2025 – PAGE 124 – CARDIOLOGY

BUNDLE BRANCH BLOCKS

Make the diagnosis of a left or right bundle branch block by locating the RsR′ (AKA “rabbit ears”).

• RBBB: RsR′ is where the leads on the RIGHT side of the chest are placed (especially V1 & V2). Note that a RBBB is a common finding in healthy individuals
• LBBB: RsR′ is where the leads on the LEFT side of the chest are placed (especially V5 & V6).

SEPTAL DEFECTS

CARDIAC SHUNT PEARLS & MNEMONICS

PEARLS: When it comes to isolated septal defects, a RIGHT to LEFT shunt is generally much more serious than a LEFT to RIGHT shunt. In a LEFT to RIGHT shunt the blood is simply getting oxygenated multiple times, but in a RIGHT to LEFT shunt, oxygenation is being bypassed, resulting in possible hypoxemia, cyanosis, and death!

• NOTE: In cyanotic heart disease, this pearl may not apply because sometimes septal defects are a corrective measure, and the blood on the RIGHT side has some oxygenated blood that needs to reach the periphery via a RIGHT to LEFT shunt.

MNEMONICS: Imagine the circulatory system as a ONE-WAY CIRCUIT (or a ONE-WAY RACETRACK). “At any point in the cardiopulmonary circuit/racetrack, GOING TO THE LEFT (or SHUNTING TO THE LEFT) is BAD because you will leave the vascular system (or crash and burn).

ATRIAL SEPTAL DEFECTS (ASD)

Most atrial septal defects (ASDs) are asymptomatic and do not require repair. Findings on exam may include a FIXED SPLIT S2, a parasternal impulse/heave or a soft LUSB mid-systolic murmur (“takes time to get enough blood in atrium to make a sound”). The most common types of ASD are ostium secundum (70%) and ostium primum (20%). (An “ostium” is a small hole or opening.)

• A SECUNDUM ASD is the most common type of ASD. Repair is required if the LEFT TO RIGHT shunt progresses to a ratio of > 2:1 (technically if > 1.7:1). The ratio refers to the volume of blood going into the pulmonary circulation compared to the volume of blood going out of the LV.
• OSTIUM PRIMUM ASD: This is much less common but more serious, so these should be repaired EARLY. Having a primum ASD is not a contraindication to getting pregnant as long as the LEFT TO RIGHT shunt ratio is less than 2:1. If the patient develops a RIGHT TO LEFT shunt, pregnancy is contraindicated, and this is now called EISENMENGER’S SYNDROME. (The patient may present with CYANOTIC MUCOUS MEMBRANES.)
  • LOW-YIELD NOTE (for understanding only): Primum ASDs start off as a shunt to the RIGHT from the high pressure left side. Due to excess flow into the pulmonary circulation, pulmonary hypertension develops and eventually causes a shunt to the LEFT. Once that develops, you have Eisenmenger’s Syndrome.

VENTRICULAR SEPTAL DEFECTS (VSDS)

A ventricular septal defect (VSD) is a left-to-right shunt, with MEMBRANOUS VSDs being less likely to close than MUSCULAR VSDs. VSDs are associated with CRI-DU-CHAT (5p–) and the major TRISOMIES (13, 18 & 21), with Trisomy 21 also known as DOWN SYNDROME. ASDs are more common in Trisomy 13 and 18 than 21. The physical exam may show a LLSB thrill/murmur that is HOLOSYSTOLIC, a “hyperdynamic precordium,” or possibly NO murmur and a single S2 in very large VSDs with pulmonary hypertension (as in Eisenmenger syndrome). The chest X-ray (CXR) may show increased pulmonary vasculature and biventricular hypertrophy. Treatment may include diuretics, afterload reduction (e.g., captopril), digoxin, and nutritional support such as concentrated formula. Repair is indicated if the patient develops PULMONARY HYPERTENSION, FAILURE TO THRIVE, or a shunt that progresses to > 2:1.

MNEMONIC: A VSD is a SEPTAL defect, so imagine looking into the home of a three-year-old, where you see a roll of SEPTATED (perforated) stamps with pictures of TRIcycles on them, and the stamps are being licked by a CAT.