PACEMAKER AV SEQUENTIAL GENERATOR

DDD pacing with short AV interval caused RV apical activation with altered septal activation to reduce LVOT gradient and systolic anterior motion of mitral valve.Usually for symptomatic patients with high gradient in LVOT.Asymptomatic 1 st degree block or reversible AV block due to drugs.1 st degree block with depressed LV function and symptoms of LV failure.Will simply pace ventricle at backup rate in the setting of atrial tachyarrhythmia.Useful for SA node dysfunction with episodic atrial tachyarrhythmias.Prevents endless loop phenomenon or tracking of SVTs.

Sensing of both but sensed atrial events do not trigger ventricular pacing.

DDI (AV sequential, non-P-wave synchronous).

Can suffer re-entry loops where PVC is transmitted retrogradely to atria, where it is sensed and results in ventricular pacing with endless loop.

Normal sinus rhythm and AV conduction – Inhibition of both atrial and ventricular pacing.

If sinus bradycardia with AV block – Sequential atrial then ventricular pacing.

If sinus rhythm with AV block – synchronised ventricular pacing of intrinsic P waves.

If atrial bradycardia with intact AV conduction – Atrial pacing.

Upper rate limiters prevent ventricular pacing of atrial tachyarrhythmias.Atrial impulse triggers ventricular pacing unless senses autonomous ventricular activity.Sensed P-wave triggers ventricular pacing.Paces only the ventricle but senses both.VDD (Atrial synchronous ventricular inhibited).Not useful if atrial tachyarrhythmias exist as cannot pace faster than them.Indicated if impaired AV conduction and atrial bradycardia.To maintain AV synchrony in the absence of atrial sensing, pacing rate must be higher than intrinsic spontaneous atrial rate.Will pace atria, wait and then pace ventricle if no ventricular activity sensed.Spontaneous ventricular activity is sensed and low risk of R on T.Most commonly used mode in life-threatening bradycardias.Only paces if does not sense atrial activity.Indicated in sinus bradycardia providing AV conduction is intact.Asynchronous and virtually obsolete except in a few emergency situations.Placing magnet over permanent pacemaker causes sensing to be inhibited and results in asynchronous mode (AOO, VOO, DOO).Measures impedence between pacemaker unit and electrode.May respond to certain activities e.g.Activity sensors: Vibration detectors (accelerometers or piezoelectric crystal).If atrial activity sensed, atrial pacing is inhibited but triggers ventricular pacing Third position D indicates both triggered and inhibition responses can occur

O, none P, simple program M, multiprogram C, communicating (telemetry) R, rate modulation O, none T, triggered I, inhibited D, dual (D + I) O, none A, atria V, ventricle D, dual (A+V) S, single chamber

If this occurs, try transcutaneous pacing at a higher current.

Defibrillation can lead to global myocardial ischaemia which in turn also increases the pacing threshold thus causing capture failure.

Myocardial damage near lead tip caused by current transmission via the electrode to the myocardial interface.

Pacemaker inhibition due to reversion to noise mode.

After countershock, interrogate the pacemaker to ensure still functioning as can suffer from:.

PACEMAKER AV SEQUENTIAL GENERATOR

If countershock required, place pads at least 8cm from the pulse generator.Resuscitation in patients with permanent pacemakers PTX, severe ischaemia, pericardial effusion or metabolic derangement.US can be helpful for ensuring mechanical capture if poorly perfused.Fixed (asynchronous) pacing carries risk of R on T, however, there is little outcome data to support a preference for either.Set rate to 80bpm and increase by 10bpm until perfusing (up to 100/min).If less severe compromise, can titrate up from 10mA to usually 50-100mA and then maintain at 1.25x the threshold.If bradyasystolic peri-arrest, ramp up current to 100mA and titrate down once stabilised.External pads and electrodes for monitoring required.May be able to pace RV infarct when transvenous pacing fails (as can directly pace LV).70% survive with good neurological outcome vs.Transcutaneous pacing for severe hypotension with bradycardia.Only once pharmacological and electrical cardioversion have failed.Risk of inducing VF and limited by machine pacing limit of 180.Overdrive pacing for recurrent monomorphic VT.Overdrive pacing for torsades de pointes.Severe sick sinus syndrome with asystole >3s and syncope.Symptomatic high-grade AV block (Mobitz II or complete).

Pacemaker av sequential