PVC Morphology and Localization Lecture Notes

General Rules for PVC Morphology and Localization

• Bundle Branch Block (BBB) Pattern Interpretations:     * Right Bundle Branch Block (RBBB): Indicates a Site of Origin (SOO) in the Left Ventricle ($LV$).     * Left Bundle Branch Block (LBBB): Indicates a SOO in the Right Ventricle ($RV$) or the Interventricular Septum ($IVS$).

• QRS Axis Determination:     * Superior vs. Inferior Axis: Evaluated primarily using Lead $II$ and Lead $III$.     * Right vs. Left Orientation: Evaluated using Lead $I$, $aVR$, and $aVL$.

• Precordial Transition Principles:     * RBBB PVC: The transition occurs progressively earlier as the SOO moves from the base of the heart toward the apex.     * LBBB PVC: The transition occurs progressively later as the SOO moves from the septum toward the Right Ventricular ($RV$) free wall.

• QRS Complex Width:     * Narrow QRS: Suggests a Septal origin.     * Wide QRS: Suggests a Free wall origin.

Stepwise Localization Algorithm

• Step 1: Superior/Inferior Axis (Lead II and III):     * Inferior Axis ($+ve$ leads II/III): Localizes to basal areas of the heart, the outflow tract ($OT$), or the superior aspect of the Mitral Valve ($MV$) or Tricuspid Valve ($TV$).     * Superior Axis ($-ve$ leads II/III): Localizes to the inferior aspect of both ventricles.     * Inferior Lead Discordance ($+ve$ II / $-ve$ III or $-ve$ II / $+ve$ III): Typically indicates midcavitary structures.

• Step 2: Refining Morphology (Lead I and BBB Pattern):     * For Inferior Axis PVCs:         * Positive Lead I ($+ve$): Rightward structures including the posterior Right Ventricular Outflow Tract ($RVOT$), Right Coronary Cusp ($RCC$), Parahisian region, and superior aspect of the $TV$.         * Negative Lead I ($-ve$): Leftward structures including the anterior $RVOT$, Left Coronary Cusp ($LCC$), Aorto-Mitral Continuity ($AMC$), Anterolateral Mitral Annulus ($AL-MA$), and the Left Ventricular ($LV$) summit.         * Midline Structures: Areas like the $RCC-LCC$ commissure can present with a biphasic or $+/-$ morphology in Lead $I$.     * For Superior Axis PVCs:         * LBBB Pattern: Localizes to the inferior $TV$, Moderator Band ($MB$), or Cardiac Crux.         * RBBB Pattern: Localizes to the inferior $MV$, Posterior Papillary Muscle ($PPM$), or left posterior fascicle ($LPF$).

Detailed Localization Based on Precordial Transition

• Inferior Axis (Positive Leads II and III):     * Positive Lead I (Rightward/Midline):         * Negative $aVL$ and Transition $\geq V4$: Tricuspid Valve ($TV$) free wall.         * Negative $aVL$ and Transition $\leq V3$: $TV$ septum or Parahisian region.         * Any $R$ or $r$ in $aVL$ and Transition $\geq V4$: Posterior $RVOT$.         * Any $R$ or $r$ in $aVL$ and Transition $V3$: Posterior $RVOT$ or $RCC$ (determined by $V2$ transition rate).         * Any $R$ or $r$ in $aVL$ and Transition $\leq V2$: Right Coronary Cusp ($RCC$).     * Negative Lead I (Leftward from Midline):         * Transition $\geq V3$: Anterior $RVOT$.         * Transition $V2$: Left Coronary Cusp ($LCC$) (often features notched $V1$) or $LV$ summit (often features a pseudo-delta wave).         * Transition $V1$ (RBBB): $LCC$ (notched $V1$), $LV$ summit (pseudo-delta), $AMC$ ($qR$ in $V1$), Top of $MV$ ($R$ or $Rsr'$ in $V1$), Anterolateral Papillary Muscle ($APM$) ($R, Rsr',$ or $qR$ in $V1$), or Left Anterior Fascicle ($LAF$) ($rsR'$ in $V1$, narrow $QRS$).

• Superior Axis (Negative Leads II and III):     * LBBB (Right Ventricle, Crux):         * Transition $\geq V4$: $TV$ free wall or Moderator Band ($MB$).         * Transition $V3$: $TV$ septum or Cardiac Crux (marked by $QS$ in inferior leads and pseudo-delta wave).     * RBBB (Left Ventricle):         * $R/S$ in V6 > 1: Inferior Mitral Valve ($R$ or $Rsr'$ in $V1$).         * $R/S$ in $V6 \leq 1$: Posteromedial Papillary Muscle ($PPM/PMPM$) ($R, Rsr',$ or $QR$ in $V1$) or Left Posterior Fascicle ($LPF$) ($rsR'$ in $V1$, narrow $QRS$).

• Inferior Lead Discordance:     * Positive II / Negative III:         * Lateral $TV$ ($rS$ in $V1$, transition in $V4-V5$).         * Moderator Band ($MB$) ($QS$ or $rS$ in $V1$, transition in $V5-V6$).         * Parahisian ($QS$ in $V1$, transition in $V2-V3$, narrow $QRS$).     * Negative II / Positive III:         * Lateral $MV$ ($R/S$ in V6 > 1).         * Anterolateral Papillary Muscle ($APM$) ($R/S$ in V6 < 1).

Specific Anatomical Site Characteristics

• Outflow Tract PVC Precordial Transitions:     * Transition refers to the lead ($V1-V6$) where the QRS changes from predominantly negative to positive.     * LVOT PVCs: Transition typically occurs at or earlier than the sinus transition.     * RVOT PVCs: Transition typically occurs later than the sinus transition.     * RVOT Septum vs. Free Wall: $RVOT$ free wall structures are more anterior, resulting in a later transition ($V4-V5$) compared to septal or posterior origins ($V2-V3$).

• Aortic Root and Coronary Cusps:     * RCC (Right Coronary Cusp): LBBB, transition at or before $V3$ ($V2$ transition ratio $\geq 0.6$), and $QS$ in $V1$.     * LCC (Left Coronary Cusp): LBBB, transition at or before $V3$, often notched $V1$.     * NCC (Non-Coronary Cusp): Morphological features demonstrated by specific ECG trace provided in Figure 81-4.     * RCC-LCC Junction: Often manifests as a biphasic pattern in lead $I$.

• Left Ventricular Summit (LVS) and Aorto-Mitral Continuity (AMC):     * Arrhythmias from posterior structures produce earlier transitions than anterior structures.     * LV Summit: Features RBBB or LBBB with $V2$ or $V3$ transition, taller $R$ wave in $III$ than in $II$, pseudo-delta wave, and/or Maximum Deflection Index ($MDI$) > 0.55, plus a $V2$ "pattern break."     * AMC: Features an inferior axis and a signature $qR$ pattern in Lead $V1$.

• Papillary Muscle and Fascicular VT/PVCs:     * Anterolateral PM (APM): RBBB, $R, Rsr',$ or $QR$ in $V1$; late $R/S$ transition; Lead $II$ might be negative; $R/S$ in V6 < 1.     * Posteromedial PM (PMPM/PPM): RBBB, $R, Rsr',$ or $qR$ in $V1$; $R$ and $S$ present in $V5$.     * Left Anterior Fascicle (LAF): $rsR'$ in $V1$, narrow $QRS$, often superior axis.     * Left Posterior Fascicle (LPF): Often associated with superior axis, narrow $QRS$, and $rsR'$ in $V1$.

• Tricuspid and Mitral Annulus:     * Tricuspid Valve (TV) Top: LBBB, variable transition, $QS$ or $rS$ in $V1$, positive $aVL$ (differentiating it from negative $aVL$ in $RVOT$), and Lead $III$ may be negative.     * Anterolateral MV: RBBB, positive concordance in precordial leads, and $R$ or $Rsr'$ in $V1$.     * Cardiac Crux: LBBB, $V2$ transition, left superior axis, $QS$ in inferior leads, pseudo-delta wave, and/or MDI > 0.55.

Summary of Characteristic Waveforms (Figure 81-4)

• Para-Hisian: Hallmark is an isoelectrical or "W" pattern in lead $aVL$ and a more positive $R$ wave in Lead $I$.

• Anterior Free-Wall (AF): Characteristic lower amplitude, notched inferior leads, and late precordial transition.

• Septal Origins (AS, MS, PS):     * Anteroseptal (AS): Negative Lead $I$.     * Midseptal (MS): Multiphasic Lead $I$.     * Posteroseptal (PS): Positive Lead $I$.