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(Part 2 (finally😍)) 🤓Escape rhythms and ectopic beats Definitions Escape rhythm: a non-sinus pacemaker takes over from a non-functioning SA node. Beat occurs after the next expected sinus beat. HR is <60, except in 'accelerated' escape rhythm, which is 60-100. Ectopic beat: a non-sinus beat occurs before the next expected sinus beat. Often irregular ventricular ectopics, which are non-pathological; can also be regular e.g. ventricular bigeminy. ECG findings in escape rhythms Atrial escape rhythms: HR 40-60, P wave may be inverted. Junctional escape rhythms: HR 40-60, P wave hidden in QRS complex Ventricular escape rhythms: HR 20-40, broad QRS. Cardiac axis deviation Cardiac axis which is less than -30° (left axis deviation, LAD) or greater than +90° (right axis deviation, RAD). ECG Look at the QRS complexes in the limb leads: In LAD, they're Leaving (QRS pointing away from each other): +ve QRS (dominant R) in I and aVL, -ve QRS (dominant S) in II and aVF. In RAD, they're Romantic (QRS pointing towards each other): -ve QRS (dominant S) in I and aVL, +ve QRS (dominant R) in III and aVF. Causes LAD: Left anterior fascicular block. LBBB LVH Inferior MI RAD: Left posterior fascicular block. RVH Lateral MI Lung disease: PE, COPD. ↑K+ May be a normal variant. WPW syndrome and ventricular ectopics can cause either. Acute management of bradycardia Atropine 500 mcg IV if there is cardiac ischaemia, syncope, SBP <90, or HF. Further measures if there is inadequate response or risk of asystole: further atropine (up to 3 mg), transcutaenous pacing, adrenaline infusion, or isoprenaline infusion (β1 agonist). Risk of asystole is defined as severe AV block (3rd degree or 2nd degree type 2), recent asystole, or ventricular pauses (> 3 s). Definitive management with transvenous and/or permanent pacemaker. Pacemakers and ICDs Implantable devices used to control cardiac rhythm, collectively known as cardiac conduction devices. Devices and indications Implantable cardioverter-defibrillators (ICDs) are used to prevent sudden cardiac death (SCD) in: {LVSD with EF <35%} plus {wide QRS [120-149 ms] or high SCD risk}. Sustained VT causing syncope or haemodynamic instability. Congenital high risk conditions e.g. long QT, Brugada, HCM. Secondary prevention: post VF or VT cardiac arrest. Permanent pacemakers (PPMs) are used to maintain an adequate heart rate in: AV block: 3rd degree or 2nd degree type 2. Sinus node dysfunction with symptomatic bradycardia. Carotid sinus syndrome. Cardiac resynchronization therapy (CRT, aka biventricular pacemaker): Indication: {LVSD NYHA class 2-4 with EF <35%} plus {very wide QRS [>150 ms] or LBBB}. Can be pacer only (CRT-P) or include an ICD function (CRT-D). Structure and mechanism Pulse generator – comprising a battery, control circuits, and transmitter/receiver – is placed in the infraclavicular area (subcutaneously or submuscularly). Requires reimplantation every 5-10 years due to battery lifespan. Pacing leads (one or two) extend from the generator, transvenously, into the right atrium and/or ventricle (plus left ventricle in CRT), with the tips implanted in the myocardium. These leads both sense cardiac depolarization and deliver cardiac stimulation. PPMs can provide either a fixed impulse rate ('asynchronous'), or an impulse in response to absent depolarization ('synchronous'). ICDs respond to ventricular tachycardias with a defibrillation shock. Many devices also have a pacer function, both to treat co-morbid arrhythmias and to deliver antitachycardia pacing before shocking. Pacemaker codes and modes Standard 5 letter code to describe PPMs, with often just the first 3 used: Where it's pacing: Atria, Ventricles, or Dual (A+V). Where it's sensing: Atria, Ventricles, or Dual (A+V). Response to sensing depolarization: Triggers pacing, Inhibits pacing (i.e. doesn't pace), Dual (triggers and inhibits). Rate modulation: ability to adjust HR in response to physiological need. Anti-tachycardia function: Pacing, Shock, or Dual (P+S). Common modes: VVI: no pacing if ventricular depolarization detected, otherwise it paces. AAI is the same for the atria. DDD: senses both A and V, and takes over if either don't work. VDD: used in AV block, as it senses both A and V but only paces V. VOO: asynchronous pacing, which should be used during surgery as diathermy may affect device. Interpreting pacemaker ECGs Most pacemaker leads sit in RV causing LBBB pattern, though a minority are LV and RBBB. If patient's heart rate is above PPM threshold, pacing spikes will be appropriately absent. See pacemaker and ICD complications for abnormal ECG findings in presence of PPM. Device interrogation and manipulation Investigate cardiac symptoms in PPM/ICD patients as usual, including with an ECG, but specific device interrogation may also be needed: Should be done by specialists using specialist devices. Even in asymptomatic patients it is done regularly e.g. 3-monthly. Pacemaker/ICD magnets allow basic device manipulation. When placed over a PPM, it will revert to asynchronous mode (good if device is undersensing or overpacing), and when placed over an ICD, it will prevent shocks (but not pacing). Pacemaker and ICD complications General Acute (post-placement): pneumothorax, infection, bleeding (including pocket haematoma). Device-related pain. ICD malfunctions Inappropriate ICD shocks: may be triggered by atrial arrhythmias (AF, SVT) or device malfunction. Failure to shock. If this occurs, treat ventricular dysrhythmias as usual e.g. external defibrillation, anti-arrhythmic drugs. PPM malfunctions Bradycardia Failure to output/pace: no impulse (e.g. due to device malfunction, battery failure) and hence no pacing artefact on ECG. Failure to capture i.e. no response from heart (e.g. due to poor lead contact, cardiac problem). ECG shows pacing spikes not followed by atrial or ventricular activity. Oversensing: noise (e.g. movement artefacts) misinterpreted as cardiac activity and hence PPM fails to pace. Tachycardia Pacemaker-mediated tachycardia: PPM forms re-entrant loop. Less common with new devices. Sensor-induced tachycardia: noise (e.g. movement artefacts) misinterpreted as physiologically increased heart rate and PPM increases rate. Occurs in newer devices which allow physiologically-varied heart rate in response to need. Can also be due to all the usual causes of tachycardia e.g. physiological response, SVT. Other dysrhythmias Undersensing (e.g. due to poor lead contact), leading to asynchronous pacing. Suggested by pacing spikes within or just after QRS. Pacemaker syndrome: AV dyssyncrhony due to PPM failing to perfectly replicate normal cardiac contraction. Causes reduced cardiac output, fatigue, dizziness, and palpitations.

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