srakaview.blogg.se - Ivcd rhythm strip

Short PR interval: preexcitation (ie, accessory pathway b/t atria & ventricles) or junctional rhythm.

Avoids inaccuracies in which early portion of P wave or QRS is isoelectric.

Measure in lead with largest, widest P wave & longest QRS interval.

Parasympathetic predominates => slower HR => longer PR interval.Sympathetic predominates => faster HR => shorter PR interval.Hence, PR interval varies with heart rate (HR).Controlled by autonomic nervous system – sympathetic & parasympathetic balance.HV interval = time b/t His bundle spike & onset of ventricular deflections.AH interval = time b/t lower part of RA & His bundle spike.Most of PR interval reflects slow conduction through AV node (ie, proximal to His bundle).Cardiac events: (1) atrial depolarization & repolarization (2) stimulation of AV node, His bundle, bundle branches, & Purkinje system.Does not include duration of SA conduction (ie, conduction from SA node to RA).Represents time for impulse to travel from atria (adjacent to SA node) through AV node, bundle of His, bundle branches, & Purkinje fibers until ventricular depolarization begins.“PQ” interval used interchangeably if Q wave is initial wave of QRS thus, representing actual measured period.Note: includes both atrial depolarization (P wave) & atrial repolarization (Tp wave).PR interval: measured from P wave onset to QRS complex onset.there are significant numbers of false positives and false negatives, but the more of these clues satisfied in a given tracing, the more likely it is “V Tach” otherwise the choice is “wide complex SVT”. Please note that these findings as stated above are not 100% specific or 100% sensitive, i.e. If LBBB pattern and there is a Q or QS in Lead V6 Notching on the initial downstroke of a predominately negative QRS complex in Lead avRĢ0. If LBBB pattern and initial R > 1 mm wide Lead V1ġ9.

If RBBB pattern and rS complex in Lead V6ġ8. If RBBB pattern and all positive lead V1ġ7. If LBBB pattern and |Q-R| > 1.5 mm wide in Leads V1 or V2ġ6. If |R-S| interval > 2.5 mm wide in any one precordial lead where |R-S| is beginning of QRS to low point of S-waveġ4. Absence of an RS complex in all precordial leadsġ3. Previous old tracing demonstrating QRS complexes of a different morphology than the current tracingġ2. Precordial leads V1 to V6 all positiveġ1. Lead V1 all upright with taller initial rabbit earĨ.

Ventricular activation-velocity ratio Vi / Vt 0.14 secĦ.

Notching present on the initial downstroke of a predominately negative QRS complex – suggests V Tach.

Initial R-wave or Q-wave width > 1mm – suggests V Tach.

The challenge most often becomes, is this V Tach or is it Wide Complex SVT? Most importantly, the clinical picture is the most important clue but otherwise the following findings are more suggestive of V Tach: Now for the focus of this particular topic: It is due to a circular conduction (circus). This mechanism of V Tach is called reentry. If this cyclic impulse is sustained (3 times or greater) it is labeled ventricular tachycardia. If the proximal end of Branch I has adequately recovered (repolarize) and is receptive (not refractory), the cycle will repeat itself. At this point, the signal has traveled in a circle and has returned to its starting point. When the signal traverses Branch I and reaches the distal end, if the distal end of Branch II has adequately repolarized (not refractory), one might suggest that the signal then retrograde propagates up Branch II (this is indeed what happens).

Mechanism 2: Reentry ( most common) – Reentry tachycardia can occur from the spontaneous discharge of a terminal Purkinje cell if its subsequent propagation encounters a branch in its pathway:īranch I – Normally conducted (Antegrade) pathwayīranch II – Refractory pathway (Antegrade signal is blocked).

Mechanism 1: Increased automaticity ( uncommon) – If an irritable focus of the terminal Purkinje cells discharges at a rapid rate, > 150 bpm, this will produce a QRS complex as discussed previously (wide > 0.12 sec, bizarre-shaped).

It is clearly true that V Tach is a more life threatening rhythm and that the treatment mode is very different from SVT.

What is most important is the recognition of V Tach and differentiating it from wide complex SVT. (I will discuss these two mechanisms below, primarily for the sake of completeness, and is not intended to represent a thorough discussion of these topics.) Ventricular Tachycardia occurs via two common mechanisms: increased automaticity and reentry. It might degenerate to Ventricular Fibrillation and death.ĭevelopment Mechanisms of Ventricular Tachycardia Clinical comment: This is a life-threatening rhythm and must be addressed promptly.