B P7 C69 Pacemakers and Implantable Cardioverter-Defibrillators Flashcards
ICDs are indicated for prevention of sudden death from VT/VF, either as _____________________ in patients who have been resuscitated from VT/VF or ____________________ in patients who have not had VT/VF but are at sufficiently high risk to warrant protection with an ICD.
Secondary prevention
Primary prevention
Evaluated implantable cardioverter–defibrillator vs antiarrhythmic drugs in patients who had been resuscitated from near-fatal ventricular fibrillation or who had undergone cardioversion from sustained ventricular tachycardia
One group of patients was treated with implantation of a cardioverter–defibrillator; the other received class III antiarrhythmic drugs, primarily amiodarone at empirically determined doses
Among survivors of ventricular fibrillation or sustained ventricular tachycardia causing severe symptoms, the implantable cardioverter–defibrillator is superior to antiarrhythmic drugs for increasing overall survival.
AVID trial (Antiarrhythmics versus Implantable Defibrillators (AVID) Trial)
Ito lang may benefit sa mortality/survival vs CIDS and CASH
Prospective, multicenter, randomized comparison of implantable cardioverter-defibrillator (ICD) versus antiarrhythmic drug therapy in survivors of cardiac arrest secondary to documented ventricular arrhythmia
Patients were randomized to an ICD, amiodarone, propafenone, or metoprolol (ICD versus antiarrhythmic agents randomization ratio 1:3)
During long-term follow-up of cardiac arrest survivors, therapy with an ICD is associated with a 23% (nonsignificant) reduction of all-cause mortality rates when compared with treatment with amiodarone/metoprolol. The benefit of ICD therapy is more evident during the first 5 years after the index event.
CASH trial (Randomized Comparison of Antiarrhythmic Drug Therapy With Implantable Defibrillators in Patients Resuscitated From Cardiac Arrest - The Cardiac Arrest Study Hamburg (CASH)
Long term benefit ito. Kailangan mo magtrabaho matagal - para magka CASH
A total of 659 patients with resuscitated VF or VT or with unmonitored syncope were randomly assigned to treatment with the ICD or with amiodarone.
A 20% relative risk reduction occurred in all-cause mortality and a 33% reduction occurred in arrhythmic mortality with ICD therapy compared with amiodarone; this reduction did not reach statistical significance.
CIDS trial (Canadian Implantable Defibrillator Study (CIDS)
A Randomized Trial of the Implantable Cardioverter Defibrillator Against Amiodarone)
Clinical trials do not support ICD implantation in low-LVEF patients within _________ of myocardial infarction (MI) or _______ of surgical revascularization;
40 days
90 days
Class 1 indications for primary prevention of SCD in patients with IHD
In patients with LVEF of 35% or less that is due to ischemic heart disease who are at least 40 days’ post-MI and at least 90 days postrevascularization, and with NYHA class II or III HF despite GDMT, an ICD is recommended if meaningful survival of greater than 1 year is expected
In patients with LVEF of 30% or less that is due to ischemic heart disease who are at least 40 days’ postMI and at least 90 days postrevascularization, and with NYHA class I HF despite GDMT, an ICD is recommended if meaningful survival of greater than 1 year is expected
In patients with NSVT due to prior MI, LVEF of 40% or less and inducible sustained VT or VF at electrophysiological study, an ICD is recommended if meaningful survival of greater than 1 year is expected
Class 1 indications for secondary prevention of SCD in patients with IHD
In patients with ischemic heart disease, who either survive SCA due to VT/VF or experience hemodynamically unstable VT or stable sustained VT not due to reversible causes, an ICD is recommended if meaningful survival greater than 1 year is expected.
In patients with ischemic heart disease and unexplained syncope who have inducible sustained monomorphic VT on electrophysiological study, an ICD is recommended if meaningful survival of greater than 1 year is expected
Give class 1 indications for ICD implantation among patients with NICM
Class 1 - SCA survivor/sustained VT (2ndary prevention)
Class 1 - NYHA II, III, LVEF </= 35% and an ICD candidate (1mary prevention)
Electrical therapy for cardiac arrhythmias includes low-voltage (typically _____V) pacing stimuli (pulses) and high-voltage (typically _____ V) stimuli (shocks)
Low voltage: 1 to 5 V
Shock: 500 to 1400 V
Pacemakers deliver _____ to treat bradycardia.
ICDs deliver _____ to defibrillate ventricular fibrillation (VF) or to cardiovert ventricular tachycardia (VT).
Pacing pulses
Shocks
ICDs also have _____ pacing functions that can deliver pacing pulses to treat bradycardia, as well as _____ pacing functions that can deliver sequences of rapid pacing pulses to treat ventricular or atrial tachyarrhythmias
Antibradycardia
Antitachycardia
Cardiac resynchronization therapy (CRT) pacemakers (CRT-P) or ICDs (CRT-D) also provide electrical therapy for heart failure in the form of pacing pulses that _____ the ventricular contraction sequence.
Resynchronize
Transvenous system pulse generators are typically located subcutaneously in the _____, though in pediatric patients, some older larger devices, or devices with leads inserted via the femoral vein or epicardially, the pulse generator may be in the abdomen. Pacemaker pulse generators are _____ than ICD devices
Upper chest
Smaller
Transvenous pacemaker leads are typically implanted with lead tips in the _____.
Epicardial leads may be tunneled to the devices
RV and RA
ICDs are readily identified by the presence of _____ on the leads
Defibrillation coils
For CRT, leads may be placed in a _____.
LV branch of the coronary sinus or on the LV epicardium.
Subcutaneous ICDs are typically placed subcutaneously in the _____ with leads tunneled subcutaneously.
Leadless devices can also be visualized _____
SC ICD: left chest along the axillary line
Leadless device: Radiographically
Conventional pacemaker components include a _____.The lead system consists of one to three leads that are connected to the pacemaker PG via the lead pin.
Pulse generator (PG) that contains the battery and circuitry and the lead system
Conventional single-chamber systems have one lead that usually connect to the _____.
Dual-chamber systems usually have leads that connect to the right ventricle and RA
RV endocardium or in some cases to the right atrium (RA)
Cardiac resynchronization devices have a third lead that is placed to pace the left ventricle (LV) via a lead in a branch of the _____.
Coronary sinus or implanted on the LV epicardial surface
_____ pacemakers are also commercially available and include self-contained devices implanted via a catheter to the right ventricle
Leadless
Modern cardiac pacemakers perform a number of functions, but their most critical two actions remain _____.
Pacing and Sensing
Pacing means delivering a small (compared with a defibrillation shock) electrical stimulus of “1 to 5 V that captures a small myocardial region adjacent to the pacing electrode yielding a propagating wavefront in the chambers of interest (i.e.,the atria or ventricles)
Pacing thresholds frequently vary over time early after implantation. For active fixation leads, transient myocardial injury elicited by securing them produces an elevated threshold for _____.
Minutes to hours
Inflammation at the electrode tissue interface leads to a subacute threshold rise resolving in about ____ weeks.
6 weeks
Drugs, electrolyte perturbations, and metabolic changes also affect pacing thresholds.
_____ can elevate thresholds. Some studies, but not all, have found that _____ may elevate the pacing threshold as well.
_____ may also result in loss of capture.
Elevate threshold:
Severe hyperkalemia
Significant hyperglycemia
Severe hypothyroidism
Acidosis or alkalosis
Sodium channel blocking drugs (flecainide, propafenone, and others, as well as amiodarone
Loss of capture:
Acute ischemia and chronic infarction
Effects on Pacing threshold
- Higher threshold
Class 1C drugs (e.g., flecainide)
Amiodarone (chronic effect, especially atrial thresholds) - Lower pacing threshold
Glucocorticoids
Isoproterenol and epinephrine
Effects on Pacing burden
Increased atrial pacing burden:
* Drugs that cause sinus bradycardia (e.g., beta blockers, amiodarone, lithium)
Increased ventricular pacing burden:
* Drugs that slow AV conduction (e.g., beta blockers, amiodarone)
Frequency of VT or VF
- Increased
Antiarrhythmic drugs
Drugs with proarrhythmic side effects
Drugs that interact with proarrhythmic drugs - Decreased
Beta blockers
Antiarrhythmic drugs (e.g., sotalol, amiodarone)
ICD: Therapy for VT or VF
Defibrillation energy requirement increase vs increase
Defibrillation energy requirement:
Increase (class IB, class IC, chronic amiodarone, verapamil)
Decrease (sotalol, dofetilide)
Apart from pacemakers functioning in the asynchronous modes (_____), pacemakers need to accurately detect underlying atrial and/or ventricular native signals in order to know whether to and when to deliver a pacing stimulus
VOO, DOO
NASPE/BPEG Generic Code for Bradycardia Pacing
I Chamber Paced
II Chamber Sensed
III Response to Sensing
IV Rate Modulation
Severe bradycardia and/or complete heart block with a junctional or ventricular escape adversely affects cardiac output. Instituting ventricular pacing at normal rates dramatically improves cardiac output by _____%.
Restoring AV synchrony augments cardiac output still more by about ___%
25-30%
+20%
Nevertheless, there are additional advantages of maintaining the AV relationship. When patients were randomized to different rate responsive modes, most preferred a mode that maintained AV synchrony (i.e., _____ rather than VVIR)
DDDR
Moreover, pacemaker syndrome occurs in 3% to 30% of patients who have ongoing sinus activity (i.e., not atrial fibrillation) when subjected to ventricular pacing. Its manifestations include ______
Datigue, dyspnea, dizziness, neck pulsations, chest pain, and hypotension
Pacemaker syndrome is most common when a fixed VA relationship is present, wherein the _____.
Dual-chamber as compared with single-chamber pacing leads to ______ occurrence of atrial fibrillation and of stroke and better quality of life in follow-up.
Atrial contractions encounter closed AV valves
Reduced
For dual-chamber pacing the AV interval is of importance. Pacemaker syndrome can occur with a _____ PR interval analogously to the problem with VA conduction alluded to above.
On the other hand, too short of an AV interval or a marked interatrial conduction delay adversely affects performance. A hemodynamically optimal AV interval is typically about 150 msec at rest and somewhat less with exertion.
Severely prolonged PR interval
The potential deleterious effects of RV pacing were initially obscured by the advantages of _____. Although slightly reduced LV function occurs acutely, even in patients with normal ventricular function, RV pacing rarely exhibits clinically obvious adverse effects in the short term in such patients.
Elegant studies of direct His bundle stimulation clearly identified that both the contribution of atrial systole (by varying PR interval) and ventricular activation sequence (by comparing atrial- His bundle with atrial-RV) influenced ventricular function.
(1) Any pacing over severe bradycardia
(2) AV sequential pacing over ventricular-only pacing
(3) Rate-responsive pacing over fixed-rate pacing.
The ameliorative role of biventricular pacing (CRT) in treating LBBB-related ventricular dysfunction cemented this observation since conduction with LBBB resembles RV apical pacing. Studies comparing ventricular pacing to native ventricular activation, especially in those with LV systolic dysfunction, demonstrated significantly increased heart failure events. The magnitude of the detriment with RV pacing worsened with ____.
Greater QRS prolongation
Worse baseline LV function
____ is the simplest mode. From the first through third letter, respectively, the mode paces only in the ventricle, does not sense the atrium or ventricle (O),and behaves asynchronously (O).There is one timing clock, the ventricular escape interval.
For example, for VOO 60 bpm, the ventricular escape interval is 1000 msec (60,000 msec/min/ 60/min = 1000 msec). Thus every 1000 msec the pacemaker delivers a ventricular pacing pulse (even if a native ventricular beat has occurred).
VOO
___ implies pacing in the ventricle (V) and sensing in the ventricle (V), and if a sensed event occurs, the next scheduled pacing pulse is inhibited (I).The sensed event resets the ventricular escape interval.This mode adds a ventricular refractory period, during which sensed events are ignored.This prevents double counting ventricular events or local T waves and falsely inhibiting pacing.
VVI
In most pacemakers, applying a magnet converts the function from VVI to ____. Depending upon the manufacturer, model, and programming magnet application may also change the pacing rate and/or initiate other temporary behavior (e.g., performing a pacing threshold test).
VOO
The VOO mode is useful when oversensing is present as in a lead fracture or is anticipated due to electrocautery or other electromagnetic interference (EMI).
With respect to single chamber atrial pacing, ___ is analogous to VOO and AAI resembles VVI. In AAI, the device paces only in the atrium and senses in the atrium. In response to a sensed event, the next scheduled pacing pulse is inhibited, resetting the atrial escape interval.This mode, like VVI, has a refractory period, the atrial refractory period, during which sensed events are ignored. This prevents double counting atrial signals, or inappropriate sensing of far-field ventricular events that would falsely inhibit pacing.This mode is infrequently used due to the absence of ventricular support in the event of AV block.
AOO
