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206 Section 3 Cardiovascular Disease

Supraventricular Figure 21.1 Supraventricular structures
VetBooks.ir Sinus node myocardium, the atrioventricular node (AV
include the sinus node, the atrial
node), the His bundle and the ostia of the
veins entering the atria. Supraventricular
rhythms are characterized by a narrow
AV node QRS complex, while ventricular rhythms
are characterized by a wide and “bizarre”
QRS complex.

Ventricular

Table 21.1 Differential diagnosis of supraventricular arrhythmias

Rate (beats/min) P‐waves (II,III,aVF) QRS complexes P:QRS relationship Regularity

Sinus bradycardia <60 (D) Positive Narrow P before QRS Regular, or regularly
<100 (C) Wandering 1:1 irregular (sinus arrhythmia)
pacemaker
Sick sinus Variable pauses Positive Narrow Irregular
syndrome >3 s Negative Wide (VEB) P before QRS
Occasionally absent
Atrial standstill 20–60 (D) Absent Wide(VEB) None Regular
First‐degree AV WNL Positive Narrow P before QRS Regular, or regularly
block Wandering 1:1 irregular (sinus arrhythmia
pacemaker
Second‐degree WNL pauses Positive Narrow P before QRS Irregular
AV block Wide(BBB) Isolated P
Third‐degree AV 20–60 (D) Positive Narrow (JEB) None Regular
block 80–140 (C) Wide (VEB)
Atrial fibrillation 100–120 Lone AF Absent Narrow None Irregular
150–180 No CHF Fibrillation waves Rarely
>180 CHF wide(BBB)
Focal atrial 210–230 Positive Narrow P before QRS Regular or irregular
tachycardia Negative Rarely
wide(BBB)
Atrial flutter 180–350 Absent Narrow None regular or irregular
Flutter waves Rarely
wide(BBB)
Junctional 120–200 Negative Narrow P during or after Regular
tachycardia Rarely QRS
wide(BBB)
AV reciprocating 190–300 Negative Narrow P after QRS Regular
tachycardia Rarely
wide(BBB)
AF, atrial fibrillation; AV, atrioventricular; BBB, bundle branch block; C, cat; CHF, congestive heart failure; D, dog; JEB, junctional escape beat;
VEB, ventricular escape beat.