Ebook Goldberger’s clinical electrocardiography: Part 2
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Ebook Goldberger’s clinical electrocardiography: Part 2
■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2ular (AV) conduction disturbances. These abnormalities can be classified in multiple ways. This review/overview chapter categorizes arrhythmias into two major groups: bradycardias and tachycardias. The tachycardia group is then subdivided into narrow and wide (broad) QRS complex variants, which are Ebook Goldberger’s clinical electrocardiography: Part 2a major locus ol ECG differential diagnosis in acute care medicine and in referrals to cardiologists.BRADYCARDIAS (BRADYARRHYTHMIAS)The term bradycardEbook Goldberger’s clinical electrocardiography: Part 2
ia (or bradyarrhythmia) refers to arrhythmias and conduction abnormalities that produce a heart rate <60 bears/min. Fortunately, their differential di■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2ive major groups (Box 19.1), recognizing t hat sometimes more than one rhythm is present (e.g., sinus bradycardia with complete heart block and an idioventricular escape rhythm).Sinus Bradycardia and Related Rhythms Sinus bradycardia IS Simply sinus rhythm With a rare <60 bears/min (Fig. 19.1). when Ebook Goldberger’s clinical electrocardiography: Part 2 1:1 (normal) AV' conduction is present, each QRS complex is preceded by a p wave that is positive in lead II and negative in lead aVR. Some individuaEbook Goldberger’s clinical electrocardiography: Part 2
ls, especially trained athletes at rest and adults during deep sleep, may have sinus bradycardia with rates as low as 30-40 beats/min.Sinus bradycardi■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2onstiJt.inkling.coin foe additional online material for this chapter.194rest) or to actual S/\ block (see chapter 13). Inappropriate sinus bradycardia may be seen with the sick sinus syndrome (discussed below). The most extreme example of sinus node dysfunction is SA node arrest (see chapters 13 and Ebook Goldberger’s clinical electrocardiography: Part 2 21). As now described, sinus bradycardia may also be associated with wandering atrial pacemaker (WAP), in addition, sinus rhythm with atrial bigem inEbook Goldberger’s clinical electrocardiography: Part 2
y—where each premature atrial complex (PAC) is blocked (nonconducted) may mimic sinus bradycardia.Wandering Atrial PacemakerWandering atrial (supraven■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2arying configuration with a relatively normal or slow heart rate. The p wave variations reflect shifting of rhe intrinsic pacemaker between the sinus node (and likely regions within the SA node, itself), and different atrial sites. WAP may be seen in a variety of settings. often it appears in normal Ebook Goldberger’s clinical electrocardiography: Part 2 persons (particularly during sleep or states of high vagal cone), as a physiologic variant. It may also occur with certain drug toxicities, sick sinuEbook Goldberger’s clinical electrocardiography: Part 2
s syndrome, and different tyỊMĩs of organic heart disease.Clinicians should be aware that WAP is quite distinct from multifocal atrial tachycardia (MA■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2bur With rates between 60 and 100 bears/min, rhe more general term “multifocal atrial rhythm” can be used. MAT is most likely to be mistaken for atrial fibrillation, with both producing a rapid irregular rate; conversely, AF is sometimes misinterpreted as MAT.Sinus Rhythm with Frequent Blocked PACs Ebook Goldberger’s clinical electrocardiography: Part 2Clinicians should also be aware char when sinus rhythm is present with frequent blocked PACsCHAPTER 19 Bradycardias (Bradyarrhythmias) 195(Fig. 19.3),Ebook Goldberger’s clinical electrocardiography: Part 2
the rhythm will mimic sinus bradycardia. The early cycle PACs are not conducted because of refractoriness of the AV node from the previous sinus beat■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2ycardias; Simplified Classification•Sinus bradycardia, including sinoatrial block and wandering atrial pacemaker•Atrioventricular (AV) junctional (nodal) and ectopic atrial escape rhythms•AV heart block (second- or third-degree) or AV dissociation variants•Atrial fibrillation or flutter with a slow Ebook Goldberger’s clinical electrocardiography: Part 2ventricular response•Idioventricular escape rhythm (rule outhyperkalemia)AV Junctional (Nodal) andRelated RhythmsWith a slow AV junctional escape rhytEbook Goldberger’s clinical electrocardiography: Part 2
hm (Fig. 19.4) either che p waves (seen immediately before or just after the QRS complexes) are retrograde (inverted in lead li and upright in lead aV■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2luding WAP (see previous discussion). One type of ectopic atrial rhythm—termed low atrial rhythm—was discussed in Chapter 13.AV Heart Block (Second- or Third-Degree)/AV DissociationA slow, regular ventricular rate of 60 beals/min or less (even as low as 20 beals/min) is the rule with complete heart Ebook Goldberger’s clinical electrocardiography: Part 2block because of the slow intrinsic rate of rhe nodal (junctional) or idioventricular pacemaker (Fig. 19.5). In addition, paLient-s with second-degreeEbook Goldberger’s clinical electrocardiography: Part 2
block (ntxlal or infranodal) often haveSinus BradycardiaFig. 19.1 Marked sinus bradycardia ar about 40,'min. Sinus arrhythmia is also prcscnc. Sinus ■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2ne in a noting athlete or in a healthy person during sleep) or may he due Io drug elTect/loxicily, sinus nixie dysfunction, etc., as discussed in c;hapler 13. The PR interval here is also slightly prolonged (0.24 sec), also consistent with increased vagal tone, intrinsic atrioventricular (AV) nodal Ebook Goldberger’s clinical electrocardiography: Part 2conduction slowing, or with certain drugs that depress activity in the sinoatrial (SA) and AV nodes (c.g.. beta blockers).196 PART III Special TopicsEbook Goldberger’s clinical electrocardiography: Part 2
and ReviewsFig. 19.3 Superficially, Illis rhythm liKiks like sinus bradycardia. Huwever, Careful inspection reveals subtle bloikeil premature atrial c■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu Ebook Goldberger’s clinical electrocardiography: Part 2ricles because of refractoriness of the atrioventricular node. The effective pulse rate will be about 50/min. Shown are modified leads II and Vj from a Holter recording.ECG baseline between the QRS complexes is perfectly flat. Í.C.. no p waves or other atrial activity is evident. This pattern is due Ebook Goldberger’s clinical electrocardiography: Part 2 to simuhannous activation of the atria ami ventricles by the junctional (nixlal) paotmaker, such that thi- p waves an*, masked by the QRS complexes.■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricu■r CHAPTER 19IBradycardias and“Tachycardias: Review andDifferential DiagnosisPreceding chapters have described the major arrhythmias and atrioventricuGọi ngay
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