Ectopic Heartbeats

Mechanisms of Ectopic Beat Formation

1. Abnormal Automaticity (Enhanced Ectopic Focus)

2. Reentry

Causes of Ectopic Foci

• Local areas of myocardial ischemia
• Small calcified plaques pressing on adjacent cardiac muscle
• Toxic irritation of the AV node, Purkinje system, or myocardium: infection, drugs, nicotine, caffeine, digitalis toxicity
• Mechanical irritation (e.g., catheter tip touching the endocardium during cardiac catheterization)
• Electrolyte imbalances (hypokalemia, hypomagnesemia)
• Hypoxia, sympathetic excess, thyrotoxicosis
• Guyton & Hall Textbook of Medical Physiology, p. 168

Classification by Site of Origin

1. Atrial Premature Contractions (PACs)

• Early P wave with an abnormal morphology (different from the sinus P wave)
• P wave is frequently inscribed within the preceding T wave, making morphology unclear
• PR interval may be shortened (if ectopic focus is near the AV node) or prolonged
• QRS is usually narrow (normal) - conducted normally through the bundle of His and ventricles
• Compensatory pause follows - the premature impulse discharged the sinus node early, resetting its timing

Atrial premature beat - Guyton & Hall, Fig. 13.9

Frequent atrial ectopics with varying conduction - some conducted with RBBB aberrancy, some nonconducted, some in pairs - Braunwald's Heart Disease, Fig. 65.1

• In the vast majority, PACs are benign and require only reassurance
• However, Haïssaguerre et al.'s landmark work showed PACs from pulmonary vein sleeves can trigger atrial fibrillation (AF)
• Excess PACs (>30/hour or runs >20 beats) are associated with incident AF, stroke, and death
• Patients with excess PACs and CHADS-VASc ≥ 2 have an annual stroke risk comparable to patients with known AF
• Very frequent PACs (20-40% daily burden) may cause reversible cardiomyopathy

2. Junctional (AV Nodal) Premature Contractions

• P wave is absent or hidden - the impulse travels retrogradely into the atria and forward into the ventricles simultaneously, superimposing the P wave onto the QRS-T complex
• The QRS complex is usually narrow (normal configuration)
• The P wave, if visible, appears just before or just after the QRS and is typically inverted in inferior leads

AV nodal premature contraction showing P wave hidden within QRS - Guyton & Hall, Fig. 13.10

3. Premature Ventricular Contractions (PVCs)

1. Wide, bizarre QRS complex (usually >120 ms) - the impulse travels through the ventricular myocardium rather than the fast-conducting Purkinje system
2. High voltage - in a normal beat, both ventricles depolarize nearly simultaneously so the vectors partially cancel out. In a PVC, one ventricle depolarizes ahead of the other, generating large electrical potentials
3. T wave polarity opposite to the QRS - because slow muscle conduction means the first areas to depolarize are also the first to repolarize, creating discordance
4. Full compensatory pause - the SA node timing is usually undisturbed; the post-PVC pause brings the next sinus beat back on schedule

PVCs alternating with normal beats (bigeminy). Vectorial analysis (lower panel) localizes the ectopic focus to the base of the ventricles - Guyton & Hall, Fig. 13.11

• Isolated, infrequent PVCs in an otherwise healthy heart are usually benign (nicotine, caffeine, fatigue, emotion)
• PVC burden >20% of beats is associated with cardiac dilation and cardiomyopathy - often reversible with treatment
• PVCs occurring in the vulnerable period (on the T wave, "R-on-T phenomenon") risk triggering ventricular fibrillation
• PVCs in the setting of ischemia, structural heart disease, or after MI carry significantly higher risk

Symptoms

• A sense that the heart gave an "extra beat" or "missed a beat"
• Palpitations or fluttering in the chest or throat
• A thudding or pounding sensation (the forceful beat after the pause)
• Occasional brief dizziness or faintness

Diagnosis

• 12-lead ECG - detects ectopic beats occurring at the time of recording
• Ambulatory Holter monitoring (24-48 hours) - quantifies ectopic burden; essential for assessing frequency and patterns
• Event recorder / loop recorder - for infrequent symptoms; allows patient-triggered recording
• Echocardiogram - to assess for underlying structural heart disease and cardiomyopathy (especially if PVC burden is high)

Treatment

• Eliminate triggers (caffeine, alcohol, sleep deprivation, stimulants)
• Beta-blocker or non-dihydropyridine calcium channel blocker (verapamil, diltiazem)
• Antiarrhythmic drugs (e.g., flecainide) in refractory cases
• Catheter ablation for high-burden, unifocal, drug-refractory symptomatic PACs

• Address reversible causes (ischemia, electrolyte abnormalities, thyrotoxicosis)
• Beta-blockers - first-line for symptomatic PVCs
• Antiarrhythmics (flecainide, propafenone for structurally normal heart; amiodarone, mexiletine if structural disease)
• Catheter ablation - highly effective, especially for unifocal PVCs; indicated for symptomatic or high-burden PVCs causing cardiomyopathy

Proximal Femur Nailing (Cephalomedullary Nailing)

Indications

• Miller's Review of Orthopaedics 9th Ed, p. 918
• Rockwood and Green's Fractures in Adults 10th Ed

Implant Principles

• Proximal entry angle: typically 4-6° valgus (trochanteric entry)
• Anterior bow: nail bow must match the anterior bow of the femur to avoid anterior cortex perforation distally
• Lag screw: single-screw design (e.g., PFNA, Gamma nail, TFN) or dual-screw design (e.g., InterTAN)
• Blade vs. screw: Cephalad blade has more medial migration risk than a cephalad screw

Surgical Setup and Positioning

• Flexed and abducted in a lithotomy stirrup (C-arm goes between legs)
• Extended in the "scissor" position (C-arm from opposite side) - preferred when contralateral hip motion is limited

Patient positioning on fracture table - Rockwood & Green, Fig. 54-22

Fracture Reduction - The Most Critical Step

AP view:

• Reduce to anatomical or slight valgus - valgus is associated with the lowest risk of implant cut-out and less limb shortening
• A slight medial cortex gap in valgus is acceptable - it closes rapidly with fracture collapse
• Varus must never be accepted - mechanically unstable, leads to progressive varus collapse and cut-out

Lateral view:

• Femoral head, neck, and trochanteric region must align in a straight line
• Sagittal sag is more common in bariatric patients, high-energy injuries, and comminuted fractures

Reduction aids when closed reduction fails:

• Posterior reduction aid (attached to fracture table - provides upward pressure)
• Vertical crutch/support under the fracture site
• Bone lever or clamp placed percutaneously
• Formal open reduction (rare - mainly for A3/reverse oblique/subtrochanteric)
• Cerclage wires after open reduction in selected cases

Fracture reduction: varus (A) must be corrected to valgus (B) - Rockwood & Green, Fig. 54-23

Surgical Technique - Step by Step

• Rockwood and Green's Fractures in Adults 10th Ed, p. 2726-2727

The Tip-Apex Distance (TAD)

Tip-Apex Distance (TAD) calculation - Miller's Review of Orthopaedics, Fig. 11.16

• TAD <25 mm - strongly associated with lowest cut-out rate
• TAD >25 mm - significantly higher risk of screw cut-out
• The ideal lag screw position is center-center on AP, center on lateral

Nail Length - Short vs. Long

Postoperative Care and Weight Bearing

• Immediate or early full weight bearing is the goal in elderly patients
• Physiotherapy and mobilization start on day 1 post-op
• Prophylactic anticoagulation for VTE prevention
• Transfer to a pressure-relieving mattress as soon as possible

Complications and Their Prevention

• Rockwood and Green's Fractures in Adults 10th Ed, p. 2730

Cut-out of cephalomedullary nail lag-bladed screw due to varus collapse. Revision arthroplasty required. - Rockwood & Green, Fig. 54-33

CM Nail vs. Sliding Hip Screw (SHS) - Decision Guide

• Miller's Review of Orthopaedics 9th Ed, p. 918