12.1 Arrhythmia Detection & Cardioversion

Arrhythmia Detection & Cardioversion

ARRT Cardiac-Interventional Procedures 1.D Electrophysiology is the R.T.(CI) job around arrhythmia detection, a diagnostic EP study, and cardioversion versus defibrillation: what the surface ECG is, where the catheters sit, how the recording system is used, and when a shock is synchronized on the R wave versus unsynchronized. The same Focus of Questions that sits over interventional procedures still applies: indications, contraindications, access, equipment, image use, complications, and closure.

Quick Answer: A diagnostic EP study records from high right atrium (HRA), His bundle, RV apex, and coronary sinus (CS). AH is AV-nodal time; HV is His–Purkinje time. Synchronized cardioversion shocks on the R wave for unstable SVT, AF, AFL, or VT with a pulse. Defibrillation is unsynchronized for pulseless VT/VF. Elective AF cardioversion needs anticoagulation because of left-atrial thrombus — often a TEE first.

Indications, contraindications, and the Focus-of-Questions frame

Indications for a diagnostic EP study include documented or suspected supraventricular tachycardia (SVT), a wide-complex tachycardia that is not yet named, syncope when bradyarrhythmia or inducible VT is on the table, risk stratification after infarction or in cardiomyopathy, and mapping before ablation. Cardioversion is indicated for unstable SVT, AF, AFL, or VT with a pulse (hypotension, ischemia, acute heart failure, shock) and for elective restoration of sinus rhythm. Defibrillation is indicated for pulseless VT and ventricular fibrillation (VF).

Contraindications are practical. Do not start an elective left-sided study or elective AF cardioversion with a known left-atrial appendage (LAA) thrombus. Uncorrected coagulopathy, active infection at the planned access site, and a patient who needs immediate defibrillation rather than a diagnostic catheter session are stops. Pregnancy is a relative fluoro problem. Complete heart block is a pacing problem, not a shock-the-AV-node problem.

Access, equipment, and image use

Access for a diagnostic EP study is almost always femoral venous, often with multiple venous sheaths so HRA, His, RV, and CS catheters can coexist. Internal jugular access is used when CS cannulation from below is difficult or when a temporary pacing wire is the real goal. Arterial access is not required for a right-heart-only study; it appears when LV mapping or an arterial line is planned.

Equipment the technologist must name: multi-electrode diagnostic catheters, a recording and stimulation system, a programmable stimulator, fluoroscopy, a defibrillator with sync capability already on the pads, pulse oximetry and capnography if sedation is used, and a crash cart. 3-D electroanatomic mapping is an adjunct, not a substitute for knowing where the His catheter is on fluoro.

Image use. Fluoro places catheters and watches for perforation. Teaching views: RAO elongates the AV groove and helps CS and His; LAO opens septum versus free wall. ICE is more ablation than a simple diagnostic study, but the same skill — look at the septum, look at the pericardium — starts here. The EP recorder is an imaging device of a different kind: intracardiac electrograms timed against the surface ECG.

Complications include vascular injury, tamponade from a stiff RV-apex catheter, AV block if you bump the His, thromboembolism, and radiation. Closure for a venous-only study is hemostasis: manual pressure, a figure-of-8 stitch, or a venous closure device per lab protocol — not an arterial collagen plug unless you actually stuck an artery.

Catheter positions: HRA, His, RV apex, CS

High right atrium (HRA). Near the SA node at the SVC–RA junction. It records atrial activation closest to sinus and is a common pacing site for sinus-node and atrial stimulation.

His bundle. Across the superior tricuspid annulus. A good His electrogram shows A (atrial), H (His), and V (ventricular) on one shaft. That is the only catheter that lets you split AH from HV.

RV apex. A stable ventricular recording and pacing site. It is also a perforation site if the tip is stiff and the wall is thin.

Coronary sinus (CS). The CS ostium is in the RA; the body runs in the AV groove and records left atrial and basal left ventricular signals without entering the LA cavity. CS is not an arterial catheter.

AH and HV intervals — teaching, not unpublished ARRT cutoffs

Typical EP-lab teaching (ranges move with autonomic tone; these are not unpublished ARRT cutoffs):

• AH interval: about 60–125 ms. This is AV-nodal conduction time (atrial electrogram at the His catheter to the His deflection). It lengthens with vagal tone and decrement, and shortens with catecholamines.
• HV interval: about 35–55 ms. This is His–Purkinje conduction (His deflection to earliest ventricular activation). HV prolongation means infranodal disease. Block below the His produces a wide, unreliable escape — a different emergency from AV-nodal (AH) block, which often has a narrower junctional escape.

Complete heart block on the surface ECG is P waves marching through a slow ventricular escape. The His catheter tells you where: above His versus at or below His. That location decides whether atropine is even a reasonable thought (more nodal) versus immediate pacing (infranodal).

Programmed stimulation and 3-D mapping conceptually

Programmed electrical stimulation (PES) uses a drive train (S1) plus extra-stimuli (S2, S3, S4) and burst or decremental pacing. The goals are to measure refractory periods, induce the clinical SVT or VT, and prove the circuit. The technologist's job is a working stimulator, labeled channels, and a defibrillator that is already attached. Induction of VT is not a surprise party.

3-D mapping (electroanatomic mapping) tags catheter location in space and paints activation or voltage onto a chamber shell. Conceptually it reduces fluoro and shows scar versus healthy tissue. It does not remove the need to know HRA versus His versus CS on the raw electrograms. ARRT is not asking you to recite a vendor algorithm.

Surface ECG the CI tech must recognize

Sinus tachycardia versus SVT. Sinus has P waves with a consistent PR and a plausible rate for pain, anemia, or volume. SVT is typically abrupt, often with a different P-wave relationship. A sudden, regular, narrow tachycardia in a crashing patient is a synchronized-cardioversion candidate if instability is present.

Atrial fibrillation (AF). Irregularly irregular, no discrete P waves, variable ventricular response. Unstable AF with a pulse is synchronized cardioversion, not defibrillation.

Atrial flutter (AFL). Typical (cavotricuspid isthmus, CTI) flutter is a macro-reentry around the tricuspid annulus. Teaching ECG: atrial rate near 300/min and inferior sawtooth in counterclockwise typical flutter. Ventricular response is often 2:1 (~150). Typical AFL is a right-atrial problem — that matters when the next section isolates pulmonary veins.

VT versus SVT with aberrancy. Practical cath-lab rule: a wide-complex tachycardia is VT until proven otherwise, especially with prior infarct. Findings that support VT: AV dissociation, fusion or capture beats, a very wide bizarre QRS in a scarred ventricle. Aberrancy exists; it is not your first bet while the blood pressure is 60.

Complete heart block. Dissociated P waves and a slow escape. Treat with pacing (transcutaneous while you place a wire) — not with an unsynchronized shock.

Synchronized cardioversion versus defibrillation

Synchronized cardioversion times the shock to the R wave so you do not land on the T wave (vulnerable period → VF). Use it for unstable SVT, AF, AFL, and VT with a pulse.

Defibrillation is unsynchronized energy for pulseless VT and VF. There is no reliable R wave in VF. Waiting for a sync marker in pulseless VT is how you delay a shock the patient does not have time for.

Sedation and airway. Elective cardioversion is a sedation and airway case: NPO when it is truly elective, oxygen, suction, capnography, a plan to support ventilation, and a physician-directed sedative. Emergency cardioversion of a crashing patient is not delayed for a cosmetic propofol nap, but someone still owns the airway.

Pads. Anterior–lateral: right infraclavicular and left apical/axillary. Anterior–posterior (AP): anterior precordium and left posterior — often preferred for AF because more current traverses the atria. Remove transdermal patches, dry the chest, and stay off a preexisting generator when you can (pads several centimeters away). Confirm SYNC is actually capturing QRS complexes before you charge for a pulse-present rhythm.

Anticoagulation before elective AF cardioversion

AF allows stasis in the LAA. A shock can embolize that clot as a stroke. Typical guideline-level teaching (not an ARRT-published hour count): if AF has lasted >48 hours or duration is unknown, do not perform elective cardioversion without therapeutic anticoagulation (classically ≥3 weeks before and continued ≥4 weeks after) or a TEE that excludes LAA thrombus, with anticoagulation around the procedure. Hemodynamically unstable AF is still shocked — thrombus risk does not outrank a collapsing blood pressure — but you do not skip anticoagulation thinking for a scheduled outpatient AF cardioversion.

Rhythm / synchronized? / energy conceptually

Typical biphasic teaching — conceptual energy bands, not unpublished ARRT joule lists. Follow the defibrillator's labeled sequence.

Worked case

AF of unknown duration, BP 88/54, awake, pads on. Check SYNC — there are R waves. This is not VF. Charge a synchronized biphasic shock. If the same patient later has no pulse and a sinusoidal VF waveform, turn sync off and defibrillate. If instead the monitor shows P waves marching through a slow wide escape, you are in CHB: pace, do not keep shocking.

Exam traps

• Unsynchronized shock for AF with a pulse.
• Waiting for a sync marker in pulseless VT/VF.
• Calling typical flutter a pulmonary-vein problem.
• Treating CHB with defibrillation.
• Elective AF cardioversion with no anticoagulation/TEE plan.
• Measuring HV on the HRA catheter.