the PR relationship with the P wave morphology. Retrograde P waves The combination of retrograde P waves and a long RP interval is usually caused by either "atypical" AVNRT or by AVRT with a slowly conducting accessory pathway (also known as permanent junctional reciprocating tachycardia [PJRT]); this combination can also be seen in AT with a focus that is close to the AV node [7]. P waves are inverted in the inferior leads as the atria are depolarized from bottom to top. (See 'Retrograde P waves' above.) Abnormal P wave morphology The combination of abnormal P wave morphology and a long RP interval usually suggests some form of AT. However, this pattern can also occur in the atypical or uncommon form of AVNRT and in AVRT with a slowly conducting accessory pathway [7]. (See 'Abnormal P waves' above.) The atypical form of AVNRT, which accounts for 10 percent of AVNRT [14], is characterized by antegrade conduction down a fast pathway and retrograde conduction through a slow pathway. As a result, the P wave occurs very late in the cardiac cycle (positioning it near to the next QRS complex) ( figure 7). (See "Atrioventricular nodal reentrant tachycardia".) In AVRT with a slowly conducting accessory pathway, antegrade conduction probably occurs through the AV node, and retrograde conduction through a slowly conducting accessory pathway [1,13]. Because of slow conduction through the retrograde limb of the circuit, the retrograde P wave occurs late in the cardiac cycle. (See "Atrioventricular reentrant tachycardia (AVRT) associated with an accessory pathway".) Undetectable P waves If atrial activity is not evident despite the use of carotid sinus massage and/or adenosine to "unmask" atrial activity, the most common rhythm is AVNRT [7]. Other possible rhythms are AF, AVRT, and junctional tachycardia. Although AF is typically an irregularly irregular rhythm, when the ventricular rate is very rapid, it may appear to be more regular. Vagal maneuvers produce a transient decrease in the ventricular rate with AF, which may make the irregularity more evident. Junctional tachycardia is an arrhythmia arising from a discrete focus within the AV node or His bundle. In children, junctional tachycardia, also known as junctional ectopic tachycardia (JET), is usually associated with significant underlying heart disease. In adults, this rhythm, generally called nonparoxysmal junctional tachycardia (NPJT), is seen with acute myocardial infarction, https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 16/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate digitalis toxicity, and myocarditis. (See "Supraventricular arrhythmias after myocardial infarction".) Atrial activity during junctional tachycardia is variable. Retrograde atrial activation may occur, with a P wave that either follows each QRS complex or is concealed in the QRS complex. If retrograde conduction does not occur, independent atrial activity may be seen, with complete AV dissociation that must be distinguished from AV dissociation due to complete heart block (in complete heart block, the atrial rate exceeds the ventricular rate). Electrophysiologic testing In some cases, narrow QRS complex tachycardias cannot be discriminated from each other using noninvasive testing. An electrophysiologic study (EPS) can provide a definitive diagnosis but is only used when a definitive diagnosis will influence therapy. [13]. For some arrhythmias, EPS with ablation can also be curative. For these reasons, invasive EP testing to define the mechanism of SVT is rarely carried out as a standalone diagnostic procedure, but rather as a "prelude" to ablation. Diagnostic EP may be indicated to determine the mechanism of the arrhythmia in the following patients with a narrow QRS complex tachycardia: Those with severe symptoms such as syncope or presyncope in association with the arrhythmia, particularly if the resting ECG manifests the pattern of preexcitation with a delta wave ( waveform 9) or a short PR interval without a delta wave. Those with underlying organic heart disease who develop angina or acute HF during their arrhythmia, even if the rate is relatively slow. EPS and catheter ablation are discussed in greater detail elsewhere. (See "Invasive diagnostic cardiac electrophysiology studies" and "Overview of catheter ablation of cardiac arrhythmias", section on 'Introduction'.) Other cardiac testing In addition to close scrutiny of the available ECG data, patients with narrow QRS complex tachycardia should generally have a baseline echocardiogram to assess for any evidence of significant underlying structural heart disease [15]. In some patients, additional cardiac testing may be required to identify or characterize an arrhythmia; its use depends upon the particular arrhythmia and symptoms but may include one or more of the following tests: Ambulatory ECG monitoring (for patients without a definitive ECG-based diagnosis of their arrhythmia). Exercise stress testing (for patients with exercise-associated arrhythmias). https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 17/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Stress testing (exercise or pharmacologic) for underlying myocardial ischemia (for those with symptoms of angina and risk factors for coronary artery disease). SOCIETY GUIDELINE LINKS Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Atrial fibrillation" and "Society guideline links: Arrhythmias in adults" and "Society guideline links: Supraventricular arrhythmias".) INFORMATION FOR PATIENTS UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." th th The Basics patient education pieces are written in plain language, at the 5 to 6 grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more th th sophisticated, and more detailed. These articles are written at the 10 to 12 grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon. Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.) Basics topic (see "Patient education: Supraventricular tachycardia (SVT) (The Basics)") SUMMARY AND RECOMMENDATIONS Definitions Tachycardias, defined as abnormal heart rhythms with a ventricular rate of 100 or more beats per minute (bpm), can present with either a narrow or wide QRS complex. A narrow QRS complex (<120 ms) reflects rapid activation of the ventricles via the normal His-Purkinje system, which in turn suggests that the arrhythmia originates above or within the His bundle (ie, a supraventricular tachycardia). The site of origin may be in the sinus node, the atria, the atrioventricular (AV) node, the His bundle, or some combination of these sites. (See 'Introduction' above and 'Definitions' above.) https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 18/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Clinical manifestations Most commonly, patients with a narrow QRS complex tachycardia present with palpitations, usually abrupt in onset. Other presenting symptoms may include syncope or presyncope, lightheadedness, dizziness, diaphoresis, chest pain, or shortness of breath. (See 'Clinical manifestations' above.) Diagnosis The diagnosis of a narrow QRS complex tachycardia requires only a surface ECG that shows a heart rate greater than 100 bpm along with narrow QRS complexes that are less than 120 ms in duration. (See 'Diagnosis' above.) Types of narrow QRS complex tachycardia The differential diagnosis of narrow QRS complex tachycardias is broad ( table 1), including atrial fibrillation (AF), atrial flutter, sinus tachycardia (ST), and a variety of paroxysmal supraventricular tachycardias. (See 'Types of narrow QRS complex tachycardia' above.) Evaluation Evaluation of a patient with a narrow QRS complex tachycardia involves two primary components: assessment of the patient for symptoms and signs of hemodynamic stability (or instability), and assessment of the patient's ECG for clues to the type of tachycardia present. (See 'Evaluation' above.) Unstable patients If a patient has clinically significant hemodynamic instability and the rhythm is not ST, or if there is any doubt that the rhythm is sinus tachycardia, urgent conversion to sinus rhythm is recommended ( algorithm 1). If it is certain that the patient's rhythm is ST, and clinically significant cardiac symptoms are present, management should be focused on the underlying cardiac disorder and on treating any contributing cause of the rapid heart rate (such as myocardial ischemia due to coronary heart disease, respiratory or cardiac failure, hypovolemia, anemia, fever, pain, or anxiety). Stable patients If the patient is not experiencing hemodynamic instability, a nonemergency approach to the diagnosis of the patient's rhythm can be undertaken ( algorithm 2). Approach to identifying the type of SVT Following the determination of hemodynamic stability, the next steps in the assessment of a narrow QRS complex tachycardia include: Determine if the rhythm appears to be regular or irregular. (See 'Assessing the ECG for regularity of the rhythm' above.) https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 19/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Determine the atrial activity by identifying and characterizing the atrial rate, P-wave morphology, RP relationship, and AV relationship. (See 'Atrial rate' above and 'P wave morphology' above and 'RP relationship' above.) Role of electrophysiologic testing In some cases, narrow QRS complex tachycardias cannot be discriminated from each other using noninvasive testing. An electrophysiologic study (EPS) can provide a definitive diagnosis but is only used when a definitive diagnosis will influence therapy. (See 'Electrophysiologic testing' above.) Other cardiac testing In some patients, additional cardiac testing may be required to identify or characterize an arrhythmia; its use depends upon the particular arrhythmia and symptoms. (See 'Other cardiac testing' above.) Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Ganz LI, Friedman PL. Supraventricular tachycardia. N Engl J Med 1995; 332:162. 2. Katritsis DG, Josephson ME. Differential diagnosis of regular, narrow-QRS tachycardias. Heart Rhythm 2015; 12:1667. 3. Khurshid S, Choi SH, Weng LC, et al. Frequency of Cardiac Rhythm Abnormalities in a Half Million Adults. Circ Arrhythm Electrophysiol 2018; 11:e006273. 4. Ferguson JD, DiMarco JP. Contemporary management of paroxysmal supraventricular tachycardia. Circulation 2003; 107:1096. 5. Trohman RG. Supraventricular tachycardia: implications for the intensivist. Crit Care Med 2000; 28:N129. 6. Knight BP, Ebinger M, Oral H, et al. Diagnostic value of tachycardia features and pacing maneuvers during paroxysmal supraventricular tachycardia. J Am Coll Cardiol 2000; 36:574. 7. Blomstr m-Lundqvist C, Scheinman MM, Aliot EM, et al. ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Supraventricular Arrhythmias). Circulation 2003; 108:1871. 8. Kalbfleisch SJ, el-Atassi R, Calkins H, et al. Differentiation of paroxysmal narrow QRS complex tachycardias using the 12-lead electrocardiogram. J Am Coll Cardiol 1993; 21:85. https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 20/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate 9. Accardi AJ, Miller R, Holmes JF. Enhanced diagnosis of narrow complex tachycardias with increased electrocardiograph speed. J Emerg Med 2002; 22:123. 10. Link MS. Clinical practice. Evaluation and initial treatment of supraventricular tachycardia. N Engl J Med 2012; 367:1438. 11. Smith GD, Dyson K, Taylor D, et al. Effectiveness of the Valsalva Manoeuvre for reversion of supraventricular tachycardia. Cochrane Database Syst Rev 2013; :CD009502. 12. Ellenbogen KA, Thames MD, DiMarco JP, et al. Electrophysiological effects of adenosine in the transplanted human heart. Evidence of supersensitivity. Circulation 1990; 81:821. 13. Chauhan VS, Krahn AD, Klein GJ, et al. Supraventricular tachycardia. Med Clin North Am 2001; 85:193. 14. Akhtar M, Jazayeri MR, Sra J, et al. Atrioventricular nodal reentry. Clinical, electrophysiological, and therapeutic considerations. Circulation 1993; 88:282. 15. Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardiaThe Task Force for the management of patients with supraventricular tachycardia of the European Society of Cardiology (ESC). Eur Heart J 2020; 41:655. Topic 943 Version 36.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 21/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate GRAPHICS Classification of narrow QRS complex tachycardias by structures required for initiation and maintenance Atrial tissue only AV junction Sinus tachycardia AV nodal reentrant tachycardia (AVNRT) Inappropriate sinus tachycardia Atrioventricular reentrant tachycardia (AVRT) Sinoatrial nodal reentrant tachycardia (SANRT) Junctional tachycardia Intraatrial reentrant tachycardia (IART) Junctional ectopic tachycardia in children Atrial tachycardia Nonparoxysmal junctional tachycardia in adults Multifocal atrial tachycardia Atrial fibrillation Atrial flutter Graphic 58019 Version 2.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 22/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Sites of reentry in supraventricular tachyarrhythmias Reentry may occur around a fixed anatomic obstacle or may be functional, developing in the absence of an anatomic obstacle and resulting from the intrinsic heterogeneity of electrophysiologic properties of the myocardial tissue. Reentrant circuits leading to a supraventricular tachyarrhythmia may develop in various parts of the heart: within and around the sinoatrial node (sinus node reentry); within the atrial myocardium (atrial tachycardia, atrial flutter, or atrial fibrillation); within the atrioventricular (AV) node due to the presence of a slow and fast pathway (atrioventricular nodal reentrant tachycardia); or involving the AV node and an accessory pathway (AP) (atrioventricular reentrant tachycardia). LAF: left anterior fascicle; LPF: left posterior fascicle. Graphic 82249 Version 4.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 23/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Mechanisms of reentry in cardiac arrhythmias Schematic representation of possible reentrant circuits. The thick black arrow represents the circulating impulse; thin black lines represent advancing wavefronts in completely refractory tissue; speckled areas are partially refractory tissue; white areas are fully excitable tissue. A is the original model of circus movement around a fixed obstacle. There is a fully excitable gap, and the length and location of the circuit are fixed. B represents circus movement around 2 fixed anatomic obstacles. A fully excitable gap is present. C represents rapidly conducting bundles forming closed loops that serve as preferential circuits through which the impulse may travel. D is the leading circle type of reentry which does not require an anatomic obstacle. Instead, the impulse propagates around a functionally refractory core and among neighboring fibers that have different electrophysiologic properties. Since the refractoriness of the core is variable, the circuit size changes but will be the smallest possible circuit that can continue to propagate an impulse. Functional circuits tend to be small, rapid, and unstable. E represents reentry around a fixed anatomic obstacle, but a fully excitable gap is absent. F demonstrates an area of slowed conduction (hatched lines) between anatomic boundaries, while in G all areas of slowed conduction neighbor an anatomic obstacle. H represents anisotropic reentry. There are differences in the conduction of a single impulse in various fibers as a result of differences in their orientation. https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 24/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Courtesy of Philip J Podrid, MD, FACC. Graphic 52134 Version 5.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 25/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Algorithm for the evaluation of narrow QRS complex tachycardias in unstable patients IV: intravenous. Graphic 109811 Version 2.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 26/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Algorithm for the evaluation of narrow QRS complex tachycardias in stable pati AVNRT: atrioventricular nodal reentrant tachycardia; AVRT: atrioventricular reentrant tachycardia (due to an a electrocardiogram; SANRT: sinoatrial nodal reentrant tachycardia. Graphic 76920 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 27/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Single-lead electrocardiogram (ECG) showing atrial fibrillation Lead V1 showing coarse AF with moderate ventricular response. The two characteristic findings in AF are present: the very rapid atrial fibrillatory waves (f waves), which are variable in appearance; and the irregularly irregular ventricular response as the R-R interval between beats is unpredictable. Coarse AF may appear similar to atrial flutter. However, the variable height and duration of the f waves differentiate them from atrial flutter (F) waves, which are identical in appearance and occur at a constant rate of about 250 to 350 beats/min. AF: atrial fibrillation. Courtesy of Ary Goldberger, MD. Graphic 73958 Version 6.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 28/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Single-lead electrocardiogram (ECG) showing atrial fibrillation with minimally apparent atrial activity F waves are not apparent in this lead, as the only finding suggestive of AF is the irregularly irrregular ventricular response. AF: atrial fibrillation. Courtesy of Morton Arnsdorf, MD. Graphic 53988 Version 4.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 29/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Electrocardiogram single-lead multifocal atrial tachycardia Clinical features: Elderly patients Decompensation of pulmonary disease Postoperative Arrhythmia usually does not cause severe hemodynamic compromise High mortality ECG features: P waves have 3 forms Atrial rate is usually 100 to 200 bpm Atrial rate is irregular PR interval varies Isoelectric baseline between P waves May progress to atrial fibrillation ECG: electrocardiogram; bpm: beats per minute. Courtesy of Alfred Buxton, MD. Graphic 127222 Version 1.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 30/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Approach to adenosine dosing in stable adults with suspected supraventricular tachyarrhythmia This figure summarizes the initial dosing, administration, and need for repeat dosing of adenosine in a hemo stable adult with suspected AV node-dependent SVT. Adenosine can be used as a diagnostic aid to identify th rhythm or as a therapy to terminate SVTs that rely on AV node conduction. AV node-dependent SVTs include A reentrant tachycardia (AVNRT) and AV reentrant (or reciprocating) tachycardia (AVRT). The management of su node-dependent SVT in hemodynamically stable adults commonly starts with a trial of 1 or more vagal mane proceeding to adenosine therapy. If the patient has hemodynamically unstable SVT, cardioversion is indicate UpToDate content for details on management of SVTs. https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 31/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate AV: atrioventricular; SVT: supraventricular tachycardia; IV: intravenous; ACC: American College of Cardiology; American Heart Association; HRS: Heart Rhythm Society; ECG: electrocardiogram. Lower adenosine doses are indicated in certain clinical settings. If central venous administration is perform adenosine dose is 3 mg; if needed (SVT persists and there is no AV block), the dose may be increased to 6 mg mg for subsequent doses. For heart transplant recipients, the initial adenosine dose is 1 mg; if needed (SVT p there is no AV block), the dose may be increased to 2 mg and then 3 mg for subsequent doses. An 18 mg dose is more likely to be required to produce AV block in patients with a body weight >70 kg, par [1] those weighing >110 kg. When a third dose is indicated, an alternative approach is to administer 12 mg (in mg) as described in the 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients with Supraventr Tachycardia. [2] SVT termination in response to adenosine includes SVT termination closely followed by SVT recurrence. Refer to UpToDate content on treatment of SVT for dosing of second-line AV nodal blockers. If the SVT pers second-line AV nodal blocker therapy, electrical cardioversion is performed, as discussed in UpToDate conten treatment of SVT. SVTs that are not AV node dependent include atrial flutter, atrial fibrillation, and atrial tachycardia. When AV is induced by adenosine, the ECG may reveal atrial activity diagnostic of these rhythms. References: 1. Prabhu S, Mackin V, McLellan AJA, et al. Determining the optimal dose of adenosine for unmasking dormant pulmonary vein co following atrial brillation ablation: Electrophysiological and hemodynamic assessment. DORMANT-AF study. J Cardiovasc Electr 28:13. 2. Page RL, Joglar JA, Caldwell MA, et al. 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Hea Society. Circulation 2016; 133:e506. Graphic 141417 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 32/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Atrial flutter at a rate of 250 beats/minute with 2:1 AV conduction in the presence of left bundle branch block Although every other flutter wave can be seen at the end of the T wave in the first part of the tracing (arrows), a sinus mechanism cannot be excluded. The flutter waves become clearly apparent after carotid sinus massage is applied to slow conduction through the AV node, thereby increasing the degree of AV block. AV: atrioventricular Courtesy of Morton Arnsdorf, MD. Graphic 76876 Version 3.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 33/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Single-lead electrocardiogram showing atrial flutter The atrial rate in this tracing of atrial waves is 300 beats per minute, and the flutter waves, which are "saw toothed," are uniform in morphology, amplitude, and cycle length. Impulse conduction to the ventricles is dependent upon the electrophysiologic characteristics of the atrioventricular node. Most commonly, every other atrial impulse is conducted and there is 2:1 block. However, when conduction through the atrioventricular node is impaired as a result of underlying disease, drugs, or increased vagal tone, there may be higher degrees of block, which may be variable, resulting in a regularly irregular ventricular rate. Graphic 82303 Version 6.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 34/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Electrocardiogram in atypical atrial flutter There are three findings that distinguish this arrhythmia from typical atrial flutter: the flutter rate is faster at 375 beats/minute; there is no isoelectric interval between the flutter waves; and there is more apparent positivity in leads II, III, and avF. The high degree of AV block is due to digoxin and some underlying AV nodal disease. Courtesy of Morton Arnsdorf, MD. Graphic 68846 Version 3.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 35/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Electrocardiogram (ECG) showing sinus tachycardia at a rate of 150 beats/min Note the difficulty in separating the P waves from the T waves in the standard leads. The P waves are most evident in lead V1 (arrow) where the terminal negativity suggests left atrial enlargement. Courtesy of Morton Arnsdorf, MD. Graphic 78938 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 36/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Single-lead electrocardiogram (ECG) showing sinoatrial (SA) nodal reentrant tachycardia Electrocardiogram showing SA nodal reentrant tachycardia. The first three beats are normal sinus beats at a rate of about 107 beats/min; the fourth beat is an atrial premature beat that is followed by a return to sinus rhythm. The eighth beat (arrow) represents the sudden onset of SA nodal reentrant tachycardia at a rate of about 145 beats/min. Since the P waves are similar to the sinus beats, the diagnosis is suggested only by the abrupt onset of the tachycardia. Courtesy of Morton F Arnsdorf, MD. Graphic 76364 Version 5.0 Normal rhythm strip Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton F Arnsdorf, MD. Graphic 59022 Version 3.0 https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation/print 37/45 7/5/23, 10:40 AM Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation - UpToDate Typical atrioventricular nodal reentrant tachycardia The first two complexes are normal sinus beats with a normal P wave followed by a QRS complex. The third complex, an atrial premature beat (APB), has a prolonged PR interval; it initiates a common or typical atrioventricular nodal reentrant tachycardia (AVNRT) in which antegrade conduction to the ventricle is via the slow pathway and