How do you tell between svt and sinus tachy on ekg?

Answer 1

In any case where there is uncertainty always assume that the rhytm is v tach. One reason is that sustained v tach may be stable for a while , but tends to deteriorate into ventricular fibrillation after a period of time. Unfortunately that period of time is often very short , making the differentiation more difficult because of time constraints. The other reason to assume v tach is that treatment as SVT especially with calcium channel blockers may be lethal if the rhythm is in fact v tach V tach can be categorized in 3 ways : 1 . Sustained or non sustained (over 30 seconds is sustained) 2 . Monomorphic or polmorphic 3 . Pulseless v tach or v tach with pulses With pulseless v tach always think ACLS course of the American Heart Association . The treatment is exactly the same as for pulseless v fib For patients with a pulse and wide complex tachycardia the differentiation needs to be attempted. This can be easy , difficult or sometimes even impossible from the ECG tracing alone . To reiterate when in doubt think v tach . One of the many usefel guides to differentiating the two rhythms is the clinical context . A patient with any history of MI and also a patient with no history of previous tachyarrythmia points you to v tach .The young patient with a history of multiple episodes of tachyarrythmia which resulted in simple treatment and release from emergency rooms in the past likely does have SVT again. The full story on ECG differentiation of v tach from supraventricular tachycardia with "aberrent conduction" or in simple English : SVT with coexisting bundle branch block , is beyond the scope of this answer. But there are a number of points that are myths , real old myths , canards that just fail to die . One myth is that the patient with v tach will tolerate the arrythmia better than the one with SVT ; FALSE! These patients can be stable for a while after initally seen , but deteriorate into vfib at some later time.The SVT patient can tolerate the rhytm of v tach just as poorly as the SVT patient! The ability to tolerate a tachyarrythmia depends on the rate, the size of the heart , and the severity of the underlying condition causing the arrythmia ; not whether it is ventricular or supraventricular. The ECG provides many helpful clues to differentiate the two rhythms . For example, and this is one example only , concordant complexes are almost always v tach . Concordant meaning all the chest leads from V1-V6 show predominantly upright complexes , or else all show predominantly negative complexes But for the nonexpert clinician always think v tach unless certain it is SVT . And hold off on the calcium blockers! Calcium blockers are useful in treating SVT but can be lethal in v tach ,as previously stated. If you really can't tell , either treat as v tach , or if at all possible get an expert opinion . Not always possible before treating as v tach , because if the patient is unstable time may not permit this , and if the patient is pulseless time will definitely not permit this. . But in the stable patient , in whom calcium blocker treatment is being considered for presumed SVT hold off- get an expert opion first if in any doubt whatsoever.