Why we look lead V1 to diagnose RVH but look at V4R , to diagnose RV infarction ?
Posted Jul 02 2009 5:04pm
The right ventricle is a unique chamber of the heart . It is the anterior most chamber and triangular in shape. Even though the walls of RV are not clearly demarcated , it does have anterior , posterior, and lateral free surfaces . Anatomically it has a inflow body, apex and outflow portions . The apex of right ventricle , blends with the lower IVS at an acute angle.
How does RVH occur anatomically ?
The anatomy of RV is such that it does not allow it a concentric RVH ( like LVH ) . In fact , there is a disproportionate free wall , anterior wall hypertrophy many situations like PHT /Pulmonary stenosis. The infero posterior aspect of RV rarely show hypertrophy.
Since RV is the anterior most chamber, located just beneath the left border of sternum RVH brings the RV further closer to chest wall .This makes the V1 lead to show tall R in V1.
What happens in RVMI?
Unfortunately, when we refer to RVMI, we generally do not make any efforts to locate or estimate it’s size. Since RV has , anterior , lateral and posterior surface , the site and the extent of the mI will have a major impact on the ECG features .
Most often the RVMIoccur as a part of infero posterior MI .Hence , it is uncommon for the anterior surface of RV to get involved. But , it can be involved if RCA gives of a large RV branch that reach the anterior surface of RV.
Anterior RVMI can occur as a part of LAD MI , if a large conal branch cross the RV surface.
What prevents the lead V1 from showing the ST elevation of RVMI?
Most of the RVMI do not involve the anterior surface of the RVso , less chances for ST elevation
Further , if a true posterior wall MI occur as a part of RVMI (Which is often the case !) V1 can never show ST elevation as the posterior MI tend to have a ST depressing effect in the V1, V2 leads.
Extensive IWMI , can have reciprocal ST depression in V1-V2.This again , prevents V1 lead to show the ST elevation
So many times , even though V1 lead is just sitting over the chamber RV it fails to pick the ST elevation forces of RVMI
Advantage of V4 R ?
V4R records remote RV forces , as these signals are not contaminated by the inferio posterior ST forces. Hence a 1mm ST elevation in right sided chest leads have good sensitivity and specificity to diagnose RVMI .
When can V1 show ST elevation in RVMI?
If the RV anterior wall is predominantly involved ( Ie Anterior RVMI ) ST elevation can occur in V 1 like a anteroseptal MI.
Rarely a q RBB can occur in V1 in isolated RVMI.
V1 lead , though anatomically proximal to RV has less value in diagnosing RVMI since this lead picks up Infero posterior negative ST forces and get neutralised. So relying on lead V1 to diagnose RVMI is not adviced, except when anterior surface of RV is involved.