Most SVTs are due to re-entrant circuits as you see here. Thinking about where that circuit exists can help you better understand the EKG, how to diagnose and ultimately treat.
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1️⃣AVNRT is the most common one we think of SVT. This is a re-entrant circuit within the AV node itself when it has “dual node” physiology with both a slow and fast pathway. A PAC or PVC at the right millisecond of the cycle can sneak in an impulse to activate that circuit.
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2️⃣ AVRT also involves the AV node for one limb of the circuit but uses an accessory pathway (WPW) as the second part. This can be an “orthodromic” AVRT with the circuit going down the AV node and back up the pathway — or “antidromic” when it goes down the pathway first and then up the node. The QRS is wide in antidromic AVRT as it conducts down the acessory pathway like a delta wave.
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3️⃣ Atrial tachycardia can be re-entry or due to “automaticity” due to an irritable focus that will recurrently fire PACs that can produce runs of tachycardia with a different p wave morphology.
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4️⃣ Atrial flutter is a re-entry circuit around the right atrium facilitated by a piece of conducting tissue called the cavo-tricuspid isthmus. The big saw tooth waves arise from the impulse circling around the RA.
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💉 Adenosine temporarily halts AV nodal conduction and is super helpful in making the diagnosis. It will break the circuit in AVNRT and AVRT and establish sinus rhythm. For atrial flutter and atach it will briefly halt conduction to the ventricle and reveal the atrial and flutter waves marching through.
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💊 Meds such as beta blockers and calcium channel blockers can slow conduction down the AV node for rate control and suppress PACs that initiate the SVT. Anti arrhythmic meds may also be used.
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Definitive treatment for these arrhythmias may include catheter ablation by applying heat energy to the conduction tissue causing the problem abolishing the circuit or the focus!
.
1️⃣AVNRT is the most common one we think of SVT. This is a re-entrant circuit within the AV node itself when it has “dual node” physiology with both a slow and fast pathway. A PAC or PVC at the right millisecond of the cycle can sneak in an impulse to activate that circuit.
.
2️⃣ AVRT also involves the AV node for one limb of the circuit but uses an accessory pathway (WPW) as the second part. This can be an “orthodromic” AVRT with the circuit going down the AV node and back up the pathway — or “antidromic” when it goes down the pathway first and then up the node. The QRS is wide in antidromic AVRT as it conducts down the acessory pathway like a delta wave.
.
3️⃣ Atrial tachycardia can be re-entry or due to “automaticity” due to an irritable focus that will recurrently fire PACs that can produce runs of tachycardia with a different p wave morphology.
.
4️⃣ Atrial flutter is a re-entry circuit around the right atrium facilitated by a piece of conducting tissue called the cavo-tricuspid isthmus. The big saw tooth waves arise from the impulse circling around the RA.
.
.
💉 Adenosine temporarily halts AV nodal conduction and is super helpful in making the diagnosis. It will break the circuit in AVNRT and AVRT and establish sinus rhythm. For atrial flutter and atach it will briefly halt conduction to the ventricle and reveal the atrial and flutter waves marching through.
.
💊 Meds such as beta blockers and calcium channel blockers can slow conduction down the AV node for rate control and suppress PACs that initiate the SVT. Anti arrhythmic meds may also be used.
.
.
Definitive treatment for these arrhythmias may include catheter ablation by applying heat energy to the conduction tissue causing the problem abolishing the circuit or the focus!
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