Intermittent Heart Block Research Articles

PO-04-058 AN UNUSUAL CASE OF ATRIAL SENSING BY A DEFIBRILLATOR LEAD CAUSING ASYSTOLE

Integrated bipolar transvenous defibrillator leads (IL) offer advantages over dedicated bipolar defibrillator leads (BL): IL have a simplified construction and are less prone to anodal stimulation. A potential problem for the IL is oversensing due to a large sensing area. We present a case of an IL with intermittent asystole treated by exchange of the IL for a BL. N/A N/A A 51-year-old female with hypertrophic cardiomyopathy received a Boston Scientific (BS) dual chamber ICD in 2011 with a IL (BS 0185) for VT and intermittent heart block. In May 2022, she underwent an uncomplicated generator change. Six months later she presented with presyncopal events. Hospital telemetry showed DDD pacing with intermittent lack of ventricular output and no escape rhythm. There was no evidence of lead dislodgement and manipulation of the pocket did not reproduce an event. Device interrogation showed normal and stable lead thresholds and impedances. She was now pacemaker dependent. Spontaneous asystole was captured by the intracardiac electrogram (IEGM) demonstrating atrial far-field sensing with inhibition of RV pacing. Decreasing the RV sensitivity did not resolve the issue. We urgently turned on “Electrocautery Protection Mode” (DOO 60 and V Tachy Mode-OFF) restoring 100% dual chamber pacing and capture. We suspected that atrial far field sensing was due to the IL design. The size and position of the sensing anode can allow for far-field atrial sensing and inhibition of RV output. Intraoperative manipulation and testing of the generator and leads showed normal parameters. The patient underwent extraction of the IL, and a BL (Medtronic 6935m) was implanted. A BL was selected due to its distal, and closely spaced, pace/sense electrode design. The device was reprogrammed to her prior settings with no further episodes or symptoms occurring. This case shows an unusual problem with the IL design. Capturing this event by IEGM was diagnostic. Reducing the IL sensitivity is not optimal, making the patient vulnerable to undersensing of ventricular fibrillation. Discussion with BS Technical Services confirms that this phenomenon is rarely seen and more likely to occur in patients with a small RV. We suspect that changes in body habitus, a small RV cavity, and progression of heart block exposed the problem years after implant. Exchange of a IL with a BL provided a lasting solution.

B-PO03-200 MULTI-CENTER STUDY EVALUATING THE OUTCOME OF PACEMAKER AND IMPLANTABLE CARDIOVERTER DEFIBRILLATOR IMPLANTS IN PEDIATRIC HEART TRANSPLANT RECIPIENTS

Cardiac implantable electronic devices (CIED) are implanted in up to 12% of pediatric patients following orthotopic heart transplant (OHT). Little is known regarding long-term CIED device use and complications. Describe the device requirements among pediatric OHT recipients who underwent CIED placement and associated complications. This is a multi-center retrospective study, that included pediatric OHT recipients occurring after 1/1/2000, who had a permanent pacemaker (PPM) or ICD placed at </= 25 years old. Fifteen patients (60% female) were identified (13 PPM, 2 ICD). Median age at OHT was 3.1 years (IQR: 0.7, 11.3) and at CIED placement was 10 years (2.1, 15.6). The median time from OHT to CIED placement was 2.2 years (0.2, 8.2). High grade heart block (HB) (7 intermittent, 2 persistent) was the most common indication for pacing (9 patients, 60%), followed by sinus node dysfunction. A single chamber ICD was placed for VT/VF associated with acute rejection and a dual chamber ICD was placed for primary prevention in a patient with HB and non-sustained VT. Most PPM were epicardial (69%), dual chamber systems (62%) while both the ICDs were transvenous (11 and 20 years at implant). CIED-related complications occurred in 27% at a median follow up of 1.5 years (0.5, 3.7), and included infection requiring explant (1: at 6 months), lead fracture (2: at 4.2 and 2.4 years) and lead dislodgment (1: at 7 months). At follow up (median 6.9 years - 3.8, 11.4)33% died (all PPM) and 13% had a re-transplant. In the remaining 8 patients, 63% (intermittent HB: 3, persistent HB:1, intermittent HB and SND: 1) were not using their device or had it removed (median: 8 years, IQR: 6, 11). Neither of the patients with ICD had a shock over a combined follow up of 14 years. In this cohort of pediatric OHT recipients with CIED, intermittent HB was the most common reason for pacing. Complications were not infrequent, and many patients did not need the device long term.

Within-patient comparison of His-bundle pacing, right ventricular pacing, and right ventricular pacing avoidance algorithms in patients with PR prolongation: Acute hemodynamic study.

A prolonged PR interval may adversely affect ventricular filling and, therefore, cardiac function. AV delay can be corrected using right ventricular pacing (RVP), but this induces ventricular dyssynchrony, itself harmful. Therefore, in intermittent heart block, pacing avoidance algorithms are often implemented. We tested His-bundle pacing (HBP) as an alternative. Outpatients with a long PR interval (>200 ms) and intermittent need for ventricular pacing were recruited. We measured within-patient differences in high-precision hemodynamics between AV-optimized RVP and HBP, as well as a pacing avoidance algorithm (Managed Ventricular Pacing [MVP]). We recruited 18 patients. Mean left ventricular ejection fraction was 44.3 ± 9%. Mean intrinsic PR interval was 266 ± 42 ms and QRS duration was 123 ± 29 ms. RVP lengthened QRS duration (+54 ms, 95% CI 42-67 ms, p < .0001) while HBP delivered a shorter QRS duration than RVP (-56 ms, 95% CI -67 to -46 ms, p < .0001). HBP did not increase QRS duration (-2 ms, 95% CI -8 to 13 ms, p = .6). HBP improved acute systolic blood pressure by mean of 5.0 mmHg (95% CI 2.8-7.1 mmHg, p < .0001) compared to RVP and by 3.5 mmHg (95% CI 1.9-5.0 mmHg, p = .0002) compared to the pacing avoidance algorithm. There was no significant difference in hemodynamics between RVP and ventricular pacing avoidance (p = .055). HBP provides better acute cardiac function than pacing avoidance algorithms and RVP, in patients with prolonged PR intervals. HBP allows normalization of prolonged AV delays (unlike pacing avoidance) and does not cause ventricular dyssynchrony (unlike RVP). Clinical trials may be justified to assess whether these acute improvements translate into longer term clinical benefits in patients with bradycardia indications for pacing.

Propagation Failure by TRPM4 Overexpression

Transient receptor potential melastatin member 4 (TRPM4) channels are nonselective monovalent cationic channels found in human atria and conduction system. Overexpression of TRPM4 channels has been found in families suffering from inherited cardiac arrhythmias, notably heart block. In this study, we integrate a mathematical formulation of the TRPM4 channel into a Purkinje cell model (Pan-Rudy model). Instead of simply adding the channel to the model, a combination of existing currents equivalent to the TRPM4 current was constructed, based on TRPM4 current dynamics. The equivalent current was then replaced by the TRPM4 current to preserve the model action potential. Single-cell behavior showed early afterdepolarizations for increases in TRPM4 channel expression above twofold. In a homogeneous strand of tissue, propagation conducted faithfully for lower expression levels but failed completely for more than a doubling of TRPM4 channel expression. Only with a heterogeneous distribution of channel expression was intermittent heart block seen. This study suggests that in Purkinje fibers, TRPM4 channels may account for sodium background current (INab), and that a heterogeneous expression of TRPM4 channels in the His/Purkinje system is required for type II heart block, as seen clinically.

Minimizing ventricular pacing by a novel atrioventricular (AV) delay hysteresis algorithm in patients with intact or compromised intrinsic AV conduction and different atrial and ventricular lead locations

Purpose. To investigate if an advanced AV search hysteresis (AVSH) algorithm, Ventricular Intrinsic Preference (VIP™), reduces the incidence of ventricular pacing (VP) in sinus node dysfunction (SND) with both intact and compromised AV conduction and with intermittent AV block regardless of the lead positions in the right atria and the ventricle.Methods. Patients were classified as having intact AV (AVi) conduction if the PR interval was ≤ 210 ms on ECG and 1:1 AV conduction during atrial pacing up to 120 bpm with PR interval ≤ 350 ms. Otherwise the AV conduction was classified as compromised (AVc). Both AVi and AVc patients were randomized to VIP ON or OFF. VIP performed an intrinsic AV conduction search every 30 s for three consecutive atrial cycles with the extension of the sensed and paced AV (SAV/PAV) delays from basic values of 150/200 ms to 300/350 ms. Extended AV intervals were allowed for three cycles when VP occurred before returning to basic AV delays. The primary end-point was %VP at 12 months.Results. Among 389 patients, 30.1% had intact and 69.9% had compromised AV conduction. The mean %VP at 12 months was 9.6% by VIP compared to 51.8% with standard AV settings in patients with AVi (P < 0.0001) and 28.0% versus 78.9% (P < 0.0001) with AVc. With VIP, excessive %VP among most used lead positions was not seen. Conversely, when VIP was off %VP was low only in patients who had leads in the RA septal–RV septal position (23.0%).Conclusions. VIP feature reduces VP both in patients with SND and with intermittent heart block regardless of the lead positions in the right atria and the ventricle.

Conduction Abnormalities in Pediatric Patients With Restrictive Cardiomyopathy

Pediatric restrictive cardiomyopathy carries a poor prognosis secondary to a high risk of sudden death previously attributed to ventricular tachyarrhythmias. The extent of conduction abnormalities in this population and their relationship to life-threatening events has not been previously reported. A retrospective study of pediatric patients with restrictive cardiomyopathy diagnosed between April 1994 and May 2011 was performed. Demographic, cardiac, and ECG characteristics and the mechanisms of serious arrhythmic events (death or episode of acute hemodynamic compromise thought to be secondary to arrhythmia) were evaluated. Sixteen patients (1-17 years of age) were reviewed, with 5 sudden cardiac events noted, including 4 deaths. Two deaths were caused by development of acute heart block; another patient with syncope had intermittent heart block and survived as the result of pacing features of an implanted defibrillator system. The median PR interval (222 versus 144 ms; P<0.01) and the QRS duration (111 versus 74; P=0.01) were significantly longer in those who had an acute cardiac event. Older age at presentation was associated with sudden cardiac events (P<0.01). No other functional or echocardiographic variables were associated with a sudden cardiac event. Pediatric patients with restrictive cardiomyopathy are at risk for acute high-grade heart block, and, in this cohort, bradycardic events represented a significant portion of all arrhythmic events. Aggressive ECG monitoring strategies looking for conduction system disease should be ongoing in all patients with restrictive cardiomyopathy. Implantation of a defibrillator/pacemaker should be considered as prophylactic management.

Abstract 9589: Conduction Abnormalities in Pediatric Patients with Restrictive Cardiomyopathy

Introduction: Pediatric restrictive cardiomyopathy (RCM) carries a poor prognosis secondary to a high risk of sudden cardiac death. Sudden death in pediatric patients has previously been attributed to ventricular tachyarrhythmias. There are many reasons why patients with RCM might develop conduction system disease and it is conceivable that in the acute setting, this might be a triggering event for sudden death. Methods: A single center, retrospective chort of pediatric patients with RCM, diagnosed between April 1994 and April 2011 was analyzed for conduction system abnormalities and potential triggering events for sudden death. Patient demographic, cardiac and electrocardiographic characteristics were reviewed. Incidence of sudden cardiac events was determined (defined as death or an episode of acute hemodynamic compromise felt to be secondary to a cardiac arrhythmia). Non-parametric statistical methods were used to determine associations between clinical characteristics and sudden cardiac events. Results: Fifteen patients (1 - 17 years) were reviewed; there were 5 sudden cardiac events including 4 deaths. Two of the deaths were precipitated by the abrupt onset of complete heart block. Another patient with syncope had intermittent heart block and survived as a result of the defibrillator pacing features. Sudden cardiac events were statistically associated with an older age ( p &lt;0.01 ). On initial presentation, the median PR interval (222 vs. 140 msec; p &lt; 0.01 ) and the median QRS duration (111 vs. 73.5; p = 0.01 ) was significantly longer in those having an acute cardiac event. No other functional or echocardiographic variables were associated with a sudden cardiac event. Conclusion: Pediatric patients with RCM are at risk for acute high grade heart block and bradycardic events may represent a significant portion of all arrhythmic events. Since PR interval prolongation and wider QRS complex were associated with acute cardiac events, these findings suggest increased monitoring for bradyarrhythmic episodes with consideration for prophylactic pacemaker implantation in certain patients. Particular care should be taken in patients with RCM and evidence of conduction system disease.

Persistent Fetal Sinus Bradycardia Associated with Maternal Anti-SSA/Ro and Anti-SSB/La Antibodies

To study the clinical course and outcome of fetal sinus bradycardia (SB) due to maternal antibody-induced sinus node dysfunction. We reviewed the maternal, prenatal, and postnatal findings of fetuses with SB associated with elevated maternal anti-SSA/Ro and anti-SSB/La antibodies. Of the 6 cases diagnosed prenatally, 3 had isolated SB persisting after birth and had a good prognosis. Three fetuses with SB and severe myocardial involvement (congenital complete heart block and/or endocardial fibroelastosis) succumbed in utero in spite of treatment. Postmortem histopathology in 1 fetus showed inflammatory destruction of the sinus and atrioventricular nodes. SB was detected incidentally in a 7-year-old girl. She had intermittent heart block with progressive sinus arrest requiring permanent pacemaker. Fetal SB associated with maternal autoantibodies may persist in childhood, with a good prognosis in the absence of widespread cardiac involvement.

Pericardial constriction after cardiac transplantation

In this study we present a series of 5 cases that developed constrictive pericarditis after orthotopic heart transplantation. All 5 patients had pericardial effusion of non-infectious etiology in the early post-transplant period. They subsequently presented with heart failure unresponsive to standard medical management. The diagnosis was made by comprehensive echo-Doppler studies. Findings were confirmed at surgical inspection and complete pericardiectomy led to improvement in hemodynamics in 4 patients. One patient had relief from constriction but died of non-cardiac complications. One patient with constriction has been re-listed for transplantation due to intermittent heart block and associated cardiac allograft vasculopathy. Early diagnosis of pericardial constriction after orthotopic heart transplantation requires a high index of clinical suspicion and optimal use of Doppler echocardiography. Early diagnosis and timely surgical pericardiectomy may correct this condition entirely and result in satisfactory long-term results.

Transcriptional coactivators PGC-1α and PGC-lβ control overlapping programs required for perinatal maturation of the heart

Oxidative tissues such as heart undergo a dramatic perinatal mitochondrial biogenesis to meet the high-energy demands after birth. PPARgamma coactivator-1 (PGC-1) alpha and beta have been implicated in the transcriptional control of cellular energy metabolism. Mice with combined deficiency of PGC-1alpha and PGC-1beta (PGC-1alphabeta(-/-) mice) were generated to investigate the convergence of their functions in vivo. The phenotype of PGC-1beta(-/-) mice was minimal under nonstressed conditions, including normal heart function, similar to that of PGC-1alpha(-/-) mice generated previously. In striking contrast to the singly deficient PGC-1 lines, PGC-1alphabeta(-/-) mice died shortly after birth with small hearts, bradycardia, intermittent heart block, and a markedly reduced cardiac output. Cardiac-specific ablation of the PGC-1beta gene on a PGC-1alpha-deficient background phenocopied the generalized PGC-1alphabeta(-/-) mice. The hearts of the PGC-1alphabeta(-/-) mice exhibited signatures of a maturational defect including reduced growth, a late fetal arrest in mitochondrial biogenesis, and persistence of a fetal pattern of gene expression. Brown adipose tissue (BAT) of PGC-1alphabeta(-/-) mice also exhibited a severe abnormality in function and mitochondrial density. We conclude that PGC-1alpha and PGC-1beta share roles that collectively are necessary for the postnatal metabolic and functional maturation of heart and BAT.

Irregular Rhythm in a Man with Unstable Angina

A 66-year-old man was hospitalized for an exacerbation of angina pectoris. He had hypertension and had had chronic stable angina for 10 years and type 1 diabetes mellitus for 27 years. Three years earlier, the patient had had a single-lead ventricular pacemaker implanted to treat intermittent heart block. Recently, angina had been present with less exertion than before; two episodes occurred while the patient was at rest on the day of admission. His medications included furosemide, potassium, verapamil, digoxin, lisinopril, warfarin, insulin, and long-acting oral nitrates.The patient's vital signs included a pulse of 100 with an intermittently irregular rhythm; blood pressure, 147/88 mm Hg; respirations, 16 per min; temperature, 36.2° C; and arterial oxygen saturation, 96% by pulse oximetry. The only other significant findings were diminished arterial pulses in the feet, signs of peripheral neuropathy, and moderate retinopathy. No further angina occured after the patient was confined to complete bed rest. The ECG is shown.

Congenitally corrected transposition presenting at 24 years: errors of management

AbstractA 24-year-old female without previous symptoms or known heart disease consulted a general practitioner with dyspnoea which had slowly worsened over a period of two years. She was treated for asthma, without investigations, until she presented with rapid atrial fibrillation, chest pain and pulmonary oedema necessitating admission to hospital, where she was found to have “mitral” regur-gitation (of the left-sided atrioventricular valve) and congenitally corrected transposition. At operation the grossly regurgitant left-sided morphologically tricuspid valve was replaced by a “top-hat” inverted aortic valve homograft. The procedure resulted in intermittent heart block, needing a pacemaker, and continued myocardial failure which progressed with new right-sided valvar regurgitation. She died a few months later. Post mortem examination confirmed the double discordance, and showed a fistula around the tricuspid valvar prosthesis, left atrial thrombus and changes in the mitral valve. There was also an unsuspected area of old myocardial ischaemia, associated with severe hypoplasia of the circumflex branch of the right-sided coronary artery. This was considered probably to have been of embolic origin.

Syncope and Functional Infranodal Block

Letters15 December 1990Syncope and Functional Infranodal BlockArchana Patel, MD, Daniel Goldman, MDArchana Patel, MDSearch for more papers by this author, Daniel Goldman, MDSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/0003-4819-113-12-994 SectionsAboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail ExcerptTo the Editors:We read with interest the article by Manolis and colleagues (1) and offer the following comments. Their Figure 6 shows an early atrial premature beat that blocks below the bundle of His, and in the legend the authors state, "The probability of intermittent heart block causing syncope in this patient was sufficiently high to merit a permanent pacemaker" (1). We would like to point out that block of early atrial premature beats below the His bundle can be a physiologic type of block with no pathologic significance, because in some patients the effective refractory period of the...

Feasibility and cost savings of outpatient electrophysiologic testing

The feasibility of outpatient electrophysiologic testing was examined by reviewing 100 consecutive outpatient tests performed in 95 patients. Seventy-one of the patients (75%) had no underlying heart disease. The electrophysiologic tests were performed to evaluate supraventricular tachycardias (n = 47), nonsustained ventricular tachycardia (n = 20), unexplained syncope (n = 21), palpitation (n = 9) or intermittent heart block (n = 2). A mean of 2.8 ± 0.5 6F electrode catheters were inserted through a femoral vein. An electrode catheter was inserted into a subclavian or internal jugular vein in 28 tests and a 5F cannula was inserted into a femoral artery to monitor the blood pressure in 20 tests. The results of 61 tests (61%) were abnormal. Patients were monitored for a mean of 3.8 ± 1.2 h after the procedure and then discharged. No complications occurred.For cost analysis a subgroup of 60 of these patients was matched for age, gender, heart disease and indication for electrophysiologic testing with a group of 60 patients who underwent electrophysiologic testing as inpatients. Physicians' fees for the two groups were similar; however, the mean hospital charge was $5,845 ± 3,763 for the inpatient group compared with only $2,120 ± 1,244 for the outpatient group (p < 0.001). Thus, outpatient electrophysiologic testing is feasible and safe and results in substantial cost savings in patients without life-threatening arrhythmias.

Prognosis in patients with intra-Hisian conduction disturbances

Intra-Hisian delay is usually associated with fascicular conduction abnormalities. We report our experience in 23 patients who had intra-Hisian delay as their only conduction defect. First-degree intra-Hisian delay (His bundle deflection ≥ 30 msec) was present in 17 patients, 5 of whom also had split His potentials. Three of these patients received permanent pacemakers, all of whom had a history of syncope. Higher degrees of intra-Hisian delay were observed either spontaneously or in response to atrial pacing in 6 patients. Five of these patients were treated with permanent pacing, 4 of whom had symptomatic bradyarrhythmias and/or syncope. No patient has had a recurrence of symptoms following pacemaker insertion during the mean 31-month follow-up. No patient with first-degree intra-Hisian delay not receiving a pacemaker developed symptomatic bradyarrhythmias or syncope during a mean follow-up of 21 months. We conclude that first-degree intra-Hisian delay has a favorable short-term prognosis and is not associated with progression of symptomatic conduction disease. Data, however, are insufficient to draw firm conclusions regarding the significance of higher degrees of intra-Hisian delay. Prior documentation of intermittent heart block or recurrent syncope in the majority of these patients, nevertheless, suggests that they may be at risk for developing symptomatic bradyarrhythmias.

Significance of isolated H-V interval prolongation in symptomatic patients without documented heart block

Paced and unpaced control groups were followed to establish the roles of pacers and infranodal (H-V) conduction in 59 patients with symptoms consistent with intermittent heart block (HB). To reduce the number of variables compared with previous studies, patients were included only when (1) prior ECG monitoring and medical-neurologic evaluation failed to document HB or other cause for symptoms; (2) His bundle studies were normal or showed only H-V prolongation, and (3) there was no history of a recent myocardial infarction. Of 35 patients with prolonged H-V interval, 18 received permanent pacers, while 17 remained unpaced. Eighteen unpaced patients constituted the normal H-V Group (after two were lost to follow-up and four received pacers). All groups were similar in types of heart diseases, NYHA classification, general medical condition, age and sex, thus providing adequate controls. All patients with normal H-V intervals remained stable (no deaths or progression to HB) for a mean follow-up period of 22 months. Among 18 patients with prolonged H-V intervals who received pacers, there were three deaths, none sudden, during a mean of 23 months; four patients developed HB unaccompanied by symptoms. Among 17 patients with prolonged H-V intervals who were not paced, eight died (three suddenly) and three progressed to HB with symptoms, leaving only six stable after six months follow-up. All these parameters were significantly worse in the unpaced patients with prolonged H-V intervals. These results suggest that patients with intermittent symptoms consistent with heart block, whose H-V interval is ≥ 60 msec. should receive a permanent pacer even if intermittent HB cannot be documented before implant.

Letter: Serious complication of intracardiac catheters.

To the Editor.— The article by Donald H. Kuiper (230:877, 1974) describes a serious complication of intracardiac catheters. A similar article appeared in the New England Journal of Medicine this year (290:890, 1974). This tragic complication may occur with intracardiac central venous lines, catheters used for hyperalimentation, or cardiac pacemaker electrode catheters. In a letter to the editor of the New England Journal of Medicine (291:679, 1974), I described a case of perforation of the right ventricle by a coronary sinus pacing catheter. This catheter was used for administration of intravenous fluids in a patient with intermittent heart block after cardiac catheterization. The correct diagnosis was made when the patient sustained a cardiac arrest, and a life-saving subxiphoid pericardicentesis was performed. It was then discovered that aspiration through the pacemaker catheter produced serosanguinous fluid. If sudden cardiac arrest or hypotension occurs in a patient with a central venous type of

Late Displacement of Cardiac Pacemaker Electrode Due to Heavyweight Pulse Generator

ENDOCARDIAL pacing has been shown to be a satisfactory method for long-term cardiac pacing. The electrode complications of malposition, displacement, fracture, migration, and perforation have been well described in previous publications. 1,2 We have recently observed a retraction of the endocardial electrode by the downward migration of the heavy pulse generator. This complication is prevented by anchoring the pacemaker to the clavicle or by creating a pacemaker under the pectoral muscle or both. Report of Cases A 78-year-old man was admitted to New York University Hospital with intermittent heart block requiring cardiac pacing. A Medtronic pacemaker weighing 200 gm was inserted in a subcutaneous infrapectoral pocket with a bipolar electrode inserted via the cephalic vein into the apex of the right ventricle. Postoperatively the patient did well until the 12th month when failure of capture was noted. Chest x-ray film showed retraction of the catheter into the right atrium

ECG Patterns Useful in the Diagnosis of Intermittent Heart Block

Blockages in any of the three intraventricular conduction pathways (the right bundle branch, and anterior superior radiations and posterior inferior radiations of the left bundle branch) have specific effects on the QRS pattern as seen on the standard electrocardiogram. The presence of block in two of the three pathways (manifested by right bundle branch block and left axis deviation, right bundle branch block and right axis deviation, alternating complete right and left bundle branch block, or to a lesser extent left bundle branch block) has been found in many patients with documented intermittent heart block or in patients who subsequently develop permanent complete heart block. The presence of this QRS pattern in patients with histories of syncope or dizziness suggests that their symptoms may be due to intermittent heart block. Such patients should be monitored to document heart block, or should have permanent demand pacemakers implanted, or both.

ECG patterns useful in the diagnosis of intermittent heart block

Blockages in any of the three intraventricular conduction pathways (the right bundle branch, and anterior superior radiations and posterior inferior radiations of the left bundle branch) have specific effects on the QRS pattern as seen on the standard electrocardiogram. The presence of block in two of the three pathways (manifested by right bundle branch block and left axis deviation, right bundle branch block and right axis deviation, alternating complete right and left bundle branch block, or to a lesser extent left bundle branch block) has been found in many patients with documented intermittent heart block or in patients who subsequently develop permanent complete heart block. The presence of this QRS pattern in patients with histories of syncope or dizziness suggests that their symptoms may be due to intermittent heart block. Such patients should be monitored to document heart block, or should have permanent demand pacemakers implanted, or both.