Pacemaker Syndrome Clinical Presentation

No specific set of criteria has been developed for diagnosis of pacemaker syndrome. Most of the signs and symptoms of pacemaker syndrome are nonspecific, and many are prevalent in the elderly population at baseline.^[34] Diagnosis from history depends heavily on correlation between onset of symptoms and onset of pacing or change in pacing mode, with attention to type and severity of symptoms. In the clinical setting, pacemaker interrogation and programming plays a crucial role in determining pacemaker mode contribution to symptoms.

• Symptoms: In their detailed review of pacemaker syndrome, Ausubel and Furman^[21] categorized symptoms on the basis of presumed etiology. Augmenting their list with that of Ellenbogen and colleagues^[8] provides the following:

  • Neurologic - Dizziness, near syncope, and confusion
  • Heart failure - Dyspnea, orthopnea, paroxysmal nocturnal dyspnea, and edema
  • Hypotension - Apprehension, mental status change, diaphoresis, and signs of orthostasis and shock
  • Low cardiac output - Fatigue, weakness, dyspnea on exertion, lethargy, and lightheadedness
  • Hemodynamic - Pulsation in the neck and abdomen, choking sensation, jaw pain, right upper quadrant (RUQ) pain, chest colds, headache
  • Arrhythmias - Palpitations
  • Rate related - Chest fullness or pain

The focus of physical examination is on findings related to etiologies of symptoms mentioned in History. In particular, the examiner should look for the following:

• Vital signs may reveal hypotension, tachycardia, tachypnea, or low oxygen saturation.
• Pulse amplitude may vary, and blood pressure may fluctuate.
• Look for neck vein distension and cannon waves in the neck veins.
• Lungs may exhibit crackles.
• Cardiac examination may reveal regurgitant murmurs and variability of heart sounds.
• Liver may be pulsatile, and the RUQ may be tender to palpation. Ascites may be present in severe cases.
• The lower extremities may be edematous.
• Neurologic examination may reveal confusion, dizziness, or altered mental status.

Risk factors

• In the MOST trial, low baseline sinus rate and higher programmed lower rate limit were the only preimplantation variables that predicted development of pacemaker syndrome.^[22] Postimplantation, an increased percentage of ventricular paced beats was the only variable in the multivariate analysis that significantly predicted development of pacemaker syndrome.
• Patients with intact VA conduction are at greater risk for developing pacemaker syndrome. As many as 90% of patients with preserved AV conduction have intact VA conduction, and 30-40% of patients with complete AV block have preserved VA conduction. Patients may have intact VA conduction not apparent at the time of pacemaker implantation or may develop VA conduction at any time after implantation.
• Patients with noncompliant ventricles and diastolic dysfunction are particularly sensitive to loss of atrial contribution to ventricular filling. This includes patients with cardiomyopathy (hypertensive, hypertrophic, restrictive) and elderly individuals.
• Other factors correlated with development of pacemaker syndrome include decreased stroke volume, decreased cardiac output, and decreased left atrial total emptying fraction associated with ventricular pacing.

Situations in which AV dyssynchrony may arise

Classically, pacemaker syndrome has been observed in the setting of VVI pacing. Since the advent of dual-chamber pacing, however, examples of pacemaker syndrome have been reported in the setting of many additional pacing modes.^[35]

• Ventricular inhibited, with and without rate modulation (VVI[R]) pacing: The ventricle is paced independent of atrial activity, yielding AV dissociation, or VA conduction results in AV dyssynchrony. An example of 1:1 retrograde VA conduction during VVI pacing is shown in the image below. Retrogradely conducted P waves are visible directly following each ventricular-paced complex.
• Atrial inhibited, rate-modulated (AAIR) pacing: Exercise induces pacemaker-mediated rate increase. The paced-A to sensed-R (AR) interval increases when a steep rate-response curve precipitates an increased pacing rate prior to expected catecholamine surge, or progression of AV nodal disease leads to increased AR interval. Interatrial and intra-atrial conduction delays may also lead to an increased AR interval. These conditions may arise outside the setting of an implanted pacemaker.
• Single-lead, atrial synchronous, ventricular triggered and inhibited, with and without rate modulation (VDD[R]) pacing: Native atrial rate falls below programmed lower rate limit and VVI(R) pacing supervenes. See figure above.
• Dual-mode, ventricular inhibited, with and without rate modulation (DDI[R]) pacing

  • In complete AV block, when sinus rate exceeds the programmed lower rate, ventricular stimulation does not track atrial activation because ventricular triggered mode is absent. AV dissociation occurs, with atrial contraction driven by sinus node activity and ventricular contraction driven by the pacemaker.
  • In high-grade AV block, either fixed or transient, a ventricular premature contraction (VPC) creates retrograde atrial depolarization, which occurs after the postventricular atrial refractory period (PVARP), inhibiting the atrial channel. The subsequent ventricular stimulation occurs at the lower rate limit, creating the next retrograde atrial depolarization. This process results in functional VVI pacing because all pacemaker-mediated atrial stimuli are inhibited. Also, any sensed atrial activity, including an atrial premature contraction (APC) or extracardiac myopotential, may initiate the cycle.
  • In the absence of complete AV block, spontaneous atrial depolarization occurs just at the end of atrial refractoriness, resulting in long AR interval.
  • In the setting of atrial tachyarrhythmias, many DDD mode pacemakers exhibit mode switching to DDI pacing when the native atrial rate exceeds the programmed mode switching rate, thus avoiding pacemaker-mediated ventricular tracking of the atrial tachycardia. This type of mode switching, however, by definition creates AV dyssynchrony. In the specific case of crosstalk, in which ventricular depolarizations are sensed in the atrial channel as atrial activity, the apparent sensed atrial rate becomes twice the actual atrial rate, and inappropriate mode switching to DDI pacing occurs. In such cases, the programmed atrial sensing threshold may be increased to avoid crosstalk sensing.
• DVI pacing: Spontaneous atrial escape occurs earlier than programmed atrial stimulation, and no corresponding ventricular stimulation is triggered. The result is loss of AV synchrony.
• DDD pacing^[36]

  • When the spontaneous atrial rate exceeds the programmed upper rate limit, the pacemaker responds in various ways.
    • Pseudo-Wenckebach AV block, which yields a ventricular rate slower than the atrial rate
    • Higher degree pacemaker AV block
    • Fallback, in which ventricular rate decreases independent of atrial rate
  • All of these pacer responses result in ventricular dissociation from atrial activity, and the physiologic AV relationship is lost.
  • In complete heart block, an atrial depolarization occurs within the PVARP, creating atrial myocardial refractoriness. The next pacemaker atrial stimulus does not result in atrial depolarization, but the associated ventricular stimulus leads to retrograde VA conduction. This conduction causes subsequent atrial depolarization, again occurring within the PVARP, such that it does not initiate an AV interval but does create an atrial myocardial refractory period. Functional VVI pacing results even though the pacemaker continues producing atrial stimuli, because these are muted by atrial refractoriness. Schuller and Brandt labeled this phenomenon pseudoatrial exit block.^[35]
  • Jais and colleagues reported a case of pacemaker syndrome in the DDD mode in the absence of any pacing stimuli.^[37] The setting was sinus tachycardia with excessive PR prolongation, both of which contributed to a shortened RP interval. In this example, the native P wave occurred so soon after the previous QRS that the P wave fell within the PVARP period. No pacemaker AV interval was initiated, but the P wave eventually was conducted, producing a native ventricular depolarization.
  • This process may have been initiated by a VPC that resulted in pacemaker mode reversion to a longer PVARP period, effectively masking subsequent P waves. Hemodynamic compromise may have precipitated a further increase in heart rate, moving the P wave further back in the PVARP period. During normal DDD mode operation, this type of excessive PR prolongation is prevented and AV synchrony maintained by ventricular stimulation after the programmed AV delay. In the example by Jais and colleagues, AV dyssynchrony was facilitated by failure of P wave sensing secondary to a relatively long PVARP period. The elements leading to this scenario included prolonged PR interval, sinus tachycardia, and relatively long PVARP period.
• Degenerate mode reversion

  • Pacemaker resets from DDD[R] to VVI or ventricular paced (VOO) mode under the following circumstances: interference of noise or dying battery, detection of inappropriate mode switching during automated pacemaker memory review, or detection of irregularities in memory data bits during automated pacemaker memory review.^[37]
  • An example of mode reversion is demonstrated in the first image below, which depicts a patient who had bipolar leads in both chambers and was paced in the DDD mode. Atrial and ventricular stimuli are noted as low-voltage spikes on surface ECG. During routine automated pacemaker memory review, a data bit fault was detected and the pacemaker reverted to VVI mode with unipolar ventricular stimulation, as seen in the second image below. The patient developed symptoms of pacemaker syndrome that resolved upon reprogramming of the pacemaker. AV dissociation can be seen in the second image below, as evidenced by successively shorter PR intervals between native atrial depolarizations and ventricular pacemaker-stimuli. Pronounced PR interval prolongation. The effect of this PR interval prolongation on AV dyssynchrony is demonstrated in this ECG image. AV dyssynchrony resulting from severe PR interval prolongation in the setting of sinus rhythm. In this ECG, the PR interval is prolonged to the point that the P wave occurs coincident with the peak of the T wave. Compare to the prior image of the same patient with a slower sinus rate.
• Accelerated junctional rhythm, sometimes occurring after AV junctional ablation, with or without VA conduction or accelerated ventricular rhythm can precipitate pacemaker syndrome. An example of a junctional rhythm with retrogradely conducted P waves is shown in the image below. Junctional rhythm with retrogradely conducted P waves. If symptoms of pacemaker syndrome develop, increasing the lower rate limit for pacing may help to restore AV synchrony.
• An example of an idioventricular rhythm with retrogradely conducted P waves is shown in the image below. In such cases, the lower rate limit can be programmed to be greater than the junctional or ventricular rate causing symptoms, thus restoring pacemaker-mediated AV synchrony. Alternatively, beta-blocker therapy can be instituted to slow the native junctional or ventricular rhythm to less than the lower rate limit already programmed. Accelerated idioventricular rhythm with retrogradely conducted P waves. This ECG demonstrates a mechanism of AV dyssynchrony that might lead to pseudopacemaker syndrome.
• Pacemaker lead malfunction can result in loss of atrial capture. In such cases, pacemaker ventricular stimulation may become dissociated from atrial depolarization, leading to AV dyssynchrony. One approach in such cases is to increase the voltage or duration of atrial stimulation to restore atrial capture. Ultimately, atrial lead repositioning or replacement may become necessary.
• During managed ventricular pacing (MVP) mode, in which AAI(R) pacing predominates, functional undersensing of native P waves can occur during intermittent AV block.^[38] This occurs when a native P wave falls in the atrial refractory period (ARP) and is functionally ignored by the logic of the MVP pacing mode. In MVP mode, the ARP is dependent on the R-R interval and not the P-P interval; the ARP is set to 75% of the R-R interval for rates 75 beats per minute or faster, and 600 ms for rates slower than 75 beats per minute. Therefore, when 2:1 AV block occurs, the ARP may be long enough to mask the succeeding native P wave, leading to AV dyssynchrony.